低矿化度注水引起粘土膨胀对储层衰竭过程中微粒运移和渗透率下降的影响
Fines Migration and Permeability Decline during Reservoir Depletion Coupled with Clay Swelling due to Low-Salinity Water Injection: An Analytical Study
摘要：
微粒运移行为既可以促进也可以阻碍储层内的流体流动，对于需要基本理解的产能优化至关重要。目前的工作重点是有效应力积累的贡献，由于油藏枯竭和盐水盐度降低，从低矿化度水注入。用应力和盐度相关的临界滞留浓度函数对颗粒分离进行了分析研究。地层有效应力的增加导致储层结构内的变形，这是由于微裂纹和孔隙尺寸减小。移动通道的尺寸减小促进颗粒分离，而临界保留浓度降低。敏感性研究表明，在有效应力的影响下，颗粒尺寸和流体速度是通过影响颗粒分离力来控制细粒迁移的主导参数。随着盐水盐度的降低（例如通过低盐度水注入），附着在孔隙表面上的粘土颗粒越来越膨胀，导致有效孔隙空间和流动通道的减少。孔隙空间的减小直接阻碍了悬浮颗粒和流体的运移，导致渗透率下降。初始粘土颗粒尺寸被认为是控制颗粒脱离行为的关键因素。由于分离力较弱，小的初始颗粒尺寸不太可能从孔隙表面分离，因此分析发现临界保留浓度不变，导致渗透率随盐水盐度的下降可忽略不计。考虑到这两种效应，有效应力和盐水盐度，应力依赖的影响占主导地位的盐度依赖的影响，在低有效应力，而这两个贡献相等，在高有效应力。
英文摘要：
Fines migration behavior can either promote or obstruct fluid flow within the reservoir and is crucial for productivity optimization that needs fundamental understanding. The present work focuses on the contributions from effective stress build-up due to reservoir depletion and decreases in brine salinity from low-salinity water injection. Particle detachment is studied analytically by using the critical retention concentration function modified with stress and salinity dependents. Increase in formation effective stress leads to deformations within the reservoir configurations due to micro-cracks and reduced pore dimensions. Decreased size of the travelling channels promotes particle detachment, while the critical retention concentration decreases. A sensitivity study reveals that, under influence of effective stress, particle size and fluid velocity are dominant parameters controlling the fines migration by influencing the particle detaching forces. With decreasing brine salinity (e.g. via low-salinity water injection), clay particles that are attached on the pore surface increasingly swell, leading to reduction in effective pore space and flow channel. Decreased pore space directly obstructs travelling of suspended particles and fluids which results in permeability decline. Initial clay particle size is found to be a critical factor controlling particle detachment behavior. Small initial particle sizes are not likely to detach from the pore surface as a result of weak detaching forces, hence the analysis finds the critical retention concentration unchanged resulting in negligible permeability decline as a function of brine salinity. Considering both effects, effective stress and brine salinity, stress-dependent effects dominate salinity-dependent effects at low effective stress while the two contribute equally at high effective stress.
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