HYDROCARBON EXPLORATION

Sedimentary Basin

Sedimentary basin refers to any geographical feature exhibiting subsidence and consequent infilling by sedimentation.

As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification.

SANDSTONE BRECCIA CONGLOMERATE

SHALE

ROCK SALT

FOSSILIFEROUS GYPSUM

COALLIMESTONE

Sedimentary rock types

Relative thicknesses of laminations, beds and strata

Sphericity of grains Texture

Sorting Fabrics

Waterlain beds Mass flow

Sedimentary rock characteristics

Geology

Geophysics

Seismic

Well Logging

By studying these sedimentary beds in outcrops and other surface features, geologists can infer where the underground porous reservoirs and impermeable traps might lie

Understanding of the shapes of the sedimentary rock layers. Early geophysical methods involved gravity-magnetic mapping, measuring the earth's gravity and magnetic responses at a number of points and plotting the results on a map

Geophysicists interpret these results to gain an understanding of the shapes sizes and orientation of rock layers, - stratigraphy and tectonics. To evaluate what kinds of rock are at which depths, how porous the rocks are, and whether there is oil and gas or water in the pore spaces.

Finding oil and gas

GEOLOGICAL

GEOPHYSICAL

GRAVITY

MAGNETIC

SEISMIC

GEOCHEMICAL

SNIFFER

What we look for :GEOLOGIC SETTING

A SIGNIFICANT SEDIMENTARY THICKNESS

FAVOURABLE STRUCTURAL FEATURE

PETROLEUM SYSTEM

Exploration Techniques

Structural elements

Lithology

Paleontological study

Environment of deposition

Stratigraphy

Evolutionary sequence of structure

Geological surveys

Geological field studies

Relative surface variation of Earth's gravitational acceleration over geologic structures

Gravity Magnetic Studies

AEROMAGNETIC RECONNAISSANCE SURVEY

Onland – Seismic surveys (Vibrosis)

Animation courtesy of Elf Aquitaine.

Marine seismic data acquisition

Surface

Layer-1

Layer-2

Layer-3

Arrival

time

0

Depth & Time

ShotReceivers

The seismic trace

Seismic Section (Land)

Seismic section – Deep Water

Semi‐detailed

Detailed 3D

Coarse Grid(reconnaitory)

Seismic imaging

High resolution‐3D

Viewing 3D data in many ways

Xline Sec

tionInline Section

Time SliceChair Display

Seabed Logging

Resistivity Profile

• All geological media have some sort of electrical conductivity.

• Difference in conductivity between shale & sandstone is relatively small when they’re water saturated.

• The conductivity falls markedly when the sandstone is filled with oil.

Seabed Logging

H2OH2O

Water-Filled Reservoir= Low Resistivity

Less Refraction of Wavesto the Receivers

HCHC

Hydrocarbon-Filled Reservoir= High Resistivity

Refraction of Wavesto the Receivers

From Seismic to map

TrapA trap is a geologic or a stratigraphic feature capable of

retaining hydrocarbons. Hydrocarbon traps that result from changes in rock type or pinch-outs, unconformities, or other sedimentary features such as reefs or buildups are called stratigraphic traps. Hydrocarbon traps that form in Geologic structures such as folds and faults are called structural traps

The key components of PETROLEUM SYSTEM (S) are (1) source rocks, (2) timing of generation, (3) migration (4) trap, and (5) seal

Petroleum System

Drilling …..

MUD LOGGING

DITCH SAMPLING

SUBSURFACE PRESSURE MONITORING

HC SHOW

TEMP MONITORING

BLOW OUT PREVENTION

CORING

LWD

MWD

Drilling…

RIG

VERTICAL

INCLINED

HORIZONTAL

EXTENDED REACH WELL

SAKHALIN-1 WELL HORIZONTAL DISTANCE 10 KM.

Well Profiles

Open hole logging – Formation Evaluation

DIRECT INFORMATION -ROCK FRAGMENTS & FLUIDS

Dill cuttings, mud shows

Sidewall samples, Cores or core slices, Production tests, Formation wireline samplers, Dill-stem tests

INDIRECT INFORMATION -WIRELINE LOGS

PHYSICAL PHENOMENON MEASURED PARAMETER

acoustic -waves sonic velocities

acoustic impedance

gamma / gamma scattering electron density

photoelectric cross section

thermal neutron density hydrogen density

thermal neutron decay thermal neutron cross section

neutron activation elemental concentrations

natural gamma radiation API

spontaneous potential membrane potential

electromagnetic waves electric resistivity / conductivity

LOCATE: reservoir DETECT: fluid content

fluid type : gas / oil / waterEVALUATE: lithology

mechanical propertiesgross / net reservoir thicknessporosity permeabilitycapillary propertiessalinity of the wateroriginal hydrocarbon saturationresidual hydrocarbon saturationpercent oil/gas/waterreservoir pressure

Objectives of a Petrophysical Interpretation

Formation Evaluation

Wire line logs - Open Hole

RESISTI VITY

DENSITY

POROSITY

RADIOCATIVITY SPECTRUM

TRANSIT TIME

Well completion

Perforation of reservoir

Reserves are those quantities of petroleum which are anticipated to be commercially recovered from known accumulations from a given date forward.

All reserve estimates involve some degree of uncertainty

PROVED UNPROVED

PROBABLE POSSIBLE

Reserves

Volumetrics

OIIP = Area x thickness x porosity x saturation

FVF

GIIP = Area x thickness x porosity x saturation x Bg

Recoverable Reserves: IIP x Recovery Factor

1. Primary recovery

• Reservoir pressure causes OIL to flow to the surface

•The simplest way of maintaining production flow rates is to use downhole pumps. (15-20%)

2. Secondary recovery

•Secondary recovery methods were developed to improve the recovery factor.The most common method involves flooding the reservoir with water. This involves injecting water into the reservoir to artificially increase the reservoir pressure and press the oil into the production wells (30-40%)

3. Tertiary recovery (EOR = enhanced oil recovery)

•The following methods can be used to improve the crude's flow qualities:

- Injecting steam into a reservoir heats up the crude and reduces its viscosity.

- The same effect can be achieved by pumping in solvents.

•Upto 50 % of the original oil in place can be exploited by means of tertiary recovery

Production

Injection Well

Production Well

Injection Well

1. Water

2. Polymer

Production

Classification of crude oil is often by its relative weight or viscosity ("light", "intermediate" or "heavy");

Refiners may also refer to it as "sweet", which means it contains relatively little sulfur, or as "sour", which means it contains substantial amounts of sulfur and requires more refining in order to meet current product specifications

Classification of crude oil

The world reference oils :

Brent Crude comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea .

Oil production from Europe, Africa and Middle Eastern oil flowing Westtends to be priced off the price of this oil, which forms a benchmark.

•West Texas intermidiate (WTI) for North American oil.

•Dubai used as benchmark for the Asia - Pacific region for Middle East Oil

•Tapis (from Malaysia, used as a reference for light Far East oil)

•Minas (from Indonesia, used as a reference for heavy Far East oil)