Coring Operations

The EXLOG Series of Petroleum Geology and Engineering Handbooks

Coring Operations Procedures for Sampling and Analysis of Bottombole and Sidewall Cores

Written and compiled by EXLOG staff

Edited by Alun Whittaker

~

" D. Reidel Publishing Company A Member of the Kluwer Academic Publishers Group Dqrdrecht/Boston/Lancaster

International Human Resources Development Corporation • Boston

ACKNOWLEDGMENTS FOR FIGURES

The following figures are reprinted by permission of the Petroleum Extension Service, The University of Texas at Austin, in cooperation with the International Association of Drilling Contractors:

Figures 1-2, 1-3, 1-6, 1-9 are from Lessons in Well Servicing and Workover, Lesson 2: Petroleum Geology and Reservoirs. Copyright © 1975 by the University of Texas at Austin.

© 1985 by EXLOG® .• All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission of the publisher ex­cept in the case of brief quotations embodied in critical articles and reviews. For infor­mation address: IHRDC, Publishers, 137 Newbury Street, Boston, MA 02116.

Softcover reprint of the hardcover 1 st edition 1985

Ubrary of Congress Cataloging in Publication Data

Main entry under title:

Coring operations.

(The EXLOG series of petroleum, geology, and engineering handbooks) Includes index.

1. Core drilling. 2. Drill core analysis. 3. Oil well logging.

I. Whittaker, Alun. II. EXLOG (Firm) III. Series. TN871.2.c647 1985 622'.1828 85-2289 ISBN-13: 978-94-010-8863-3 e-ISBN-13: 978-94-009-5357-4 DOl: 10.1 007/978-94-009-5357-4

[90-277-1980-2 D. Reidel]

Published by D. Reidel Publishing Company P.O. Box 17, 3300 AA Dordrecht, Holland in copublication with IHRDC

Sold and distributed in North America by IHRDC

In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, Holland

'EXLOG is a registered service mark of Exploration Logging Inc., a Baker Drilling Equipment Company.

CONTENTS List of Illustrations ix Preface xiii

1. INTRODUCTION GENERAL 1

QUANTITATIVE CORE ANALYSIS 1 QUALITATIVE CORE EVELUA TION 1 THE ROLE OF THE LOGGING GEOLOGIST 2

Core Retrieval 2 Core Sampling 2 Core Description 2 Core Packing and Shipping 2 Core Analysis 3

RESERVOIR CHARACTERISTICS 3 POROSITY 3 PERMEABILITY 4 SATURATION 5 RESERVOIR GEOLOGY 5 DISTRIBUTION OF FLUIDS 12 PHASE RELATIONSHIPS 14

CORE CHARACTERISnCS 17 POROSITY 17

Measurement 17 Limitations 20

PERMEABILITY 22 Measurement 22 Limitations 24

SATURATION 28 Measurement 28 Limitation 30

2. CORING PROCEDURES GENERAL 33 BOTTOMHOLE CORING 33

CONVENTIONAL CORING 33 The Core Bit 34 The Core Barrel 36

The Outer Barrel 36 The Inner Barrel 37

Coring 37 RETRIEVABLE CORE BARRELS 39

Wireline 39 Reverse Circulation 41

RUBBER SLEEVE CORE BARREL 41 ORIENTED CORE BARREL 42 PRESSURE CORE BARREL 43

vi

CORE EJECTOR BIT 45 SIDEWALL CORING 46

WIRELINE CORE GUN 46 WIRELINE CORE SLICER 49 ROTARY SIDEWALL CORER 49

3. RETRIEVAL AND SAMPLING OF CORES GENERAL 51 CONVENTIONAL CORES 51

LONG-TERM PLANNING 51 PICKING A CORE POINT 53 SET-UP TO CORE 54 LOGGING THE CORE 54

Depth and Footage 55 Low Weight-on-bit 55 Gradual Changes in Weight-on-bit 55 Lost core 55

Rate of Penetration 56 Gas Evaluation 56 Oil Evaluation 58 Cuttings Lithology 59

MUD TESTS 59 Salinity 59 Nitrate Ion 60

PREPARATION FOR CORE RETRIEVAL 62 Work Area 62 Rig Floor 63

REMOVING CORE FROM THE BARREL 64 RETRIEVING THE CORE 65 BOXING THE CORE 66 SAMPLING FOR CORE ANALYSIS 70

Sample Selection 71 Sample Preservation 72

GEOLOGICAL EVALUATION 73 Macroscopic Examination 73 Microscopic Examination 74 Hydrocarbon Evaluation 75

SPECIAL SAMPLES 76 Core Slabbing 76 Thin Sections 77 Acetate Peels 78

SHIPPING THE CORE 79 RETRIEVABLE BARREL CORES 83

LOGGING 83 SAMPLING 83

RUBBER SLEEVED CORES 83 LOGGING 83 SAMPLING 83

ORIENTED CORES 84

PRESSURED CORES 84 LOGGING 84 RECOVERY 84

EJECTOR CORES 85 SIDEWALL CST CORES 85

GUN SET-UP 85 Hole Size 85 Formation Hardness 86 Misftres and Lost Bullets 86

EXTRACTION 86 CORE EVALUATION 87

Recovery 87 Lithology 88 Hydrocarbons 88 Core Analysis 88 Logging 89

SIDEWALL CORE SLICES 89 ROTARY SIDEWALL CORES 90

4. CORE ANALYSIS METHODS PRINCIPLES 91

POROSITY PERMEABILITY 94 SATURATION 97

Retort Procedure 97 Extraction Distillation Procedure 99

SAMPLE PREPARATION 101 SATURATION SAMPLE 101 PERMEABILITY SAMPLE 101 POROSITY SAMPLE 101 SAMPLE EXTRACTION AND DRYING 102

Solvent Extraction 102 Drying 103

SEALING THE PERMEABILITY SAMPLE IN WAX 104 ANALYTICAL PROCEDURE 104

PREPARATION 104 Long-Term 104 Short-Term 107

EQUIPMENT CALIBRATION 108 Saturation Stills 108 Porometer 110

Mercury Level Check 110 Air Removal 110 Calibration 111

Permeameter 112 Solid Plug Calibration Test 113 Flow comparison Test 114

CORE ANALYSIS TEST 116 Optional Total Porosity Test 148

vii

viii

Oil Gravity Tests 148 Water Salinity Tests 152

CORE ANALYSIS CALCULATIONS 154 Effective Porosity 154 Permeability 156 Saturations 158 Alternate Methods 160

The Oil Correction 160 The Pore Volume Calculation 161 Total Porosity 161

PRESENTATION OF CORE ANALYSIS DATA 162 SIDEWALL CORE ANALYSIS 164

CORE DESCRIPTION 164 CORE ANALYSIS 166

Sample Preparation 166 Porosity and Permeability 166 Saturation 167

CARE OF THE CORE ANALYSIS KIT 167 CLEANUP AND STORAGE 167 TEAR OUT AND SHIPPING 168

Index 171

ILLUSTRATIONS 1-1 Absolute Porosity, Effective Porosity and Permeability 4 1-2 Cubic and Rhombohedral Packing 5 1-3 Pore Size Modification in Sandstones 6 1-4 Porosity Reduction with Compaction and Cementation 7 1-5 Pore Size Reduction with Solution and Recrystallization 7 1-6 Typical Porosity Decrease with Depth 7 1-7 Carbonate Porosity Types 9 1-8

1-9 1-10

1-11

1-12

1-13

1-14

Carbonate Porosity Types and Scale 10

Porosity Modification in Carbonates 10

Carbonate Interparticle and Intraparticle Porosity Types Relative Permeability and Productivity 12 Idealized Reservoir Composition 13

Idealized Reservoir Productivity 14

Phase Distribution for Single Pure Hydrocarbons 15

11

1-15 Phase Distribution in a Two-Component Hydrocarbon Mixture 16 1-16 Ruska Porometer 18

1-17 Glass Volumeter for Determination of Absolute Porosity 20

1-18 Flushing of a Permeable Formation while Coring 21

1-19 Ruska Permeameter 23

1-20 Permeability Variation within a Core Sample 25

1-21 Comparison of Theoretical and Actual Flow Conditions 27 1-22 Saturation Still 29

1-23 Fluid Recovery, Water-Based Drilling Fluid without Flushing 30

1-24 Fluid Recovery, Water-Based Drilling Fluid with Flushing 31

1-25 Fluid Recovery, Oil-Based Drilling Fluid 31

2-1 Conventional Core Barrel 34

2-2 Core Bits 35

2-3 Operation of a Conventional Core Barrel 36

2-4 Wireline-Retrievable Core Barrels 40

2-5 Rubber Sleeve Core Barrel 41

2-6 Pressure Core Barrel 44 2-7 Core Ejector Bit and Crusher Sub 46

2-8 Sidewall Core (CST) Gun and Recovery Sequence 47

2-9 Wireline Core Slicer 48

3-1 Supplies Required for Coring Operations 52

3-2 Correlation of Drilling Exponents with a Sonic Log 53

3-3 Core Log Prior to Recovery 56

3-4 Core Log Completed After Recovery 57

3-5 Oil and Gas Relogged from Rat-Hole 58

x

3-6 Labeling and Stacking of Catching Set 63 3-7 Removing Core from the Barrel 65

3-8 Sequential Core Processing by Two Geologists 67 3-9 Core Box Numbering 68 3-10 Labeling of Core Orientation, Fit and Rubble 69 3-11 Core Recovery Tally Sheet 70

3-12 Core Description Log 74 3-13 Core Slabber 76 3-14 Visual Examination of Etched Slab 77

3-15 Thin Section Preparation 78 3-16a Substitution Codes: Encoding 80 3-16b Substitution Codes: Decoding 81

3-17 Report of Core Processing and Shipping Details 82 3-18 Selection of Correct Bullet Fasteners for In-Gauge Hole and Overgauge Hole 86 3-19 Removal of Sidewall Cores 87 3-20 Sidewall Core Report 88 3-21 Sidewall Cores on the Formation Evaluation Log 89 3-22 Core Slices on the Formation Evaluation Log 90 4-1 Ruska porometer 91 4-2 Ruska Permeameter 94 4-3 Permeameter Core Holder 95

4-4 Saturation Still Retort 98 4-5 Saturation Still Calibration Graph 99 4-6 Extraction-Distillation Apparatus 100 4-7 Solvent Extraction 103 4-8 Core Analysis Procedures 105

4-9 Plug in Stills 108 4-10 Install Collecting Tubes 109 4-11 Calibrate Porometer with Calibration Plugs III 4-12 Porometer Calibration Plot 112

4-13 Permeameter Solid Plug Calibration 113 4-14 Permeameter Outflow Rate Graph (Example Only) 114 4-15 Gas Viscosity Graph 115 4-16 Line Up Samples in Order, Left to Right 116 4-17 Number Samples and Record Depths 117

4-18 Break Out Two-Inch Piece from Center of Sample 118 4-19 Shape Porosity Sample 118 4-20 Weigh Porosity Sample 119 4-21

4-22

4-23 4-24

Record Depth, Weight and Lithology Weigh Saturation Sample 120 Load Retort 12 1

Clean Up Work Area 121

119

4-25 Load Retorts into Stills 122 4-26 Turn Water On 123 4-27 Set Timer 123 4-28 Plot Water Calibration Graph 124 4-29 Reading Collection Tubes 125 4-30 Cut Permeability Sample Plugs 126 4-31 Cutting Plug 127 4-32 Preparing Sample Plug 127 4-33 Number Sample Plugs 128 4-34 Measure Plugs and Record Length and Diameter 129 4-35 Weigh Porosity Sample and Record Dry Weight 132 4-36 Line Up Samples in Order 132 4-37 Open Porometer 133 4-38 Insert Porosity Sample 133

4-39 Record Bulk Volume 134 4-40 Close Needle Valve Finger Tight 135 4-41 Back-Off Pressure 136 4-42 4-43 4-44 4-45

Keep O-Ring, Seal and Mercury Surface Clean 137 Remove Collecting Tubes and Record Recovered Water and Oil

Separate Oil for Gravity Test 139 Remove Retorts 139

4-46 Line Up Permeability Plugs in Order 140 4-47 Insert Plugs into Sleeves 141 4-48 Pour Wax into Sleeves 141 4-49 Mark Sample Number on Wax 142 4-50 Insert Sample in Core Holder 142 4-51 Mount Core Holder and Tighten 143 4-52 Adjust Airflow 144 4-53 Read Flowmeter 144 4-54 Record Permeameter Readings 145 4-55 4-56 4-57 4-58 4-59 4-60

Remove Core Holder and Insert Next Sample

Clean Retorts when Cool 147 Clean Collecting Tubes 147 Total Porosity Worksheet 149 Oil Drop Gravity Test 150 Porometer Calibration 154

4-61 Effective Porosity Worksheet 155 4-62 Permeameter Outflow Graph (Example Only)

4-63 Permeability Worksheet 157 4-64 4-65 4-66

Gas Temperature Viscosity Plot

Gravity Correction Plot 158 Saturation Worksheet 159

4-67 Volume Correction Plot 159 4~68 Total Porosity Worksheet 161 4-69 Core Analysis Log 163 4-70 Break Core Laterally 164

157

4-71 Split Shorter Piece Longitudinally 164

146

138

PREFACE This coring operations reference handbook is intended as a practical guide for the logging geologist to procedures, activities, and responsibilities required when bottomhole or sidewall coring is performed at the wellsite. Not all of the operations described are common practice in all logging units; however, familiarity with them is a necessary part of general ex­ploration knowledge and professionalism.

Chapter 1 discusses the concepts of porosity, permeability, and saturation, how these properties are determined in core analysis, and their significance in controlling rest:rvoir performance. Chapter 2 deals with the various techniques used in coring. Chapter 3 ex­plains the routine role of the logging geologist in core retrieval, sampling, and qualitative evaluation. Chapter 4 details operating procedures for quantitative wellsite core analysis equipment.