页岩气藏水相损害评价与尺度性

页岩气藏基质储渗空间为纳米尺度，超低含水饱和度，高黏土矿物含量，发育微裂缝，需经压裂改造投产，气体产出是一个多尺度、多种传质过程，但压裂液易产生滞留，影响气体产出。页岩渗透率为纳达西级，难以利用测量损害前后渗透率的传统方法评价页岩气层损害。采用四川露头页岩岩样和4种滑溜水压裂液体系，利用压力衰减法，结合水相渗吸实验和气驱水返排实验，评价了压裂液滤液对岩心尺度的损害程度，分析了页岩气藏工作液损害评价的指标，认为传统渗透能力恢复率或渗透率恢复率不能作为页岩气层损害评价的唯一指标。基于评价结果，结合目前部分压裂液返排率低的气井产量反而比较高的非常规现象分析，指出页岩压裂液诱发水相圈闭损害是一个动态过程，具有尺度性，在评价过程还要考虑滞留压裂液对气体传递的积极作用，压裂液作用及返排制度是未来5~10年值得研究的重点问题。

Evaluation and scale effect of aqeous phase damage in shale gas reservoir

Shale gas reservoir is characterized by nanometer-scaled pore-throats,ultra-low water saturation,high content of clay and some micro fractures.The key technology of shale gas development is hydraulic fracturing.The fracturing fluid remained in factures invades into shale matrix and causes aqueous phase trapping and water sensitivity damage which decrease gas relative permeability sharply.Shale reservoirs have a nano-Darcy permeability;therefore,it is difficult to evaluate formation damage by traditional methods which measure permeability before and after the interaction of fluids and core plugs.The paper conducted experiments of pressure depletion,spontaneous filtration imbibition and nitrogen displacement using shale outcrop samples from Sichuan and four types of fracturing fluid to evaluate the damage of fracturing fluid.The evaluation indexes of shale gas reservoir damage are analyzed,and it is considered that the traditional permeability recovery rate or permeability recovery rate cannot be the only index for evaluating the damage of shale gas reservoirs.Based on the evaluation results,the abnormal phenomenon of low displacement rate corresponding relatively high gas output is analyzed.And some conclusions are gained: aqueous phase trapping caused by fracturing fluid is a dynamic process;the positive effects for gas flow must be considered in the evaluation of aqueous phase trapping;flowback of fracturing fluid in shale gas is the key point in the future 5 to 10 years.