玛湖致密砾岩注氮气驱机理及应用效果评价

针对玛湖致密砾岩储层采用的水平井+体积压裂衰竭开发，产量递减快的问题，分别在室内和现场开展了注氮气提高采收率研究。室内实验通过气驱相态、混相能力、驱油效果等方法评价了M区块的提高采收率潜力。实验结果表明，氮气在原油中溶解度小，驱油机理主要依靠自身的膨胀性驱油，且氮气的最小混相压力62.3 MPa，目前M区块很难达到混相驱。现场在玛湖油田M区块选择一个1注5采的井组开展注氮气先导试验，并取得了较好的效果。单井评价了产油量、油压、气油比、氮气浓度等4个参数指标的见效特征；井组分析了注气前和注气过程中产量的变化，累增油1 953 t。最后结合地质和工程认识，总结了影响注气效果的主控因素。本次注氮气应用效果显著，验证了致密砾岩储层水平井+体积压裂注氮气提高采收率是一项可行的技术。

Mechanism and Application Effect Evaluation of Nitrogen Flooding in Mahu Tight Conglomerate

In order to solve the problem of rapid production decline caused by horizontal well + volume fracturing in Mahu tight conglomerate reservoir, nitrogen injection was carried out in laboratory and field to enhance oil recovery. The EOR potential of Block M is evaluated by gas drive phase behavior, miscibility and oil displacement effect. The experimental results show that the solubility of nitrogen in crude oil is small that the displacement mechanism mainly depends on its own expansibility, and that the minimum miscible pressure of nitrogen is 62.3 MPa, so it is difficult to achieve miscible flooding in Block M. A pilot test of nitrogen injection was carried out in Block M of Mahu Oilfield, and good results were obtained. The effective characteristics of oil production, oil pressure, gas oil ratio and nitrogen concentration were studied and evaluated; the change of production before and during gas injection for well group is analyzed. The increase of a total of 1 953 t of oil is obtained. Finally, based on the geological and engineering data, the main controlling factors affecting gas injection effect are systematically evaluated, which proves that horizontal well + volume fracturing nitrogen injection is a feasible technology to enhance oil recovery in tight conglomerate reservoir.