玛湖风城组高含盐储层水力压裂裂缝扩展规律

Fracture Propagation Law of Hydraulic Fracturing in High-Salinity Reservoir of Fengcheng Formation in Mahu

玛湖风城组地层含盐量高,导致压裂施工压力高、水力裂缝穿透盐层扩展难度大、加砂难度大等问题。基于相似准则制备等效含盐岩样开展真三轴压裂实验,并基于有限元法和内聚力单元法开展含盐储层裂缝扩展数值模拟研究,探索了含盐量、黏度、排量等因素对裂缝扩展行为的影响。研究结果表明,与常规砂岩相比,含盐储层破裂压力更高,塑性更强,纯盐隔层的存在会阻碍裂缝纵向扩展;压裂液黏度越小,对含盐储层的溶蚀越强,施工压力就越低;排量越高,压裂摩阻越高,施工压力越高。现场应采用清水配置高黏(120mPa·s)压裂液和大排量(单簇排量5m^(3)/min)施工,实现水力裂缝有效穿透纯盐隔层并形成较大缝宽。研究成果对玛湖地区含盐储层的改造具有重要指导意义。

The high salt content of Fengcheng Formation in Mahu leads to high operating pressures,difficulty in fracture propagation when penetrating salt layers,and increased difficulty in adding proppant.True triaxial fracturing experiments are carried out on equiva-lent salt-bearing rock samples prepared according to similarity criteria,and fracture propagation in salt-bearing reservoirs is numeri-cally simulated using the finite element and cohesive element methods.The influence of salt content,viscosity,pump rate,and other factors on fracture propagation is explored.The results show that the fracture opening pressure of salt-bearing reservoirs is greater than that of conventional sandstone reservoirs,and their plasticity is stronger.The existence of pure salt interlayers hinders the longitudinal propagation of fractures.The lower the fluid viscosity,the stronger the dissolution of the salt-bearing reservoir and the lower the operat-ing pressure.The higher the pump rate,the higher the fracturing friction and the operating pressure.In field,high viscosity fluid(120 mPa·s)with clean water and high pump rate(5 m^(3)/min per single cluster)have been adopted to achieve effective penetration into pure salt bar-riers and form wider fractures.These results have important guiding significance for the stimulation of salt-bearing reservoirs in Mahu area.