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Abstract

Gas wells are often subject to periodic or cyclic curtailment. Currently available methods are poorly suited for analyzing production data from these wells. Using methods presented in this paper, an equivalent continuous flowing pressure can be calculated from pressures measured at the end of the flow and shutin periods during each cycle. This equivalent continuous flowing pressure is then used for production data analysis in conjunction with the average flow rate. This method is applicable for boundary dominated flow, transient radial flow, and transient linear flow of slightly compressible liquids in a homogeneous formation. The method may be applied to gas well production data through the use of pseudopressure or normalized pressure.

Introduction

Production data analysis is often used for reserves estimation and performance prediction, and for estimating reservoir characteristics such as permeability, drainage area, and degree of stimulation. Current methods of analyzing production data assume either constant flowing bottomhole pressure or production at constant rate. Simultaneously varying bottomhole pressure and rate may be taken into account by using either special plotting functions or superposition. Use of either special plotting functions or superposition requires detailed historical flowing bottomhole pressures and rates.

Gas wells are often subject to cyclic production for a variety of reasons. Often, monthly production is limited by market demand. Under these circumstances, a well may be open to flow until its allocated production is achieved, then shut in for the remainder of the month. In other cases, wells are open to flow only part of each year because of seasonal market demand. Still other gas wells cannot flow continuously because of liquid loadup. These wells may be produced until they load up, then shut in to allow the reservoir pressure to build up high enough near the well to allow the accumulated wellbore liquids to be lifted.

Current production analysis methods cannot readily account for the cyclic nature of production from these wells. In this paper, we present a method for obtaining an equivalent continuous flowing bottomhole pressure from measurements of the flowing pressure at the end of the flow period and the shutin pressure at the end of the shutin period. continuous flowing bottomhole pressure is then combined with the average flow rate over the entire production cycle for use in existing production data analysis methods.

In the next section, we briefly review the production data analysis literature. We also present a qualitative motivation for the new method, define terminology, and discuss the results of our investigation. The following section presents an example of the use of the new averaging method. The final section presents the conclusions reached in this study.

Discussion

Review of Literature

In 1973, Fetkovich presented dimensionless rate-time type curves combining transient, radial flow solutions to the diffusivity equation with Arps empirical decline curve equations. The Fetkovich type curves assume constant pressure production.

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