WPS Starting Point

Rev 1

5/26/2011 2

2011

For more information contact:

Halliburton Energy Services Fort Worth Training Center

1128 Everman Parkway

Fort Worth, Texas 76140

U.S.A.

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Introduction

This document was prepared as supporting material for the Wireline and Perforating Services (WPS)

Technical Training Program (TTP). It covers many, but not all modules presented during the 3 week

course. You will not find included here, Explosive User Safety & Radiation Safety, Well-Logging

Assistant both are available in iLearn.

Specific tool information is available from Technical Services documentation, posted on the WPS

portal. For detailed operations procedures, consult the online WPS Halliburton Management

System (HMS).

Drilling rig operations are covered in the Technomedia Oil well Drilling series.

Some of the material included here is edited from the manual EL-1007; Open-hole Log Analysis &

Formation Evaluation 1991, which was revised by Dale Heysse. Contributors included: Calvin

Kessler, David Hampton, Paul Harness, Milt Enderlin, Doug Seifert & Richard Bateman on whose

work EL-1007 was based.

.

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Table of Contents Introduction .................................................................................................................................................... 3 Chapter 1 Of Rocks & Fluids .................................................................................................................... 8

Hydrocarbons ............................................................................................................................................................................................. 8 Conventional Hydrocarbons....................................................................................................................................................................... 9 Unconventional Hydrocarbons ................................................................................................................................................................... 9 Geology The Study of the Earth ........................................................................................................................................................... 10 Geology The composition of the earth .................................................................................................................................................. 11 Geology Weathering and Erosion ......................................................................................................................................................... 13 Geology Rocks ...................................................................................................................................................................................... 13 Geology Traps ...................................................................................................................................................................................... 16 Locating Reservoirs ................................................................................................................................................................................. 17 Reservoirs ................................................................................................................................................................................................ 19 Drilling ...................................................................................................................................................................................................... 22 Drilling Mud .............................................................................................................................................................................................. 23 Mud Additives .......................................................................................................................................................................................... 23 Muds & Logging ....................................................................................................................................................................................... 24

Chapter 2 Wireline Measurements ......................................................................................................... 26 Natural Gamma Ray ................................................................................................................................................................................ 26 Origin of Natural Gamma Rays ................................................................................................................................................................ 26 Tool Physics ............................................................................................................................................................................................. 26 Operational Issues ................................................................................................................................................................................... 27 Use of the GR .......................................................................................................................................................................................... 28 Compensated Spectral Natural Gamma Ray .......................................................................................................................................... 28 Density ..................................................................................................................................................................................................... 29 Tool Physics ............................................................................................................................................................................................. 29 Operational Issues ................................................................................................................................................................................... 31 Uses of the Density .................................................................................................................................................................................. 32 Neutron (TTP Module) ............................................................................................................................................................................. 33 Tool Physics ............................................................................................................................................................................................. 33 Operational Issues ................................................................................................................................................................................... 35 Uses of the Neutron ................................................................................................................................................................................. 36 Spontaneous Potential ............................................................................................................................................................................. 37 Source of the SP ...................................................................................................................................................................................... 37 Recording the SP ..................................................................................................................................................................................... 38 Factors Affecting the SP .......................................................................................................................................................................... 38 Use of the SP ........................................................................................................................................................................................... 39 Operational issues ................................................................................................................................................................................... 39 Resistivity ................................................................................................................................................................................................. 40 Origins ...................................................................................................................................................................................................... 40 Laterolog .................................................................................................................................................................................................. 42 Measurement Technique ......................................................................................................................................................................... 42 Tool Physics ............................................................................................................................................................................................. 43 Operational Issues ................................................................................................................................................................................... 44 Uses of the Laterolog ............................................................................................................................................................................... 44 Micro-resistivity ........................................................................................................................................................................................ 44 Induction .................................................................................................................................................................................................. 45 Measurement Technique ......................................................................................................................................................................... 45 Factors Affecting the Induction ................................................................................................................................................................ 46 Use of the Induction ................................................................................................................................................................................. 46

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Operational issues .................................................................................................................................................................................... 46 Sonic ......................................................................................................................................................................................................... 52 Tool Physics ............................................................................................................................................................................................. 52 Operational Issues.................................................................................................................................................................................... 54 Uses of the Sonic ..................................................................................................................................................................................... 54 Cement Bond Log..................................................................................................................................................................................... 55 Tool Physics ............................................................................................................................................................................................. 55 Tool design ............................................................................................................................................................................................... 56 Tool response ........................................................................................................................................................................................... 57 Operational Issues.................................................................................................................................................................................... 58 Uses of the CBL ....................................................................................................................................................................................... 59 Ultrasonic tools ......................................................................................................................................................................................... 59

Chapter 3 Wireline Operations ............................................................................................................... 60 Practical Wireline Electronics ................................................................................................................................................................... 60

Logging System ....................................................................................................................................................................................................... 60 Power ....................................................................................................................................................................................................... 60 Circuit Analysis ......................................................................................................................................................................................... 60 Capacitance & Inductance ....................................................................................................................................................................... 62 Transformers ............................................................................................................................................................................................ 62 Wireline ..................................................................................................................................................................................................... 62 Cable model ............................................................................................................................................................................................. 63 Power transmission .................................................................................................................................................................................. 64 AC & DC power transmission techniques ................................................................................................................................................ 64 Communication Data ............................................................................................................................................................................. 65 Troubleshooting ........................................................................................................................................................................................ 65 Resistance, Resistivity, Conductivity & Electric Fields ............................................................................................................................. 67 Ohms Law & Darcys Equation similarity .............................................................................................................................................. 67

References ................................................................................................................................................................................................................ 67 Tool Mnemonics, PM1 & Connector Conventions ................................................................................................................................... 68 Tool Mneumonics Background ................................................................................................................................................................. 70 Preventative Maintenance ........................................................................................................................................................................ 68 Connectors ............................................................................................................................................................................................... 69 Open Hole Tool Mneumonics ................................................................................................................................................................... 71 Cased Hole Tool Mneumonics ................................................................................................................................................................. 72 General Mneumonics ............................................................................................................................................................................... 73 Cable Care ........................................................................................................................................................................................... 74

Construction .............................................................................................................................................................................................................. 74 Electrical ................................................................................................................................................................................................... 76 Operational Issues.................................................................................................................................................................................... 76 Weak-point Selection ........................................................................................................................................................................ 78

Getting stuck ............................................................................................................................................................................................................. 78 Tension measurement ........................................................................................................................................................................................... 79 Weak points ............................................................................................................................................................................................................... 79 Ideal weak point ....................................................................................................................................................................................................... 80 Maximum Safe Pull ................................................................................................................................................................................................. 81 Minimum & Maximum pull-out tension ............................................................................................................................................................. 81 Cased-hole weak points ........................................................................................................................................................................................ 82

Depth and Tension ............................................................................................................................................................................ 83 Tension ....................................................................................................................................................................................................................... 83 Depth ........................................................................................................................................................................................................................... 83 Stretch ......................................................................................................................................................................................................................... 84 Wheel calibration factor ......................................................................................................................................................................................... 84

Winch Control & Vertical make-up................................................................................................................................................ 85 Winch control ............................................................................................................................................................................................................ 85 Vertical make-up ...................................................................................................................................................................................................... 85 Horizontal tool make-up ........................................................................................................................................................................................ 86

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Rigging up/down tips .............................................................................................................................................................................................. 86 Running in hole (RIH)/ logging/pulling out of hole (POOH) etc ............................................................................................................... 88 Pressure ..................................................................................................................................................................................................................... 96 WHPC Hardware ..................................................................................................................................................................................................... 96 Operational procedures ....................................................................................................................................................................................... 100 Arriving on location: .............................................................................................................................................................................................. 101 During logging: ....................................................................................................................................................................................................... 102 Rigging down: ......................................................................................................................................................................................................... 102 References .............................................................................................................................................................................................................. 102

Chapter 4 Other Product Service Lines...............................................................................................105 Completions ....................................................................................................................................................................................... 105

Hardware .................................................................................................................................................................................................................. 105 Artificial Lift ............................................................................................................................................................................................. 108 Pump Jack ............................................................................................................................................................................................. 108 Hydraulic Pumps .................................................................................................................................................................................... 108 Electrical Submersible Pumps ESP ....................................................................................................................................................... 109 Gas Lift ................................................................................................................................................................................................... 109 Plunger Lift ............................................................................................................................................................................................. 109 Progressive-Cavity Pump ...................................................................................................................................................................... 109 Cementing .............................................................................................................................................................................................. 111

Design ....................................................................................................................................................................................................................... 111 Hardware .................................................................................................................................................................................................................. 111 Volumes .................................................................................................................................................................................................................... 112 Additives ................................................................................................................................................................................................................... 112 Pumping Schedule ................................................................................................................................................................................................ 113 Formations & Fluid flow ....................................................................................................................................................................................... 115 Production Optimization ...................................................................................................................................................................................... 117 Proppant Fracturing .............................................................................................................................................................................................. 117 Design Calculations .............................................................................................................................................................................................. 118 Pumping Schedule ................................................................................................................................................................................................ 118 Additives ................................................................................................................................................................................................................... 119

Coiled Tubing ......................................................................................................................................................................................... 120 Reserve Estimation ......................................................................................................................................................................... 122

Oil & Gas in place Estimation ........................................................................................................................................................................ 123 Reserve Estimation ............................................................................................................................................................................................... 124 Recovery Factors .................................................................................................................................................................................................. 124 Formation Volume Factors ................................................................................................................................................................................. 124 Depth and Net Pay Measurements ................................................................................................................................................................. 124 Deviated Wells & Dipping Beds ........................................................................................................................................................................ 124 Reservoir Volumes ................................................................................................................................................................................................ 125

Rock Fluid Systems..................................................................................................................................................................... 126 The Genesis of Reservoir Rocks ..................................................................................................................................................................... 127 Porosity ..................................................................................................................................................................................................................... 127 Permeability ............................................................................................................................................................................................................. 127 Fluid Distribution in the Reservoir .................................................................................................................................................................... 128 Relative Permeability ........................................................................................................................................................................................... 129 Relative Permeability Ratios .............................................................................................................................................................................. 130 Imbibition and Drainage ...................................................................................................................................................................................... 130 Measurement of Porosity .................................................................................................................................................................................... 130 Measurement of Permeability ........................................................................................................................................................................... 130 Measurement of Saturation ................................................................................................................................................................................ 131 Water Resistivity .................................................................................................................................................................................................... 131 Saturation ................................................................................................................................................................................................................. 132 Practical Petrophysics ......................................................................................................................................................................................... 132 Averaging ................................................................................................................................................................................................................. 133 Summary .................................................................................................................................................................................................................. 133

Coring .................................................................................................................................................................................................. 134 Wireline Coring ....................................................................................................................................................................................................... 135 Conventional Coring ............................................................................................................................................................................................. 136

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Summary .................................................................................................................................................................................................................. 136 Measurement While Drilling .......................................................................................................................................................... 137

MWD Measurements ........................................................................................................................................................................................... 137 MWD Telemetry ..................................................................................................................................................................................................... 137 MWD Surface Equipment ................................................................................................................................................................................... 138 Tool Features ............................................................................................................................................................................................................ 47 Tool Theory ............................................................................................................................................................................................................... 49 Borehole Correction ................................................................................................................................................................................................ 50 High Resolution Array Induction Log Sensitivity to Invasion ................................................................................................................ 51

Dielectric .............................................................................................................................................................................................. 139 Measurement Technique .................................................................................................................................................................................... 139 Factors Affecting the Dielectric ......................................................................................................................................................................... 139 Use of the Dielectric ............................................................................................................................................................................................. 140

Appendix II Office Procedures .................................................................................................141 Outlook Properties, ESS & Expenses (TTP Module) ........................................................................................................... 141

Outlook Properties ................................................................................................................................................................................................ 142 ESS .............................................................................................................................................................................................................................. 146 Expenses .................................................................................................................................................................................................................. 147 References .............................................................................................................................................................................................................. 157

Appendix III Logging Support ..................................................................................................158 Portal Overview & Report posting (TTP Module) .................................................................................................................. 158

Appendix IV Tool Specifications .............................................................................................170 HALWORLD ....................................................................................................................................................................................... 170

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Chapter 1 Of Rocks & Fluids For hydrocarbons to be found we need the following pre-requisites: source, pathway, reservoir,

trap and a seal. This section outlines the each of these requirements.

Hydrocarbons

Hydrocarbons are one of the most important fuel sources in the world today; they are of utmost

importance for transportation and power generation. They offer very high specific energies and are

convenient to use. They are fossil fuels; trapped in place millions of years ago and include coal, gas

and oil. They are a finite resource. Wireline Logging is primarily concerned with identifying the

location, quality and quantity of these resources, essentially crude oil and gas.

Hydrocarbons are the result of the accumulation of small aquatic organisms in warm shallow seas

and lakes. These accumulations were deposited millions of years ago, in the Mesozoic and

Cenozoic eras, together with inorganic sediments. The fine inorganic sediments which contain this

material is eventually converted to rock. Under the action of anaerobic bacteria (bacteria that do not

require oxygen to live), the organic material is converted into Kerogen, which is then altered by heat

and pressure to form oil and gas deposits. In some cases, the hydrocarbon fluids are displaced by

increasing pressure from the buildup of sediments (overburden) and eventually accumulate in the

conventional reservoirs we drill today. These source rocks are often shales; since they accumulate in

the low energy environment found where the organic material tends to accumulate. The calm

environment found at the bottom of a sea prevents disturbing the sediments and stops oxygen from

mixing into the sediments. While the permeability of shale is extremely low (they are considered

impermeable by conventional standards) in the course of geologic time, the hydrocarbons can move

out of the shale and into reservoir rocks.

Fossils AGI Shale

Many geologists believe that much of the easy oil and gas has already been found and that future

extraction will require ever more sophisticated technology and energy input. Giant oil and gas fields

which were once prolific producers are now in decline and the search is intense to locate economic

reserves in many parts of the world. Attention has turned in some instances to non-conventional

reserves as a way of offsetting the decline in conventional oil and gas.

A term that is used to quantify the energy cost of hydrocarbon extraction is EROEI (energy return on

energy invested), the term is self-explanatory; essentially it tells us how much energy we get from our

produced hydrocarbon in relation to how much energy is invested to obtain the hydrocarbon. Much of

the controversy surrounding EROEI is related to how far back into the energy chain we should go to

make this calculation. Ultimately this is an economic decision. Obviously when oil fetches $100 a

barrel, companies can afford to spend more money to produce it versus $20 a barrel.

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Conventional Hydrocarbons

Oil & Gas; petroleum fluids, are found in many countries all over the world. Crude oil is classified by

API number, heavy viscous oils have low API numbers, light crudes have higher numbers. The

Specific Gravity (SG) is the ratio of the density of the hydrocarbon to the density of fresh water which

is 8.33 #/gal. Utilizing the API Gravity equation below would yield an API gravity for fresh water of 10.

API Gravity = (141.5/ SG) 131.5

Behavior of these fluids is described by a phase diagram which is often plotted as a function of

reservoir temperature and pressure. Bringing petroleum fluids from downhole conditions to surface

conditions results in compositional changes, as gas is released and oil volume shrinks. This

shrinkage is called the Formation Volume Factor, 0 , and represents the ratio of the oil at downhole

conditions compared to the volume at standard conditions. It normally ranges between 1 and 1.6.

Reservoir volumes are usually expressed at standard conditions (60 degF @ 1Atm).

Temperature and pressure are a function of depth; both contribute to the process of changing solid

hydrocarbon (Kerogen) into Oil & Gas. At relatively shallow depths, biogenic gas tends to form, at

intermediate depths Kerogen matures to form oil and thermogenic gas and at greater depths only

gas will likely be found. Further increases in depth (and hence temperature and pressure) result in the

degradation of hydrocarbons. The set of conditions (temperature and pressure) under which

petroleum is formed is termed the petroleum window.

Unconventional Hydrocarbons

Tar sands, bituminous sands, oil sands; though technically not tar, these sands contain viscous,

heavy oil. Extraction can be through viscosity reduction; using steam or solvent injection, or the sands

can be strip mined and processed on surface, if the accumulations are not too deep. Major

accumulations are found in Canada and Venezuela; in the US tar sands are found in Utah.

Oil shales; not necessarily shale and accumulations of organic material are in the form of Kerogen

not oil! Further processing of the Kerogen is either in-situ or at surface. Essentially the material has to

be heated and the resulting vapor condensed, in order to generate synthetic oil or gas through

pyrolysis. Major accumulations are found in Brazil, Russia and the US.

Gas shales; are often the source beds for hydrocarbons. While their permeabilities are extremely low,

these organic rich shales are often brittle enough to allow modern fracturing techniques along with

horizontal drilling to provide an economical production increase. Some wells also produce oil in

addition to gas. Major accumulations are found in the Barnett, Woodford, Marcellus, Haynesville,

Mancos, Eagle Ford, and Bakken shales just to name a few in the US.

Coal Bed Methane; methane (Natural Gas) is adsorbed onto the coal surface and released

(desorbed) when pressure on the coal seam is reduced. Once a well is drilled, production is from

fractured cleats in the coal formation, production rates are strongly dependent on the degree of

fracturing or cleat density. Both the US and Canada have deposits of coal bed methane.

Methane Hydrate; methane hydrate is found on the sea floor and in accumulations underground. It

exists in solid form and is present in sediments or sedimentary rock within a particular range of

temperature and pressure. One of the problems with this type of deposit is that it is often widely

dispersed and as a consequence may be uneconomical to extract with current technologies.

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Geology The Study of the Earth

The earth is estimated to be 4.6 BILLION years old using the uranium-lead method which uses the

quantities of Uranium-235 related to its stable decay component Lead-207. . Dinosaurs appeared on

earth about 230 million years ago and went extinct about 65 million years ago The first Homonoids

appeared on the earth around 2 million years ago with Homo Sapian less than 300,000 years ago. As

you can see geologic time is very different from the human perspective of time.

Geologists break the age of the earth into 4 separate eras of time: The Cenozoic, the Mesozoic, the

Paleozoic, and the Pre-Cambrian, from youngest to oldest. The attached geologic timetable shows

the time range for each era and its constituent periods. Note that the majority of todays hydrocarbon

reservoirs were formed during the Mesozoic era. Geologists will often refer to the Period of the rock to

relate its age. For example, a Pennsylvanian rock will be around 265 million years old. They can

determine the age of the rock through radioactive half-life determination or some basic geologic

principles like examining fossils found in the rock.

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Geologic Principles

The principles of uniformitarianism, superposition, faunal succession, cross-cutting relationships and

original horizontality also help geologists determine the age of different rocks.

Uniformitarianism means that the geologic processes which occur today operate the same as those

that occurred in the past.

Superposition says that in a series of undisturbed formations, the oldest formation is at the bottom of

the sequence.

Faunal succession indicates that the simpler the fossils, the older the rock.

Cross-cutting and intrusive relationship simply states that the older formation is cut by the

younger.

Original horizontality refers to the fact that sediments are normally deposited horizontally.

By utilizing these basic principles, a geologist works much like a CSI technician trying to determine

what happened in the past to create the formation they are examining.

Geology The composition of the earth

The earth is not a solid ball of dirt. It is actually composed of 3 components. A central core consisting

of a solid iron/nickel inner center surrounded by a liquid outer core. These are surrounded by a plastic

mantle and finally a rigid crust. The crust is primarily made of silicon, oxygen, and aluminum.

Earth model - USGS

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The crust is actually composed of 14 major and 38 smaller tectonic plates. These plates float on the

mantle constantly moving in different directions. Their position has changed significantly over the

millions of years of movement upon the mantle. The ancient oceans which are responsible for the

sediments which spurred our modern day hydrocarbons once covered a drastically different portion of

the earth compared to todays modern oceans. The tectonic forces generated by the plates are

responsible for many of the deformations of the earths crust like faults and anticlines which can result

in the structures which are favorable for hydrocarbon reservoirs. The diagram below shows the

ancient supercontinent of Pangaea and how it split up and moved over the last 225 million years. The

rocks these plates are composed of undergo weathering and erosion to form the sediments from

which our hydrocarbon reservoirs are made from. It is interesting to note that areas which produce

hydrocarbon in the modern day were most often covered by oceans in the past in part due to the

movement of the plates. The Himalayas were formed by the collision of the Indo-Australian plate with

the Eurasian plate starting about 70 million years ago eventually closing off the Tethys Ocean. That

collision is still ongoing today and Mount Everest at a height of 29,035.44 feet grows about 2 inches

per year. The rocks found on Mount Everest are composed of sediments deposited in a marine

environment. The deposits in the Tethys Ocean are the source for much of the oil now being

produced in the Middle East.

Plate Tectonics - USGS

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Geology Weathering and Erosion

The breakdown of rocks into sediments is accomplished through the process of weathering. There

are two basic classifications: Physical and Chemical. In physical weathering involves forces upon the

rock which cause it to crack or break into smaller blocks. This can be accomplished through changes

in stress or temperature or even from water expanding when it freezes. One result of physical

weathering is to increase the surface area of the rock which can then be acted upon by chemical

weathering causing the further breakdown of a rock into its constituents by oxidation, hydrolysis, and

carbonation. For example, many clays are the result of the weathering of feldspar, an abundant

mineral in igneous rock. Erosion is the actual movement of weathered particles typically by gravity,

water, air, or glaciers. Much erosion involves transport by water, such as a stream, alluvial, lacustrian,

a delta, a beach, deltaic, or other marine environments as well as well as non-water movement like

Aeolian (wind) transport, glacial or basic mass movement (gravity). The type of depositional

environment can often be determined by inspecting the actual makeup of the rock. This depositional

history can yield clues to additional properties we might expect within the reservoir like horizontal

versus vertical permeability, reservoir extent, drainage area, and help with determining the location of

the next well to be drilled.

Geology Rocks

The sediments described, undergo changes due to temperature and pressure as they are converted

to the rocks we are typically confronted with when we log. Bear in mind that these sediments will most

likely have accumulated submerged in water (seas, lakes, swamps etc). They will gradually be

compacted by the weight of overlying materials; individual grains may be cemented together by the

precipitation of minerals in solution or clays. This process of converting loose sediments to solid rock

is known as lithification. Chemical changes (crystallization) may take place within and between the

rock minerals and surrounding fluids. Finally through compaction and heat the fluids contained in the

rock may be squeezed out or driven off (desiccation). The whole process is known as Diagenesis.

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Rocks are classified at a basic level into three types;

Igneous

Metamorphic

Sedimentary

Igneous rocks are those that are formed from magma, the molten material produced from volcanic

activity, around 65% of the earths crust consists of this type of rock. Magma from a volcano which is

extruded onto the surface yields igneous rock (extrusive) with fine crystalline structure because of its

rapid cooling. Magma which cools underground in structures know as plutons (intrusive) can show

large crystals in its structure because of the time allowed for crystal growth before the rock hardens.

Igneous rock can be transformed into sedimentary rock through erosion and deposition, followed by

the changes described above. Metamorphic rocks are those which have been altered as a result of

intense heat and or pressure, deep under the earths surface, about 27% of the earth surface consists

of this type of rock. These rocks may be eroded in the same way as igneous rocks and deposited as

sediments. Sedimentary rocks which compose around 8% of the earths crust, are formed from the

destruction of other rocks by weathering and depositional processes, they are the primary target for

the exploration geologist looking for hydrocarbons. Each of these rock types can be transformed into

the other, depending on the processes at work; this is often depicted by a rock cycle diagram.

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Sediments are of primary interest, they can be divided onto two categories Clastics and non-

Clastics. Clastics are formed from grains of different rocks and classified by grain size, starting

from large conglomerates, through finer Sandstones & siltstones to very fine grained Shale. Non-

Clastic rocks typically form from precipitation of minerals are further split into Chemical or bio-

Chemical. Within those groups, the rock types of interest are carbonates i.e. Limestone or Dolomite

and to a lesser degree Evaporites such as Anhydrite, Gypsum and Halite.

Igneous Metamorphic Sedimentary

o Clastic Conglomerate Sandstone (SiO2) Siltstone Shale

o Non-Clastic Chemical

Carbonates o Limestone (CaCO3) o Dolomite (CaMg(CO3)2

Evaporites o Anhydrite (CaSO4) o Gypsum (CaSO4.nH2O) o Halite (NaCl)

Bio-Chemical Carbonates

o Limestone

Coal

Conglomerate AGI Shale - AGI

Of the sedimentary hydrocarbon reservoirs that are known to exist around 60% are sandstone, 35%

are carbonate (either limestone or dolomite) and 5% are of other rock types.

Note: A reservoir is no more than a sponge, a place where fluids can accumulate; the actual source

of hydrocarbon is unlikely to be the reservoir rock itself, though in some instances this may be the

case. Metamorphic and Igneous rock formations are unlikely to be source rocks, conducive to

hydrocarbon generation, but hydrocarbon reservoirs of these rock types do exist. Evidently the

hydrocarbons migrated there from the original source rocks, found a place to accumulate, and were

trapped, to be found as crude oil or gas (i.e. not changed or degraded).

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Geology Traps

From the point of view of hydrocarbon exploration, we are particularly interested in locating trapping

mechanisms, places where hydrocarbons can be prevented from escaping. We can divide such

mechanisms into two groups:

Stratigraphic

Structural

Structural traps are those related to the gross movement of formations and include anticlines and

faults (reverse and normal) In either case the trapping mechanism requires that fluids are prevented

from leaving the reservoir by some form of impermeable boundary (most often shale or an

evaporite). The first example of the fault below is known as a normal fault. A normal fault is one in

which the hanging wall moves down relative to the foot wall (which is what would normally happen

based solely on gravity) The second example which shows the foot wall and hanging wall is a reverse

fault.

Anticline

Normal Fault AGI Reverse Fault - USGS

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Stratigraphic traps are those trapping mechanisms related to changes within a formation; examples

are Pinch-out, Lens and Unconformities. A pinch-out is where the reservoir rock thins, or is

pinched-out between impermeable shale formations, a lens is similar; an isolated sand body which

pinches-out in all directions. An unconformity is the result of erosion of a permeable formation

followed by the deposition of an impermeable shale barrier. A reef is another type of stratigraphic trap

formed by the accumulation of coral and calcareous material in an offshore marine environment

which are then covered over by impermeable shale and can be very prolific reservoirs.

Lenticular Trap AGI Angular unconformity (Eroded monocline) AGI

Locating Reservoirs The question arises How to locate potential reservoirs? It is useful to consider the scale of the

problem. At one extreme we are looking for very large structures, which may or may not be apparent

at the surface, this is taking a macro-view. At the other extreme we are investigating details of the

reservoir on a much smaller scale, possibly using Wireline techniques, this is more a micro-view.

Coverage on a large scale is achieved by resorting to satellite (which look for changes in the earths

surface which might indicate changes in vegetation due to hydrocarbon seepage at the surface or

surface structures which might indicate underground trap), magnetic (which look for changes in the

earths magnetic field which might indicate an intrusion of high iron content igneous rock which could

generate structure for a trap) or gravity (which look for changes in the earths gravity which might

indicate an intrusion of a low density salt dome which could generate structure for a trap) surveys,

looking for anomalies that can be interpreted from large scale maps. In some instances hydrocarbons

may even be identified from shows at surface. As we reduce scale, data and maps can be generated

offshore and on land from seismic surveys.

Anticline Salt Dome

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Seismic uses a sound source (often a vibroseis unit or an air gun) to bounce acoustic waves off

underground bed boundaries and measure the time it takes for it to travel the round trip utilizing

geophones (microphones) placed on the surface to determine the location of structure which could

generate a trap.

Potential reservoirs can be further investigated by drilling actual wells and taking physical samples of

the fluids or the rock in which it is store. In addition, exploration logging will be done, Often times in

these instances multiple logging runs with maximum data recovery are likely to be attempted to fully

evaluate the reservoir, including rock and fluid sampling. Drill Stem Testing (DST) utilizes packers

and downhole control valves and pressure transducers to allow a temporary completion of the well to

determine its production capabilities. Exploration software allows reservoir models to be created to

predict how a reservoir will produce.

In development fields, reduced logging programs will probably be implemented to define reservoir

margins and changes within the reservoir, possibly using some form of log correlation technique to

further reduce the costs of data acquisition. Geologic maps are generated from the various forms of

data collected on potential reservoirs. These range from structural contour maps in which lines of

equal elevation are shown (similar to topographic except sub-surface or sub-sea) to isopach maps

which show the thickness of a specific formation throughout a field. Cross-sectional maps can be

generated using well logs from the wells within a field or from seismic data which has been calibrated

to show actual depth of formations.

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Reservoirs

Success for the Oil Company depends on finding hydrocarbons that can be economically produced.

Whether or not the well is economically viable will depend on Oil in Place

0

)1.(.. wStAOIP

Area (A), Thickness (t) & Depth: measurement of area & thickness yield reservoir volume.

Formation depth may have implications for the type of hydrocarbons we expect to find.

Porosity (): this is a measure of the volume of void space in a sample of rock expressed as a

percentage of the total volume of the sample. Pore space is a function of how the original grains were

transported, packed, sorted, compacted and cemented. Using this property together with reservoir

volume information will yield an estimate of reservoir fluid volume. The porosity can be impacted by a

number of things which occur during diagenesis The higher the compaction (higher overburden

normally goes with deeper depth) the lower the porosity. The shape of the sediments refers to

whether they are spherical or more angular. The more spherical the grain typically the higher the

porosity. Sorting refers to how similar are the grain sizes. The better the sorting (more similar),

typically the higher the porosity. Packing refers to how the grains are stacked on each other. Cubic

packing typically yields the highest porosity 47%. Rhombohedral packing yields porosities around

26%. This is based on perfect spherical well sorted grains. Finally cementation effects the porosity.

The more cement in between the grains, the less pore space is available. The porosity is relatively

independent of the grain size.

Cubic Packing Rhombohedral Packing

Pores which are connected and allow the flow of fluids represent effective porosity. It should be noted

that our density and neutron tools measure total porosity which includes both the connected and

isolated porosity. Because of the physics involved, our acoustic tools tend to measure a minimum

porosity (the fastest travel path for the acoustic signal). A difference between total porosity and

minimum porosity would tend to indicate secondary porosity present in the formation. Often times,

secondary porosity is isolated but this can vary by formation.

5/26/2011 20

Water Saturation (Sw): using this together with reservoir fluid volume will help us to identify how

much of the fluid in the reservoir is water and lead us to an estimate of probable hydrocarbon content

in the reservoir. Considering the environment in which sediments are deposited (lakes, seas etc), you

might expect there to be some amount of water present regardless of the presence of hydrocarbons.

Not only is this the case, but it is generally not possible to displace all of the water, a percentage of

which remains adhered to the rock matrix (irreducible water saturation) in water-wet reservoirs.

Practical estimation of Sw is made possible by using wireline logging methods. Water Saturation is

commonly determined using Archies Equation which contains some parameters (a, m, & n) which

can change depending on the lithology and properties of the reservoir.

t

mwn

w xR

axRS

Permeability: is a measure of the ease with which fluids can flow through the rock. It is described by

Darcys Law

ALQ

P.

.. (Steady-state, linear flow)

Porosity alone doesnt guarantee that we can produce fluids; we need effective porosity so that fluids

can flow through the formation towards the borehole and ultimately be produced at surface.

Interestingly, and as you might expect, rock may have quite different permeability in one direction

compared to another. The reason for this is simply that stresses within the rock cause distortion of the

rock structure and alignment of mineral crystals, void spaces and channels. Reservoir fluids may be

water or some combination of water, gas and oil. Each fluid tends to segregate on the basis of

density, so we expect to find water deepest in the formation, oil next and gas shallowest in the

formation. Segregation tends not to be abrupt however and at each interface there is a transition zone

where one fluid blends into another. Fluid movement is complicated and a function of capillary

pressure. If a single fluid is present in the pore space, then we use the absolute permeability

measurement. Since we generally deal with mixtures of fluids (multiple-phases) fluid movement is

dictated by the relative ease of movement of each fluid component and is called effective

permeability. The relative permeability is the ratio of the effective perm to the absolute perm and

varies with the percentage of that fluid contained in the pore space.

5/26/2011 21

Formation volume factor (0): this factor converts hydrocarbon volume at reservoir conditions to

volume at standard conditions of temperature & pressure (60 degF @ 1Atm).

Pressure: pressure at any point in the borehole is a function of depth, since buried formations are

subject to overburden from formations above (gradient ~1 psi/ft for fluid filled rock, 0.43psi/ft for

water). As you might also suspect; the action of drilling through a formation disturbs the existing

stress pattern and the newly drilled borehole may distort or collapse due to stresses which are no

longer held in equilibrium.

Hydrostatic pressure (psi) = 0.05195 x Mud wt (#/gal) x TVD (ft)

Sometimes because of the structure of a formation it may exhibit a formation pressure higher than

would be normally expected based on its depth. This can be the cause of a sudden kick while drilling

a well or even a blowout.

Temperature: temperature is a function of depth; deep formations tend to be hotter, simply because

there is a thermal gradient as we move closer towards the center of the earth (~1.5degF/100ft).

Hydrocarbon type is also a function of temperature; long periods of exposure at high temperatures

tend to alter the chemical composition of hydrocarbons (petroleum window)

Reservoir - Drives: a reservoir may produce hydrocarbons under its own natural drive mechanism;

water or gas. Water drive is the most efficient, but even then it is generally the case that 50% of the

original hydrocarbon is left in place as residual hydrocarbon. A gas drive can result from gas

dissolved in the hydrocarbon (solution drive) or may be in the form of a pressurized gas cap above

the water layer. Some drives are a combination of both mechanisms. Gravity drive is also possible,

resulting from the difference in specific gravity of the layered reservoir fluids. In some cases natural

drive mechanisms are not sufficient to produce hydrocarbons and some other artificial lift technology

is required.

References

Images, Online Earth Science Databank American Geological Institute

Practical Petroleum Geology Petroleum Extension Service

Fundamentals of Petroleum Petroleum Extension Service

Oil Well Drilling Technomedia Series (CD set)

Crude History Channel documentary film

A Crude Awakening Lava Productions documentary film

The Partys over New Society Publishers; Richard Heinberg

Images Online - USGS

5/26/2011 22

Drilling

From the Field Professionals point of view, its useful to have a general idea of what types of drilling

rigs are used, what purpose the various components of the rig serve and how they might affect

logging operations.

History - Edwin L Drake drilled the first commercial oil well in the US in an area outside of Titusville

Pennsylvania called Oil Creek. Oil continuously seeped into the creek but not in commercial

quantities. James Townsend hired Drake to drill to the source of the oil which he and Uncle Billy

Smith found at a depth of 69 feet. It yielded around 10 barrels per day which was about a forty-fold

increase over the total daily production in Titusville.

You can read more about the history of oil at: http://www.priweb.org/ed/pgws/index.html

To learn about drilling rigs, complete the 10 chapters of Technomedias Oil Well Drilling series

available through your DVD or through I-Learn. On I-Learn, do a search utilizing the following script.

5/26/2011 23

Drilling Mud

From the Field Professionals point of view, its useful to have a general idea of what types of drilling mud are used, what purpose mud serves and why and how mud affects logging operations. Most well bores are drilled with liquids; in some parts of the world wells are also drilled with foam or air. Liquid muds are either Water-based (WBM) or Oil-based (OBM). Early rotary drilled wells were drilled with simple, non-engineered water based muds; these were later refined and improved to aid faster drilling and formation containment, in deep, hot wells and difficult formations. More recently other fluids, such as Oil-based and Synthetic (Oil) based muds have been developed to meet specific drilling requirements. Difficult in this case means formations that have a tendency to swell, cave-in, dissolve or collapse, as a result of the interaction between the mud and formation, e.g. Shales and Salt formations.

Muds are designed to exhibit certain properties; these will largely depend on the types of formation to

be drilled. A mud engineer spends much of his time monitoring and modifying mud properties in order

to prevent:

Formation fluids from coming to the surface (kick or blowout).

hole collapse

Formation permeability damage.

The mud system is dynamic; although drilling starts with a mud program based on previous

experience of the area to be drilled, the program will be changed depending on the specific properties

of the formations encountered. Drilling through successive formations; solids (rock) and fluids will be

mixed into the mud, changing its volume, and its chemical and mechanical properties. The mud

engineer will monitor these properties and modify them by adding appropriate solid or liquid additives

to the system. Different sections of the hole may, in some instances require a complete mud change

out, depending on the type of formation to be drilled and problem formations that are encountered

during drilling.

Mud Additives

Water and Oil-based, muds are a mixture of various solids and liquids; together they impart

mechanical properties such as density (weight) and viscosity.

Mud weight is particularly important, because it ensures that the hydrostatic pressure in the hole is

sufficient to prevent formation fluids from escaping from the formation and coming to surface, Mud

weight is increased by adding a heavy mineral such as Barite. Theres a limit however, we need to

avoid increasing mud weight to the point where the total pressure (hydrostatic + friction pressure) in

the borehole (expressed by equivalent circulating density) exceeds the mechanical strength of the

formation, causing it to be fractured.

Viscosity is another important mechanical property, cuttings produced by the drill bit need to be

carried away to the surface; viscosity is increased by the addition of Bentonite, it can also be

reduced by using thinners like lignosulfonate.

Viscosity (actually plastic viscosity), Yield point and Gel strength are all mud mechanical properties

and are closely monitored by the mud engineer. Viscosity is the slope of a graph of shear rate (X-

axis) versus shear stress (Y-axis). Readings are taken using a Fann viscometer, at various shear

rates. Plastic viscosity is then deduced from the resulting gradient. Extrapolating the line back to 0

shear rate provides a value of yield point. Gel strength is determined by comparing peak shear stress

at the same shear rate after waiting a specified length of time. These parameters are optimized by the

mud engineer, using various chemical additives in order to hold mud solids in suspension and carry

cuttings to the surface. (Refer: Bingham plastic model).

Chemical properties; for example pH and Chlorides can be modified to stabilize Clays and minimize

permeability damage in productive formations. Salt formations will probably be drilled with salt-

5/26/2011 24

saturated WBM or with OBM, to avoid massive washouts. Mud pH properties will be designed to

stabilize formations that contain Clays and prevent sloughing (caving) and swelling; the addition of

caustic soda is used to alter pH properties (mud systems are generally alkaline).

Since mud is a mixture of solids and liquids, and borehole pressure is generally higher than formation

pressure (over-balanced), there is a tendency for the liquid phase (mud filtrate) to be driven into the

formation by this pressure differential, displacing any formation fluids away from the borehole. As this

happens mud solids are deposited on the borehole wall forming a mud cake. Eventually sufficient

mud cake will be deposited to prevent further loss of mud fluids; this will usually be of the order of a

few tenths of an inch at most, if the mud is correctly designed. In some troublesome zones, special

lost circulation material is used to control loss of mud filtrate or whole mud.

Some wells are drilled with borehole pressure slightly less than formation pressure (under-

balanced), under these conditions drilling rates can be much higher and the cost of drilling the well

reduced. Formation damage from mud filtrate invasion, and differential sticking of the drill pipe is

largely eliminated, however there is always the possibility of losing control of the well. Low weight

conventional muds, 2-phase foams and pure gas are all potential under-balanced drilling (UBD)

fluids.

Note: Oil-based muds are widely used for drilling deviated holes and are less prone to react with

certain formations than water-based mud, however they are generally more expensive to use than

conventional water-based muds, and may raise environmental issues, depending on the base oil

used.

Muds & Logging

From a logging perspective the drilling mud will have bearing on the types of tools that can be run.

Water-based muds are electrically conductive, whereas oil-based muds, foams and gases are non-

conductive. Some of our tools, notably the Dual-Laterolog, Micro-Spherically focused log and

Spontaneous Potential, Rely on the electrical conductivity of the mud and cant be run in non-

conductive muds. Density tools are affected by the presence of mud chemicals, particularly Barite.

Air-drilled holes pose a problem for certain types of Neutron tool.

Logging tools generally measure properties close to the borehole; these properties are affected by

formation solids (rock) and formation fluids, mud filtrate mud cake and whole mud. In order to

account for, and in some cases, correct for these effects, we need to acquire some basic mud

information:

Type of mud

Weight (lb/gal)

pH

Chlorides content (ppm)

Fluid loss (cc)

Mud filtrate resistivity, Rmf (m)

Whole mud resistivity, Rm (m)

Mud cake resistivity, Rmc (m)

5/26/2011 25

Some of this data we can obtain from the mud engineer or drilling record,

some we measure from a mud sample (highlighted). The sample needs to

be representative of the mud in the borehole and is usually taken from a flow

line. The mud is pressed under 100psi for 30 minutes in order to separate it

into cake and filtrate before making the measurement, (which includes fluid

loss).

For oil-based muds there will be no entry for resistivity, since these muds are

not conductive when subjected to the low voltages associated with the

standard mud meter.

Solids are largely non-conductive, so mud resistivities will follow:

mfmmc RRR

Note: resistivities of salt solutions generally drop as temperature is

increased, so mud resistivities have to be stated together with the

temperature of the sample at the time of measurement, In order to obtain

equivalent readings at a different temperature we need to make correction using Arps Equation:

77.677.6

1

221 TT

RR

Note: OBMs may have a significant amount of water present and invert oil-based muds actually have

more water than oil, but the water, which is most likely salt saturated, is present in the form of isolated

globules, where the continuous phase is oil, so they are non-conductive.

How well the mud system is designed to match the formations being drilled and how well the hole is

conditioned (circulated and tripped) prior to logging will greatly influence how easy it is for the

logging tools to reach the bottom of the well. Washouts, cave-ins, mud balling, formation swelling,

differential sticking are a function of mud properties and drilling procedures.

In some cases, faced with highly deviated or horizontal wells, where gravity offers little or no

assistance getting to total depth (TD), and no matter how good the condition of the hole, another

method of tool conveyance is required. Conventional wireline limits in those cases is around ~ 65

degrees or so from vertical, and is probably more successful in holes drilled with oil-based mud,

which appear to offer a reduced coefficient of friction and may produce and closer gage hole, with

fewer washouts.

References

Oil Well Drilling Technomedia Series (CD set)

5/26/2011 26

Chapter 2 Wireline Measurements

Natural Gamma Ray

The Gamma Ray tool is the basic component of many open and cased-hole services; it is designed to

measure naturally occurring radiation present in downhole formations.

Origin of Natural Gamma Rays

Gamma rays originate from three sources in nature. These are the radioactive elements of the

Potassium group, Uranium group, and the Thorium group. Uranium 235, Uranium 238 and Thorium

232 all decay, via long chains of daughter products, to stable lead isotopes. An isotope of Potassium,

40, decays to Argon and emits a gamma ray. It should be noted that each type of decay is

characterized by a gamma ray of a specific energy. This is an important concept since it is used as

the basis for analysis of data from the natural gamma spectroscopy tools.

On average, shale contains 6 ppm uranium, 12 ppm thorium and 2% potassium. Since the various

gamma ray sources produce different numbers and energies of gamma rays, it is more informative to

consider this mix of radioactive materials on a common basis by referring to potassium equivalents

(the amount of potassium that would produce the same number of gamma rays per unit of time).

Reduced to a common denominator, the average shale contains uranium equivalent to 4.3%

potassium, thorium equivalent to 3.5% potassium, and 2% potassium. This "average** shale is a rare

find. Shale is a mixture of clay minerals, sand, silts and other extraneous materials; thus, there can be

no standard gamma ray activity for shale. Indeed, the main clay minerals vary enormously in their

natural radioactivity. Kaolinite has almost no potassium whereas Illite contains between 4% and 8%

potassium. Montmorillonite contains less than 1% potassium. Natural radioactivity may also be due to

the presence of dissolved potassium or other salts in the water contained in the pores of the shale.

Tool Physics

Traditionally, two types of gamma ray detectors have been used in the logging industry: Geiger-

Mueller and scintillation detectors. Today most gamma ray tools use scintillation detectors

containing a Sodium Iodide crystal; newer and more efficient crystal materials are constantly being

discovered but the principles of operation are the same.

When a gamma ray strikes the crystal, a single photon of light is emitted. This tiny flash of light then

strikes a photocathode (probably made from Cesium-Antimony or Silver-Magnesium). Each photon

hitting the photocathode releases an avalanche of electrons, these, in turn, are accelerated by an

electric field to strike another electrode producing an even bigger electron shower. This process is

repeated through a number of stages until a small voltage pulse is detected.

The detected pulse is amplified, shaped

and discriminated for noise before being

sent to a counter for transmission as a raw

gamma measurement of count rate.

Gamma ray Photo Multiplier Tube

5/26/2011 27

As with all logging tools; the physics of the measurement, the environment and tool design, place

limits on the ability of a tool to resolve thin beds (vertical resolution) and to survey deep into the

undisturbed formation (depth of investigation).

Gamma ray logs and most other logs require

standardization, so they can be compared

within and across companies. A calibration

standard for the Gamma ray was devised by

the American Petroleum Institute (API) and is

represented by a test pit at the University of

Houston. This contains specially doped

artificial shale surrounded by non-radioactive

zones, set behind a specific size of casing. One

Gamma API unit is defined as 1/200th the

difference between the hot and cold zones.

In practice a reference tool is calibrated at the

Houston pit and the response of this tool

transferred to field locations through the use of a

calibration blanket impregnated with Thorium 232.

Gamma ray measurement, and for that matter any

other measurement involving the decay of

radioactive materials, is inherently statistical in

nature and logging speed adversely affects log

quality. In order to collect sufficient gamma rays at

any section or interval of the borehole it is

necessary to maintain logging speed within

specification. Equally, when comparing Gamma

ray measurements over the same section dont

expect a perfect match or repeat! Gamma tools

are usually logged at 30-45 fpm.

Operational Issues

Gamma ray logs are subject to a number of perturbing effects including:

Tool position in the hole (centered or eccentered)

Hole size

Mud weight

Casing size and weight

Cement thickness

Most of the above is not surprising since gamma rays are attenuated to some extent by materials

placed between the detector and the formation. It is possible to run a Gamma tool in cased hole and

attenuation with multiple string of cemented casing can make the response difficult to interpret.

Similarly, in open-hole the position of the Gamma tool will depend on the position of other tools in the

toolstring, which could be intentionally centered or eccentered.

Since there are innumerable combinations of hole size, mud weight and tool position, logging service

companies publish charts to correct their gamma ray logs back to a standard set of conditions.

5/26/2011 28

Use of the GR

The Gamma tool is widely used as a depth correlation device. It is run with many services

these days, even with perforating and other cased-hole, explosive services, in order to

correlate with original open-hole logs. It provides correlation for sidewall cores in oil-based

mud, where an SP cannot be run.

Since radioactive isotopes are often associated with the clay minerals in shales, it is a

commonly accepted practice to use the relative gamma ray deflection as a shale volume

indicator. The simplest procedure is to scale the gamma ray linearly between its minimum

(clean) and maximum (shaly) values from 0 to 100% shale. The Gamma Ray Index is

defined as:

cleanshale

clean

GRGR

GRGRlog

A number of studies have shown that this is not necessarily the best method and have

proposed other relationships; Steiber, Clavier etc.

Gamma rays are recorded both in cased and open-hole, they are also incorporated in a tool

as a sub-assembly; for example in open and cased-hole telemetry sections (GTET, D4TG,

TTTC) or in cased hole correlation devices (GPLT, GPST).

Compensated Spectral Natural Gamma Ray

Since radioactive decay produces a unique gamma ray with a characteristic energy; just counting

how many gamma rays a formation produces can be taken a step further, by counting both the

number and energy of detected gamma rays. If the number of occurrences is plotted against the

energy, a spectrum can be produced that is characteristic of the formation logged. This spectrum

can be thought of as a mixture of the three individual spectra belonging to Uranium, Thorium and

Potassium. Some unique combination of these three radioactive families will have the same

spectrum as the observed one. The trick is to find that combination.

Two general techniques are in use for the interpretation of spectral natural gamma ray logs. One is

the use of the Uranium curve (or the ratios Uranium/Thorium, Uranium/Potassium, and

Thorium/Potassium) as an indicator of fractures. Another technique is to apply the Uranium, Thorium

and Potassium concentrations together with other log data to determine mineralogy and clay type.

The size of the gamma pulse exiting the photomultiplier is related directly to the energy level of the

gamma which struck the crystal. In order to accurately measure the spectrum, some method of

stabilization must be used to compensate for temperature effects on the photomultiplier. As the

temperature of the PMT changes, its resistance changes and this impacts the size of the gamma

pulse. The CSNG uses a small embedded 0.05 Ci Am241 (americium) source to provide a known 60

Kev peak to adjust the spectrum coming from the PM tube. An Alpha-gamma coincidence technique

(Am241 emits an alpha particle and a 60 Kev gamma ray simultaneously) uses a separate CaF

detector (transparent to gamma rays) which detects the alpha particle and then relates any 60 Kev

gammas which arrive at the same time.

5/26/2011 29

Density

The density tool is used primarily as a porosity indicator; in conjunction with other log measurements

(neutron tool),