Interactive Well-Test Analysis Using Microcomputers
Authors: McVay D.A. , Hill N.C. , Lancaster D.E. , Lee W.J. , Holditch S.A. 
Published: December 2007

In spite of the proliferation of well-test analysis literature in recent years, many pressure-transient tests are still being misinterpreted, partly because a logical procedure is lacking and incomplete analysis is partly because a logical procedure is lacking and incomplete analysis is performed by nonexpert analysts. The time and difficulty involved in hand-analysis techniques often discourage a complete, consistent analysis. A properly designed computer program that uses interactive graphics can improve the accuracy of test interpretations by enabling the engineer to perform thorough and consistent analyses quickly and easily. Microcomputers are ideally suited for such a program because of their computing power, portability, and relatively low costs. The development of microcomputers and well-test-analysis software places "expert" interpretive capabilities within the reach of most engineers.

Introduction

The development of powerful microcomputers is having a profound influence on pressure-transient test analysis of oil and gas wells. Computer-aided well-test analysis is not new; many papers have been written in the last several years describing software packages for well-test analysis with either conventional techniques or automated history-matching methods. Until the recent development of inexpensive, powerful microcomputers, however, these programs were usually available only to companies with mainframe computers and software development staffs. With the microcomputer and welltest analysis software. a sophisticated set of analysis tools has become available to most petroleum engineers.

Well-test analysis is an ideal application for microcomputers. The reasons are many.Microcomputers take the "dogwork" out of hand-calculation techniques. Many of the calculations involved are difficult enough to discourage hand calculation, yet are not so time-consuming that they cannot be performed easily and quickly on a microcomputer (unlike reservoir simulation at the present time). In addition, another time-consuming part of hand-analysis techniques, plot generation, is easily performed by the microcomputer.Microcomputers encourage the use of more-sophisticated analysis methods, as in the use of pseudopressures and pseudotimes for gas well-test analysis. In many cases, these plotting pseudotimes for gas well-test analysis. In many cases, these plotting functions are not used because of the difficulty and time required to generate them. Maintaining a microcomputer program makes it easy to stay current with the latest well-test-analysis technology.The interactive graphics capabilities of the microcomputer are ideal for well-test analysis. A complete analysis with many techniques can be performed very quickly with interactive graphics. By hand, it is tempting to stop after one or two techniques have been tried. This can sometimes lead to an incorrect interpretation.Microcomputers are portable. which means that they can be used at the test site to analyze the test while it is being conducted. This minimizes test duration, which can result in substantial cost savings.Microcomputers and available well-test-analysis software are relatively inexpensive. This makes quality well-test interpretation available to many more engineers. The improved quality of well-test interpretation industry-wide can only increase the acceptance and use of pressure-transient testing as a reservoir-defining tool.

The objective of this paper is to present ideas on the design of a well-test analysis program that best takes advantage of the capabilities of the microcomputer. A philosophy on how to analyze a well test properly is discussed, because it is an integral part of the design of the program.