致密油藏CO_(2)前置压裂流体相互作用机理

Behavior of CO_(2) Pre-fracturing Fluid in Tight Reservoir

目前,致密油藏的高效开采仍是世界研究的重点及难点,其中CO_(2)压裂技术受到广泛重视。为了进一步明确CO_(2)前置压裂流体之间的相互作用机理,利用室内实验对地层条件下CO_(2)注入后原油高压物性(密度、黏度、压缩系数等)的改变情况进行研究,明确CO_(2)与原油的相互作用关系,其次通过数值模拟手段对压裂不同阶段中CO_(2)存在方式、原油黏度等性质进行研究。结果表明,首先CO_(2)的注入会导致原油密度明显增加,黏度降低,同时CO_(2)的注入会提高地层的可压缩性,提高地层的弹性能量。其次在压裂及焖井阶段,CO_(2)主要存在于油相中。在返排过程中,CO_(2)逐渐从油相中脱离,以气相的形式存在。由于不同阶段CO_(2)相态的改变以及CO_(2)对原油组分具有萃取作用,使得原油黏度在返排过程中升高,密度下降。研究成果对致密油藏CO_(2)前置压裂流体作用机理有了更深刻的认识,为进一步开展CO_(2)压裂的后续研究奠定了坚实的基础。

At present,the efficient exploitation of tight reservoirs is focus and difficulty of the study in the world,in which CO_(2) fracturing technology has been widely valued.To clarify the interaction mechanism in CO_(2) pre-fracturing fluids between CO_(2) and crude oil,using laboratory experiments,changes in high-pressure physical properties(density,viscosity,compression coefficient,etc.)of crude oil after CO_(2) injection under formation conditions were studied.The existence form of CO_(2),and viscosity and density of crude oil in different stages of fracturing were scrutinized in numerical simulation.Results show that the CO_(2) injection could significantly increase the density of crude oil and decrease the viscosity.Meanwhile,the CO_(2) injection can improve the compressibility of the formation and improve the elastic energy of the formation.During fracturing and soaking,CO_(2) exists mainly in oil phase.During the flowback and in the fracturing and manhole,CO_(2) escapes from oil phase into gas phase.Due to the change of CO_(2) in phase state at different stages and the extraction effect of CO_(2) on crude oil components,the viscosity of crude oil increases and the density decreases during flowback.Therefore,the behavior of pre-fracturing fluid in tight reservoirs is well understood,which lays a solid foundation for future study on CO_(2) fracturing.