American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the Gas Technology and Peripheral Waterflooding Symposium of the Society of Petroleum Engineers of AIME, to be held in Liberal, Kansas, November 14–15, 1968. Permission to copy is restricted to an abstract of not more than 300 words. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract

A computerized technique, using a modified least-squares method to analyze wellhead shut in pressure vs. cumulative gas production decline curves, is presented for interpretation of low pressure, shallow (3,000 ft.) gas well reserves. A pilot study indicates benefits of the program to be (1) uniform method of analysis; (2) more accurate results; and (3) availability of the results for use in other computer applications. Analysis of several field case histories is presented.

Introduction

Decline curves provide a major tool to the evaluation engineer for the determination of individual well and total field reserves and often give some indication of the producing mechanism of the reservoir.

The number of decline curves on file may number into the many thousands for a large company. Most companies generally update their curves on a yearly basis with the addition of current production data. Depending upon the number of curves, the process of updating and reinterpreting the decline curves may require the efforts of several people over a period of months.

The use of decline curves for reserve evaluation work is most prevalent in fields which have been producing for a number of years. This criteria is necessary in order to accumulate sufficient production data from which to establish some rate of decline. The Hugoton Field in Kansas, Oklahoma and Texas and the West Panhandle Field in Texas are two such fields. Both of these fields have been producing natural gas for more than thirty year producing natural gas for more than thirty year Decline curves on the approximately 10,000 individual wells in the fields are extensive and well defined. Both fields produce from volumetric reservoirs within the Chase group of formations.

The yearly task of updating and reinterpreting the decline curves of a major operator in these fields is a large undertaking. Last year a study was made to determine the feasibility of updating, analyzing and interpreting some 1,350 Hugoton and West Panhandle Field decline curves using a high speed digital computer.

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