Numerical Simulation Of The North Ricinus Cardium A Reservoir

Abstract

Abstract The North Ricinus Cardium A Pool is a beach barrier system located on the edge of the disturbed belt, approximately 130, km northwest of Calgary, Alberta. The current operating mode for the pool involves a cycling scheme in the retrograde gas cap with the oil leg on primary depletion. A standard 3D-3 phase black oil model, modified with several specialized subroutines, was used to simulate the cycling scheme in the history match and prediction modes. Pseudo-relative permeability curves were used to describe displacement of rich gas by lean gas in the gas cap, while two sets of relative permeability curves were required to match oil production. The model was subsequently utilized to establish reserves and to optimize natural gas liquid recovery by infill drilling in the gas cap. Introduction The Ricinus Cardium A Pool, discovered in January 1969, is located approximately 130 kilometres northwest of Calgary, FIGURE 1. Location map. (Available in full paper) FIGURE 2. North Ricinus geology.(Available in full paper) Alberta (Fig. 1). The pool initially was considered to be a large retrograde condensate gas cap in association with a relatively small oil leg containing a high shrinkage oil. An application in June 1971(1) to concurrently produce the gas and oil based on good production practice was refused by the ERCB. In July 1972 a scheme to cycle the gas cap was subsequently approved with the provision that the operator show cause after one year of production why a VRR of unity need not be maintained(2). Gas cap cycling commenced in April 1973 and a performance review submitted in July 1974(3) indicated that a VRR of between 0.85 and 1.00 had no appreciable effect on gas cap liquid recoveries and the ERCB did not impose a full voidage replacement ratio at that time. Subsequent step out drilling to the north indicated that the oil leg was much larger than previously estimated; and in May 1979, the ERCB(4) requested a study to determine the effect of VRR on the oil recovery and also an updated estimate of original reservoir volumes. A black oil reservoir simulation study, incorporating special modifications, was initiated in June 1979 to address the ERCB's concerns. The model was subsequently utilized to establish pool reserves and to investigate optimization of natural gas liquid recovery by infill drilling. Geology The Ricinus Cardium Pools occur in the Cardium A Sand of Upper Cretaceous age. The reservoir is a beach barrier system trending 20 km in a northwesterly direction and averaging 3 – 5 km in width at a mean depth of 1325 m ss (Fig. 2). The reservoirs are complex structural traps occurring at the edge of the disturbed belt. The Cardium A Pool consists of a retrograde gas cap condensate overlying a volatile oil pool in a weakly folded synclinal structure that plunges gently to the northwest with the gas oil contact occurring at 1463 m ss. A major under thrust forms a pressure barrier to the Cardium K pool to the southwest with porosity pinchouts forming the reservoir boundaries in other directions (Fig. 2).