考虑压裂液渗吸的压后压裂液返排的数值模拟

Abstract

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.