考虑化学渗透压作用下页岩气储层压裂液的自发渗吸特征

Spontaneous imbibition characteristics of fracturing fluid in shale gas reservoir considering chemical osmotic pressure

裂缝-基质之间矿化度差异引起的化学渗透压对页岩压裂液返排和气井产能计算有着重要的影响。通过建立考虑化学渗透压作用下的渗吸动力模型,描述页岩自发渗吸过程中的驱动力类型。以鄂尔多斯盆地本溪组页岩为研究对象,开展页岩自发渗吸核磁扫描实验,研究黏土矿物、矿化度和表面活性剂对含水饱和度分布的影响。并以实验测定的含水饱和度分布曲线为拟合目标,获得了兼具毛管压力和化学渗透压双重作用下的毛管压力曲线。结果表明,页岩在自发渗吸过程中,随着渗吸时间的增加,吸水量呈现先快速增加后逐渐变缓的趋势,而渗吸速率则快速下降。页岩中黏土矿物含量越高、裂缝-基质间化学势差越大,渗吸驱动力越强,渗吸前缘距离和吸水量越大,而表面活性剂会降低毛管压力,引起驱动力下降,导致渗吸效果大幅降低。将修正后的毛管压力曲线应用于页岩气井产量预测,大幅提高了模型的计算精度。该研究成果为鄂尔多斯盆地页岩气藏高效开发提供了方法和依据。

The chemical osmotic pressure caused by salinity difference between fracture and matrix has an important influence on shale fracturing fluid flowback and gas well productivity calculation.The driving force types of shale spontaneous imbibition were described by establishing an imbibition dynamic model considering chemical osmotic pressure.Taking Benxi Formation shale in Ordos Basin as the research object,the effects of clay minerals,salinity and surfactant on water saturation distribution curve were studied through the shale spontaneous imbibition NMR scanning experiment.The capillary pressure curve under the dual action of capillary pressure and chemical osmotic pressure was obtained with the water saturation distribution curve measured by experiment as the fitting target.The results show that with the increase of imbibition time,the water absorption of shale increases rapidly first and then gradually slows down,while the imbibition rate decreases rapidly.The higher the clay mineral content in shale and the greater the chemical potential difference between matrix and fracture,the stronger the imbibition driving force is,and the greater the imbibition front distance and water absorption capacity are.The surfactant can reduce the capillary pressure and cause the driving force to drop,leading to the significant weakening of imbibition effect.The modified capillary pressure curve was applied to production prediction of shale gas well,which greatly improves the calculation accuracy of the model.The results provide a method and basis for efficient development of shale gas reservoir in Ordos Basin.