基于页岩气井压后返排液氯离子分析的压后效果评价

EVALUATION OF POST-PRESSURE EFFECT BASED ON CHLORINE ION ANALYSIS OF BACK-FLOW FLUID AFTER FRACTURING IN SHALE GAS WELLS

页岩具有低孔隙度、特低渗透率的特征,只有通过储层改造后才能获得经济开发效益。水平井钻井与多段多簇压裂是页岩气效益开发的关键核心技术,为提高页岩气单井产量,以储层改造体积和裂缝复杂程度最大化为目标函数,但现有裂缝复杂程度表征及气井产能预测方法有限。压裂液的返排动态可表征储层压后的裂缝形态,是影响压后产能的重要因素,通过对返排液测试数据的分析总结表明,压裂返排液氯离子浓度变化分为3个区域:快速上涨区,缓慢上涨区,趋于平稳区。同区块邻井在相同压裂工艺及返排制度下,返排液氯离子浓度变化趋于一致;页岩气井排液期间返排率越低,氯离子浓度变化幅度越小,即快速上涨区与缓慢上涨区持续时间越短,裂缝复杂程度越高,压裂改造效果越好;页岩气井最大瞬时产气量出现在平稳区初期。丰富了页岩气压裂后评估技术体系,为气井产能预测提供了支撑。

Shale is characterized by low porosity and extremely low permeability,and economic development benefit can be obtained only after reservoir stimulation.Horizontal well drilling and multi-stage multi-cluster fracturing are the key technologies for shale gas benefit development.To increase the shale gas production per well,the target function is to maximize the reservoir stimulation volume(SRV)and fracture complexity.However,existing fracture complexity characterization and gas well productivity prediction methods are limited.The analysis and summary of the discharge test data show that the change of chloride ion concentration in the fracturing flowback fluid can be divided into three areas:rapid rise area,slow rise area and stable area.Under the same fracturing technology and flowback system in adjacent Wells in the same block,the changes of chloride ion concentration in flowback fluid tend to be the same.The lower the backflow rate during the drainage period of shale gas wells,the smaller the change range of chloride ion concentration,that is,the shorter the duration of rapid rising zone and slow rising zone,the higher the fracture complexity,and the better the fracturing effect.The maximum instantaneous gas production of shale gas wells appears at the initial stage of the stationary zone.The post-fracturing evaluation technology system of shale gas has been enriched,providing support for gas well productivity prediction.