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

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

Performance of the Cockfield "D" sand gas condensate reservoir during cycling and subsequent blowdown is compared with calculations using the conventional layer model assumptions. Actual performance during cycling was better than that calculated using the Dykstra-Parsons and Stiles techniques of determining permeabilities for layers (adapted by analogy from their permeabilities for layers (adapted by analogy from their waterflood prediction methods) but not as favorable as that calculated by the Miller-Lents technique of determining such permeabilities from core data. Comparison of calculations with a similar layer model with actual performance indicates that permeability profile effects continue to be important in determining condensate content of gas produced during blowdown of the reservoir following cycling.

Introduction

The Cockfield "D" sand in the Washington Field, St. Landry Parish, Louisiana, was found to contain gas-condensate by the completion of the Thistlethwait Land and Cattle Co. No. 1 at a depth of 9313 feet in December 1951. Subsequently 18 producing wells and 6 dry holes have defined the extent and geologic characteristics of this reservoir. Limited volumes of gas were sold from November 1953 to May 1955 to determine performance characteristics of the reservoir. performance characteristics of the reservoir. The field was shut-in until unitization was achieved and facilities installed for gas injection. Cycling operations were started in October 1956. Gas injection was continued until October 1967; then gas was sold until April 1975 when the reservoir was shut-in for conversion to gas storage for a major gas-pipeline system.

The primary purpose of this paper is to compare the actual cycling performance of this reservoir with published prediction techniques. The concepts of flow in stratified reservoir rock systems during gas injection are also extended to the post cycling period - an area of technology just barely mentioned in petroleum literature. This is important in the economic decision of when to stop cycling and to start blowdown of a gas-condensate reservoir. Other aspects of reservoir performance discussed include an early long time injection-production interference test conducted to aid in selection of the tall pattern used for cycling, and a comparison of volumetric estimates of gas-in-place with actual production.

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