Formation Evaluation and Well Test Analysis- Group 3 n 4

7/31/2019 Formation Evaluation and Well Test Analysis- Group 3 n 4

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UNIVERSITI TEKNOLOGI PETRONAS

Formation Evaluation and

Well Test AnalysisNotes for Advanced Well Test Analysis Class from Group 3

and Group 4

Group 4:Buoy Rina, 12945

Makuach James makeny, 11749

Nik Mohammad Fadhlan bin Nik Kamaruddin, 12105

Sermphon Klaiseengern, 11823

Nurulhuda Bt Abdul Hamid, 11574

Group 3:Nurain bt. Minggu, 12153

Nik Fazril Ain Bt Sapian, 12103

Bior Atem Bior, 12920

Mai Thi Lien, 12962

Saw Li Juan, 11580


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1 Well Logging

1.1 Definition

The practice of making a detailed record (a well log) of the geologicformations penetrated

by a borehole(also known as borehole logging)

1.2 Types of Logging Environments

1. Open-hole logging refers to logging operations that are performed on a well before thewellbore has been cased and cemented. In other words, the logging is done through the

bare rock sides of the formation. This is the most common type of logging method

because the measurements are not obstructed and it's done during or after the well has

been drilled. This is the log type most frequently used in hydrocarbon exploration.

2. Cased-hole logging involves retrieving logging measurements through the well casing, orthe metal piping that is inserted into the well during completion operations. Cased-hole

logging is performed more rarely but still provides valuable information about the well.

1.3 Types of Logging Tools

1. Geological logginglogging based on visual inspection of samples brought to the surface(include drilling time logs, core logs, sample logs, and mud logs)

2. Wireline / Geophysical logging - logging based on physical measurements made byinstruments lowered into the borehole (include mechanical methods, electrical methods,

magnetic susceptibility logs and radioactive methods).This is the logging technique in

which after a well has finished drilling and reached TD (total depth), the logging tool is

lowered down the hole the hole on a cable (the wireline). As the tool is brought to the

surface ,it measures data (gamma ray, resistivity, etc) from which the log for the well is

constructed.

Table 1: Common wireline geophysical well measurements (Rider, 1996)
http://en.wikipedia.org/wiki/Geologichttp://en.wikipedia.org/wiki/Geologichttp://en.wikipedia.org/wiki/Mud_loghttp://en.wikipedia.org/wiki/Mud_loghttp://en.wikipedia.org/wiki/Geologic


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Table 2: Principal Use Of Wireline Logs

Wireline Logs Primary Use

Spontaneous Potential Logs

Gamma Ray Logs

Used for Correlation. The primary interpretive target is

the gross lithology(the distinction between reservoir and

non- reservoir layers)

Porosity Logs(Sonic,Logs, Density Logsand Neutron Logs)

When used individually, each of the logs has a responseto lithology which must be accounted for.When used more than 1 log at a same time (two or

three), lithology can be estimated and a more accurate

porosity can be derived.

Resistivity Logs Used for determination of hydrocarbon bearing versus

water-bearing zone

Nuclear-Magnetic Resonance

Logs

Used for determination of lithology-independent

measurement of effective porosity as well as total

porosity (overcoming many of the limitations ofconventional porosity measurements: neutron, density

and sonic logs)

1.4 Usage of Well Logging

What information can be defined from logs:

Physical rock characteristic Lithology and mineralogy of formation Porosity, Permeability Pore GeometryLogging data is used for:

Identify productive zones Determine depth and thickness of zone Distinguish between Oil, Water and Gas in the reservoir Estimate Hydrocarbon reserves

1.5 Measurement While drilling(MWD), Logging While Drilling(LWD)

For many years, well logging tools were lowered into the well at regular intervals while

drilling to retrieve data. With the advent of directional drilling, well logging had to develop to be

able to log a well that was no longer vertical. Logging While Drilling and Measurement-While-

Drilling (or MWD) place the logging tools on the end of the drilling column. That way, drillers

can use the information immediately to determine the direction and future of the well.

Logging-While-Drilling (LWD), a type of well logging that incorporates the logging

tools into the drill string, administering, interpreting and transmitting real-time formation

measurements to the surface.


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By locating well logging tools near the drill bit on the end of the drilling apparatus, LWD

enables drillers to log wells that exceed 60 degrees, which makes pushing the tool through the

well impossible.

Providing information on porosity, resistivity, acoustic waveform, hole direction, and

weight on bit, LWD transmits logging measurements at regular intervals while drilling is takingplace.

A type of LWD, Measurement-While-Drilling (MWD) specifically refers to measurement

of formation properties which is done continuously during the drilling process.


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2 Well Test Analysis

2.1 Objectives of well test analysis

To evaluate well condition and reservoir characterization.

To obtain reservoir parameters for reservoir description. To determine whether all the drilled length of oil well is also a producing zone. To estimate skin factor or drilling and completion-related damage to an oil well to

proceed with well stimulation that should be made.

To yield quantitative estimates of the well

conditions, the efficiency of stimulation,

treatment on well productivity can be evaluated.

Pressure measurements can be

interpreted

Used to determine the areal extent of a reservoir

and to estimate the volumes of fluid in place.

Several transient tests

Measure the direction of trends in the reservoir.

Estimate variations in rock permeability in the

vertical and areal senses.

Values of vertical and horizontal

permeability.

Average reservoir pressure, PAv

Pressure transient yields estimates

of the followings

Can be directly used in material balance

calculations.

Uses of Oil Well Tests

To estimate in-situ rock permeability and well

conditions.Well tests on the standard source

Numerical simulation processProvides values for well block permeability and

well conditions.

Values derived from well test Used to calculate variations in permeability

between wells and its trends for model input.


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2.2 Pressure Transient Well Tests

Detailed reservoir information is essential for Petroleum Engineer to analyze current behavior

and future performance of the reservoir.

2.2.1 DefinitionPressure transient testing is designed to provide engineer with a quantitative analysis of the

reservoir properties. It is conducted by creating a pressure disturbance in the reservoir and

recording response at the wellbore. As for example is by recording bottom hole flowing pressure,

Pwf as a function of time. The pressure behavior of a reservoir following a rate change directly

reflects the geometry and flow properties of the reservoir.

Information available from a well test:

1. Effective permeability

2. Formation damage or stimulation

3. Flow barriers and fluid contacts

4. Volumetric average reservoir pressure

5. Drainage pore volume

5. Detection, length, capacity of fractures

6. Communication between wells.

Table 1: Reservoir Properties Obtained from Pressure Transient Tests

Type of Tests Properties Development Stage

Drill Stem Tests (DST) Reservoir behavior

Permeability

Skin

Fracture length

Reservoir pressure

Reservoir limit

Boundaries

Exploration and appraisal

wells

Repeat formation tests/ Multiple

formation tests

Pressure profile Exploration and appraisal

wells

Drawdown tests Reservoir behavior

Permeability

Skin

Fracture length

Reservoir limit

Boundaries

Primary, secondary and

enhanced recovery


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Buildup Tests Reservoir behavior

Permeability

Skin

Fracture length

Reservoir limit

Boundaries


enhanced recovery

Falloff test Skin

Reservoir Pressure

Fracture length

Boundaries

Secondary and enhanced

recovery

Interference and pulse tests Communication between wells

Reservoir type behavior

Porosity

Interwell permeability

Vertical permeability


enhanced recovery

Layered reservoir tests Properties of individual layers

Horizontal permeability

Vertical Permeability

Skin

Average layer pressure

Outer boundaries

Throughout reservoir life

Step-rate tests Formation parting pressure

Permeability

Skin

Secondary and enhanced

recovery

2.3 Deliverability Tests

2.3.1 Definition:

Test designed to measure production capabilities of a well under specific conditions, where it is

primarily used for gas wells, but also applicable for oil wells. Parameters commonly obtained

from deliverability tests:

Absolute Open Flow (AOF) potential To generate Inflow Performance Relationship (IPR)

Table 2: Types of Deliverability Tests, Procedure and its Limitations

Type of tests Procedure Limitations


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Flow-After-

Flow Tests

By producing the well at series of differentstabilized flow rates and measuring BHFP at

the sandface.

Conventionally it is carried out with asequence of increasing flow rates, however if

stabilized flow rate is attained, flow ratesequence will not affect the tests.

To achieve stabilized flowing rate

requires a long time, especially in low

permeability formations.

Single Point

Tests

To overcome limitation of Flow-After-Flowtests.

Conducted by flowing the well at single rateuntil BHFP is stabilized.

Analysis of results requires priorinformation on well deliverability

behavior (previous tests, correlations

with other wells producing in the

same field at same conditions).

Must ensure well has been inproduction long enough to avoid

wellbore storage effect and pseudo-steady regime.

Isochronal

Tests

Developed to shorten time taken for wellsthat takes a long time to stabilized.

Conducted by alternately producing the well,then shutting the well and allowing it to build

up to the average pressure before begins with

next production period. Pressure is recorded

at several time increments during each flow.

Suitable for low permeability

formations.

Modified

Isochronal

Tests

To further shortened time taken duringisochronal tests.

Follow same procedure as isochronal,excepts that the shut-in periods are for same

duration and must be equal of longer than the

length of the flow period.

Shut-in sand face pressure is recorded insteadof recording the average reservoir pressure.

Less accurate that isochronal test.As duration of shut-ins period

increases, accuracy if tests also

increases.


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3 Analysis Methods of Pressure Transient Test Data

3.1 Log-log Scale Presentation of Pressure Responses

Normally, for a given test period, change in pressure is plotted against the change in time

on log-log scale. The analysis of well test pressure data on log-log scale is a global approach as it

covers all flow regimes rather than a specific flow regime as in the case of straight-line methods.

A typical presentation of well test pressure data on log-log scale is illustrated in the

below figure.

Once log-log plot of pressure data is obtained, it is compared with a set of theoretical

curves generated from general dimensionless solution. The purpose of this comparison is to

define the model which well describes the obtained pressure data. Usually, the dimensionless

terms are expressed as:

pD=Ap , A=f(k,h)

tD=Bt, B=f(k,C,s)

On log-log scale, dimensionless pressure and time can be expressed as:

Log(pD)=Log(A) + Log(p)

Log(tD)=Log(B)+ Log(t)

Change in A or B term cause the log-log plot of pressure data to shift vertically or

horizontally respectively. Thus, by matching the log-log plot of actual pressure data with the

global or theoretical log-log plot of dimensionless solution, key reservoir properties like khproduct or near-wellbore skin can be characterized.

Figure 1: Typical log-log plot of pressure data


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3.2 Type Curves

Type Curves are generated by obtaining solutions to the flow equations with specified

initial and boundary conditions; in which some solutions are analytical and others are based in

finite-difference approximation. Many of type curves are used to determine formation

permeability and to characterize damage and stimulation of the tested well. Some testes are used

to determine the beginning of the MTR for Horner Analysis. Most of the curves are generated by

simulating constantrate pressure drawdown (or injection); however most can also be applied to

buildup (or falloff) tests in equivalent shut-in time us used as the time variable on the graph. The

test has further advantage for test interpretation on the distorted data of wellbore storage or for

the fractured well. Type Curve is preplotted family of pressure drawdown curves. The most

fundamental of these curves is a plot of dimensionless pressure change, pD, vs. dimensionless

time change, tD.

3.2.1 Rameys Type Curves

Rameys Type Curve were generated for the situation of a constant-rate pressure

drawdown test in a reservoir with slightly compressible, single-phase, liquid flowing; sufficient

homogeneity such that the radial diffusity equation adequately models flow in the reservoir;

uniform drainage pressure in the drainage-area of the well before production; infinite acting

reservoir (no boundary effects during the flow period of interest fir test analysis purposes);

constant withdrawal rate at the surface; and wellbore storage and concentrated wellbore damage

or stimulation characterized by a skin factor, s,. If one or more of these assumptions is invalid in

a specific case, there is no assurance that the use of type curves can lead to a valid test

interpretation.

Figure 2: Type curves for constant production rate, infinite acting reservoir (Ramey)


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3.2.2 McKinleys Type Curves

McKinley proposed type curves with the primary objective of characterizing damage or

stimulation in a drawdown or buildup test in which well bore storage distorts most or all of the

data, thus making thus characterization possible with relatively short-term tests. The reservoir

properties calculated using the early part of the test are liable to be less accurate than those

calculated from the straight line of the Horner plot or MDH plot.

Figure 3: McKinleys type curve

3.2.3 Gringarten Type Curves

Gringarten et al. developed type curves for hydraulically fractured wells in which

vertical fractures with two equal length wings were created. The curve assumes uniform flux into

the fracture ( same flow rate per unit cross sectional area of fracture from wellbore to fracture

tip). This type curve also assumes no pressure drop from fracture tip to wellbore.

This type curve can be used for a constant rate drawdown for a slightly compressible

liquid, buildup tests and also for gas wells.


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Figure 4: Gringarten type curve for vertically fractured well

3.2.4 Bourdet Type curve

This type curve is a plot of dimensionless pressure PD vs the dimensionless time group

TD/CD for wells with wellbore storage and skin in an infinite acting reservoir with homogeneous

behaviour. The aims are is to calculate the reservoir permeability, wellbore storage coefficientCD and skin factor.

Figure 5: Bourdet type curve for radial flow behavior


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4 References

1. Basic Well Log Analysis(2nd Edition), George Asquith and Daniel Krygowski, AAPGMethods In Exploration Series 16, The American Association Of Petroelum Geologists,

Tulsa Oklahoma.

2. Lee,J.: "Analysis of Well Tests Using Type Curves", Well Testing, SPE Text Book Series, v.1, 1982

3. Bourdet D.: Well Test Analysis: The Use of Advanced Interpretation Models - (Handbookof petroleum exploration and production), 2002.

4. Tarek A.: Reservoir Engineering Handbook.5. Amanat U. C.: Oil Well Testing Handbook.

Formation Evaluation and Well Test Analysis- Group 3 n 4

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