An Experimental Study of CO2 Huff-N-Puff Enhanced Oil Recovery in Three Forks Formation, Williston Basin

Abstract

ABSTRACT: The primary oil recovery in the Bakken Petroleum System is still small, with a range of 5% to 12% of the original oil in place (OOIP). This study aims to investigate the potential and the performance of CO2 injection with HnP on the recovery factor (RF) in Upper Three Forks (UTF) and Middle Three Forks (MTF) formations, Sanish Field, Williston Basin, North Dakota (ND). In order to achieve this purpose, a series of laboratory experiments were applied where the performance of cyclic CO2-EOR was evaluated under different scenarios of injection with various operational conditions. Different parameters were considered to understand the mechanisms of HnP CO2-EOR, including the pressure of injection above and under the minimum miscibility pressure (MMP), the effect of soaking time on production, and several injection cycles to maximize the oil recovery. Then a comparison of the performance of CO2-EOR with ethane (C2) and propane (C3) under the same operating condition to evaluate the feasibility of different gases in the HnP approach. In addition, X-ray diffraction mineral analysis (XRD) was performed on four samples taken from UTF and MTF to determine the mineral composition in both formations. The results showed that the most recoverable formation was UTF with 56% of RF during the first cycle, while MTF showed only 37%. Increasing the number of cycling from one to four cycles showed that RF increased up to 88% and 75% in UTF and MTF, respectively. In addition, injection pressure seems to have a significant effect on RF in both formations, where the results showed that increasing the pressure from 800 Psi to 3600 Psi improved RF from 15% and 16% to 56% and 37% in UTF and MTF, respectively. Moreover, increasing the soaking time from 4 hrs to 48 hrs, RF increased from 37% and 25% to 72% and 39% in UTF and MTF, respectively. The results from comparison of different gases injections showed that, with injection pressures of 3600 Psi and soaking time of 24 hrs, ethane was the most effective gas in both formations, followed by propane and CO2, respectively. In conclusion, CO2 HnP has good potential in the lab and can be a promising method in unconventional reservoirs. This research work may provide an improved understanding of the CO2 HnP enhanced recovery strategy for unconventional reservoirs.