Dynamic Well Testing in Petroleum Exploration and Development

Huinong Zhuang, Yongxin Han, Hedong Sun, Xiaohua Liu

• Publisher: Elsevier
• Year: 2020
• Print ISBN: 9780128191620
• eBook ISBN: 9780128191637
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Dynamic Well Testing in Petroleum Exploration and Development, Second Edition, describes the process of obtaining information about a reservoir through examining and analyzing the pressure-transient response caused by a change in production rate. The book provides the reader with modern petroleum exploration and well testing interpretation methods, including their basic theory and graph analysis. It emphasizes their applications to tested wells and reservoirs during the whole process of exploration and development under special geological and development conditions in oil and gas fields, taking reservoir research and performance analysis to a new level.This distinctive approach features extensive analysis and application of many pressure data plots acquired from well testing in China through advanced interpretation software that can be tailored to specific reservoir environments.- Presents the latest research results of conventional and unconventional gas field dynamic well testing- Focuses on advances in gas field dynamic well testing, including well testing techniques, well test interpretation models and theoretical developments- Includes more than 100 case studies and 250 illustrations—many in full color—that aid in the retention of key concepts

Chapter 1

Introduction

Abstract

Well testing is systems engineering and includes well test design, pressure data acquisition and interpretation, and dynamic description of the oil/gas well and the oil/gas reservoir. This book combines all of these to illustrate the process of operation and the methods of well testing, and provides many field examples to validate them.

This chapter introduces the parameters possibly obtained from a well test and the problems commonly met in the field that can possibly be resolved by well testing and its study in different stages, from exploration to development of the fields. This study of gas reservoirs can be called dynamic description of gas reservoirs. Geophysical prospecting, geology-well logging, and this study are three pillar technologies, and this study has its own special and irreplaceable functions.

In addition, this chapter introduces the new idea of dynamic description of a gas reservoir on the basis of well test studies, including studies on deliverability of gas wells, dynamic models, pressure gradient distribution, and deciphering of geological information from gas reservoirs, which enables reservoir engineers interested in this new idea to start off by gaining knowledge of the characteristics of reservoir structure and the law of deliverability decay of the well and/or the gas reservoir.

Keywords

Modern well test; Well test model; Graphical analysis; Systems engineering; Gas reservoir dynamic description; Dynamic deliverability; Dynamic reserves

Outline

• 1.1 The purpose of this book
  • 1.1.1 Well test: A kind of system engineering
  • 1.1.2 Well test: Multilateral cooperation
  • 1.1.3 Writing approaches of this book
• 1.2 Role of well test in gas field exploration and development
  • 1.2.1 Role of well test in exploration
  • 1.2.2 Role of well test in predevelopment
  • 1.2.3 Role of well test in development
• 1.3 Keys of well test analysis
  • 1.3.1 Direct and inverse problems in well test research
  • 1.3.2 How to understand direct problems
  • 1.3.3 Describing gas reservoirs with well test analysis: Resolving inverse problem
  • 1.3.4 Computer aided well test analysis
• 1.4 Characteristics of modern well test technology
  • 1.4.1 One of the three key technologies of reservoir characterizations
  • 1.4.2 Methods of gas reservoir dynamic description

1.1 The purpose of this book

The modern well test has been around since the beginning of the 1980s. In China, during the implementation of reform and opening up policies, modern well test methods, interpretation software, and advanced test instruments, tools, and equipment were introduced almost simultaneously. Looking back at the advances made since the early 1980s, it is very exciting to see that new developed knowledge and techniques have been applied successfully in the discovery, development preparation, and development operation of many major gas fields in China. However, it should also be noted that application of the modern well test sometimes and in some places is still not good enough and needs to be improved further.

The well test today is very different from that of three or four decades ago. Just as in all other fields, due to the application of computers and advances in science and technology, engineers today seldom make calculations manually; well test analysts and reservoir engineers no longer frequently look up complicated formulas in well test books and perform tedious computations with calculators; the results can be obtained easily by simply selecting some menu items of software.

But does this mean that well test work has become much easier? The answer is no; on the contrary, as research activities go further, the well test does not become easier, but faces greater challenges.

First of all, well test analysis is required to provide not only simple parameters such as reservoir permeability, but also more detailed information about reservoirs, such as their types and boundary conditions, and ultimately to deliver a “dynamic model” of gas wells and gas reservoirs—that is, a dynamic model reflecting the conditions of the gas well and the gas reservoir truly and correctly, which can be used in gas field evaluation and performance forecasting.

In China, there are many reservoir types, so well test analysis becomes much more difficult. As far as the reservoir type is concerned, there are sandstone porous reservoirs, fissured reservoirs and fractured vuggy in carbonate rocks, biothermal massive limestone reservoirs, and irregularly distributed block shaped reservoirs in volcanic rocks; as far as the planar structure of a reservoir is concerned, there are well extended, uniformly distributed large area formations, fault dissected reservoirs with complicated boundaries, and banded lithologic reservoirs formed by fluvial facies sedimentation; as far as the fluid type is concerned, there are common dry gas reservoirs, condensate gas reservoirs, and gas cap gas reservoirs with oil rings and edge water or bottom water; and as far as reservoir pressure is concerned, there are gas reservoirs with normal pressure coefficients, extremely thick gas reservoirs with super high pressure, and underpressured gas reservoirs. As indicated, these reservoirs are richly varied, which has undoubtedly brought about new challenges to well test analysts and reservoir engineers.

Moreover, the quality of pressure data nowadays is no longer as it was in the early 1980s. At that time, pressure data were acquired by mechanical pressure gauges and the number of pressure data points read out from a pressure chart would be about 100 or even fewer than that. The results interpreted from such pressure data are not only simple, but also will not be controversial. Today, however, the number of data points acquired by electronic pressure gauges is usually as many as 10,000, or even 1,000,000; they consist not only of the pressure buildup interval but also the pressure “whole history,” including all flow and shut in intervals during the testing. Even very slight differences, if any, between the well test interpretation model obtained from analysis and the actual conditions, that is, the tested reservoir and the tested well, will be shown at once in the verification process during interpretation so that no careless error is allowed.

1.1.1 Well test: A kind of system engineering

Therefore, we can say that the well test today no longer merely means several formulas and simple calculations, but rather is a kind of systems engineering that includes several parts as follows:

1. 1. Timely proposing of appropriate test projects by those persons in charge of exploration and development.
2. 2. Creating an optimized well test design.
3. 3. Acquiring accurate pressure and flow rate data onsite.
4. 4. Interpreting acquired pressure data by well test interpretation software and integrating geological data and test technique; performing reservoir parameters evaluation.
5. 5. Providing dynamic descriptions of gas wells and gas reservoirs by integrating the pressure and production history data acquired during production tests of gas wells.
6. 6. Creating new well test models when necessary and adding them into well test interpretation software for future application.

1.1.2 Well test: Multilateral cooperation

The work listed previously should be carried out by different departments; each of them is associated with others, and each one affects the final results:

1. 1. Only when leaders of the competent authorities have thoroughly recognized the important role of well test data in describing gas reservoir characterization and guiding development of the gas field can they arrange test projects in a timely manner and provide financial support for such projects to be executed.
2. 2. Only by conducting optimized designs can we get better results with less effort and acquire pressure data that can explain and resolve our problems.
3. 3. The acquisition of pressure data is usually done by service companies. The test crew of the service company, although working pursuant to the contract, should recognize what good data are and how to meet design requirements. The well test supervisor must check data before acceptance according to the design requirements, to ensure the success of data acquisition.
4. 4. Data analysis will ultimately demonstrate the application value of the test results. In this book, such analysis is summarized as a “dynamic reservoir description,” which means using dynamic data acquired in gas wells, such as pressure and flow rate, as the main basis to evaluate the gas production potential of gas wells, while at the same time providing a description of geological conditions within the gas drainage area that affect gas deliverability and its stability, including reservoir structures, reservoir parameters, boundary distribution, and dynamic reserves controlled by this individual well, thereby guiding deliverability planning and development plan design for the gas field. T...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• About the author
• Chapter 1: Introduction
• Chapter 2: Basic concepts and gas flow equations
• Chapter 3: Gas well deliverability test and field examples
• Chapter 4: Analyzing gas reservoir characteristics with pressure gradient method
• Chapter 5: Gas reservoir dynamic model and well test
• Chapter 6: Interference test and pulse test
• Chapter 7: Coalbed methane well test analysis
• Chapter 8: Gas field pilot production test and dynamic description of gas reservoir
• Chapter 9: Well test design
• Nomenclature [with China statutory units (CSU)]
• Appendix A: Commonly used units in different unit systems
• Appendix B: Unit conversion from China statutory unit (CSU) system to other unit systems
• Appendix C: Formulas commonly used in a well test under the China statutory unit system
• Appendix D: Method for conversion of coefficients in a formula from one unit system to another
• References
• Index