Reservoir Stimulation Studies Reveal Key to Maximizing Waterflood Oil Recovery of Virginia Hills Beaverhill Lake "A" Pool

Abstract

Abstract Two comprehensive simulation studies were performed on this reservoir to evaluate waterflood performance to determine the long-term production and the injection policy for the field. The results of these studies revealed that the key to maximizing economic oil recovery from the pool is to improve the vertical conformance of the waterflood. The major biohermal reservoir is found at an average depth of 5600 ft subsea and contains under-saturated crude oil in two partially overlying, non-communicating zones. Fifteen of the field's 117 wells were converted to water injectors in an irregular peripheral water/load pressure maintenance scheme. The simulation models history matched 5 years of primary performance and 10 years of waterflood performance. As it was not practical to simulate the entire field in three dimensions, a four-layer, two-phase, three-dimensional (3-D) reservoir simulation study was done on all area approximately representing the area of influence of the largest infection well. Results indicated that there was a degree of sub-layering within the layers described in this model, Flood-front saturation profiles from the history- matched three-dimensional model were employed to derive pseudo relative permeability relationships for the two-dimensional (2-D) areal model and an excellent history match of the performance of the entire pool was achieved. The study recommended a program of production logging to establish actual production/injection profiles. Results of subsequent attempts to workover wells to improve the flood profiles are discussed. Introduction It has been common practice in the oil industry for a number of yearsto conduct comprehensive reservoir engineering studies to design enhanced recovery schemes for oil reservoirs. A more recent very valuable use for in-depth reservoir studies is to optimize the performance of existing enhanced recovery schemes. Reservoir model studies on reservoirs which have considerable production history can be used to determine ways to improve performance through changes in production and injection policy, to justify remedial action to correct adverse performance und to investigate the ramifications of alternate ourses of action. Reservoir models can also be used as effective performance surveillance tools. The opportunity to improve performance of an enhanced recovery scheme is greatest when the pool is unrestricted by market demand or other arbitrary rate restrictions, because the full benefits of the changes can be realized as soon as he field responds to the change. Whenever the demand for crude oil approaches or exceeds the productive capacity of a reservoir, opportunity to optimize performance by onducting a comprehensive engineering study presents itself. To be most effective, these studies should be interdisciplinary efforts including input from reservoir petrophysical, geological and production engineering disciplines. The studies described in this paper were performed as a cooperative effort involving all of the above disciplines and the results illustrate some of the advantages gained by this cooperative approach.