Formation Evaluation Techniques

(Coring, Well Logging, Well Testing)

Drilling Engineering II

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

Contents

Formation Evaluation

Coring Logging Well Testing Comparison

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”.

Types of formation evaluation

Coring

Well logging

Well testing

CoringIntroduction – Significance – Types

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.

Objective Permeability information

Capillary pressure data

Data for refining log calculations

Reserves estimate

Types of Coring

Bottom hole coring

Side wall coring

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.

Types of Bottom Hole Coring

Conventional coring

Wireline retrievable coring

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

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

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.

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

Routine core analysis (RCA) Normally we perform a routine analysis of the core

Properties to be determined: Porosity

Permeability

Saturation

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.

Properties to be determined Porosity Saturation Permeability Capillary pressure test Relative permeability test Connate water saturation Wettability Resistivity Mineralogical composition Electric measurement

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.

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

Well LoggingDefinition – Significance – Interpretation

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.

What logs tell us? Significance Lithology Porosity Permeability Resistivity Saturation Fluids in the pores of the reservoir rocks

Standard Log

Sample of Well Log

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

Mud Logging Detailed record of borehole vs

depth by examining the rock cuttings

brought to the surface by drilling mud

Sample of Mud Log

Logging Equipment Sonde - used for Log measurements- lowered on a cable from a winch,

mounted on a logging truck.

Electric Logs

1. Spontaneous Potential Log 2. Resistivity Log

(SP Log)

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

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

Reason of Self Potential

SP log

SP log

Limitations Oil based mud or synthetic mud Same salinity Mostly used in sand stones Air and gas drilling

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

Interpretation goals Resistivity of formation water Indication of permeability Correlation Porosity

Resistivity Log

Gamma Ray Log It measures the radio-activity of formation.

Shales are more radio-active

Interpretation Goals Correlation of formations

Lithology

Estimate of shale content

Source rock identification

Gamma Ray Log

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.

Caliper Log It measures the diameter of well-bore

Importance Hole size is used for correction of readings from other tools

Well TestingIntroduction – Types – Significance

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.

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

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

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

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

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 )

Input Data Well Data

Wellbore radius Well Geometry Depths

Reservoir & Fluid parameters Formation thickness, h Porosity Sw Oil Viscosity FVF Compressibilities

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:

Properties which can be determined Reservoir Description Permeability Reservoir Heterogeneities Boundaries Pressures Well Description Production Potential Well Geometry

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)

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.

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.

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)

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.

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)

Comparison

LithologyCoring

• Lithology can be Indicated

Logging• Exact Depth of different formations can be known• Bed thickness can also be known

Well Testing• No lithology

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.

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

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

Any Questions?