致密油藏储层改造区域渗流时间尺度分析

摘要

基于致密油藏具有低孔低渗、储层非均质性、各向异性等特征,建立致密油藏储层改造区域(SRV)渗流模型.模型考虑因孔隙、裂缝迂曲分叉以及流动截面随空间变化,导致流体在介质中运移时间较长,进而储层压力梯度影响后续的流动,即时间滞后效应;对渗流模型在拉普拉斯空间中采用有限元方法求解,实现对井底流动压力的时间尺度分析,有效描述储层渗透率、孔隙度以及孔隙、裂缝的几何形态对井底流动压力的影响.结果表明:储层强烈的非均质性是导致多个时间尺度共存的原因;通过流动的时间滞后效应,对孔隙、裂缝微观几何形态进行尺度升级,时间滞后效应使早期井底流压降低,迂曲、分叉的水力裂缝可减慢压力的传播,进而促使SRV中的流体更早地采出;窜流的不平衡效应对晚期渗流影响较大,同时可减弱远井地带对井底流动的影响,并且能够更好地描述SRV、水力裂缝之间的渗流差异;定产量生产可以减弱远井低渗地带对井底流动压力的影响.%On the basis of the low permeability and porosity, inhomogeneity and anisotropy, a flow model in the stimulated reservoir volume (SRV) of a tight reservoir was established in the present work. Due to the variation in flow regime and the tortuous flow region,the fluid remains within the pore and the fracture for a longer time. Therefore,the flow pressure affects the fluid flow afterwards. This is explained by the time lag effect. The finite element method in Laplace domain was used to obtain the solution of the proposed model,through which the analysis of temporal scales for the wellbore pressure was conduc-ted. And the impacts of the shapes of pore and fracture,the permeability and the porosity on the wellbore flow pressure were characterized. The results show that the strong reservoir heterogeneity was the reason for the co-existence of multiple temporal scales. And the scales of the micro-geometry of pores and fractures were updated through the time lag of the fluid flow. It is found that the wellbore flow pressure is reduced due to the time lag initially. Consequently, the pressure propagation is slowed down due to the tortuous flow region and the bifurcate artificial fracture,resulting in the exploitation of more fluid in the SRV. While the impact of unsteady coupling was evident for the fluid flowed afterwards,the impact of the region far from the wellbore on the wellbore flow pressure was weakened. In addition, the difference in flow velocities of different media is also described in more details. Also,the impact of the region far from the wellbore on the bottom hole pressure is also found to be weakened by the constant well rate.