Study On Productivity Model Of Fracturing Horizontal Wells In Tight Reservoirs Considering The Effect Of Natural Fractures

Unconventional oil reservoirs such as low-permeability and tight oil reservoirs are supplementing fossil energy in our country,and their contributions are increasing.However,the extremely low permeability and pore throat radius of tight reservoirs lead to poor connectivity,high seepage resistance,and low natural productivity.The existence of natural fractures and capillary pressure are two typical characteristics of tight oil reservoirs.Recent literatures show that natural fractures play an important role in improving the productivity of tight oil reservoirs;with the transient change in the wetting phase saturation,the capillary pressure shows a trend of dynamic change,that is,its value is closely related to the change of wetting phase saturation.However,in the current production prediction method of fracturing horizontal wells in tight reservoirs,natural fractures are often ignored,and the capillary pressure is also regarded as a static value,making the prediction results unreasonable.In view of the above problems,by considering the existence of natural fractures,this article modifies the conventional flow model to make it more in line with the actual situation of the reservoir,and by monitoring the changing rate of wetting phase saturation during the production process,the static capillary pressure model is perfected as a dynamic capillary pressure model,and a productivity prediction model for fracturing horizontal wells in tight reservoirs is established to study the effects of natural fractures and dynamic capillary pressure on the productivity of fracturing horizontal wells.The main research contents and achievements are as follows:(1)Based on the traditional fluid flow equations,a productivity prediction model for fracturing horizontal wells in tight reservoirs considering the effects of natural fractures and dynamic capillary forces was established.Through the production data of well X1 in a tight reservoir,the proposed productivity prediction model is verified,and the comparison with the actual production data proves the effectiveness of the model.(2)Productivity sensitivity analysis was conducted for the production parameters and geological parameters of horizontal wells.The analysis results show that artificial fracture half-length is the one that has the greatest impact on the production of the horizontal well,followed by artificial fracture height,matrix permeability,production pressure difference and crude oil viscosity.Artificial fracture conductivity has the least impact.(3)The proportion of natural fractures in the reservoir has a great influence on the productivity of horizontal wells,and the permeability of natural fractures has a very limited effect on the productivity of horizontal wells.(4)In the early production stage,due to the relatively high production of horizontal wells,it leads to a large change in water saturation,which makes the effect of dynamic capillary pressure more obvious and needs attention;in the later production stage,the water saturation change is small and the dynamic capillary pressure will gradually approach the static capillary pressure.