AN ANALYTICAL METHODOLOGY TO DETERMINE OIL IN PLACE: AQUIFER INFLUX AND ULTIMATE SWEEP EFFICIENCY OF A MATURE HEAVY OIL WATERFLOOD IN THE WILMINGTON BASIN

The significance of and goal of this paper is to outline a methodology to better understand the impact of water injection on the overall efficiency and recovery factor of heavy oil reservoirs under mature water flood. The methodology presented in the paper would be a useful toolkit for the evaluation of the performance and efficiency of current waterfloods. This paper describes both conventional and unconventional analytical techniques to determine and quantify original oil in place, size of water influx and ultimate sweep efficiency of a mature Wilmington field. This reservoir has been under both active peripheral water injection and natural water influx since the early 1960s. The analytical techniques indicate that the field is a continuous reservoir with original oil in place of approximately 250 MMBO. The derived original oil in place value from the study is in alignment with the reservoir simulation study and with the geological and petrophysical evaluation previously conducted. The paper constructs a methodology to evaluate the relative strength of the water influx, allowing a reservoir engineer to identify weak, moderate and strong influx drive mechanisms and hence plan for appropriate injection support. Finally the effectiveness of the sweep efficiency was determined by using oil recovery versus hydrocarbon pore volume injected, type curves obtained from core studies of various crude oil viscosities. It was determined that the water influx volume was relatively small compared to the volume of water injected and was calculated to be at 8% of the total water injected. The sweep efficiency was determined to be approximately 55% based on the relative distance of the peripheral injection.