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C O M P A C T L O G G I N G

Compact Calibration Guide Issue 2 November 2002 Page 1 of 26

Reeves Technologies

Compact

CalibrationGuide

Issue

2


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CONTENTS

1. Introduction ....................................................................................................... 3

2. Calibration Philosophy..................................................................................... 4

2.1 Calibration Objectives And Definitions................................................................................4

2.2 Designation .............................................................................................................................5

2.3 Normalisation..........................................................................................................................52.3.1 The Need For Normalisation 52.3.2 The Mechanics Of Normalisation 62.3.3 The Base Normalisation And Field Check Principle 72.3.4 The Calibration Trail - Traceability 72.3.5 Calibrator Design 82.3.6 Normalisation Frequency 9

2.4 Characterisation .....................................................................................................................92.4.1 Characterisation Objectives 92.4.2 Physical Experiments 102.4.3 Mathematical Models 10

2.5 Combination..........................................................................................................................10

3. Signal Processing........................................................................................... 11

3.1 Sample Rates ........................................................................................................................113.1.1 Optimum Sample Rate 12

3.2 Smoothing Filters .................................................................................................................123.2.1 Optimum Smoothing Filter 13

4. Calibration Catalogue..................................................................................... 14

4.1 Resistivity Tools ...................................................................................................................154.1.1 Shallow Focussed Electric Log (MFE) 154.1.2 Array Induction Sonde (MAI) 164.1.3 Spontaneous Potential (SP) 18

4.2 Nuclear Tools ........................................................................................................................184.2.1 Gamma Ray 184.2.2 Compact Photodensity Sonde (MPD) 194.2.3 Compact Dual Neutron Sonde (MDN) 22

4.3 Acoustic Tools ......................................................................................................................234.3.1 Compact Sonic Sonde (MSS) 23

4.4 Caliper Tools .........................................................................................................................24

4.5 Temperature Logs ................................................................................................................25

4.6 Pressure ................................................................................................................................26


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1. INTRODUCTION

The Compact Calibration Guide is concerned with the acquisition and processing ofReeves Compact Systems well log data.

Starting with the raw output from logging tool transducers, the Guide follows thecalibration process through to the generation of logs scaled in engineering units. It showshow calibration information presented on a log tail is traceable to primary standards, and itspecifies the maximum expected inter-tool normalisation errors for each measurement.

The Guide also includes a consideration of basic digital signal processing principles asapplied to the presentation of log data, and indicates how the choice of digital filter

influences spatial resolution, precision and nuclear log signal-to-noise ratios.


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2.2.2.2. CALIBRATION PHILOSOPHY

2.1 CALIBRATION OBJECTIVES AND DEFINITIONS

Log calibration encompasses a range of procedures whose objectives are to ensure that logdata represents a true record of the physical properties being measured, and in particularthat their values are traceable to those of standards whose properties are known to a highlevel of accuracy.

The procedures are designation, normalisation, characterisation and combination.

Designationis the identification of a new tool type, or level of modification to an existingtype, which causes it to have a new and unique set of response characteristics.

Normalisationis the process that ensures all examples of the same tool type respond in thesame way to a common stimulus.

Characterisationis the process of relating normalised tool outputs to the formationproperty of interest, and of defining the environmental perturbations on that response.

Combination refers to the manner in which individual measurements are brought together

to form a compensated measurement.

In the logging industry, calibration is frequency a colloquial reference to normalisation. Inparticular, we refer to calibration jigs (or calibrators), and present normalisationinformation in a calibration "tail". In this context, normalisation and calibration are usedsynonymously.

An explanation of the meaning and interpretation of calibration tails occupies the majorpart of this document.


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2.2 DESIGNATION

Designation by measurement principle is obvious. However, tools which nominallyperform the same function may encompass a range of designs. This is because more thanone design may have been made to cover a range of operating conditions, or moregenerally, because tool designs are subject to a programme of continuous improvement.

The question arises - at what level of modification does a tool become a new tool with anew response function?

Tool geometry modifications (for example, spacing and collimation) invariably result in the

designation of a new response function, whilst a discrete electronic component changetypically does not. The effects of some modifications can be determined only byexperiment - when a response function change is indicated, a new tool series is designatedalong with a new set of response characteristics.

2.32.32.32.3 NORMALISATION

2.3.1 The Need for Normalisation

Once a generic tool type has been designated, its formation and environmental responsecharacteristics must be defined; this need only be done once for one tool, since it isassumed that all tools of the same type share the same set of response characteristics.However, no two tools are ever identical, so provision must be made to equalise theiroutputs to a common reference standard. This is the process of normalisation.

Differences between tools are random and systematic. Examples of random variation aremanufacturing tolerances, and variations in the thickness of pressure casings caused bywear. An example of a systematic variation is the decay of a radioactive source (Cs-137,for example, decays 2.3% per year).

The process of normalisation is intended to correct for differences of this type that aresmall. The raw responses from all tools of the same type (counts, volts and so forth) areassumed to be related to each other in a simple way, usually in a linear fashion. There are asmall number of exceptions to the linearity assumption, and in these cases more complexnormalisations are used. For example, some caliper mechanisms do not behave linearly,and in this case the full measurement range is split into sub-ranges which are each taken as

linear.


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It is stressed that normalisation takes place in the raw output domain (sometimes afterapplication of a so-called design normalisation to scale the output into the appropriate

engineering unit range). This permits the assumption of linearity to be made valid by theappropriate level of control during the manufacturing and operating processes.

2.3.2 The Mechanics of Normalisation

Linear transformation (from raw units into normalised units) uses a gain term and anoffset. In other words:

Normalised Unit = m(Raw Unit) +c

where m and c are gain and offset respectively. They are derived by subjecting the tools toa standard input or environment. For example, some resistivity tools are normalised usingprecision resistors, whilst nuclear tools are generally subjected to standard fluxes.

In order to define both m and c it is necessary to have two reference points. In some cases

it can be determined that c is zero (or less than the normalisation error) in which case onlyone non-zero reference is used. This is sometimes called a one-point normalisation.

The normalisation procedure is therefore to record raw output whilst subjecting the tool tothe two references in turn. This gives the simultaneous equations:

Reference 1 = m (Raw 1) + c

Reference 2 = m (Raw 2 )+ c

whence

m = (Reference 2 - Reference 1) / (Raw 2 - Raw 1)

and

c = Reference 1 - m (Raw 1)

In the case of nuclear logs, the measurements are made over a sufficiently long period oftime to allow the uncertainty due to counting statistics to be ignored.


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2.3.3 The Base Normalisation and Field Check Principle

When a normalisation procedure is simple and environmental effects are small, the bestplace to perform it is at the wellsite immediately prior to logging. This is the case, forexample, with the gamma ray tool.

In general, however, normalisation procedure demand several measurements per tool, theresults may be influenced by the local environment, and attention to detail is required.Consequently, the best place to normalise is usually at a base location where conditions canbe controlled, and where operational pressures are at a minimum. This is the BaseCalibration.

The gains and offsets obtained in this way are generally more accurate than can be obtainedat the wellsite. Moreover, the stability of modern systems is such that this considerationoutweighs any desirability for wellsite calibration. Consequently for the majority of tools,the m and c values used during logging are those obtained at base, and a check procedure isused to confirm or otherwise the appropriateness of the values at the wellsite.

The check may be a sub-set of the base calibration, or may use a special field portable jig orinternal standard. In each case, a Field Check At Basemeasurement is compared to abefore surveyField Checkmade at the wellsite using the same procedure. This in turn iscompared with an After Survey Checkas a quality control on stability during logging.

Values obtained during each phase of the check procedure should agree to within quotedtolerances. However, failure to agree is not proof of a tool fault.

If the tolerances are not met, the engineer will take other information into account (forexample, whether circumstances allowed the tool to be cleaned to the appropriate degreeprior to the check), and select one of the following courses of action:

1. repeat the Check

2. accept the log and perform a full Base Calibration as soon as feasible after the job

3. run a back-up tool.

2.3.4 The Calibration Trail - Traceability

The reference standards used to characterise the response of a tool are unique. They are theprimarycalibration set. The standards used during normalisation are also commonlyreferred to as calibrators; they are replicated at each operating base and their values

referenced to the primary calibration set. They are the secondaryor basestandards.


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In some cases the base standards are physically large, and it may be inconvenient totransport and use them in the field. Consequently the check measurements may be

performed using tertiaryor fieldstandards which are themselves calibrated against a basestandard.

In this way, a calibration trail or chain is established which enables the response of a tool tobe traced all the way back to the primary standard.

In the calibration trail, there is a level below that of field standard, and that is the internalcalibrator. This is used when it is not possible to perform a field check because of, forexample, interference from nearby structures (this can be particularly problematic onoffshore installations). Examples are the precision voltages generated internally within theArray Induction tool, and the lock source counts from density tools.

2.3.5 Calibrator Design

The design of a calibrator is a function of its purpose. Primary calibrators are typicallylarge, enclosing the entire volume of investigation of the logging tool; they arehomogeneous and their properties are known to a high level of accuracy. Examples arefree space, test wells drilled (and cored) through real earth formations, artificial formations

made of real earth materials, cast or moulded blocks such as aluminium and nylon, andlarge bodies of water such as lakes and reservoirs. The values assigned to primarycalibrators are determined using independent means.

Field standards, on the other hand, need not be large. In most cases, they are used aschecks, with portability and ease of use being important design considerations. Care may beneeded to avoid environmental perturbations i.e. the possibility that the tool readings maybe influenced by materials close to the tool during the check measurement.

For all calibrator types, their design needs to take account of the practicalities of making avalid logging measurement.

In particular, it must be easy to control the position of the calibrator with respect to thetool. So, for example, the density tool base normalisation and field checks are performedwith the tool horizontal, source and detector windows uppermost, and the calibratorresting on top, then gravity does most of the positioning work.

Another design consideration for all calibrators is that they should provide a measurementthat is within the range of interest and in a manner similar to real earth formations. So, forexample, a gamma calibrator comprises multiple sources embedded in nylon, which wrapsaround the gamma detector to give a uniform flux whose spectrum is typical of realformations.


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2.3.6 Normalisation Frequency

Base normalisations are performed at intervals which have been defined on the basis ofknown tool properties, rates of usage, and past experience (in the form of normalisationhistories). The recommended intervals are specified for each tool in Section 4. The typicalinterval is one month; occasionally three or six-month intervals are specified. Where baseand field procedures are the same (the gamma ray, for example) the normalisation may beperformed immediately prior to each job.

2.4 CHARACTERISATION

2.4.1 Characterisation Objectives

Characterisation is the process of relating normalised tool output to formation propertiesof interest, taking due account of environment related perturbing influences. Workingwith normalised outputs means this process need only be performed once for eachdesignated tool type.

The first stage in this process is to define the transform between raw transducer output andthe formation property under standard conditions. Standard conditions are usually (butnot always) an 8 inch (203mm) diameter borehole filled with fresh water (density 1.0gm/ccor 8.3lb/gal) at 70F (21C) and 1 atmosphere. Nuclear tools are standardly eccentred,whilst mandrel resistivity tools are standardly centralised. Transforms are defined bynoting the tool output as the formation property of interest is changed; the environmentand (as far as possible) other formation properties are maintained constant.

The second stage is to define the departure characteristics. These are the variations in tooloutput caused by changes in hole size, mud weight and so forth, and which occur even ifthe formation property stays constant.

In some cases, the corrections may be independent of formation properties. This is the case(to a good approximation) with the borehole size correction for induction measurements.In other cases, the corrections can change in a complex way dependent on formationproperties. This is the case for neutron porosity standoff corrections, for example.

The characterisation equations may be empirical, or they may be constrained by theoreticalconsiderations. Wherever possible, theory is used to predict the form of all transforms anddepartures. In this way, a small number of calibration points are likely to define all theequation unknowns, and the response is likely to be well behaved between and beyond thecalibration points.

Empirical characterisation must use a sufficiently large number of calibration points toallow a proper definition of tool behaviour. The response characteristics of tools aredetermined using physical experimentation or mathematical modelling.


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2.4.2 Physical Experiments

These are measurements made with real logging tools in simulated formations, or inmaterials whose properties are known to a high level of accuracy. They are also needed tobenchmark the results of mathematical modelling. Among the many physical test facilitieshosted by Reeves Technologies is the industry standard Callisto neutron porosity facility,and numerous density and Pe test blocks.

2.4.3 Mathematical Models

These predict measurement performance using computational techniques - both analytical(deterministic) and stochastic (or a mixture of the two). A key advantage is their ability togive results for formations and environments that are difficult to realise physically. Thesetechniques were used at a very early stage in the design and development of all Compactseries tools, and were a key element in measurement optimisation.

The nuclear measurements (Density, Pe and Gamma Ray) were characterised using theMonte Carlomethod in which "virtual" particles are tracked from source to detector viainteractions whose outcome is determined by the toss of a virtual coin. The electricalmeasurements (Array Induction, Focussed Electric and Laterologs) were characterised usinganalytical and finite element techniques.

2.5 COMBINATION

Some additional immunity to environmental effects is often achieved by combiningmeasurements to form a compensated log. Wherever possible this is done in the linearengineering unit domain. For example, the compensated density, is computed according to

SLc AA )1( +=

Here A is a constant, and the L and S subscripts refer to long and short spacingsrespectively. In this case the individual logs have been separately normalised andcharacterised; this approach is both consistent with theoretical considerations, and makesthe individual logs available for resolution enhancement in an appropriate form. Thisaspect is addressed in Section 3.5.

Of great importance in the definition of combination measurements are the verticalinvestigation characteristics. In particular it is essential that the measure points are depth-matched, and the intrinsic vertical averaging is matched. The former is achieved by making

the appropriate depth shifts, whilst vertical response matching is performed by smearingthe short spacing(s) to match the resolution of the long spacing.


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3. SIGNAL PROCESSING

This section deals with sampling and filtering. These influence the perceived verticalresolution and precision of logs.

3.1 SAMPLE RATES

Reeves logs are generated from sampled data. The rate of sampling is such that there are

always sufficient samples to allow a continuous log to be reconstructed with theappropriate amount of vertical resolution - the finer the resolution of the measurement, thegreater the sample rate.

Table 1 shows the available sample rates and corresponding increment between samples.

SAMPLE RATE

samples/metre

INCREMENT

mm (inches)

10

40

100

200

500

100 (3.9)

25 (1.0)

10 (0.4)

5 (0.2)

2 (0.1)

Table 1 Available sample rates and corresponding increments

The rate for all lithology logs is 10 samples/metre, which allows reproduction of spatialfrequencies as high as 5 cycles/metre.

Enhanced resolution lithology logging uses a rate of 40 samples/metre, which allowsfrequencies as high as 20 cycles/metre to be reproduced.

The higher sample rates have been reserved for future dipmeter and formation imagelogging developments.


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3.1.1 Optimum Sample Rate

The optimum sample rate is the minimum rate that permits reproduction of the highestmeaningful frequency in a measurement.

It is not normally convenient to record mixed sample rates from one tool string, so the ratethat is used depends on the highest resolution measurement in the string (under samplingresults in the loss of vertical resolution).

Consequently, some curves may be over sampled. In the case of nuclear logs, this meansthat the standard deviation per sample is unnecessarily high, and smoothing filters areemployed to bring the noise back to optimum levels.

3.2 SMOOTHING FILTERS

The filtered outputXfat depth d is:

Xf= (....W-1Xd-1+ WoXd+W1Xd+....)

Where Wiare the filter coefficients.

The variance ofXfis therefore given by:

11

2

1

2

0

2

12

... + ++= dddf XXXX WWW

Assuming the variances are the same over the averaged interval, the variance reduction istherefore:

222/ iWdXXf =

and the fractional change in standard deviation is:

( ) 2/12/ iWdXXf = (1)

A number of filters are available to cover the range of noise reduction requirements, andthese are listed in Table 2. They are either moving averages (MA) in which the filterweights are equal, or convolved moving averages (CMA) which are two MA filtersconvolved together. For example a 3 MA filter is a 3 level filter whose weights are (1/3,1/3, 1/3), and a 3/5 CMA is a 7 level filter with weights (1/15, 2/15, 1/5, 1/5, 1/5, 2/15,1/15). The relative change in standard deviation per sample is also given in the table.


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Filter Number Description Relative StandardDeviation

0

1

2

3

4

5

6

7

8

9

No Filter

3 MA

3/5 MA

3/9 MA

11 MA

Differential Filter

3/7 MA

5/7 MA

5 MA

User Defined

1.00

0.58

0.41

0.32

0.30

-

0.35

0.33

0.45

-

Table 2. Standard filters and the associated reduction in standard deviation per sample.

3.2.1 Optimum Smoothing Filter

If a log has been sampled at the optimum rate, any smoothing will degrade resolution. If anuclear log has been over sampled the standard deviation per sample increase by the squareroot of the ratio of the rate used to the optimum rate.

If the standard deviation associated with the optimum rate is xowe have:

2/1)/(/ oxoxd RR= (2)

where R is the rate used and Ro the optimum rate. Combining (1) and (2) we get:

2/ io WRR = (3)

Equation (3) defines the equivalence between filtering and changing the sample rate, andallows the optimum filter to be chosen for any over sampled rate.

For example, if a measurement produces a maximum frequency of 1.5 cycles/metre, theoptimum sample rate is 3 samples/metre. For an actual rate of 10 samples/metre, there willbe no loss of resolution with a filter whose sum of squares of weights is equal to (or greaterthan) 0.30. From equation (1) this corresponds to a standard deviation change of 0.55.The simplest filter that most closely matches this criterion is the 3MA. In practice, a

somewhat heavier filter may be desirable in order to smooth the additional uncertaintiesassociated with formation heterogeneity and tool dynamics in rugose holes. The defaultfilter for nuclear logs is the 3/5 CMA.


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4.4.4.4. CALIBRATION CATALOGUE

This section describes primary calibration, base normalisation and field check proceduresfor each tool, and specifies tolerances on uncalibrated and check values for use in qualitycontrol procedures (see section 2.3.3). Example calibration records from Compact's 32-bitacquisition software are reproduced.

Calibration records for each measurement are stored in the Reeves format Curve file forthat measurement, and is also encoded on certain styles of LIS format customer files (so-called Pagoda-compatible files). Part of the calibration procedure is to compare the currentcalibration set with the last (which is held in a separate calibrations database file)

The calibration tail on a paper log is a summary of the Curve file calibration data. In

general, the calibration record for each measurement comprises two parts:

1. Calibration Record. This displays pairings of raw measurements due to thereference standards, and the standard values themselves, from which gains and offsets arecomputed; check values used to confirm correct functioning of each tool are alsopresented. The Calibration Record is stamped with the tool (or sub) number to which itrefers, and the date of the calibration and check (if present).

2. Measurement Constants.These are engineer editable values that control theprocessing of the calibrated data. Examples are matrix density (used to calculate density

porosity), borehole fluid salinity, and formation Sigma (for neutron porosity environmentalcorrections).

The tool-specific calibration procedures are detailed below, illustrated with actualCalibration Records. The accompanying tables summarise each step in the procedure, andspecify the expected tolerances on the measured (pre-calibrated) values.


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4.1 RESISTIVITY TOOLS

4.1.1 Shallow Focussed Electric Log (MFE)

Primary calibration is by precision resistor connected externally to the tool's electrodes.Field checks use an internal reference, and are performed with the tool in air.

Resistivity is computed as:

= m(kR+c)

where R is the resistance measured by the tool (sense electrode potential divided bycurrent), k the tool coefficient (or k-factor), and m and c the calibration gain and offset.

In the calibration record, the measured value is R and the calibrated value is .

Two measurements, Reference 1 and Reference 2 are needed to determine m and c. Thedesign of the MFE is such that c=0, and Reference 1 is therefore set to zero.

These calibrations are normally performed on a monthly basis.

Step Description Values Comments

1

2

3

4

5

Reference 1

Reference 2

Base Check

Field Check

After Survey Check

00

98080 (measured)

277 2%

Step 3 2%

Step 4 2%

Zero Offset

127 ohm-m

ohm-m

FE Calibration MFE 009 Base Calibration on 10-FEB-1999 11:33Field Check on 12-FEB-1999 13:44

Base Calibration

Measured Calibrated (ohm-m)

Reference 1 0.0 0.0 Reference 2 976.9 127.0

Base Check 277.1

Field Check 277.1

FE Check MFE 009 Before Survey Check on 12-FEB-1999 13:44 After Survey Check on 12-FEB-1999 15:58

Before (ohm-m) After (ohm-m) 277.1 276.0


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4.1.2 Array Induction Sonde (MAI)

The Array Induction Sonde makes four measurements of conductivity, each output channelbeing independently calibrated.

Base calibration is from a copper loop and precision resistors placed around the tool, co-planar with the measure points of each channel. The loop simulates a conductiveformation; the apparent conductivity of the loop is different for each channel.

Base calibrations are performed at specific locations known to have negligible or very lowbackground conductivity (determined from measurements made with tools calibrated in atrue zero conductivity environment). Non-zero backgrounds offset the calibration; they are

backed out, and reported as Site Corrections in the Induction Constants part of thecalibration record.

Field checks use two internal references that present different apparent conductivities toeach channel. The field internals are compared to internal values obtained during basenormalisation. The internals are also used in the after survey check.

The four channels are typically combined into Deep, Medium and Shallow curves. Valuesfor these curves resulting from the Field Checks are presented for information.

It is recommended that the loop calibration is performed monthly.

Induction Calibration MAI 015 Base Calibration on 10-FEB-1999 10:41 Field Check on 12-FEB-1999 08:32

Base Calibration

Test Loop Calibration Measured Calibrated (mmho-m) Channel Low High Low High

1 14.1 453.3 9.3 966.2

2 5.8 371.6 7.6 821.4

3 3.4 246.8 5.2 566.1 4 2.4 129.4 2.6 279.2

Array Temperature 15.0 Deg C

Channel Base Check (mmho/m) Field Check (mmho/m) 1 15.4 15.4

2 31.3 31.3

3 28.5 28.5

4 18.5 18.5

Deep 15.9 15.9

Medium 42.7 42.7 Shallow 49.0 49.0

Array Temperature 14.0 14.0 Deg C

Induction Check MAI 015 Before Survey Check on 12-FEB-1999 08:32 After Survey Check on 12-FEB-1999 16:32

Channel Before Survey (mmho/m) After Survey (mmho/m) 1 15.4 15.4

2 31.3 31.3

3 28.5 28.5

4 18.5 18.5

Deep 15.9 15.9 Medium 42.7 42.7 Shallow 49.0 49.0

Array Temperature 14.0 14.0 Deg C


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1 Test loop values

Channel 1

Low: 1425

High: 45020%

(measured)

9.3 mS

966.2 mS

(calibrated)

2 Test loop values

Channel 2

Low: 625

High: 37020%

(measured)

7.6 mS

821.4 mS

(calibrated)

3 Test loop values

Channel 3

Low: 425

High: 25020%

(measured)

5.2 mS

566.1 mS

(calibrated)

4 Test loop values

Channel 4

Low: 225

High: 13020%

(measured)

2.6 mS

279.2 mS

(calibrated)

5 Base & Field Checks

Channel 1

15 20mS


Channel 2

30 20mS


Channel 3

30 20mS


Channel 4

20 20mS

9 After Survey Checks

All Channels

Before Field Check

2mS

Note:

1mS = 1 mmho/m.


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4.1.3 Spontaneous Potential (SP)

Spontaneous potentials result from ionic activity differences between formations, orbetween the borehole and formation. The SP log is a relative measurement - its absolutevalue has no significance. Calibration ensures that the log has the correct sensitivity.

Tool output is in millivolts. The primary (and only) calibrator is an external precisionvoltage source. Two reference signals are selected, typically close to 100mV; the tooloutput is transformed to the reference signal using the appropriate gain and offset. Thiscalibration is performed in the field prior to logging.

4.2 NUCLEAR TOOLS

Unless noted otherwise, all count rates are counts per second.

4.2.1 Gamma Ray

A gamma measurement is made in the Compact Gamma Comms (MCG) sub. It logsnaturally occurring gamma rays having energies in excess of approximately 100keV.

The raw output is the number of counts per second from a sodium iodide crystal andphoto-multiplier tube. This is scaled into API units using a gain factor determined from atest jig.

The primary gamma calibrator is the API test pit in Houston: 1 API unit is defined as 1/200of the difference between high and low activity zones in the pit. Secondary calibrators are

split nylon doughnuts that are wrapped around the tool, and contain low activityradioactive materials that simulate the flux from typical earth formations. This calibrationis performed in the field prior to logging, and repeated after survey as a check.

Gamma Calibration MCG 021Field Calibration on 7-JAN-1999 13:10

Measured Calibrated (API)

Background 49 33

Calibrator (Gross) 417 954 Calibrator (Net) 368 921

Gamma Check MCG 021 Field Calibration on 7-JAN-1999 13:10 After Survey Check on 8-JAN-1999 00:12

Before (API) After (API) Background 33 70

Calibrator (Gross) 954 992

Calibrator (Net) 921 922

SP Calibration MCG 021Field Calibration on 7-JAN-1999 13:15

Measured Calibrated (mV) Reference 1 106.8 103.3 Reference 2 -99.9 -103.3


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1 Background - Natural background

2 Gross counts - Counts depend onbackground level

3 Net counts Gross-background

= API value of thecalibrator after gain

value applied

4 Step 1-3 repeatedafter survey

Step 33% In API units

4.2.2 Compact PhotoDensity Sonde (MPD)

The Compact PhotoDensity Sonde provides formation density and borehole caliper logs,plus a lithology-sensitive Pe measurement.

The formation density log is a compensated measurement derived from near and far spacedmeasurements which have been individually calibrated and characterised. Primarycalibration was established in specially commissioned calibration blocks, and the Callistotest facility.

The Pe curve is derived from the ratio of soft (low energy) counts to hard (high energy)counts from the near spaced detector. Primary calibration was established in the samecalibration facilities.

Raw count rates are transformed into normalised counts (Standard Density Units - SDUs)using secondary base standards.

Density processing transforms normalised hard energy counts into electron densities, e,

and then into apparent log densities a, using the relation a= 1.0704e- 0.1878. This

defines a progressive Z/A correction which is applied in the range 1.678 2.71 gm/cc; the

correction is set at zero for a> 2.71 gm/cc, and -0.065 gm/cc for a


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A single Base Calibration procedure normalises the density and Pe measurements. It beginswith a background measurement; most background counts are due to the small source used

by the detector gain stabilisation system, and must be removed prior to calculating densitiesand Pe ratios. Two reference jigs are then placed in turn over the tool. Reference 1 is anylon block, Reference 2 an aluminium block with steel insert. Counts due to each aresorted into soft (WS) and hard (WH) energy bins. Density counts are transformed intonormalised density units, whilst the soft/hard ratio values are transformed into normalisedratio values.

The recommended base to field check procedure is to repeat the Reference 2 measurementat base and compare with Reference 2 counts made in the field. If a valid Reference 2 fieldmeasurement cannot be obtained for environmental reasons, it is acceptable to compare

background counts. The after survey check is a repeat of the Reference 2 or backgroundmeasurement, as appropriate.

Base calibration is performed monthly at defined physical locations known to producenegligible backscatter counts.

Photo Density Calibration MPD 008 Base Calibration on 7-JAN-1999 12:10 Field Check on 7-JAN-1999 14:20

Density CalibrationBase Calibration Measured Calibrated (sdu)

Near Far Near Far

Reference 1 53073 17940 53237 19514

Reference 2 25050 2471 25276 2557

Field Check at Base

893.6 1172.4

Field Check

895.7 1171.8

PE Calibration

Base Calibration Measured Calibrated

WS WH Ratio Ratio

Background 168 780

Reference 1 16085 52904 0.305 0.319

Reference 1 6402 24926 0.258 0.275

Field Check at Base

168.0 780.5

Field Check

168.1 784.3

Photo Density Check MPD 008 Before Survey Check on 7-JAN-1999 14:20 After Survey Check on 8-JAN-1999 00:46

Density Check Near Far

Before After Before After

895.7 890.0 1171.8 1170.0

PE Check

Before After

WS 168.1 170.0

WH 784.3 785.0


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1 Soft and Hard Background - WS and WH

Near and Far

2 Reference 1

measured count rate

50,00025%

18,00025%

Near density

Far density

3 Reference 2

measured count rate

25,00025%

2,50025%

Near density

Far density

4 Reference 2 Soft/Hard ratios 0.3020% Near Pe

5 Calibrated counts per secondand calibrated ratios

- Values stamped on jigs

6 Field Check at Base Steps 3 & 4

counts 3%

Alternative display oflock counts

7 Field Check Step 63%

Step 66%

Density & WH counts

WS counts

8 After Survey Check Step 73%Step 76%

Density & WH countsWS counts

Note:

Average counts reduce by 2.3% per year due to source decay.


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4.2.3 Compact Dual Neutron Sonde (MDN)

The Compact Dual Neutron porosity log is computed from a ratio of near and far thermalneutron count rates that have been individually normalised.

Primary calibration was established at the Callisto test facility, at test pits in Houston, andat other Reeves facilities. The secondary base standard is a large fresh water filled tankreplicated at each base, and used to normalise tools on a monthly basis. Checks areperformed using portable active jigs.

The acquisition software has the capacity to apply all relevant environmental corrections.They are listed in the Neutron Constants part of the log tail, and are applied when thecorrection parameter values depart from standard conditions (refer to the MDN Charts.

Neutron Calibration MDN 015 Base Calibration on 4-OCT-2002 09:39 Field Check on 4-OCT-2002 14:49

Base Calibration Measured Calibrated (cps)

Near Far Near Far

3202 99 3714 110

Ratio 32.324 33.764

Field Calibrator at Base Calibrated (cps)

2104 3027

Ratio 0.695

Field Check

Calibrated (cps)

2076 3048

Ratio 0.681

Neutron Check MDN 015 Before Survey Check on 4-OCT-2002 14:49 After Survey Check on 4-OCT-2002 23:16

Near(cps) Far(cps) Before After Before After

2104 2105 3027 3028

Ratio

Before After

0.695 0.695


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1 Base Calibration

(measured count rates)

3,50025%

10650%

Near

Far

2 Base Calibration

(measured ratio)

3310%

3 Calibrated counts 3714

110

Near

Far

4 Field Calibrator at Base 0.70.05 Ratio

5 Field Check Step 4 0.02 Ratio

6 After Survey Check Step 5 0.02 Ratio

4.3 ACOUSTIC TOOLS

4.3.1 Compact Sonic Sonde (MSS)

The Compact Sonic Sonde measures compressional wave slowness tc.

The fundamental measurement parameter is time. This is derived from a very accuratecrystal oscillator whose proper functioning is implicitly guaranteed in an operating tool,and does not require calibration.

Some variants of MSS also operate as Cement Bond Log tools. In this case, the E1amplitude may be normalised to produce a standard reading in free pipe. The gain factor isrecorded in the Curve File, but does not produce a printed calibration record.


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4.4 CALIPER TOOLS

Caliper tools measure borehole diameter; caliper logs are used in hole volume calculations,and may be used in certain environmental corrections.

The caliper from the Compact PhotoDensity (MPD) serves to position the density shoeagainst the borehole wall. The caliper from the Compact Two Arm Caliper (MTC) isnormally run at right angles to the MPD caliper in elliptical wells to position the densityshoe across the short axis of the well; this configuration results in an X-Y caliper output.

The calibration procedure is the same in both cases.

Base calibration uses five sleeves whose internal diameters are known to a high degree ofprecision, covering the range of expected hole sizes. Count rates from the calipertransducers are recorded for each sleeve, and a transform characteristic is computed.

A field calibration is performed at the wellsite prior to logging. One of the sleeves ismeasured with the calibration transform applied, and compared with the actual sleevediameter. The two values should agree to within the specified tolerance; residualdifferences below the tolerance level are removed by making a modification to the basecalibration characteristic.

The after survey check is a repetition of the sleeve measurements made before survey. Thebefore and after values should agree to within the specified tolerance.

Base calibrations are normally performed on a monthly basis.

Caliper Calibration MPD 008 Base Calibration on 7-JAN-1999 10:01 Field Calibration on 8-JAN-1999 14:07

Base CalibrationReading No Measured Calibrator Size (in)

1 17557 3.99

2 27294 5.96

3 37502 7.96 4 47232 9.84

5 58479 11.92

Field Calibration

Measured Caliper (in) Actual Caliper (in)

7.95 7.96

Caliper Check MPD 008 Field Calibration on 8-JAN-1999 14:07 After Survey Check on 8-JAN-1999 23:58

Before (in) After (in)

7.96 7.94


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1 Base Calibration Measured output fromfive sleeves

Values dependon tool type and

sleeve sizes

2 Calibrated diameters Sleeve diameters

3 Field Calibration Sleeve size 0.2 inch

(0.4 inch for long arm)

4 After Survey Check Step 3 sleeve size 0.2inch

(0.4 inch for long arm)

4.5 TEMPERATURE LOGS

The primary measurement of borehole temperature is from the MCG tool. Nominalaccuracy is 1.7 degrees C. The High Resolution Temperature curve recorded by MAIand MHT tools is used to compute differential temperatures, and as such the absoluteaccuracy is not specified.

Temperature measurements are made with transducers whose output is linear withtemperature. During primary calibration the transducers are exposed to ambienttemperature and a second elevated temperature. Calibrated values are determined using anindependent precision thermometer.

High Resolution Temperature Calibration MCG 015Field Calibration on 10-JAN-1999 10:11

Measured Calibrated (Deg C)

Lower 15.2 15.6

Upper 49.4 49.7


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4.6 PRESSURE

Formation and hydrostatic wellbore pressures are measured by the Compact RepeatFormation Pressure Tester (MFT). The tool contains two gauges: a strain gauge, and aQuartzdyne quartz gauge.

Initial calibration of all Quartzdyne gauges is by the manufacturer, and includes thedetermination of the temperature response characteristics. The initial calibrations arechecked every 3 months using a reference gauge supplied by Quartzdyne and calibrated bythe manufacturer at 12 month intervals. Gauges that fail the check procedure are returnedto the manufacturer for primary calibration, but otherwise the date of the manufacturer'soriginal calibration appears in the MFT Logging Constants section of the log tail. Theprimary calibration of individual gauges may therefore be older than 12 months.

The manufacturer also performs strain gauge primary calibration, and the contents of themanufacturer's calibration certificate are reproduced in the Strain Gauge Constants part ofthe MFT calibration tail. The calibrated response is recorded as a function of increasingand decreasing temperature. The strain gauge calibration is checked with a dead weighttester (or against the quartz reference gauge) every 3 months.

compact calibration guide_p

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