压裂气井返排压力新模型研究

摘要

气井压裂后返排阶段压力的准确预测对于优化返排工作制度具有重要意义,目前的返排压力模型缺乏对两相返排阶段的研究,压力模型不完善.为此,根据质量守恒原理、能量守恒原理、岩石力学理论和地层渗流理论,建立了考虑裂缝闭合前后不同返排规律和压力变化规律的返排压力新模型.新模型包含单相压裂液返排和气液两相返排的不同阶段,将压裂返排过程与地层产能综合分析,最终得到从停泵返排初期直至气井稳定产气整个过程的返排压力变化规律.现场实例表明,新模型的计算结果与现场实测压力吻合较好.放喷油嘴尺寸越大、裂缝闭合时间越短,到达稳定产气阶段的时间越短,稳定产气阶段的井底压力也越低.新模型可为现场合理返排制度的确定提供理论指导.%Accurate prediction of pressure during flowback process after hydraulic fracturing in gas well has a great significance for optimizing of flowback process,current models for calculating flowback pressure lack research on two-phase flowback process and these models are not complete.Therefore,based on principle of mass conservation,principle of energy conservation,theory of rock mechanics,and dynamics of fluids in porous media,a new flowback pressure model is established,which considers different characters and pressure changes before and after closure of hydraulic fracture.Both one-phase and two-phase flowback stage are involved in the new model,a comprehensive analysis is made which combines flowback process and formation productivity,finally the rule of flowback pressure change from initial flowback stage to stable production stage is obtained.Field application shows that the results of pressure calculated by the new model coincide well with measured pressure.The greater the nozzle size,the shorter the closing time of fracture,and the shorter the time to reach stable production stage.The new model could provide theoretical guideline for determine of reasonable flowback process in field.