页岩油注空气提高采收率在线物理模拟方法

An online physical simulation method for enhanced oil recovery by air injection in shale oil

为探索页岩油注空气驱油机理,建立了基于CT扫描和核磁共振技术的页岩油注空气提高采收率在线物理模拟方法,研究了不同衰竭压力下页岩油空气驱开发效果、不同大小孔喉微观动用特征和页岩油空气驱采油机制,分析了空气含氧量、渗透率、注入压力、裂缝对页岩注空气驱油效果和不同大小孔隙原油采出量的影响。研究表明,页岩储集层衰竭开采后注入空气可大幅提高页岩油采收率,但不同注入时机下驱油效率和不同级别孔喉动用程度存在一定差异。空气含氧量越高,低温氧化作用越强,不同大小孔隙动用程度越高,采收率越大。渗透率越高,孔喉连通性越好,流体流动能力越强,采收率越高。注入压力升高,孔喉动用下限减小,但易产生气窜现象导致突破提前,采收率先增大后减小。裂缝能加大气体与原油的接触面积,通过基质向裂缝供油提高空气波及系数和基质泄油面积,在合理生产压差下,注空气前进行适当的压裂改造有助于提高空气驱效果。

In order to understand the mechanism of air flooding shale oil,an online physical simulation method for enhanced shale oil recovery by air injection was established by integrating CT scanning and nuclear magnetic resonance(NMR).The development effect of shale oil by air flooding under different depletion pressures,the micro-production characteristics of pore throats with different sizes and the mechanism of shale oil recovery by air flooding were analyzed.The effects of air oxygen content,permeability,gas injection pressure,and fractures on the air flooding effect in shale and crude oil production in pores with different sizes were analyzed.The recovery of shale oil can be greatly improved by injecting air into the depleted shale reservoir,but the oil displacement efficiency and the production degree of different levels of pore throats vary with the injection timing.The higher the air oxygen content and the stronger the low-temperature oxidation,the higher the production degree of pores with different sizes and the higher the shale oil recovery.The higher the permeability and the better the pore throat connectivity,the stronger the fluid flow capacity and the higher the shale oil recovery.As the injection pressure increases,the lower limit of the production degree of pore throats decreases,but gas channeling may occur to cause a premature breakthrough;as a result,the recovery increases and then decreases.Fractures can effectively increase the contact area between gas and crude oil,and increase the air sweep coefficient and matrix oil drainage area by supplying oil to fractures through the matrix,which means that a proper fracturing before air injection can help to improve the oil displacement effect under a reasonable production pressure difference.