Optimization of Shut-in Time between the First and Second Fracturing by means of Pressure Decline Analysis

It is necessary to shut in the well between the first and second fracturing, with the time interval often determined by prior experience, which may result a significant error. Moreover, the selection of shut-in time will directly affect the performance of secondary fracturing. Based on previous efforts, this paper divides the fracturing process into four stages:pumping, frac fluid after-flow, fracture closure and after-closure. Considering the influences of frac fluid after-flow and proppant volume, and through the pressure decline analysis of after-closure, the calculation model was established for after-flow time and fracture closure time and the time when formation pressure became stable. By using basic fracturing parameters of the X block, the after-flow time and fracture closure times were calculated, the pressure decline after fracture closure was analyzed, and the performance of the secondary fracturing for several wells was compared. The results showed that the time when the formation pressure was stable corresponded to a reasonable shut-in time between the first and second fracturing and it marked the optimum point in time at which the best fracturing performance could be achieved. The optimum shut-in time gained from the simulation results and production after fracturing were consistent with that calculated by the model, which demonstrated that the model could accurately predict the optimum shut-in time which could be significant for guiding fracturing operations.