考虑微观特征的低渗油藏注气能力研究

Gas injection capacity of low permeability reservoirs considering microscopic characteristics

马勇新 张乔良 朱金起 马帅 王鑫 朱润华

MA Yongxin ZHANG Qiaoliang ZHU Jinqi MA Shuai WANG Xin ZHU Runhua

中海石油(中国)有限公司 湛江分公司, 广东 湛江 524057

Zhanjiang Branch of CNOOC Limited, Zhanjiang, Guangdong 524057, China

注气是提高低渗油藏采收率的重要手段，但现有注气能力的评价方法未充分考虑微观孔隙特征的影响，为此以北部湾盆地涠洲B油田中块3井区渐新统涠洲组四段的低渗储层为研究对象，综合考虑微观孔喉结构特征(如分形维数、喉道半径、曲折度等)和束缚水膜厚度的影响，建立了基于静态测井渗透率动态校正的气相有效渗透率评价模型，同时结合岩心多倍气驱实验确定评价模型的精度，协同分析了微观特征因素影响下的注气渗流规律。研究结果表明，低渗油藏的注气能力呈现3种演化阶段：注气初期(0~100 PV)气体优先驱替较大孔隙原油，使束缚水饱和度快速下降，气相渗透率跃升显著提升气驱效率；注气中期(100~1 200 PV)气相有效渗透率呈线性增长，束缚水因微喉道毛管力限制进入平稳期；注气后期(>1 200 PV)气体开始突破微孔隙水膜，使束缚水饱和度缓慢降低，但受储层亲水性与非均质性影响，导致残余油滞留形成孤立相，气相渗透率及驱油效率(极限52%)趋于稳定，油藏开发潜力受限。根据涠洲B油田实例井证明，注气初期提升注入压力可有效改善吸气指数，而后期需控制注气量以避免非均质储层中油相孤立化及生产井含水上升，保证油相析出，从而提高油藏整体气驱效率。

Gas injection is a crucial method for enhancing oil recovery in low permeability reservoirs, but current evaluation methods for gas injection capacity have not fully considered microscopic pore characteristics. Therefore, taking the low permeability reservoirs in the fourth member of the Oligocene Weizhou Formation in well block 3 in the middle block of the Weizhou B Oilfield, Beibuwan Basin as the research object, a gas-phase effective permeability evaluation model was established based on dynamic correction of static logging permeability, comprehensively considering microscopic pore-throat structural characteristics (such as fractal dimension, throat radius, and tortuosity) and the thickness of bound water film. At the same time, core multiple-cycle gas flooding experiments were used to verify the accuracy of the evaluation model, and the seepage patterns of gas injection under the influence of microscopic characteristics were analyzed. The results showed that the gas injection capacity in low permeability reservoirs undergoes three evolutionary stages: In the initial stage of gas injection (0 to 100 PV), gas preferentially displaces crude oil in larger pores, leading to a rapid reduction in bound water saturation and a sharp increase in gas-phase permeability, which significantly improves gas flooding efficiency. In the middle stage of gas injection (100 to 1 200 PV), the gas-phase effective permeability increases linearly, and the bound water enters a stable phase due to capillary force constraints in microscopic throats. In the later stage of gas injection (>1 200 PV), gas begins to break through the water film in microscopic pores, causing a slow decrease in bound water saturation. However, due to the hydrophilicity and heterogeneity of reservoirs, residual oil are trapped as an isolated phase, leading to the stabilization of gas-phase permeability and displacement efficiency (with a maximum of 52%), and limiting the development potential of reservoirs. Field verification in the Weizhou B Oilfield demonstrated that increasing injection pressure in the initial stage can effectively improve gas injectivity index, while in the later stage, it is necessary to control the gas injection amount to prevent oil phase isolation in heterogeneous reservoirs and rising water cut in production wells, thereby ensuring oil phase precipitation and improving the overall reservoir gas flooding efficiency.

中国海洋石油有限公司十四五重大科技项目“海上油田大幅度提高采收率关键技术” KJGG2021-0505

https://doi.org/10.11781/sysydz2025040913