Experimental evaluation of enhanced shale oil recovery in pore scale by CO2 in Jimusar reservoir

Abstract

With the domestic energy supply increase, exploitation of unconventional shale oil resources has drawn great attention from the industry. In this paper, laboratory studies were conducted to investigate the potential of cyclic CO2 injection process to enhanced oil recovery after primary production in shale oil reservoirs. Experimental results indicated that incremental oil production from CO2 huff-n-puff was obtained. The available literature provides limited information on examination of what pore size recovers the most incremental oil recovery by the applicability of CO2 huff-n-puff in shale formations. In this paper, the cyclic CO2 injection performance on three different reservoir rocks was investigated. The enhanced oil recovery by CO2 huff and puff is not limited to macropores, but the remaining oil in the 0.1-μm pore scale is recovered as well. The moveable oil in the large pores (1 μm<D < 10 μm) is mostly recovered at the first CO2 puff cycle. After the second cycle of CO2 huff-n-puff, oil recovery percentage from the large pores decreases significantly. The formation rocks were divided into 3 types based on the geological condition and petrophysical characteristics: type I、II and III. The incremental oil recovery from the type I rock is higher than type II and III. The oil recovery yields mostly from the pore size 0.1 μm <D < 1 μm.