Abstract
In order to determine the influence of different factors on the CO(2) huff-and-puff displacement effect, a CO(2) huff-and-puff experiment was carried out with Chang 6 tight sandstone samples in Ordos Basin as the research object. Combined with nuclear magnetic resonance technology, the influences of injection pressure, cycle numbers and soaking time on the CO(2) huff-and-puff effect were evaluated, and the optimal CO(2) huff-and-puff parameters were optimized. The microscopic degree of crude oil production in different scale pores was quantitatively characterized. The results show that the injection pressure and the cycle numbers have a significant influence on the effect of CO(2) huff-and-puff. With the increase of injection pressure, huff-and-puff cycle numbers and soaking time, the recovery efficiency increases, but the growth range decreases. When the injection pressure is increased from 6 to 12MPa, the degree of pore mobilization in the oil in macro and medium pores (≥ 10ms) increases by 13.0%-22.63%. The recovery efficiency of a single round gradually decreased with the increase of huff-and-puff rounds. The first cycle of CO(2) huff-and-puff was the main contribution of crude oil recovery. However, the production effect of micro and small pores (< 10ms) was significantly improved after multiple cycle numbers of CO(2) huff-and-puff. When the soaking time increases from 6 to 24h, the recovery efficiency increases by 11.47%-14.93%. After that, the influence of prolonged soaking time on the porosity production degree of cores with different permeability decreases. It is found that medium pores and macro pores are the main contributors to pore mobilization during multiple cycles of CO(2) huff-and-puff.