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Abstract

The prominent examples of linear flow behavior in the well test literature relate to linear flow within or to a fracture penetrated by a producing well. The resulting pressure transients generally are exhibited in the early portion of a well test and are followed by infinite-acting radial flow behavior and/or boundary effects.

In this paper, the linear flow occurs in the formation, which has a predominantly linear shape. Analysis of interference, drawdown, and build up tests is described in theory and illustrated by practical examples. The necessary equations for practical examples. The necessary equations for the analysis are provided for testing gas, geothermal steam, and oil wells.

In elongated linear flow systems, the pressure transient behavior associated with linear flow occurs late in the drawdown or build up test. The type curves provided in this work show that this pressure behavior is readily distinguishable from pressure behavior is readily distinguishable from conventional well tests, particularly in interference tests.

Introduction

Interest in the linear flow geometry was for a long time limited to application T related to water influx. The paper by Miller provided solutions for the pressure distributions in a semi-infinite or finite length linear aquifer assuming water influx into the oil zone at a constant flow rate.

More recently, Ehlig-Economides, et al. developed methods for analyzing geothermal well tests in a predominantly linear flow system. This work was motivated by the presence of parallel linear faults predominant in geothermal regions such as the one shown in Figure 1. Methods for interference analysis and for drawdown testing of geothermal steam wells were presented.

Currently, the linear flow geometry is cited as a fairly common occurrence in low permeability gas fields. Kohlhaas, del Giudice, and Abbott provided a case study of linear flow behavior for provided a case study of linear flow behavior for a gas well completed in a channel-like reservoir. They also provided equations for analyzing the linear flow portion of drawdown and buildup tests. Stright and Gordon examined rate decline behavior in gas wells in the Piceance Basin in Northwest Colorado which exhibited apparent linear flow behavior. In one case, the well penetrated a fracture in a low permeability marine sand in which a number of long permeability marine sand in which a number of long natural fractures are present and appear to be related to extensive faulting in the area. In another case, the well was completed in a long narrow sand body as evidenced by outcrops in the same area.

A recent paper by Nutakki and Mattar provided solutions for drawdown versus time for the linear flow geometry which are identical to the work done by Ehlig-Economides and Economides for geothermal steam wells. However, the method of analysis, which made use of a "pseudo-skin" factor, was distinctly different.

In this paper, the previous methods of interference and drawdown analysis for geothermal wells in a lienar flow system are reintroduced with additional coefficients for oil and gas well testing. In a subsequent paper, the draw down and buildup analysis of fractured wells in the predominantly linear flow system will be presented in detail.

THEORY

In Figure 1, the geological map from an unidentified geothermal region shows linear faults running parallel for several hundred feet. If the regional parallel for several hundred feet. If the regional faults provide impermeable boundaries to flow, then a particular well may drain a volume best described as a long narrow channel. In Figure 2 schematic diagrams of other types of depositional environments show possible reservoir geometries which would result in predominantly linear flow.

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