Unconventional Miscible EOR Experience at Prudhoe Bay: A Project Summary

摘要

This paper describes the conceptual development, reservoir simulation, and field testing of a new miscible enhanced oil recovery (EOR) technique at Prudhoe Bay. Two distinct variations of this technique have been evaluated. The vertical Miscible Injectant Stimulation Treatment (MIST) process involves completing a production well at the bottom of a thick, continuous, watered-out interval. A large slug of miscible injectant (MI) is injected, followed by a small slug of chase water. The MI sweeps rock not contacted by previous MI injection and drives EOR oil to offset producers. In the lateral MIST process, a horizontal lateral is drilled along the base of the reservoir from either a production well or an injection well. MI is injected sequentially into several intervals along the lateral to mobilize EOR oil from previously unswept areas. The lateral well is then returned to normal production or injection service. Simulation data indicated that the vertical MIST process could recover more than 200,000 STB of incremental oil per well at initial rates of up to 1,000 STB/D. Calculations for the lateral MIST process indicated potential recovery of more than 1 million bbl of incremental EOR per lateral. Field results of the MIST process have been mixed but are encouraging overall. Incremental EOR response from the first MIST lateral well through July 2000 was approximately 1,400,000 STB, resulting in a technical and economic success. Response from three subsequent MIST lateral injectors varied widely. The first vertical well MIST showed little response, but it did provide valuable insight into the performance of the process at Prudhoe Bay. The subsequent vertical well MIST, which had a much larger volume of injected MI, was very successful and has currently recovered over 1,100,000 STB.Cumulative incremental EOR from the MIST wells through July 2000 was more than 5,000,000 STB, with average incremental oil-production rates of approximately 4,000 STB/D. Based on these successful results, an ongoing program of additional MIST wells is planned.