不同注气介质驱替致密油藏微观孔隙动用特征研究

Research on the Microscopic Pore Producing Characteristics of Tight Reservoirs Displaced by Different Gas Injection Media

为了明确不同注气介质对致密油藏的微观驱油机理,基于核磁共振T2谱测试原理,开展了注N2/CO2岩心驱替试验,从微观孔隙尺度研究了注N2非混相驱和注CO2混相驱的微观驱油机理,评价了驱替过程中不同孔径孔隙原油的动用程度。试验结果显示,N2非混相驱和CO2混相驱的最终采出程度相差很小;N2驱替过程可划分为未突破期、突破初期和突破中后期3个阶段,小孔隙中的原油动用程度高于大孔隙;CO2混相驱时大孔隙中原油的动用程度大幅增加,小孔隙中的原油动用程度相对较低。岩心微观孔隙结构分布是造成N2/CO2驱替过程中大、小孔隙中原油动用程度存在差异的主要原因。研究结果表明,与CO2驱相比,致密油藏N2驱的开发效果更好,这为安塞油田采用注N2驱开发长6储层提供了理论依据。

In order to provide clarity in the microscopic oil displacement mechanisms of tight reservoirs displaced by different gas injection media,core displacement experiments of N2 and CO2 injection were carried out respectively based on the principle of NMR T2 spectrum test.The microscopic displacement mechanisms of N2 immiscible flooding and CO2 miscible flooding were studied at the microscopic pore scale,and the oil production from pores with different pore sizes during displacement was evaluated.The results show that final recovery percent from N2 immiscible flooding and CO2 miscible flooding has little difference.The N2 flooding process can be divided into three stages:the nonbreakthrough stage,the early breakthrough stage and the mid-late breakthrough stage.The recovery percent from small pores is higher than that from large pores.However,the oil recovery percent from large pores is greatly improved in CO2 miscible flooding,while it is relatively low from small pores.The distribution of microscopic pore structure is the main cause for the difference in recovery percent between large and small pores in the process of N2 and CO2 flooding.The results show that the development effect of N2 flooding in tight reservoirs is better than that of CO2 flooding,which provides a theoretical basis for the development of Chang 6 reservoir by N2 flooding in Ansai Oilfield.