三塘湖盆地马中致密油藏注水吞吐探索与实践

三塘湖盆地马郎凹陷马中致密油藏水平井投入开发后，地层压力下降快，自然递减大，投产第1年自然递减超过50%，一次投产采收率低的矛盾凸显，亟需开展提高采收率矿场试验。通过对比分析马中致密油藏储层物性、含油性及岩石润湿性，储层相对润湿指数0.18~0.48，表现为弱亲水-亲水特征，适合注水吞吐，并对注水吞吐机理及影响因素进行了深入分析研究，有效地指导了现场实践，开展先导试验注水吞吐7口井，平均单井日增油10.3 t，平均单井累计增油805 t。注水吞吐已经成为马中致密油藏一种新的有效开发方式，分析认为注水吞吐效果与吞吐水量呈正相关性，当注入压力达到超地层破裂压力吞吐效果较好，水平段轨迹位于油层中上部的井注水吞吐效果好于水平段轨迹位于油层下部的井，但随着注水吞吐轮次的增加效果减弱，下步需要研究多轮次注水吞吐后提高采收率的技术。

Study and practice of cyclic water injection in Mazhong tight oil reservoir in the Santanghu Basin

After the horizontal well in Mazhong tight oil reservoir of Malang sag, the Santanghu Basin is put into production, the formation pressure drops fast and the natural decline is great. The natural decline in the first year after the commissioning is over 50%, revealing the significant contradict of low recovery factor of primary commissioning, so it is in urgent need to carry out EOR field tests. The reservoir physical properties, oil bearing property and rock wettability of Mazhong tight oil reservoir were comparatively analyzed. It is shown that the relative wettability index of the reservoir is 0.18~0.48, and the characteristics of weak water wetting-water wetting are presented, so cyclic water injection is suitable in Mazhong tight oil reservoir. Then, the mechanisms and influential factors of cyclic water injection were analyzed deeply to provide the effective guidance for field practice. The pilot test of cyclic water injection was conducted at 7 wells and their average daily oil increment per well and average cumulative oil increment per well are 10.3 t and 805 t, respectively. So far, cyclic water injection has been a new effective development technology for Mazhong tight oil reservoir. In conclusion, the effect of cyclic water injection is in positive correlation with the water throughput and it is better when the injection pressure reaches the super fracture pressure. In addition, the effect of the cyclic water injection in the wells whose horizontal sections are located in the middle and upper parts of the oil layer is better than that in those whose horizontal sections are located in the lower part of the oil layer. As the cycle of the cyclic water injection increases, however, the effect diminishes. Therefore, it is necessary to study the EOR technologies after multiple cycles' cyclic water injection in the following step.