formation evaluation - an overview
TRANSCRIPT
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Formation Evaluation Techniques
(Coring, Well Logging, Well Testing)
Drilling Engineering II
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Group Members M.Suleman 2014-PET-03 Usman Shaukat 2014-PET-06 Basit Ali 2014-PET-12 H.Hamza Saleem 2014-PET-17 H.Shoaib Maqbool 2014-PET-24 Muhammad Anas 2014-PET-34 Qaiser Adeeb 2014-PET-35 Hassan Ali 2014-PET-38
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Contents
Formation Evaluation
Coring Logging Well Testing Comparison
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Formation Evaluation The process to determine the ability of reservoir to produce
hydrocarbons is known as formation evaluation.
OR Formation evaluation is used to determine the ability of a borehole to
produce petroleum. Essentially, it is the process of "recognizing a commercial well when you drill one”.
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Types of formation evaluation
Coring
Well logging
Well testing
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CoringIntroduction – Significance – Types
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Coring A cylindrical sample of rock obtained with a hollow drill is known as core.
The sample is then analyzed for determining different petro-physical properties.
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Objective Permeability information
Capillary pressure data
Data for refining log calculations
Reserves estimate
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Types of Coring
Bottom hole coring
Side wall coring
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Bottom hole coring
The coring at the time of drilling is known as bottom hole coring.
In the technique special bit is attached to BHA, hollow from inside. When drilling progresses core is being drilled and drill string is pulled out to obtain core.
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Types of Bottom Hole Coring
Conventional coring
Wireline retrievable coring
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Conventional coring The entire drill string is pulled to retrieve the core.
Advantage of conventional coring: By this method large core of 3 to 5 inch in diameter and 30 to 55ft long can be obtained
Disadvantage of conventional coring: Time consuming Un-economical
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Wireline Retrievable coring In this method core and inner barrel are retrieved without pulling the entire
drill string. This is accomplished with an overshot run down the drill pipe on a wire line.
Advantage: We don’t have to pull the entire drill string, so a lot of time is saved due to this reason.
Disadvantage: A relatively smaller core is obtained
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Side wall coring
The coring done after the drilling is side wall coring.
A hollow steel bullet is fired which imbeds itself in formation. It is then retrieved by wire while bullets contain core sample.
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Steps in Core Handling And Preservation Core Barrel’s Top and bottom are marked Core sample will be extracted from the barrel by slight hammering Top and bottom are marked on core sample Wax Coating or cellophane paper is wrapped around each section Top and Bottom are marked on the 1 ft section These are placed in wooden boxes which are transported to the lab
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Routine core analysis (RCA) Normally we perform a routine analysis of the core
Properties to be determined: Porosity
Permeability
Saturation
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Special Core Analysis (SCAL)
Special core analysis is distinguished from "routine or conventional core analysis" by adding more experiments, in particular including measurements of two-phase flow properties, determining relative permeability and capillary pressure.
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Properties to be determined Porosity Saturation Permeability Capillary pressure test Relative permeability test Connate water saturation Wettability Resistivity Mineralogical composition Electric measurement
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Why we perform SCAL In EOR, we need the imbibition capillary pressure, relative permeability,
and distribution of remaining oil saturation for effective reservoir management.
These properties have great impact on the sweep efficiency in a displacement mechanism.
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Factors affecting the laboratory Saturation Original Fluid content Properties of Reservoir fluid
Viscosity, volatility, FVF etc
Rock Permeability Drilling Fluid properties Coring Rate Care of handling
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Well LoggingDefinition – Significance – Interpretation
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What is Well logging? Practice of making a detailed record
of the geologic formations with depth
Why We do Well Logging? To collect data about wellbores and
subsurface formations. To make critical decisions about drilling,
completion and production.
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What logs tell us? Significance Lithology Porosity Permeability Resistivity Saturation Fluids in the pores of the reservoir rocks
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Standard Log
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Sample of Well Log
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Different techniquesand types of logging
Mud Logging Electric Logging
SP (Spontaneous Potential) Log Resistivity Log
Radioactivity Logging Gamma Ray Log Neutron Porosity Log
Miscellaneous Logging Caliper Log Acoustic Log Temperature Log
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Mud Logging Detailed record of borehole vs
depth by examining the rock cuttings
brought to the surface by drilling mud
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Sample of Mud Log
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Logging Equipment Sonde - used for Log measurements- lowered on a cable from a winch,
mounted on a logging truck.
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Electric Logs
1. Spontaneous Potential Log 2. Resistivity Log
(SP Log)
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SP Log The SP log is a record of direct current
voltage that develops naturally between a movable electrode in the wellbore and fixed electrode at the surface.
Self Potential develops due to salinity
contrast (b/w mud filtrate & Formation Water) Reasons for Self potential
Liquid Junction Potential Membrane Potential
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Correlation of Formations formation from well to well Estimation of Formation Water Resistivity ( R w ) Qualitative Indication of Permeability Estimation of Shale content Detection Of Permeable beds
Interpretation Goals
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Reason of Self Potential
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SP log
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SP log
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Limitations Oil based mud or synthetic mud Same salinity Mostly used in sand stones Air and gas drilling
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Resistivity Log Resistivity is the rock property on which the entire science of logging first
developed. It measures the resistivity of foramation
In reservoir, H.C, fresh water, and rock are insulators
Salt water is a conductor
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Interpretation goals Resistivity of formation water Indication of permeability Correlation Porosity
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Resistivity Log
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Gamma Ray Log It measures the radio-activity of formation.
Shales are more radio-active
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Interpretation Goals Correlation of formations
Lithology
Estimate of shale content
Source rock identification
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Gamma Ray Log
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Limitation
Clean sandstone may also give a high GR response if it contains potassium feldspars, micas, glauconite or uranium-rich waters.
In such cases, we will use modified spectral GR log.
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Caliper Log It measures the diameter of well-bore
Importance Hole size is used for correction of readings from other tools
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Well TestingIntroduction – Types – Significance
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Well Testing What is well testing? Well testing is a technique which optimizes and develops a reservoir
model capable of realistically predicting the dynamic behavior of zone of interest in terms of production rate and fluid recovery for different operating conditions.
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Methodology of well testing The inverse problem The objective of well test analysis is to describe an unknown system S
(well+reservoir) by indirect measurements (O the pressure response to I the change of rate solving S=O/I is a typical inverse problem.
I OS
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Flow Regimes The different flow regimes are usually classified in terms of rate of
change of pressure with respect to time Steady State Flow Pseudo steady state Flow Unsteady(Transient) State Flow
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Steady State Flow In the steady state flow pressure does not change with time means
pressure at every location in the reservoir remains constant For example Gas cap some type of water drives
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Pseudo State Flow When the pressure at different locations in the reservoir is declining
linearly as a function of time means with a constant rate production the drop of pressure becomes constant for each unit of time
Pseudo steady state system characterizes a closed system response
𝑑𝑝𝑑𝑡 =𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
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Transient State flow The fluid flowing conditions at which the rate of change of pressure with
respect to time at any position in the reservoir is neither zero nor constant
The pressure variation with time is a function of the well geometry and the reservoir properties such as permeability and heterogeneity.
𝑑𝑝𝑑𝑡 = 𝑓 (𝑥 , 𝑦 , 𝑧 , 𝑡 )
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Input Data Well Data
Wellbore radius Well Geometry Depths
Reservoir & Fluid parameters Formation thickness, h Porosity Sw Oil Viscosity FVF Compressibilities
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Information Obtained from Well Testing Well test responses characterize the ability of the fluid to flow through
the reservoir and to the well. Tests provide the description of the reservoir in dynamic conditions.
As the investigated reservoir volume is relatively large, the estimated parameters are average values. From pressure curve analysis it is possible to determine the following properties:
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Properties which can be determined Reservoir Description Permeability Reservoir Heterogeneities Boundaries Pressures Well Description Production Potential Well Geometry
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Types Of Well Testing(oil) Drawdown Test Buildup Test Injection Test/Fall of Test Interference Test and Pulse Testing Drill stem Testing Repeated Formation Test(RFT)
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Drawdown Test A pressure drawdown test is a simply series of bottom hole
pressure measurements made during a period of flow at constant producing rate.
Usually the well is shut-in prior to the flow test for a period of time sufficient to allow the pressure to equalize throughout the formation i.e. to reach static pressure.
It is difficult to maintain a constant flow rate so drawdown pressure data is erratic.
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Buildup Test Pressure buildup analysis describe the buildup in
wellbore pressure with the time after a well has been shut in.
Before build up test the well must have been flowing long enough to reach stabilized rate.
The flow rate is accurately controlled (zero),thats why buildup tests should be performed.
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Injection Test/Fall off test When fluid is injected into the reservoir the bottom hole pressure
increases and after shut in, it drops during the fall-off period. Properties of injected fluid are different from reservoir fluid . These tests require attention for analysis(difficult to interpret)
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Interference and Pulse Testing The bottom hole pressure is monitored in a shut-in observation well
some distance away from the producer. They evaluate communications between wells. With pulse testing, the active well is produced in a series of
alternate flow and shutting periods. The rate and duration of each flow are the same.
With interference test, the pressure response is measured in an observation well some distance away from the active well , which may be a producing or an injection well.
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Drill Stem Testing A drill stem test (DST) is a temporary completion of a wellbore that provides
information on whether or not to complete the well. The zone in question is sealed off from the rest of the wellbore by packers, and the formations' pressure and fluids are measured. Data obtained from a DST include the following:
Fluid samples Reservoir pressure (P*) Formation properties, including permeability (k), skin (S), and radius of
investigation (ri) Productivity estimates, including flow rate (Q)
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Comparison
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LithologyCoring
• Lithology can be Indicated
Logging• Exact Depth of different formations can be known• Bed thickness can also be known
Well Testing• No lithology
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PorosityCoring
• In case of heterogeneous reservoirs the porosity obtained from the core will not represent the reservoir.• As there is no O.B on core, so the porosity changes.
Logging•Indirect measurement of porosity •It only considers near well-bore region, so the porosity may be inaccurate.
Well Testing• It gives better depiction of reservoir porosity distribution.• It covers the whole reservoir, so the porosity value will be good.
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PermeabilityCoring
•True formation conditions can’t be replicated on surface
•Relative Permeability
Logging• Empirical Correlation which uses porosity and Sw
Well Testing• K = 162.6 q Bu/mh• Covers more area
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SaturationCoring
• Data is not quantitatively reliable• change in reservoir and surface conditions• mud invades the core
Logging• numerical value of saturation using Archie’s equation• value of saturation depends upon the resistivity of formation• Saturation value is only for near well bore area not hole reservoir
Well Testing•Ambigous
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Any Questions?
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