Petrophysical Engineering

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This book is the property of Shell Internationale Petroleum Maatschappij B.V., The Hague, The Netherlands. It must be promptly returned to them at any time they may so request. It is confidentially loaned to the holder for his personal information and use only, and neither its existence nor its contents shall be disclosed by the holder to any third party. The holder shall take every precaution to prevent third parties from perusing, reproducing or copying the same either wholly or in part.

The copyright of this document is vested in Shell Internationale Petroleum Maatschappij B.V., The Hague, The Netherlands. All rights reserved. Neither the whole nor any part of this document may be reproduced, stored in any retrieval system or transmitted in any form or by any means (electronic, mechanical, reprographic, recording or otherwise) without the prior written consent of the copyright owner.

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Objective

The objective of the Production Handbook is to contribute to efficient performance by all Engineering, Petroleum Engineering and Operations staff, by providing quick access to and practical guidance on their own and related disciplines’ technology.

Being a comprehensive combination of condensed technical manuals, it provides a ready source of information for reference and self-training.

It is not intended to replace detailed design manuals and state-of-the-art manuals; these should remain the first source of reference for more experienced technical specialists. Neither can the Production Handbook replace specialised training manuals.

Distribution

The Production Handbook should be available to all Engineering, Petroleum Engineering and Operations staff at or above JG5, in Group E&P Operating Companies and SIPM. These staff receive the Handbook as a personal loan; they may take it along when going on transfer within the Group but must return it when leaving for other reasons. Staff of other Functions’ parentages temporarily working in E&P companies may use library copies.

The Handbook is confidential and holders should note the conditions stated opposite the title page. Issue and recovery should be registered by company secretariats/libraries.

Reprinting and updating

The Production Handbook was first published by SIPM in 1986. It is the successor to the Field Pocketbook versions of 1933, 1947, 1952 and 1955 and the Field Handbook of 1963. The 1986 version comprised 3000 pages in five A5 ringbinders; 6000 copies were distributed.

An update of some 250 revised pages was issued in 1987 and a list of further corrections was published in the Production Newsletter of November 1988.

A complete reprint is necessary at this time (1991). For flexibility and cost-effectiveness this updated reprint is in nine paperback volumes, each one dedicated to a major discipline with clear ‘ownership’ by the SIPM-EP department concerned. These ‘custodian’ departments will initiate further updates of their respective volumes as and when necessary. Additional volumes and state-of-the-art manuals in the same format may be added later as special supplements.

Suggestions for revising and updating the Handbook should be directed to the SIPM-EP custodian department of the respective volume, using copies of the Specimen Amendment Sheet at the back of each volume.

Overall editorial custodianship of the Handbook rests with SIPM-EPD/11.

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CONTENTS LIST PRODUCTION HANDBOOK SERIES (1991)

SIPM Custodian Volume 1 Production General

– Units and Conversion Factors EPO/71

– Health, Safety and Environment EPO/6

– Quality Management EPO/72

– Economic Analysis EPE/1

Volume 2 Drilling and Transport EPO/51 – Drilling

– Civil Engineering for drilling locations – Transport in Production Operations

Volume 3 Petrophysical Engineering EPD/22

Volume 4 Reservoir Engineering EPD/22

Volume 5 Production Technology EPD/41 – Production Engineering

– Production Chemistry

Volume 6 Production Operations EPO/53

Volume 7 Process Engineering EPD/42 – Oil Processing

– Gas Processing

Custodian for Part I, Ch. 7, Terminals: EPD/13

Volume 8 Pipelines EPD/61

Volume 9 Facilities and Maintenance

– Running Equipment EPD/62

– Piping Systems EPD/62

– Electrical Engineering EPD/63

– Instrumentation EPD/64

– Telecommunications EPD/76

– Reliability and Availability Assessment EPD/13-EPO/54

– Corrosion Engineering EPD/65

– Inspection Techniques and Maintenance Terminology EPO/54

– Diving and Underwater Operations EPO/54

– Air Conditioning MFSH/11

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1991

The subjects covered in this Volume were formerly included in the 1986 version of the Production Handbook as Chapter 3, Petrophysical Engineering.

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VOLUME 3, PETROPHYSICAL ENGINEERING, REVISION 1991

SUMMARY CONTENTS LISTING page

1. Wireline Logging: General 10

2. Open Hole Logging 70

3. Wireline Coring, Testing and Sampling 130

4. Coring 144

5. Cased Hole and Production Logging 167

6. Perforating 187

7. Wellsite Geology 205

8. Safety and Environmental Control 239

9. Reservoir Compaction and Surface Subsidence 258

10. References and Further Reading 269

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Confidential-Property and Copyright: SIPM, 1991

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PETROPHYSICAL ENGINEERING

CONTENTS 1 WIRELINE LOGGING: GENERAL 10 1.1 Logging Programmes 10

1.1.1 Open Hole 10

1.1.2 Cased Hole and Production Logging 11 1.2 Preparation for Logging 12

1.3 Depth Checks and Calibration 13 1.3.1 Depth 13 1.3.2 Calibration 14 1.3.3 Depth Scales 15 1.3.4 Repeat Section 15 1.3.5 Statistical Checks 15 1.3.6 Tension Recording 15

1.3.7 Log Scales and Scale Changes 15

1.3.8 Computerised Service Unit (CSU) Filtering 15 1.3.9 Bottom Hole Temperatures 16

1.4 Field Prints, Headings and Service Reports 17

1.5 Dispatch and Transmission of Data 19 1.5.1 Dispatch 19

1.5.2 Transmission 20

1.6 Services and Codes 21

1.7 Tool Dimensions, Weights and Ratings 29 1.8 Logging Cables, Heads and Fishing Tools 45

1.9 Wireline Logging Operations in Deviated Holes 50 1.9.1 Friction Reducing Devices 50

1.9.2 Other Devices 51

1.9.3 Logging Through Casing Drill Pipe: Pumpdown Techniques 51 1.9.4 Logging of Near-Horizontal Holes 53

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Confidential-Property and Copyright: SIPM, 1991 Petrophysical Engineering

1.10 Sticking of Wireline Logging Equipment 55

1.10.1 General Guidelines on Stuck Tool, Weak Point and Fishing

Kit 56

1.10.2 Fishing for Stuck Tool 57

1.10.2.1 Open Hole 57

1.10.2.2 Cased Hole 59

1.10.2.3 Fishing through Tubing 60

1.11 Detection of Stuck Point/Back-Off Equipment 61

1.11.1 Stuck Pipe Indicator Tool 61

1.11.2 Back-Off Equipment 65

1.12 Wireline Logging Wave/Tide Compensation for Floating Rigs 65

2 OPEN HOLE LOGGING 70

2.1 Methods of Open Hole Logging 70

2.1.1 Rig-Up and Survey Checks 70

2.1.1.1 Rig-Up 70

2.1.1.2 Running in Hole 70

2.1.1.3 On Bottom 71

2.1.1.4 Surveying 71

2.1.1.5 After Survey 71

2.1.2 Induction - Spherically Focused 71

2.1.2.1 Spontaneous Potential (SP) 71

2.1.2.2 Spherically Focused Resistivity 72

2.1.2.3 Induction 72 2.1.3 Dual Laterolog 73 2.1.4 Micro Tools 73 2.1.4.1 Micro-SFL 73 2.1.4.2 Proximity Log 74 2.1.4.3 Microlaterolog 74 2.1.4.4 Microlog 74 2.1.5 Gamma Ray 75 2.1.6 Density 75 2.1.7 Neutron (Compensated) 76

2.1.8 Acoustic (Bore Hole Compensated) 77

2.1.9 Dipmeter/Diplog 78

2.1.10 Caliper 80

2.1.11 Gearhart Calibration Standards 82

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2.2 Principles of Log Evaluation 83

2.2.1 Lithology and Reservoir Thickness 84

2.2.2 Porosity 85

2.2.3 Hydrocarbon Saturation 94

2.2.3.1 Clean Rocks (Non-Argillaceous) 94

2.2.3.2 Shaly Sands 99

2.2.4 Determination of RW from SP curve – Shell Method Procedure 116

2.2.5 Reporting of Petrophysical Data 124

2.2.6 Quick-Look Evaluation Step by Step 124

3 WIRELINE CORING, TESTING AND SAMPLING 130

3.1 Sidewall Samples 130

3.1.1 Sidewall Sampling Using Explosive Bullets 130

3.1.2 Sidewall Coring Tool 131

3.2 Repeat Formation Tester 131

3.3 Sample Recovery 141

4 CORING 144

4.1 General 144

4.2 Coring Equipment 144

4.3 Coring Fluids, Hydraulics and Bits 147

4.4 Coring Criteria for Exploration and Appraisal Wells 148

4.5 Preparation for Coring 149

4.6 Instruction for Handling Cores for Petrophysical and Related Analyses 151

4.6.1 Recovery of Consolidated Cores 151

4.6.2 Cleaning, Boxing, Sampling and Labelling 151

4.6.3 Recovery of Very Friable and Loosely Consolidated Cores 158

4.6.3.1 Rubber Sleeve Coring 158

4.6.3.2 Plastic Fibreglass Core Cartridges 161

4.7 Core Description 163

4.8 Petrophysical Core Analysis: Suggested Standard Programme 166

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Petrophysical Engineering

5 CASED HOLE AND PRODUCTION LOGGING 167

5.1 Preparation for Logging 167

5.2 Operation Against Pressure 169

5.2.1 Testing Risers and Hydraulic Grease Tube (HGT) 169

5.2.2 Testing BOPs 169

5.2.3 Entering the Well 171

5.2.4 Running in Hole 172

5.2.5 PLT Logging 173

5.2.6 Pulling Out of Hole 173

5.3 Cement Bond Survey 174

5.4 Thermal Decay Time Logging 176

5.5 Electromagnetic Thickness Tool (ETT) 177

5.6 Production Logging Tool (PLT) 177

5.6.1 Flowmeter 180

5.6.2 Gradiomanometer 181

5.6.3 High Resolution Thermometer (HRT) 181

5.6.4 Continuous Pressure Manometer 181

5.6.5 Through-Tubing Caliper 181

5.6.6 Tracer Ejector Tool 182

5.7 Continuous Flowmeter 183 5.8 Gradiomanometer 185 5.9 Thermometer 186 6 PERFORATING 187 6.1 General Preparations 187 6.2 Arming Guns 189

6.3 Entering the Well 190

6.4 Depth Control 192

6.5 Retrieving the Gun 194

6.6 Gun Characteristics 196

7 WELLSITE GEOLOGY 205

7.1 Lithological Description of Sedimentary Rocks 205

7.1.1 Description and Coding of Rock Compositions 205

7.2 Hydrocarbon Detection 232

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Contents

7.2.1 Natural Fluorescence 232

7.2.2 Solvent Cuts 233

7.2.3 Solvent Cut Fluorescence 234

7.2.4 Acetone Water Test (Acetone Reaction) 234

7.2.5 Visible Staining and Bleeding 234

7.2.6 Odour 235

7.2.7 Gas Detection Analysis 235

7.2.8 Irridescence 235

7.2.9 Acid Test 235

7.2.10 Reporting Results of Tests for Hydrocarbon Shows 236

7.2.10.1 Symbols for Hydrocarbon Shows 236

7.2.10.2 Reporting Procedure Example 237

8 SAFETY AND ENVIRONMENTAL CONTROL 239

8.1 Handling and Storage of Radioactive Sources and Explosives 239 8.1.1 Radioactive Sources – Safe Working Conditions, Handling,

Storage and Transport 239

8.1.1.1 Handling Radioactive Sources on the Wellsite 239

8.1.1.2 Storage of Radioactive Sources 240

8.1.1.3 Transporting Radioactive Materials 241

8.1.1.4 Safety Equipment 242

8.1.1.5 Emergencies Involving Radioactive Sources 242

8.1.2 Explosives – Handling, Transport and Storage 243

8.2 Operating Safety and Radio Silence 245

8.2.1 Radioactive Sources – Operating Safety 245

8.2.2 Fishing for Radioactive Logging Tools 246

8.2.3 Explosives – Operating Safety 247

8.2.4 Radio Silence 248

8.3 The Presence of Hydrogen Sulphide 254

8.3.1 Toxicity of Hydrogen Sulphide Gas 254

8.3.2 Determination of Sulphide Content in Mud and Fluid

Samples 254

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9 RESERVOIR COMPACTION AND SURFACE SUBSIDENCE 258

9.1 Introduction 258

9.2 Compaction Prediction 259

9.2.1 Sandstone Reservoirs 259

9.2.1.1 Linear Compaction Model 259

9.2.1.2 Rate Type Compaction Model 261

9.2.1.3 Recommended Procedure 261

9.2.2 Compaction of Shales 262

9.2.3 Prediction of Compaction due to Pore Collapse in

High-Porosity Carbonate Reservoirs 262

9.2.3.1 The Trendline Model 262

9.2.3.2 Prediction of In-Situ Pore Collapse with the Trendline

Model 264

9.3 Calculation of Surface Subsidence 266

9.3.1 The Nucleus-of-Strain Approach 266

9.3.2 Quick-Look Procedure to Calculate Subsidence in the Deepest Point of the Subsidence Bowl Using the

Rigid-Basement Model 266

9.3.3 Detailed Calculation of Subsidence Using the

Rigid-Basement Model 267

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TABLES Table 1.7-1 Schlumberger tool data 29

Table 1.7-2 Western Atlas tool data 34

Table 1.7-3 Gearhart tool data 40

Table 1.8-1 Schlumberger logging cables and weak points 45

Table 1.8-2 Dresser Atlas logging cables and weak points 45

Table 1.8-3 Gearhart logging cables and weak points 46 Table 2.2-1 Photo-electric absorption index, bulk density, electron density and volumetric photo-electric absorption index of some common minerals and liquids 87

Table 2.2-2 Porosity tools 92

Table 2.2-3 Summary petrophysical evaluation (preliminary/final) 125

Table 4-1 Core recovery and sampling record 157

Table 6.6-1 Perforating gun performance summary – Schlumberger 196

Table 6.6-2 Perforating gun performance summary – Western Atlas 198

Table 6.6-3 Perforating gun performance summary – Gearhart 200

Table 8.1-1 Radiation limits for working conditions 239

Table 8.1-2 Approximate barrier distance from source container 241

Table 8.2.4-1 Radio shut-down during operations with explosives applicable to installations and vessels within 500 metres 249

Table 8.3.3-1 H2S determination by Dräger tube 256

Table 9.2-1 Range of compressibilities and β for various rock Types 260

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FIGURES

Figure 1-1a Schlumberger tool schematics 1 31

Figure 1-1b Schlumberger tool schematics 2 32

Figure 1-1c Schlumberger tool schematics 3 33

Figure 1-2a Western Atlas tool schematics 1 36 Figure 1-2b Western Atlas tool schematics 2 37 Figure 1-2c Western Atlas tool schematics 3 38 Figure 1-2d Western Atlas tool schematics 4 39 Figure 1-3a Gearhart tool schematics 1 41

Figure 1-3b Gearhart tool schematics 2 42

Figure 1-3c Gearhart tool schematics 3 43

Figure 1-3d Gearhart tool schematics 4 44

Figure 1-4 Cable head fishing dimensions (Schlumberger) 48

Figure 1-5 Cable head fishing dimensions (Western Atlas 49

Figure 1.11-1 Stuck pipe indicator tool (SIT) 62

Figure 1.11-2 Stuck pipe pull and torque transmission 63

Figure 1.12-1 Mechanical wave compensation device 66

Figure 1.12-2 Hydraulic-pneumatic compensating device 68

Figure 2.2-1 Importance of lithology determination 86

Figure 2.2-2a Porosity and lithology determination from formation density log and compensated neutron log (CNL*) 89 Figure 2.2-2b Porosity and lithology determination from formation density log and compensated neutron log (CNL*) 90 Figure 2.2-2c Porosity and lithology determination from sonic log and compensated neutron log (CNL*) 91

Figure 2.2-3 Density of water and NaCI solutions 93 Figure 2.2-4 Archie equations 95

Figure 2.2-5 Formation factor vs. porosity 96 Figure 2.2-6 Average values for porosity and saturation exponents 97 Figure 2.2-7 Resistivity Index vs. SW 102

Figure 2.2-8 Calculation of SW 103

Figure 2.2-9 Resistivity vs. temperature for NaCI solutions 104

Figure 2.2-10 Resistivity vs. porosity crossplot 105

Figure 2.2-11 The Waxman-Smits shaly sand model (1968) 106

Figure 2.2-12 The Archie clean sand model (1942) 106

Figure 2.2-13 B – RW temperature relationship 107

Figure 2.2-14 BRW – salinity relationship 108

Figure 2.2-15 Core conductivity 100% saturated with water 109

Figure 2.2-16 Shaly sands formation factor – porosity relationships 110

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Tables and Figures

Figure 2.2-17 Determination of cation exchange capacity Qvfrom

SP log 111

Figure 2.2-18 Graphical solution of Waxman-Smits equation 114

Figure 2.2-19 Solving Waxman-Smits by iteration 115

Figure 2.2-20 Spontaneous potential, four components 118 Figure 2.2-21 Streaming potential for various mud types 119 Figure 2.2-22 Electrochemical potential (Ec) vs. NaCI

concentration (CNaCl) for Qvshale

= 1, 2 and 4 mmol/cm3 123

Figure 2.2-23 Example of petrophysical data log 127 Figure 2.2-24a Resistivity vs. porosity crossplot, m = 1.8 128 Figure 2.2-24b Resistivity vs. porosity crossplot, m = 2.0 129

Figure 3-1 Western Atlas FMT assembly 132

Figure 3-2 Repeat formation tester system 133

Figure 3-3 Schlumberger RFT components 135

Figure 3-4 RFT pre-test permeability indications (qualitative) 137

Figure 3-5 Sample recovery at low pressure 142

Figure 4-1 Core handling procedure 154

Figure 4-2 Inner and outer labels for core boxes 155

Figure 4-3 Core description 156

Figure 4-4 Sawing device for cutting rubber sleeved cores 160 Figure 4-5 ‘Sock’ for handling fibreglass sleeved cores 162

Figure 5-1 Wireline lubricator set-up 168

Figure 5-2 BOP test stand set-up 170

Figure 5-3 Production logging tool 179

Figure 7.1-1 Guide for lithological descriptions of sedimentary

Rocks (TAPEWORM) 206

Figure 7.2-1 Oil detection in rock specimens last page Figure 9.2.3-1 Stress dependence of porosity for mouldic

limestone samples 263

Figure 9.2.3-2 Laboratory trendlines for various different

Carbonates 264

Figure 9.2.3-3 Procedure to calculate compaction due to pore

collapse from the porosity-stress trendline 265

Figure 9.3-1 Normalised subsidence above the entra of a

disc-shaped reservoir versus entraliza reservoir

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Confidential-Property and Copyright: SIPM, 1991 Wireline Logging: General

1. WIRELINE LOGGING: GENERAL

1.1 Logging Programmes

The following notes provide guidelines on open hole and cased hole logging programmes.

1.1.1 Open Hole

The policy for Wireline Logging is that exploration and appraisal wells are to be logged from the total depth to the surface and that development wells have to be logged over the intervals containing the reservoirs.

The programme for Open Hole Surveys is integral with the Drilling Programme, and is the responsibility of the Petrophysics Section.

No hard and fast rules can be laid down for logging programmes to cover all possible contingencies. The following guidelines are offered.

(a) Exploration and Appraisal Wells (i) Surface Casing Depth.

INDUCTION/SONIC/GR/SP from TD to Conductor Shoe. Transit Time In- tegration required. LITHO-DENSITY/NEUTRON/GR from TD to Conduc- tor Shoe if required to confirm gas indications. GR through casing from Conductor Shoe to surface.

Survey in 121_/

4” pilot hole.

(ii) Intermediate Logging.

INDUCTION/SONIC/GR/SP from TD to Casing Shoe or first reading previous survey, whichever is deeper. LITHO-DENSITY/NEUTRON/GR from TD to Casing Shoe or first reading previous survey, whichever is deeper. An overlap of 50 m is required with the previous run.

DIPMETER if required by Geologist/Production Geologist.

DUAL LATEROLOG/MICRO RESISTIVITY/GR/SP from TD to Casing Shoe if hydrocarbon-bearing intervals are encountered.

SIDEWALL SAMPLES, REPEAT FORMATION TESTER (Pressures and Formation Fluid samples), and CEMENT BOND LOG as requested. (iii) Final Logging.

As intermediate, with the addition of Velocity Survey if requested. CEMENT BOND/GR/CCL if casing is set for production testing.

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(b) Development Wells

(i) Surface Casing Depth

INDUCTION/SONIC/GR/SP may be requested to check gas indications. Survey in 121_/

4” pilot hole.

(ii) Intermediate Logging

As for Surface Casing Depth. Only if unexpected lithology/shows are encountered as for Intermediate Logging in Exploration and Appraisal Wells.

CEMENT BOND LOGGING may occasionally be required for confirma- tion of cementation.

(iii) Final Logging.

DUAL LATEROLOG/MSFL/GR/SP from TD to Casing Shoe.

LITHO-DENSITY/NEUTRON/GR/SP and if required INDUCTION/SONIC/ GR/SP from TD to Casing Shoe.

REPEAT FORMATION TESTER may be required for formation pressure monitoring.

CEMENT BOND/GR/CCL after casing/liner cementation.

1.1.2 Cased Hole and Production Logging

(a) The programme for perforation and completion logging is integral with the Completion Programme; perforation intervals are selected by the Petrophysics Section in conjunction with the Production Technology and Reservoir Engineering Sections.

(b) Production Logging is normally required to solve a specific production or injection problem.

Production Logging will normally be supervised by a Production Tech- nologist or Petrophysicist to ensure valid and useful results.

(c) Unscheduled Wireline Services may be requested to solve unexpected problems, e.g. Free Point Indication/Back-off, Temperature Survey for lost circulation. Responsibility for demand and supervision of these services rests with Operations Section.

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1.2 Preparation for Logging

(a) Ensure that all equipment and personnel required to carry out logging programme are on site and operational.

(b) Ensure that surveys from adjacent/nearby wells are available for com- parison /correlation.

(c) Discuss logging programme with Logging Engineer, and confirm running order of tools. It is recommended to use a tool string with a maximum amount of logging tools combined, including radioactive tools, with the objective to minimise rig time used for evaluation. Take notice of Oper- ating Safety and Radio Silence guidelines in Section 8.2.

(d) Provide Logging Engineer with the following data:

(i) Well description, location and DF elevation. Permanent datum is Mean Sea Level or ground level for offshore and land wells re- spectively.

(ii) Bit and Casing Sizes, TD and Casing Shoe Depths.

(iii) Mud type, weight, viscosity, water loss, pH and mud filtrate salinity. (iv) Changes to drilling/logging programme.

(v) Downhole conditions relevant to operation (deviation, tight spots, doglegs, sloughing shales, over-pressurised or under-pressurised formations, lost circulation intervals, gas zones, etc.).

(e) Provide samples of mud (5 dm3), mud filtrate and mud cake for resistivity measurements. The mud cake should be thick enough (5 mm) to be representative: the quantity of mud filtrate will then usually be adequate. Mud samples should be homogeneous and taken from the flowline during circulation just prior to logging. Ensure that measurements are made as soon as samples are ready.

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1.3 Depth Checks and Calibration

1.3.1 Depth

Log depths are standard reference for Shell Group Companies. All subsurface maps and markers are established by reference to the gamma ray curve of the gamma-ray density log, which is the REFERENCE SURVEY. The reference survey must be correlated with the first tool run (Resistivity) and it is therefore essential to determine depths accurately during the first run into the hole.

Depth below Derrick Floor (DF) will be determined as follows:

(a) First Survey

(i) Set tool zero at DF and set spooler at zero.

(ii) Run in hole to first bell, check first bell at spooler pulling up. (iii) Proceed to casing shoe (CS), checking bell every 30 m.

(iv) Just above CS catch mark at well, set at DF. Adjust spooler depth to read (distance from tool zero to first mark) + y Χ 30 m.

(v) Pull up and check mark at spooler. This is the bell to be used for the survey.

(vi) If the bell in (v) differs from the bell in (ii) by more than 1 m, the reason for the discrepancy must be determined (if necessary, by pulling out of the hole and re-checking surface mark) before logging.

(b) Subsequent Surveys

Subsequent surveys over the same section must be related to the first survey in the sequence. The mark at surface need be checked only roughly, and accurate correlation with the first survey made during recording of the overlap survey. It is perfectly normal, as a result of cable slack at surface, differences in tool weight, cable stretch, etc. for the bell at TD to be displaced several feet from the anticipated depth. If the discrepancy is excessive, the survey should be run by correlation with the first survey, and the tool zero checked at surface at the end of the survey. Provided the first survey was correctly recorded, both logs will then be at true depth.

Major errors between surveys usually arise as a result of movement of the travelling blocks, either when the driller moves the blocks for rig maintenance during logging, or when the brake is not properly set. If a major discrepancy occurs between surveys, it is wise to check that the blocks have not moved. Surveys are normally taped, and can be played back on correct depth without wasting further rig-time, but this can only be done if the correct depth is known.

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(c) Overlap Survey

Overlap Surveys of about 50 m with previous surveys are normally required. If a survey overlaps a previous survey in a hole which has not been cased off, depth must still be determined as in (a) (First Survey) above; NOT by correlation with the previous survey. If the discrepancy between the surveys is 0.5 m or less, the new survey may be correlated with the original. If the discrepancy is greater than 0.5 m, the reason for the discrepancy must be established before the entire open hole section is to be rerun, including the depth determination.

If logs are to be run in open hole, the cased part of which has previously been logged, the first survey must include a gamma-ray tool. Depths are initially to be determined as in (a) (First Survey) above, then a short through casing correlation film is to be made. If the discrepancy is less than 0.5 m, the new survey may be correlated with the original. If the discrepancy exceeds 0.5 m the reason for the discrepancy must be established before surveying continues.

If it is considered that the new log is more accurate, the survey may be continued, but a through-casing correlation log must be made over enough of the cased section to correct the original survey.

If it is considered that the previous survey is more accurate, the new log will be correlated with the original, but the correlation film at incorrect depth must be attached to the calibration tail with a note indicating the reason for the discrepancy.

(d) Stretch Correction

No stretch correction is to be applied to any open hole survey run at a depth of less than 3000 m. Normal stretch correction is to be applied below 3000 m and phased out to zero correction at 3000 m. When stretch correction is applied, this must be noted on the log heading of the first survey.

Spooler depth correction is not to exceed 1 m in 300 m. 1.3.2 Calibration

(i) Calibration records (see Individual Tool Calibrations) must be made before and after each survey.

(ii) If problems are encountered with tools, and any part of the equipment which could cause an alteration in recorded parameters is exchanged, the equipment must be re-calibrated. Under no circumstances is a calibration record made with one set of equipment to be presented with a survey with another set.

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1.3.3 Depth Scales

Surveys are to be recorded on 1 : 200 and 1 : 1000 scale, unless instructed otherwise.

1.3.4 Repeat Section

A repeat section should be run over the reservoir interval. If corrections or memorisations are applied, part of the repeat section is to be run without correction or memorisation, the other part with them. This is particularly important in the case of a log run for perforating depth control, when this is the only way of establishing how much depth correction has been applied. Take care that radioactivity is not induced into the formations during this operation.

1.3.5 Statistical Checks

All radiation tools are subject to statistical variations. Make a check on statistics if they appear to be excessive. The check should be made within the reservoir zone where deflections are representative of the reservoir. Pad tools must be opened, and statistics recorded for at least one minute. The check must be made in such a way that induced radioactivity from the source to the formation will not

affect the main survey. No statistical check is to be made with the TDT.

1.3.6 Tension Recording

A recording of incremental cable tension is to be made on 1 : 200 scale only over the reservoir interval. The trace is to be located on the log where it will not interfere with more important data traces.

1.3.7 Log Scales and Scale Changes

With the exception of dipmeters, SP and temperature surveys, no scale changes are to be made during the course of a logging run. When a scale change is necessary, a 50 m overlap is to be made on both scales.

1.3.8 Computerised Service Unit (CSU) Filtering

All optical (film/print) surveys made using computerised units must be recorded with zero filtering (0.00). This will result in curves with minor deviations

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from the smoothed surveys recorded using Standard Logging Units, or filtered surveys from computerised units, but this presentation must be adhered to for unitisation purposes.

1.3.9 Bottom Hole Temperatures

Three maximum thermometers should be run on each trip in the hole during open hole logging, the corresponding maximum bottom hole temperature to be reported on the log heading, together with time elapsed since circulation.

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1.4 Field Prints, Headings and Service Reports

Final print headings, and those surveys still being run by non-computerised

logging units, are in the API format. Field prints of computerised logging units have a different format. The following notes will help in checking correctness of print headings.

API Headings

Most of the information supplied on a CSU heading is identical to the API data, but could be in a different location.

Item Description Remarks

1. Location Latitude and longitude or co-ordinates of conductor. 2. Other Services Codes of other services run during this trip to well. 3. Permanent Datum This normally is Mean Sea Level (MSL) for offshore

operations and ground level for land operations.

4. Elev. Height of datum point above sea bed (ASB).

5. Log Measured from – Derrick Floor (DF).

ft. above Perm. Datum Elevation of Derrick Floor above MSL/ground level.

6. Date Day-month-year.

7. Run No. Sequence number of that exact survey in that particular well, e.g.lSF/SONIC is Run No. 1. FDC/CNL run after- wards can ALSO be Run No. 1.

8. Depth-Driller Total well depth as reported by Driller/Tool Pusher before logging.

9. Depth-Logger Maximum depth reached during this logging run ac- cording to wireline measurements (not necessarily the same as Depth-Driller).

10. Btm. Log Interval Deepest formation measured during this run (always shallower than Depth-Logger).

11. Top Log Interval Shallowest recording during this run. 12. Casing-Driller Casing OD at Drillers Casing Shoe Depth. 13. Casing-Logger Casing Shoe depth as registered by logging tool.

This must be the same on all surveys recorded through this casing.

14. Bit Size Nominal size of drill bit used.

15. Type Fluid in Hole Brief description of nature of mud/completion fluid. 16. Fluid Level Position of Well Fluid in borehole.

17. Dens. Density of hole fluid in psi/thousand feet.

18. Visc. Viscosity of hole fluid (centipoise – NOT seconds in Marsh funnel).

19. pH Acidity (pH) of hole fluid.

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21. Source of Sample Source (in mud system) of mud sample used for meas-

urement of mud resistivity. This should always be the

flowline.

22. Rm, Rmf, Rmc Resistivity of mud, mud filtrate, mud cake at measured temperature.

23. Source: Rmf, Rmc. Origin of sample used for resistivity determination, usually filter PRESS. The use of a downhole sample taken during a microtool run has now been discontin- ued.

24. Rm at BHT Mud resistivity at measured bottom hole temperature,

estimated from charts.

25. Time Since Circ. Approximate time (in hours) since mud circulation stopped.

26. Max. Rec. Temp. Maximum temperature as recorded by three maximum

thermometers in this logging run.

27. Equip. Contractor's Logging Unit number.

28. Location Contractor’s base.

29. Recorded by Logging Engineer’s name.

30. Witnessed by WSPE’s name.

31. Remarks Use this space for any comments relating to surveying

problems which could conceivably affect interpretation

of the survey (overpulls, mud additives, lost circulation

intervals, tool faults/failures, depth errors).

32. Run No. Should be the same as item 7.

33. C.D. Centralising Device (Centraliser, Caliper).

34. S.O. Stand-off (Ex-centraliser, Induction stand-off).

35. Panel No. Contractor’s serial number of equipment used for this

survey.

36. Cart. No. Contractor's cartridge number. The designation YEL-

LOW TOOL etc. WILL NOT DO.

37. Sonde No. Contractor’s sonde number. The purpose of this item is

to track down the exact equipment used for a survey, Sometimes years after a log was run.

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1.5 Dispatch and Transmission of Data

1.5.1 Dispatch

Surveyed data must be dispatched to the Opco Head Office (HO) as quickly as possible, to enable rapid decisions to be taken on other logging requirements and future rig activity. The following procedure has therefore been ad-

opted:

A. LOGGING ENGINEER

– is responsible for all survey data. He should supply:

1. Rough Print To WSPE for transmission as soon as possible. 2. Data Transmission If a data transmission link is available, transmit

openhole logs to HO.

3. Field Prints To WSPE for safehand forwarding by first means of transport after logging. One set to be retained on rig.

4. Sepias To WSPE to be dispatched with field prints. Sepias

are NOT required when data is transmitted.

5. Films To be taken by Logging Engineer or his representative to Service Company District Office by first trans-

port for finalisation.

6. Tapes (CSU) To be sent safehand with field prints to HO, except

except when surveys are data transmitted. In this case, field

tape is not required.

7. Service Order To be completed, signed and handed to WSPE as

soon as possible.

B. WSPE– is to assist the Service Company Engineer, as required, to expedite data transmission, and also carry out the following:

1. Mufax*) recorded Survey as soon as possible, 1:1000 first, 1:200 relevant section ONLY. DO NOT MUFAX HEADING, BUT MARK SCALES CLEARLY

AT HEAD OF LOG.

2. Forward Field Prints safehand by first transport after logging to HO. One complete set to be retained on rig.

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3. Forward Sepias with field prints to HO.

4. Sign Service Order, attach to computerised log data and time allocation input

sheets and forward to HO.

5. Arrange data transmission link for edit tape transmission to Wireline Company Computer Centre if required (CSU/CLS Operations).

1.5.2 Transmission

1. Data transmission is only required for open hole surveys, by formal request from HO.

2. The ‘Write’ ring must be removed from the Master tape before copying is attempted, to ensure preservation of the recorded data.

3. The Master tape must be copied, and from the copy a Field Edit Tape prepared for data transmission.

4. The Logging Company Engineer is responsible for transmission of data to the Computer Centre. On termination of transmission, the Computer Centre prepares an optical recording and confirms that the received data appear normal.

5. The WSPE notifies the Duty Petrophysicist that data transmission has been completed.

6. On receipt of log prints from the logging company's computer centre, the responsible Petrophysicist will check the transmitted log against the Mufax dispatched from the well-site, and subsequently against the 1:200 Field Prints hand-carried from the Wellsite.

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1.6 Services and Codes

Code Company Service

AC WA Borehole Compensated Acoustilog

ACBL WA Acoustic Cement Bond Log

ACL WA Long Space BHC Acoustilog

ACT SL Aluminium Clay Tool

AIS BPB Array Induction Sonde

ASL(SDT) SL Array Sonic Log

BCS HLS Borehole Compensated Sonic Tool

BGL(BGT) SL Borehole Geometry Log

BGN BPB Hole Tilt and Azimuth

BGS BPB Borehole Geometry

BHC SL Borehole Compensated Sonic Log

BHT BPB Temperature

BHTV SL Borehole Televiewer

BHTV WA Borehole Televiewer

BO SL Explosive Service (Back off)

BP BPB Plug Setting

BP SL Bridge Plug Setting

C/O WA Multiparameter Spectroscopy

Instrument Continuous Carbon/

Oxygen Log

CAC WA Circumferential Acoustilog

CAL BPB Caliper

CAL SL Caliper

CAST HLS Circumferential Acoustic Scanning Tool

CAV HLS Compensated Acoustic Velocity Tool

CBL(CBT) SL Cement Bond Log

CBL-VDL SL Cement Bond Log – Variable Density

Log

CBL/PET HLS Cement Bond Tool

CBL/VDL/CCL BPB Cement Bond Log

CCAT HLS Compensated Cement Attenuation Tool

CCL BPB Casing Collar Locator

CCL HLS Casing Collar Locator Tool

CCL SL Casing Collar Locator

CDL WA Compensated Densilog

(continued on next page)

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Code Company Service (continued)

CDR SL Directional Services-Continuous

CDS BPB Compensated Density

CDT HLS Compensated Density Tool (CDT-A)

CEL(CET) SL Cement Evaluation Log

CFM SL Flowmeter-Continuous

CFS SL Continuous Flowmeter Sonde

CHAR HLS Cased Hole Analysis and reservoir

Monitoring

CIC HLS Casing Inspection Caliper Tool

CIS SL Customer Instrument Service

CIT HLS Casing Inspection Tool

CLAM HLS Clay and Matrix Analysis

CNL(CNT) SL Compensated Neutron Log

CNL WA Compensated Neutron Log

CNS BPB Compensated Neutron

CNT HLS Compensated Neutron Tool (CNT-K)

CORA HLS Complex Reservoir Analysis

CPL(PCT) HLS Combination Production Log

CSNG HLS Compensated Spectral Natural Gamma

Tool

CSS BPB Compensated Sonic Sonde

CST SL Continuous Sample Taker

DCL HLS Dielectric Constant Tool

DCL WA Dielectric Log

DD SL Depth Determination

DEN HLS Density Tool

DGL HLS Dual Guard Tool

DIFL WA Dual Induction Focused Log

DIL HLS Dual Induction Tool

DIL SL Induction Sperically Focused Log

DIL SL Dual Induction SFL Log

DILB HLS Dual Induction Tool (DILTB)

DILT HLS Dual Induction Tool (DILTA)

DIS BPB Digital Induction Sonde

DLL HLS Dual Laterolog Tool (DDL)

DLL SL Dual Laterolog

DLL WA Dual Laterolog

DLLT HLS Dual Laterolog Tool (PLS)

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DLS BPB Dual Laterolog

DNLL WA Dual Detector Neutron Lifetime Log

DNLL WA Neutron Lifetime Log (Dual Detector)

DPL SL Deep Propagation Log

DSEN HLS Dual Spaced Epithermal Neutron Tool

DSN HLS Dual Spaced Neutron Tool

DSN2 HLS Dual Spaced Neutron/Model DSNT-A

Tool

DSNC HLS Comprobe Dual Neutron Tool

DTEMP BPB Differential Temperature

EL HLS Electric Log Tool

ENVR HLS Environmental Corrections

EPT/PCD SL Electromagnetic Propagation Log

EPT/PCD SL Powered Caliper Device

ETT SL Casing Corrosion Detector

FAC BPB Four Arm Caliper

FACT HLS Four Arm Caliper Tool

FBS SL Fullbore Spinner Flowmeter

FDC SL Formation Density Log

FDL HLS Fluid Density Tool

FDS BPB Fluid Density (Production Logging)

FED HLS Four Electode Dipmeter Tool (Four Arm)

FFS BPB Fullbore Flowmeter (Production

Logging)

FIT SL Formation Interval Tester

FLOLOG WA Flowmeter

FMS SL Formation MicroScanner Log

FMT WA Formation Multi-Tester

FMT WA Formation Tester

FPI WA Free Pipe Indicator

FPT/BO BPB Pipe Recovery

FS SL Fluid Sampling

FTL HLS Fluid Travel Tool

FWS HLS Full Wave Sonic Tool

GCT SL Continuous Guidance Tool

GEN HLS General Purpose

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Code Company Service (continued)

GEOP HLS Geophone

GMS SL Gradiomanometer

GR BPB Gamma Ray

GR HLS Gamma Ray Tool

GR SL Gamma Ray Log

GR-N WA Gamma Ray Neutron Log

GRD HLS Guard Tool

GRN HLS Gamma Ray Neutron Tool

GRVL HLS Gravel Pack Tool

GST SL Gamma Ray Spectroscopy Log

GTEM HLS Gradiomanometer Temperature Tool

HDD HLS High Density Dipmeter Tool

HDT SL High Resolution Dipmeter Log

HMS SL Manometer Temperature Sonde (HP)

HMST HLS Multiset Tester Tool

HRDIP WA Diplog (Four Arm High Resolution)

HRI HLS High Resolution Induction Tool

HTT SL High Resolution Temperature Tool

IEL HLS Induction Tool (DDL)

IEL WA Induction Electrolog

IELT HLS Induction Tool (PLS)

IFS BPB Inline Flowmeter (Production Logging)

IL SL Induction Logging

JC WA Junk Catcher

LCS BPB Long Spaced Compensated Sonic

LDL(LDT) SL Litho Density Log

LFD HLS Low Frequency Dielectric Tool

LIDA HLS Lithology Indentification Analysis

LL HLS Laterolog Tool

LL WA Laterolog

LSAV HLS Long Spaced Acoustic Velocity Tool

LSS HLS Long Spaced Sonic Tool

LSS SL Long Spaced Sonic Log

MEL HLS Microelectric Tool

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Code Company Service (continued)

METT SL Multifrequency Electromagnetic

Thickness Log

MFC SL Multi Finger Caliper Log

MFD SL Modular Formation Tester

MGL HLS Microguard Tool

MGL WA Casing Thickness Log

ML BPB Micro Log ML HLS MicroLog Tool ML WA Mini-log MLL BPB Micro Laterolog MLL HLS Microlaterolog Tool MLL WA Micro Laterolog

MSCT SL Mechanical Sidewall Coring Tool

MSFL SL Microspherically Focused Resistivity

Log

MSFL HLS Microspherically Focused Tool

MSG HLS Micro-Seismogram Frac-Finder Tool

MSI C/O WA Carbon/Oxygen Log

MTS SL Manometer Temperature Sonde

MWP SL Measurements While Perforating

NCS BPB Nuclear Combination Sonde

(GR-CN-CD)

NEU HLS Neutron Tool

NFD SL Nuclear Fluid Densimeter

NGS(NGT) SL Natural Gamma Ray Spectrometry Log

NL WA Neutron Log

NLL WA Neutron Lifetime Log

NML SL Nuclear Magnetism Log

OBD BPB Oil Based Dip Meter

OBDT WA Oil Based Mud Dipmeter Log

PAL SL Pipe Analysis Log

PDC SL Perforating Depth Control Log

PDK-100 WA Pulse and Decay

PDS BPB Photo Density Sonde

PET HLS Pulsed Echo Tool

PFC WA Perforating formation Collar

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PFM SL Flowmeter-Packer

PI SL Phasor Induction

PL HLS Production Log

PL SL Production Logs/Flow Profiles

PL SL PL/Transient Pressure and Flow Tests

PLA HLS Production Log Analysis

PLS BPB Production Logging

PML WA Proximity-Minilog

PSD BPB Precision Strata Dip Meter

PSGT HLS Pulsed Spectral Gamma Tool

PTS BPB Pressure Temperature Sonde

PTS SL Pressure Temperature Sonde

PTT BPB Temperature (Production Logging)

QPG BPB Fluid Pressure (HP Gauge) (Production

Logging)

RFS BPB Repeat Formation Sampler

RFT HLS Repeat Formation Tester Tool

RFT SL Repeat Formation Tester

RSCT HLS Rotary Sidewall Coring Tool

RSFE BPB Shallow Focussed Guard Log

SASH HLS Shaly Sand Analysis

SCG BPB Sidewall Core Gun

SDL HLS Spectral Density Tool

SED HLS Six Electrode Dipmeter Tool (Six Arm)

SFE BPB Short Focussed Guard

SFT HLS Sequential Formation Tester Tool

SFT WA Selective Formation Tester Tool

SGP BPB Fluid Pressure (Strain Gauge)

(Production Logging)

SGR HLS Spectral Gamma Ray

SGS BPB Spectral Gamma Ray

SHDT SL Stratigraphic High-Resolution Dipmeter

Log

SHDT SL Dual Dipmeter Log

SIT SL Free Point Indicator

SIT/FPIT SL Stuck Point Indicator/Free Point

Indicator

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Code Company Service (continued)

SLD HLS Spectral Litho Density Tool

SNL WA Sound (Sonan) Log

SP BPB Sontanous Potential

SP HLS Sontanous Potential

SP SL Sontanous Potential

SP WA Sontanous Potential

SPEC WA Gamma Ray Spectrum

SPIN HLS Spinner Survey Tool

SPL WA Spectralog

SW BPB Sonic Waveform

SWC HLS Sidewall Coring Tool

SWC WA Sidewall Samples

SWN HLS Sidewall Neutron Tool

SWN WA Sidewall Epithermal Neutron Log

TAC BPB Two Arm Caliper

TBP WA Thru-Tubing Bridge Plug

TCS SL Thru-Tubing Caliper Sonde

TDS BPB Thermal Neutron Decay

TDT SL Thermal (Neutron) Decay Time Log

TEMP HLS Temperature Tool

TL WA Temperature Log

TMD HLS Thermal Multigate Decay Tool

TRL WA Injection Profile by Radioactive Tracers

TVD HLS True Vertical Depth

UCC SL Ultrasonic Caliper Log

UGD BPB Acoustic Noise

UHF HLS Ultra High Frequency Tool

VCST HLS Vertical Cable Streamer Tool

VDL SL Variable Density Log

WSS/SAS/DSAS SL Downhole Seismic Array

(WST/SAT/DSAT)

WSS/SAS/DSAT SL Seismic Acquisition Tool

(WST/SAT/DSAT)

WSS/SAS/DSAS SL Well Seismic Surveys

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WTPS SL Well Tests Instruments Pressure Sonde

XYC HLS X-Y Caliper Tool

Z-Density WA Compensated Z-Densilog

Logging Company Abbreviations

SL – Schlumberger WA – Western Atlas

HLS – Halliburton Logging Services BPB – British Plaster Board

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1.8 Logging Cables, Heads and Fishing Tools

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Table 1.8-2 (continued)

*) These characters are for Rochester cables

Note: The maximum permissible pulling on a cable without customer’s order is 50% of the breaking strength of the new cable.

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Table 1.8-3 (continued)

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1.9 Wireline Logging Operations in Deviated Holes

The main problems in logging deviated holes concern the lowering of the tools in open hole and the possible collapse of pad type tools due to gravitational force. Another problem is that in a very oval hole the four pads of the dipmeter may not all be in contact with the borehole wall.

Normal wireline logging tools have been lowered successfully in properly drilled holes with deviation angles greater than 60 degrees, where all necessary care had been taken to avoid washouts, ledges, doglegs and sticking hole conditions. Under normal drilling conditions, holes with angles of greater than 45 degrees may cause difficulties in lowering wireline logging tools. In cased holes these tools can be lowered without difficulty at angles exceeding 70 degrees.

Where more rugose borehole conditions and/or increased borehole angles prevent lowering of the tools, the first step is to log these holes with standard tools adapted to reduce friction, increase tool weight and tool flexibility. These tools can be used in open holes with angles up to 70 degrees.

Under more severe open hole conditions or greater borehole angles the logging operation may have to be carried out by lowering the tools through casing, tubing or drill pipe. A pumpdown technique may have to be used to propel the tool down the pipe and into the open hole. These operations are time-consuming and evaluation results become less certain if smaller diameter logging tools have to be used because of the restricted diameter of the pipe.

For near-horizontal drilling, special techniques have been developed to lower standard logging tools to the bottom of the drill pipe and make an electrical connection between the wireline cable and the tool at logging depth.

1.9.1 Friction Reducing Devices

Two basic types of friction reducing device for open hole are available; these are an in-line wheel device, and a stand-off device made from rubber or low-friction plastic designed for operation in 57/8" diameter or larger bore-holes. For casing

and tubing operations various sizes of wheel centralisers, wheel subs and weights, designed for installation at various places in the tool string, are available. The wheel centralisers are useful for wells with very high deviation and long intervals of smooth borehole wall consisting of consolidated rock.

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1.9.2 Other Devices

Weight Increasers

For open hole operations a 2.5 m long, 33_/

8" diameter device, weighing 120 kg

and containing straight-through electrical conductors, can be installed between the cable head and the top of the tool string. More than one can be run in tandem; other designs are available for cased hole and through-tubing operations.

Tool Flexibility

A flexible adapter consisting of a 33_/

8" flex joint and two 33/8 in. in-line wheels

allowing a 4º flexure, can be installed between combination logging tools to negotiate doglegs in the hole.

Tool Guidance

A semi-flexible guide with rubber fingers connected to the bottom end of the tool string can assist in guiding the tool end past ledges or out of washouts.

The stand-off devices help the tool to overcome washouts by keeping it in the middle of the hole and help in locating the hole in a ledge at the bottom of a washout.

Schlumberger reports good results in with these friction reducing devices (Ref. 1) open hole and up to 65º hole angle.

1.9.3 Logging Through Casing Drill Pipe: Pumpdown Techniques

Another method of lowering tools past difficult hole sections is to install open ended casing, tubing or drill pipe over these sections and to log the open hole section below it. Pumping down of the tools is required where friction is too high. When the complete open hole section cannot be logged in one run, it is necessary to lower the pipe over parts of the objective section as well and to log the remaining open hole. This procedure may have to be repeated several times to obtain logs over the complete sequence. It is advisable to install a tool re-entry guide on the bottom of the pipe to facilitate re-entry of pad type tools and to avoid cable damage.

The internal diameter of the casing, tubing or drill pipe used may be too small for standard tools and slim hole tools have to be used. Allow 13 mm diameter clearance in the drill string.

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The following tools are available:

The procedure for logging through drill pipe is as follows:

(a) Run in hole with open ended drill pipe. Collars and Heviwate should only be used when essential (check clearance required for tools with the minimum ID string). Fit a guide shoe or skirt to the bottom of the string to permit easy re-entry of the logging tool. The pipe should be moved up and down slowly with the blocks to prevent sticking.

(b) Attach mud pumps via Chicksan line to a circulating head installed at the top of the drill string.

(c) Rig up logging company's top sheave wheel near the crown block using a 25 t sling.

(d) Thread logging cable over sheave wheels and through the pressure control equipment and connect tool.

(e) Set pipe in slips. Pick up pressure control equipment with tugger line; pick up tool with cable winch and run tool to 30 m below the drill floor. Slack off on tugger and connect pressure control equipment to circulating head.

(f) Reciprocate pipe and begin circulation with the mud pumps. The mud pumps should be started with caution and only 10 – 15 bar pressure is normally required to circulate the mud.

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(g) Run logging tool down inside the drill pipe as fast as possible without

causing any drop in cable tension. The pipe should not be reciprocated as the tool approaches the guide shoe.

(h) As soon as the tool is descending in open hole, move the pipe again if there is any risk of sticking.

(i) Log from the lowest depth reached. Continue circulating mud until tool is inside drill pipe.

(j) Stop moving pipe when tool approaches the guide shoe.

(k) Depending on the maximum depth reached, it may be necessary to add some more stands to the drill string and set the guide shoe about one hundred metres deeper before the next attempt is made to get the tool down to total depth.

If difficulty is encountered when re-entering the drill pipe after logging, very slow rotation of the pipe should allow re-entry.

A disadvantage of slim hole tools is the reduced accuracy of the porosity measurement (by 2–3%) and resistivity measurement due to the larger borehole effects.

1.9.4 Logging of Near-Horizontal Holes

To overcome the problems with slim hole tools and to be able to log near-horizontal holes, two systems have been developed as described below:

(a) Logging Horizontal Wells by the SIMPHOR System

The Institut Français du Pétrole and Elf Aquitaine have developed and used this method to log horizontal boreholes.

Standard open and cased hole Schlumberger logging and perforating (4" carrier) tools have been lowered into the hole inside a protective housing on the bottom of the drill-pipe string. When this string reaches the shoe of the last casing, a 7 conductor electric transmission cable connected to a sinkerbar and female electrical connector system is lowered inside the drill pipe, until it locks mechanically into the logging sonde and makes the electrical connection. The logging cable is brought outside the drill string via a side entry sub. Further adding of drill pipe brings the logging tool in the open hole and logging can commence after power is applied to the cable.

Some 500 m of near-horizontal 81/2" hole have been logged in this manner with

standard 3 to 4” OD tools using the 5" OD SIMPHOR system.

A 3" SIMPHOR is available for running tools without a protective housing.

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Logs recorded to-date using this method are: induction, spherically focussed, dual laterolog, gamma ray, neutron, BHC sonic, 4 arm-caliper, CBL, CCL and 4" perforating gun for perforating 7" liner (9 m length).

(b) Logging Deviated Holes over 65º

A prototype has been built by Schlumberger of a tool system to lower standard size logging tools in a steel envelope with a stinger on the bottom of the drill pipe. A locomotive brings an 8-conductor cable down through the drill pipe and first connects the stinger and then makes the electrical connection with the tool. Further pumping brings the tool out of the steel envelope into the open hole, and logging can commence.

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1.10 Sticking of Wireline Logging Equipment

Most Frequent Causes of Stuck Tools

(a) Differential sticking. Cable or logging tools can be stuck to the wall of the hole by differential pressure if the tools are not moved or moved at a very low speed.

(b) Key seating. Cable or logging tools can be pulled into a slot (key seat) which is sometimes cut in the (high) side of the hole by the cable during a series of logging operations, particularly so in deviated wells.

(c) Unstable hole. Hole collapsing, loose formation and hole bridging.

Prevention of Differential Sticking

(a) Move the logging cable continuously when running tools in open hole. (b) Calibration of certain tools which may be carried out in a 150 m open-hole section immediately below the casing shoe should take the shortest possible time.

(c) During WLFT, after setting the tool, the cable should be slackened off and moved ('yo-yoing') throughout the test period.

(d) Limit the number of logging runs in between bit trips in the hole particularly when heavy mud is used or frequent drag is experienced. This limit may be relaxed if the hole is in excellent condition and no drag is experienced. It is at the discretion of the Toolpusher advised by the WSPE and the Logging Engineer to decide if and when a checktrip will be made. (e) During sidewall sampling, the samples should be taken while moving the tool very slowly upwards (‘sampling on the run’).

(f) Should the Logging Unit break down whilst running tools in the open hole, the following emergency procedures should be followed:

Move the traveling block over a 3–5 m interval to move the cable, taking care that the cable does not jump out of the groove of the top sheave. Check the weight on the Martin Decker gauge.

Before starting this operation, ensure that the Logging Contractor’s weight indicator cable is not fastened to the derrick floor and can move freely. The operation should always be supervised by the Logging Engineer. If possible there should be inter-communication between the Logging Unit and the Driller so that the operation can be controlled by the more sensitive wireline logging tension meter.

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1.10.1 General Guidelines on Stuck Tool, Weak Point and Fishing Kit (a) If tool is stuck on bottom, pull to maximum safe tension and hold it. (b) If tool is stuck during logging, try to go down. If tool is free to descend, attempt to pass bridge. If tool is not free to descend, tool or cable is stuck. Pull to maximum safe tension and hold it.

(c) If the tool fails to come free after working the cable for 30-40 min, the ‘cut-and-thread’ technique should normally be attempted. The cable will hold the tool in a centralised position and serve as a guide for the overshot.

(d) On no account should an attempt be made to break the weak point

unless clear instructions have been given from base to do so.

(e) Sharp edges and abrasive formations will cause wear during working the stuck cable. The weak point above the tool is therefore no longer the weakest point necessarily. Even if successful, breaking the weak point considerably reduces the chance of recovering the tool.

(f) In a vertical hole of good condition with no sign of cable key-seating, or when inside casing, a tool can be fished with good probability, using the technique of breaking the weak point and fishing with an overshot with OD slightly smaller than bit size.

(g) NEVER break the weak point when a radioactive tool is stuck. Cutting

and threading is obligatory.

(h) Never SUDDENLY release tension on a cable. This causes 'bird cages' and broken cables. Tension should be released slowly and should not drop below half the 'normal’ logging tension.

(i) Know the cable weight, the allowed overpull and hence the maximum safe pull which can be applied at all times.

(j) Never pull more than 8,000 lb on a normal cable (break point 16,000 lb). Check the type and age of the cable.

(k) Never pull more than 2,500 lb on a small cable (break point 5,100 lb).

(I) Never pull more than 7,500 lb on a spliced cable.

(m) Never pull more than 4,500 lb on the standard weak point unless breaking is intended (and only on clear instructions from Base).