Study On Optimization Model Of Shut-in Time After Fracturing In Tight Sandstone Reservoir

Hydraulic fracturing is an effective technique to increase the production of tight reservoirs.Tight reservoir production can be divided into fracturing fluid injection stage,shut-in stage and production stage.In the shut-in stage,the fluid that leak-off the formation will be replaced with the oil in the small pores through imbibition.A large number of studies have shown that imbibition can significantly increase the production of a single well and the overall recovery.However,when some scholars study the shut-in stage,the initial pressure is often set to the original formation pressure,which is obviously unreasonable and will lead to the accuracy of the overall model is reduced.At the same time,the selection of shut-in time will also affect the production and revenue of the tight reservoir.Aiming at the volumetric balance between the fracturing fluid injection process and the shut-in process in tight reservoir,an optimal shut-in time model is established around horizontal well in tight reservoir based on the theory of seepage mechanics and combining numerical simulation.The optimal model first calculates the fracturing fluid leak-off area after the completion of shut-in through shut-in model of horizontal well in tight reservoir,then builds a formation model considering the complex area and conducts numerical simulation calculation,analyzes the production changes under different shut-in time,and finally optimizes the shut-in time.The main research contents and achievements are as follows:(1)considering the volume balance relationship of the fracturing process(Fracturing fluid injection is equal to fracturing fluid leak-off plus fracture volume change)and the shut-in process(fluid leak-off is equal to the fracture volume change),and combining the two-dimensional leak-off model and the fracture volume model,the fracturing shut-in model for vertical well in tight reservoir is established.This model fully considers the characteristics of fracturing operation,and takes the pressure distribution obtained by the fracturing model as the initial pressure value of the shut-in model,which greatly improves the accuracy of the model and provides a basis for subsequent research.(2)considering the fracturing operation characteristics of horizontal well,the fracturing shut-in model of vertical well in tight reservoir is extended,and the shut-in model of horizontal well in tight reservoir is established.At the same time,the influence of different shut-in time on the fracturing fluid leak-off area is analyzed.These results provide theoretical support for the selection of shut-in time in subsequent tight reservoir production studies.(3)based on the fracturing fluid leak-off area calculated by the horizontal well fracturing model and shut-in model of tight reservoir,a model considering the composite area is established.By using numerical simulation software,the variation of production in tight reservoir under different parameters is calculated and analyzed.(4)taking an actual horizontal well as the data basis,the optimal shut-in time is analyzed by using the shut-in time-fracturing fluid leak-off area curve and shut-in time-cumulative production diagram calculated by the above theoretical model and numerical simulation.