Kaybob South - Reservoir Simulation of a Gas Cycling Project with Bottom Water Drive

Abstract

As with all numerical simulations, the reliability of the output can be no better than the validity of the input. But here is an example of how simulation with meager data can be justified for the range of performance possibilities that it does show. possibilities that it does show. Introduction The Kaybob South field is located approximately 160 miles northwest of Edmonton, Alta., Canada (see Fig. 1). The Beaverhill Lake ‘A’ pool was discovered in 1961 on the southwestern side of the Beaverhill Lake basin. This basin is the scene of sizable oil accumulations such as Swan Hills, Judy Creek, Virginia Hills and Kaybob, but Kaybob South is the first instance of substantial sour gas production. The Kaybob South Beaverhill Lake ‘A’ pool is, in fact, one of the largest gas reservoirs in Canada. The reservoir is at a depth of 10,500 ft and is totally underlaid by water. It currently encompasses some 57,000 acres, has an elongated shape, and extends on trend with the regional strike for about 32 miles. The pool's initial gas in place may be as much as 4,000 Bcf. Because of the possibility of significant retrograde liquid losses upon depletion, it was essential to choose a method of exploiting the pool early in its development. Reservoir simulation to design the cycling project for Unit No. 1 was carried out in three phases. The first phase, involving a reservoir volume of 363 Bcf, produced the basic injection pattern and investigated produced the basic injection pattern and investigated the effects of production rate. The second phase updated pattern studies and included several voidage replacement ratios. The final simulation in Nov., 1968, confirmed the suitability of the scheme with a revised reservoir interpretation and included a study of specialized problems. This paper presents the results as applied to the latest reservoir data. Development History Gas was discovered in the Beaverhill Lake formation in 1961. The follow-up exploratory well revealed the Beaverhill Lake to be water bearing. Over the next 5 years, with mediocre success, four additional wells were drilled to the Beaverhill Lake. Significant Beaverhill Lake stepouts were made in early 1967 with the drilling of two more wells, and the estimate of initial gas in place expanded from 363 to 782 Bcf. A lull in exploration followed, during which the initial planning of a depletion mechanism was formulated. It was apparent that the pool was large enough to support a cycling scheme, and that pressure maintenance would result in a notable increase in recovery of LPG, condensate and sulfur. The planning and designing of the cycling project began in 1967 without full delineation of the reservoir limits. At the start of 1968, three wildcat wells were completed and the proved limit of the pool was extended some 10 miles to the southeast. Subsequent drilling at a brisk pace through 1968 revealed that the pool existed over a distance of 32 miles. The reservoir thickened and broadened to the southeast so much that the cycling scheme under development was hopelessly inadequate for efficient economic depletion of the entire pool. However, the design remained applicable to the earlier pool area. P. 481