考虑压裂液渗吸的压后压裂液返排的数值模拟

Numerical simulation of post-fracturing flowback considering fracturing fluid imbibition

压后压裂液返排是水力压裂施工过程中的关键步骤,在非常规致密储层中压裂液的渗吸现象不容忽视.基于油水两相渗流理论、伯努利方程和连续性方程,建立考虑压裂液渗吸的返排数值模型,通过数值计算获得返排过程中的压力和排量等数据;根据支撑剂回流模型计算压裂液返排临界出砂流量,基于控制支撑剂回流和压裂液快速返排的原则,设计一套返排制度优化方法.将数值模拟结果与中国大庆油田LX3井实际返排数据对比验证,对长庆油田M87井进行返排工作制度设计,并分析了地层产出液黏度和初始地层压力对压裂液返排的影响.结果表明:返排过程中存在地层流体向裂缝渗流现象,原始地层压力改变对压裂液返排影响明显,而地层产出液的影响甚微.LX3井返排流量和井口压力的数值计算结果与现场监测结果基本相符,平均误差分别为13.8%和15.5%,验证了返排数值模型的准确性较高,可用于指导现场压裂返排施工设计.

Fracturing fluid flowback is a key step in the process of hydraulic fracturing,and the imbibition of fracturing fluid in unconventional tight reservoirs cannot be ignored.Based on the oil-water two-phase seepage theory,Bernoulli equation and the continuity equation,we establish a numerical simulation model of post-fracturing flowback by considering the effect of fracturing fluid imbibition and obtain the pressure and flowback rate during the flowback process through programmed numerical calculation.The critical flow rate of fracturing fluid when the proppant starts to reflux is calculated according to the proppant backflow model.Then an optimization design method of flowback working system is formed based on the principle of controlling proppant backflow and rapid fluid flowback.The numerical simulation results are compared with the actual flowback data of LX3 well,and the flowback working strategy of M87 well is designed,and the effects of formation fluid viscosity and initial formation pressure on fracturing fluid flowback are analyzed.The results show that a phenomenon of formation fluid seepage to fractures is observed during the flowback,and the change of original formation pressure has a significant impact on fracturing fluid flowback,but the formation produced fluid has minor effects.The numerical results of flowrate and wellhead pressure of LX3 well are consistent with the field monitor data,with average errors of 13.8%and 15.5%respectively.It is verified that the flowback numerical model has high accuracy and can be used to guide the on-site fracturing flowback construction design in oilfield.