Applied Concepts in Fractured Reservoirs

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John C. Lorenz. Applied Concepts in Fractured Reservoirs

Table of Contents

List of Tables

List of Illustrations

Guide

Pages

Applied Concepts in Fractured Reservoirs

Copyright

Foreword

Preface

Acknowledgements

Introduction

PART 1 Understanding Natural Fractures: Fracture Types, Dimensions, and Origin. 1.1 Introduction

1.2 Nomenclature and Fracture‐Classification Systems. 1.2.1 Introduction

1.2.2 Other Classification Systems

1.2.3 Classifications for Fractures in Outcrops and Cores

1.2.4 Expulsion Fractures and Natural Hydraulic Fractures

1.2.5 Other Fracture Terminology

1.2.6 Sets, Systems, Domains, and Systematic Fractures

1.3 Fracture Characteristics and Dimensions. 1.3.1 Introduction

1.3.2 Fracture Distribution Patterns

1.3.3 Fractography

1.3.4 Fracture Dip Angles

1.3.5 Fracture Distributions

1.3.6 Fracture Heights and Terminations

1.3.7 Fracture Lengths

1.3.8 Fracture Widths, Apertures, and Mineralization

1.3.9 Fracture Spacing

1.3.10 Fracture Strike

1.3.10.1 Fracture Orientations Relative to the In Situ Stresses

1.3.11 Discussion

1.4 The Mechanics of Fracturing Rock in Extension and Shear. 1.4.1 Introduction

1.4.2 Origins of Geologic Stress Systems. 1.4.2.1 Stresses in a Tectonically Quiescent Basin

1.4.2.2 Other Potential Sources of Horizontally Isotropic Stress

1.4.2.3 Stresses in a Tectonically Active Basin

1.4.3 Rock Susceptibility to Fracture: Basic Concepts. 1.4.3.1 Introduction

1.4.3.2 Intrinsic Controls on Fracture Susceptibility

1.4.3.3 Extrinsic Controls on Fracture Susceptibility

1.4.3.4 How Rock Breaks: Grain‐Scale Cracking, Yield, and Failure

1.4.3.5 Extrapolation to the Subsurface

1.4.4 Interplay Between Developing Fractures and the In Situ Stresses

1.4.5 The Importance of Pore Pressure. 1.4.5.1 Introduction

1.4.5.2 The Relationship between Pore Pressure and Stress

1.4.5.3 Biot's Coefficient

1.4.5.4 Mohr Diagrams and Pore Pressure

1.4.5.5 Pore Pressure Makes Rock Weak and Brittle

1.4.5.6 Sources of Pore Pressure

1.4.5.7 Alternate Theories

1.4.6 Summary

1.5 Other Fracture Types. 1.5.1 Introduction

1.5.2 Deformation‐Band Shear Fractures, Compaction Bands, and Dilation Bands. 1.5.2.1 General Characteristics

1.5.2.2 Dimensions and Distributions

1.5.2.3 Origin

1.5.3 Faults and Fractures

1.5.4 Microfractures

1.5.5 Stylolites and Associated Extension Fractures

1.5.6 Bed‐Parallel Shear Fractures

1.5.7 Beef‐Filled Fractures

1.5.8 Ptygmatically Folded Fractures

1.5.9 Alteration of Fracture Systems by Dissolution

Appendix 1.A The Relationship Between Pore Pressure and the In Situ Effective Stresses. Introduction

Vertical Stress

Horizontal Stress

Effective Vertical Stress

Effective Horizontal Stress

Stress Differential

Note

PART 2 Measuring and Analyzing Fractures in Reservoirs. 2.1 Introduction

2.1.1 Reasons to Take Core

2.1.2 Analyses

2.1.3 Fracture Data Sources

2.1.4 Quantitative vs. Semi‐Quantitative Data

2.1.5 Timing of a Fracture Study

2.1.6 Need for Experience

2.1.7 Other Data Sources

2.2 Planning a Core Program for Fracture Analysis. 2.2.1 Introduction

2.2.2 Core Diameter and Length

2.2.3 Substituting Sidewall Core Samples

2.2.4 Orienting a Core

2.2.5 Drilling Parameters

2.2.6 Trip Time for Core Recovery

2.2.7 Collecting Data on Site

2.2.8 Running an Image Log

2.2.9 Back‐to‐Back Cores

2.2.10 On‐Site Processing

2.2.11 CT Scans

2.2.12 Removing Core from the Barrel

2.2.13 Core‐Jam Prevention Measures

2.2.14 Maximizing and Documenting Core Continuity

2.2.15 Slabbing Protocol

2.2.16 Scheduling Fracture Logging and other Core Processes

2.3 Logging Core for Fractures

2.3.1 Wash the Core!

2.3.2 Use all the Core and Remove it from the Core Boxes

2.3.3 Laying Out Intervals of Core for Fracture Logging

2.3.4 Core‐Logging Toolkit

2.3.5 Recording Data

2.3.6 Making and Using a Master Orientation Line

2.3.7 Differentiating Natural from Induced Fractures

2.4 Taking, Measuring and Analyzing Fracture Data

2.4.1 Fracture Type

2.4.2 Fracture Depths: Intensity and Density

2.4.3 Fracture Dip Angles. 2.4.3.1 Measuring Dip Angles

2.4.3.2 Using Dip Angles

2.4.4 Fracture Distributions

2.4.5 Fracture Heights and Terminations

2.4.6 Fracture Widths, Apertures, and Mineralization

2.4.7 Fracture Spacings

2.4.7.1 Spacings from Horizontal Core

2.4.7.2 Spacings from Vertical Core

2.4.7.3 Converting Vertical Observations to Horizontal Fracture Spacings

2.4.7.4 Spacings of Inclined and Shear Fractures

2.4.7.5 Uses of Spacings

2.4.8 Measuring and Using Fracture Strikes

2.4.8.1 Measuring Fracture Strikes in Vertical Core

2.4.8.2 Measuring Fracture Strikes in Deviated or Horizontal Cores

2.5 New Core vs. Archived Core

2.6 Oriented Core

2.6.1 Other Ways of Orienting a Core

2.7 Using CT Scans

2.8 Fracture Data from Image Logs

2.9 Comparing Fracture Data from Outcrops, Core, and Logs. 2.9.1 Introduction

2.9.2 Large‐Scale Outcrop Studies

2.9.3 Local Outcrop Studies. 2.9.3.1 Raton Basin

Fracture Model Based on Outcrop Observations

Fracture Model Based on Borehole Imagery

Fracture Model Based on Core Examination

Biases and Differences in the Three Fracture Datasets

2.9.3.2 Rifle Gap

2.9.3.3 San Ysidro

2.10 Fracture Data from 3D Seismic Surveys*

2.11 Fracture Data Acquired by LiDAR

2.12 Fracture Data from Engineering Tests

2.13 Case Studies in Estimating Fracture Effectiveness from Core. 2.13.1 Introduction

2.13.2 Case Study 1: Archived Vertical, Unoriented Core

2.13.3 Case Study 2: New, Un‐Slabbed Horizontal Core. 2.13.3.1 Introduction

2.13.3.2 Fracture Effectiveness

2.13.3.3 System Effectiveness and Permeability Anisotropy

2.13.4 Case Study 3: New, Slabbed, Vertical Core. 2.13.4.1 Introduction

2.13.4.2 Calculating Effectiveness

2.13.4.3 Description of the High‐Angle Extension Fractures

APPENDIX 2.A Workflow and List of Tests, Data

Appendix 2.B Core‐Handling,Marking, Sampling, and Analysis Protocol for Core Studies Focused on Natural Fractures

Appendix 2.C Slabbing Recommendations for Horizontal Core

Note

PART 3 Effects of Natural Fractures on Reservoirs. 3.1 Introduction

3.2 Classification

3.3 The Permeability Behavior of Individual Fractures. 3.3.1 Introduction

3.3.2 Three Categories of Fracture Effects

3.3.3 Stylolites

3.3.4 Microfractures

3.4 The Effects of Fracture Systems. 3.4.1 Introduction

3.4.2 Fracture‐Controlled Permeability Anisotropy

3.4.2.1 Case Study: The Midale Field

3.4.2.2 Case Study: The Rulison Field

3.4.2.3 Case Study: The Spraberry Formation

3.4.3 Fracture‐Controlled Sweet Spots

3.5 The Sensitivity of Fracture Permeability to Changing Stress. 3.5.1 Stress‐Sensitive Extension Fractures

3.5.1.1 Case Study: The Bulo Bulo Field

3.5.2 Stress‐Sensitive Shear Fractures

3.5.3 Damage Due to Production‐Related Scale

3.6 Fracture Volumetrics. 3.6.1 Introduction

3.6.2 Fracture Volume/Fracture Porosity

3.6.3 Fracture Permeability

3.6.4 Transfer Function

3.6.5 Fracture Surface Areas

3.7 Effects of Fractures on Drilling and Coring

3.8 Completions: The Interaction Between Natural and Hydraulic Fractures. 3.8.1 Early Conceptual Models

3.8.2 Direct Evidence of the Characteristics of Hydraulic Fractures

3.8.3 The Developing Hydraulic‐Fracture Model

3.8.4 Nuclear Stimulations

References

Index

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Отрывок из книги

John C. Lorenz

FractureStudies LLC NewMexico, USA

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Correct fracture identifications and characterizations allow the geologist, modeler, and engineer to be accurate in spotting well locations and designing horizontal wellbore azimuths. These data provide anchor points for seismic and petrophysical interpretations as well as basic data for reasonable determinations of fracture‐system volumetrics including porosity, permeability, reserves, recovery factors, and production rates. Accurate knowledge of fracture systems allows engineers to design appropriate completion and production strategies, taking advantage of or at least accommodating fracture‐controlled drainage anisotropy and stress‐sensitive permeabilities. Such in‐depth knowledge allows the petrophysicist to more accurately interpret image logs.

This volume is a companion volume to our earlier Atlas of Natural and Induced Fractures in Core (Lorenz and Cooper, 2018a). That volume provides a tool for accurately identifying different fracture types whereas this volume discusses how the different types formed, and how they affect reservoir volumetrics. The present volume is divided into three sections. Part 1, Understanding Natural Fractures: Fracture Types, Dimensions, and Origins, discusses the origin, the characteristics, the variations among, and distinctions between extension fractures and shear fractures. It also describes microfractures, fractures associated with faults, the effects of the different geomechanical properties of different lithologies on fracture development, fracture domains, and fracture corridors. The important mineralization that can occlude fracture apertures and reduce fracture permeability, as well as the dissolution that can enhance it, are included in the discussions. The characteristics of both individual fractures (length, widths, heights, apertures) and fracture populations (spacings, interconnectivity) of different fracture types are described.

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