溶解气回注提高致密油藏采收率效果及敏感性

针对致密油藏水平井产量递减快，衰竭开发采收率低等问题，提出了衰竭开发后期回注溶解气提高采收率的方法。基于新疆玛湖凹陷百口泉组地质油藏特征，建立了致密油藏多级压裂双水平井机理模型，系统研究了上述方法在致密油藏中的生产特征及敏感性。结果表明，溶解气回注可以有效提高致密油藏采收率，缓解水平井产量递减的速度。采出程度随注入量、注入速度及吞吐轮次逐渐增加；气体分子的扩散作用可增加基质的受效范围，扩大气体的作用半径；弱非均质性储层（变异系数0.2）采用溶解气吞吐提高采收率效果最佳。敏感性分析结果表明，吞吐轮次对注溶解气提高采收率的影响最大，其次是注入时间、注入速度、扩散系数、焖井时间。另外，建立的代理模型可准确预测和优化致密油藏注溶解气提高采收率效果。

Improving the Recovery Efficiency and Sensitivity of Tight Oil Reservoirs by Dissolved Gas Reinjection

To address the rapid decline in production of horizontal wells in tight oil reservoirs and low recovery of the depletion development mode, a method for improving oil recovery by reinjected dissolved gas in the late stage of depletion development is proposed. Based on the geological reservoir characteristics of the Baikouquan Formation in the Manas Lake Depression, Xinjiang, a multi-stage fracturing bilevel well mechanism model for tight oil reservoirs was established. The production characteristics and sensitivity of the above methods in tight oil reservoirs were systematically studied. The results show that dissolved gas reinjection can effectively improve the recovery efficiency of tight oil reservoirs and alleviate the rate of decline in horizontal-well production. The degree of recovery increases with the injection volume, injection speed, and huff-n-puff rounds. The diffusion of gas molecules can increase the scope of the matrix response and increase the action radius of the gas. Using dissolved gas for a weak heterogeneous reservoir (variation coefficient of 0.2) to enhance oil recovery can achieve the best effect. Sensitivity analysis demonstrates that the number of huff-n-puff rounds is the most important factor in increasing recovery with dissolved gas reinjection, followed by injection time, injection speed, diffusion coefficient, and soak time. In addition, the proposed model can accurately predict and optimize the oil recovery from tight oil reservoirs by dissolved gas reinjection.