Experimental Study on Foam-Assisted Gas Huff-and-Puff in the Jimsar Shale Oil Reservoir

Due to the fact that the Jimsar shale oil reservoir has low permeability and massive artificial and natural fractures, and gas channeling easily happens when N₂ huff-and-puff is adopted for development, there is a problem of limited sweep range of N₂ and low shale oil recovery. For a greater sweep range of N₂ and enhanced oil recovery (EOR) in the Jimsar shale oil reservoir, the Jimsar shale samples were used for foam-assisted gas huff-and-puff experiments based on the evaluation of plugging capacity of foam for shale fractures. Besides, the team analyzed the EOR mechanism of foam-assisted gas huff-and-puff, and studied the influence of the huff-and-puff rounds and matrix permeability of fractured shale samples on the oil recovery by foam-assisted gas huff-and-puff. The experimental results showed that foam could seal fractures and effectively inhibit gas channeling, and when the foam volume fraction was 50% and the gas injection rate was 2 mL/min, the breakthrough pressure could reach the maximum value, with the best effect of plugging. Compared with N₂ huff-and-puff, the foam-assisted gas huff-and-puff can improve the recovery of crude oil not only from the large and medium pores, but also from micropores. With optimal foam injection parameters, the recovery of fractured samples increase with the rounds of huff-and-puff, but the increasing extent will gradually fall. For fractured samples with high matrix permeability, the recovery of foam-assisted N₂ huff-and-puff are also high. The results can provide the guidance for the development of the Jimsar shale oil by foam-assisted gas huff-and-puff.