Productivity calculation of multi-fractured horizontal well in ultra-low permeability pressure-sensitive reservoirs

Based on the generalized Darcys law integrated the threshold pressure gradient and the pressure-sensitive effect,the method calculating multi-fractured horizontal wells productivity was established by means of elliptic flow model,average mass conservation law and equivalent wellbore radius.The effects of some factors such as threshold pressure gradient,pressure-sensitive effect,fractured parameters(fracture number,fracture length,conductivity,position and uniformity) and coefficient of deformation on the productivity were analyzed.The results show that the greater the threshold pressure gradient,the greater the effect of it on multi-fractured horizontal well(MFHW) productivity,so the threshold pressure gradient must be accounted to evaluate the MFHW productivity in ultra-low permeability reservoirs.The greater the coefficient of deformation,the greater the effect of it on MFHW productivity,and the effect of coefficient of deformation on productivity is related to producing pressure drop.In the given condition,the optimum fracture number of the horizontal well is 3-4,and the fracture length is about 200-280 m,the conductivity is 5-50 μm2·cm.The fractures with uniform long fracture length,low conductivity,placed in unequal interval are advantage to homogeneous oil production.