单裂隙端面复合形貌影响下流体渗流特征

Fluid Seepage Characteristics under Influence of Surface Composite Topography of Single Fracture

自然储层裂隙端面在一定尺度下往往会表现出非匹配特征,由此产生的开度非均一分布对流体渗流行为具有重大影响。因此,厘清裂隙复合形貌特征对渗透性能的控制作用对于油气产能的准确评估至关重要。首先,结合岩石裂隙复合形貌特征,以解析推导方式确定了粗糙裂隙中阻碍流体运移的2种效应,分别是端面粗糙效应和开度粗糙效应;其次,在通过权重算法对粗糙裂隙端面间的非匹配行为进行二维表征的基础上,采用格子Boltzmann方法进行孔隙尺度模拟再现了非匹配粗糙裂隙中流体的运移过程,并据此系统分析了流体渗流的影响特征。结果表明:由于未考虑开度非均一分布的影响,导致了三重效应渗透率预测模型对渗透率的过高估计,且预测误差取决于端面非匹配程度;开度非均一分布在一定程度上阻碍了流体的有效运移,同时也间接削弱了裂隙的渗透性能,其削弱能力受控于开度相对粗糙度。

The fracture surfaces of natural reservoir often show the mismatched feature at a certain scale,and the resulting non-uniform distribution of apertures significantly influences the fluid flow behavior.Therefore,it is crucial for the accurate evaluation of oil and gas productivity to clarify the controlling effects of the composite topography of fractures on penetrating quality.Firstly,combined with the composite topography,the two effects that hinder fluid flow in rough fractures were determined by analytical derivation,i.e.,surface roughness effect and aperture roughness effect.Then,on the basis of the two-dimensional characterization of the mismatched behavior between surfaces by using the weight algorithm,the transport processes of fluid in mismatched rough fractures were simulated by lattice Boltzmann method at pore scale,and the influence characteristics of fluid flow were analyzed.The results indicate that,due to the influence of aperture non-uniform distribution,the permeability estimated by triple-effect model is overestimated,and the prediction error depends on the degree of surface mismatch.Moreover,the aperture non-uniform distribution hinders the effective migration of fluid to some extent,and weakens the penetrating quality of fractures indirectly,which is controlled by aperture relative roughness.