Design of a Waterflood Adjacent to a Gas-Oil Contact

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 1974. 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 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. 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 discussions 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 case history is presented of the design of an enhanced recovery scheme to be implemented in the early life of a portion of an oil reservoir adjacent to a sizeable gas cap. The suitability of gas injection, solvent flooding and various waterflood configurations has been studied with extensive use of numerical simulation. Only the waterflood studies are presented herein. An attempt has been made to presented herein. An attempt has been made to determine the sensitivity of grid sizing, both areal and vertical, through the use of two dimensional areal and cross-sectional models. Data is provided on the interplay of viscous and gravity forces and the resulting fluid movements in this situation. Establishment of a water fence along the gas-oil contact results in the optimum recovery in this situation. Introduction The Kaybob South field is located approximately 160 miles northwest of Edmonton, Alberta, Canada. The Triassic "A" pool was discovered in December, 1961 with the drilling of the well HB Union Kaybob South 11-27-62-20 W5M. Development drilling resulted in 91 oil wells on 160 acre spacing. This area was subsequently unitized and placed on waterflood in November, 1967. Stepout drilling extended the pool approximately 2 miles in the updip direction, delineating an additional 5,000 acres with estimated oil reserves of 80 MMSTB and an associated gas cap of 35 BCF. This study is concerned with the design of a waterflood in this extension area. Since the thickest pay sections in the pool, up to 100 feet, have been encountered in close proximity to the gas cap, it is necessary to ensure effective displacement from this locality to optimize oil recovery. The reservoir simulation model is a tool employed by the reservoir engineer for the estimation of reservoir performance. Normally the mathematical model is used to predict the optimum development strategy only after sufficient history has been accumulated to calibrate the model by matching past performance. Since it was desirable to implement a secondary recovery scheme early in the life of the pool, virtually no history was available with which the model calculations could be verified. In this study, an attempt has been made to define the various factors that would significantly affect the results of a waterflood prediction. Extensive use was made of two-dimensional areal and cross-section models to investigate the affect of the model grid sizing.