致密油藏周期注气微观驱油机理实验研究

针对致密油藏注水难度大,气水交替难以有效实施的问题,周期注气改善注CO_2驱油效果的方法逐渐得到重视。利用大庆外围致密岩心,将致密油藏物理模拟实验方法和低磁场核磁共振仪相结合,建立了一种研究周期注气微观驱油机理的新方法,分析了不同驱油阶段岩心静置前后原油在孔隙中的变化规律,提出了周期注气指数参数,并对周期注气效果进行评价。研究结果表明:气驱至不同阶段,静置前后T_2谱图均发生变化,且不同驱替阶段T_2谱图的变化规律不同,说明不同驱替阶段停注后原油的流动规律不同,其周期注气的微观驱油机理也存在差异。驱替至一定的PV数后,周期注气指数显著增加,周期注气效果显著提高。随着驱替倍数的增加,较小孔隙中的原油逐渐得到动用。岩心实验结果表明周期注气相比于连续注气采收率提高9.92%。上述研究丰富了核磁共振技术在油田开发中的应用。

Experimental Study on Microscopic Mechanism of Oil Displacement by Cyclic Gas Injection in Tight Oil Reservoir

In order to solve the difficult water injection in tight oil reservoir and the gas-water alternative injection was difficult to implement, it was proposed that cyclic gas injection was used to improve the CO₂ displacement effect. A new method combining with physical simulation experiment and nuclear magnetic resonance technique was established to study the microscopic mechanism of oil displacement in tight oil reservoir. The microscopic distribution of oil at pre and post standing in different displacing stages was studied, and cyclic gas injection index was proposed to characterize the effect of cyclic gas injection. The experimental results indicated that T₂ spectrum of cores at pre and post standing in different displacing stages changed, and the change laws were different, which showed that flow law after stopped injecting and microscopic mechanism of oil displacement at different displacing stages were different. The cyclic gas injection index increased when displacing to a certain stage and the effect of cyclic gas injection increased greatly. The oil in smaller pores flowed gradually with the increase of displacing PV number, and the experimental results indicated that cyclic gas injection can enhance oil recovery by 9.92% compared with continuous gas injection. The research results enriched the application of NMR technique in the development of oilfield.