超临界CO在致密油藏中的扩散前缘预测

Predicting the Diffusive Front of Supercritical CO in Tight Oil Reservoirs

魏兵 尚静 蒲万芬 卡杰特·瓦列里 赵金洲

WEIBing SHANGJing PUWanfen KadetVALERIY ZHAOJinzhou

油气藏地质及开发工程国家重点实验室·西南石油大学, 四川 成都 610500 古勃金国立石油与天然气大学, 俄罗斯 莫斯科 119991

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China National State University of Oil and Gas, Gubkin University, Moscow, 119991, Russia

国内外大部分学者认为超临界CO在致密油藏中的扩散是吞吐提高采收率的关键因素之一。通过设计基质裂缝模型结合压降法搭建了测定超临界CO在饱和油岩芯中扩散系数的实验装置，系统研究了压力、储层物性等油藏条件对超临界CO扩散系数及浓度分布的影响规律，建立了超临界CO浓度场及扩散前缘的预测方法。实验结果表明，超临界CO在致密岩芯（0.06 mD）中的扩散系数为10 m/s数量级，扩散系数随着初始注气压力的升高而增大，最终趋于平缓，但在临界压力点附近出现最大扩散系数；扩散系数随基质渗透率和孔隙度增大而增大，随岩芯迂曲度的增大而快速递减。经过900 d扩散，扩散前缘仅前进了0.095 m，因此，在致密油藏CO吞吐现场作业周期内忽略扩散作用是合理的。在扩散后期，CO浓度梯度越来越小，扩散速度逐渐降低。

Most of researchers claim that supercritical CO diffusion is one of the key considerations for CO huff-puff EOR in tight reservoirs. In this paper, a matrix-fracture model was designed and applied to measuring the diffusion coefficient of supercritical CO in saturated oil cores using pressure decay method. The influence of reservoir conditions such as pressure and core petroproperties on the diffusion coefficient and concentration distribution of supercritical CO was comprehensively investigated, and a method predicting CO concentration field and diffusion front was established. The experimental results showed that the diffusion coefficient of supercritical CO in the tight core (0.06 mD) is in the order of 10 m/s. The diffusion coefficient was found to increase with the increase of the initial gas injection pressure before finally leveling off after a certain pressure. The maximum diffusion coefficient occured around the critical pressure point. In addition, the diffusion coefficient increased with the increase of matrix permeability and porosity, whereas it decreased with the increase of core tortuosity. After 900 days, diffusion in tight reservoirs, the diffusion front only advanced 0.095 m. Therefore, it is rational to neglect the diffusing effect of CO in the field operation cycle of CO injection in tight reservoirs. In the later stage of diffusion, the concentration gradient of CO became low leading to gradual decrease of diffusion.

10.11885/j.issn.1674-5086.2019.10.30.02