裂缝性致密油藏CO_(2)吞吐开采孔隙原油动用特征

Pore scale crude oil production characteristics during CO_(2)huff and puff in fractured tight reservoirs

通过对天然致密岩心进行人工造缝,试验研究致密油储层CO_(2)吞吐开采特征,分析基质渗透率、裂缝数量对CO_(2)吞吐采出程度的影响;通过核磁共振,探究CO_(2)吞吐动用孔隙范围及剩余油分布。结果表明:随着基质渗透率从(0.1~0.2)×10^(-3)μm^(2)增大至(0.4~0.5)×10^(-3)和(0.8~0.9)×10^(-3)μm^(2),无裂缝致密岩心采收率从15.81%分别提高至20.48%和26.18%,CO_(2)动用的最小孔径从0.034μm依次减小为0.023和0.012μm;在基质渗透率为(0.8~0.9)×10^(-3)μm^(2)的含单一裂缝和多裂缝的致密岩心中,采收率分别进一步提高至41.45%和52.46%,CO_(2)动用的最小孔径减小至0.003和0.005μm;基质渗透率和裂缝对采收率的提高主要体现在吞吐前两周期,对第3周期采出程度影响甚小;孔径约为0.1μm的孔隙内的原油是多周期CO_(2)吞吐开采后期的主要增油来源;CO_(2)吞吐开采后,较高基质渗透率和多裂缝的致密岩心中剩余油分布更为均匀。

The production characteristics of CO_(2)huff and puff in tight oil reservoirs were studied using natural rock cores with artificial fractures.The effects of matrix permeability and fracture on oil recovery were analyzed,and oil-production via CO_(2)huff and puff and the distribution of residual oil in pore size range were investigate using a nuclear magnetic resonance(NMR)method.The experimental results indicate that with the increase of matrix permeability from(0.1-0.2)×10^(-3)μm^(2)to(0.4-0.5)×10^(-3)μm^(2)and(0.8-0.9)×10^(-3)μm^(2),the oil recovery of the tight cores without fractures increased from 15.81%to 20.48%and 26.18%,and the minimum pore size of oil-producing decreased from 0.034μm to 0.023μm and 0.012μm.In the tight cores with a single fracture and multiple fractures with matrix permeability of(0.8-0.9)×10^(-3)μm^(2),the oil recovery increased to 41.45%and 52.46%,and the minimum pore size of oil-producing reduced to 0.003μm and 0.005μm.The improvement of oil recovery by matrix permeability and fractures mainly appeared in the first two cycles of the huff and puff process,but had little effect in the third cycle and so on.The crude oil in the pores of about 0.1μm is the main production source in the later stage of multi cycles of CO_(2)huff and puff production.The residual oil in the tight cores with high matrix permeability and multiple fractures is more evenly distributed.