Ingenieria Petrolera

Distinguished Author Series

T

Well Testing and Interpretation for Horizontal Wells
Fikri J. Kuchuk, SPE, Schlumberger Technical Services Inc.
Summary

The use of transient well testing for determining reservoir parameters and productivity of horizontal wells has become common because of the upsurge in horizontal drilling. Initially, horizontal well tests were analyzed with theconventional techniques designed for vertical wells. During the last decade, analytic solutions have been presented for the pressure behavior of horizontal wells. New flow regimes have been identified, and simple equations and flow regime existence criteria have been presented for them. The flow regimes are now used frequently to estimate horizontal and vertical permeabilities of the reservoir, wellboreskin, and reservoir pressure. Although the existing tools and interpretation techniques may be sufficient for simple systems, innovation and improvement of the present technology are still essential for well testing of horizontal wells in many reservoirs with different geological environments and different well-completion requirements.
Introduction

This paper reviews testing and interpretationmethods for horizontal wells. Since Renney's! article in 1941, many articles dealing with reservoir engineering, PI, and well-testing aspects of horizontal wells have appeared in the literature. 1-12 In the last decade, many papers have been published on the pressure behavior of horizontal wells in single-layer, homogeneous reservoirs.Jr-" Recently, numerous papers on interpretation of horizontalwell test data 2 1- 26 and on the behavior of horizontal wells in naturally fractured 27- 29 and layered30•31 reservoirs have appeared. Because of the uncertainty of regulating flow rate or keeping it constant for drawdown tests in general and buildup tests (particularly at early-times), the use of production logging tools to measure downhole flow rate during pressure well tests has increased inthe last decade. These tools have increased the scope of pressure-transient well testing by providing new measurements. Drawdown tests, for which it has often been difficult to keep the flow rate constant, can now provide the same quality of information as buildup tests. Thus, the possibility of obtaining reliable information about the well/reservoir system by using characteristic features of bothtransient tests (drawdown and buildup) has increased considerably. This is particularly crucial for horizontal wells, where the early-time transient data are the most sensitive to the vertical permeability and skin if the wellbore storage effect is minimized. Recently, production logging and
Copyright 1995 Society of Petroleum Engineers This paper is SPE 25232. Distinguished Author Series articlesare general, descriptive papers that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform thegeneral readership of recent advances in various areas of petroleum engineering. A softbound anthology, SPE Distinguished Author Series: Dec. t98t-Dec. 1983. is available from SPE's Book Order Dept.

downhole shut-in have been combined'? to acquire reliable pressure/ rate data during drawdown and buildup tests. Nonaxisymmetric drilling-fluid invasion and the long, snakelike completed wellbore makethe cleanup process difficult, particularly toward the tips of horizontal wells. Therefore, it is important to obtain flow profiles and the effective well length, which is often much less than the drilled length, for the interpretation of horizontal well tests. The effective well length is important for determining damage skin and the vertical permeability. Production logging for horizontal wells...