Research on productivity for horizontal well in low permeability pressure-sensitive reservoirs

In order to scientifically evaluate productivity for horizontal well in low permeability pressure-sensitive reservoirs,the analytical formula to calculate horizontal well's productivity were derived with the consideration of the generalized Darcy's law influenced by the threshold pressure gradient and the pressure-sensitive effect,elliptic flow model,average mass conservation law and seepage field cleavage.The reliability and practicability were confirmed in comparison to other well-known horizontal well productivity formulas.Based on this,this study analyzed the effects of some factors on the productivity.The results show that the effect of threshold pressure gradient on horizontal well productivity is related to the coefficient of deformation,while the coefficient of deformation is bigger,and the horizontal well productivity and threshold pressure gradient are in nonlinear relationship,vice versa.The nonlinear relationship between productivity and the coefficient of deformation is influenced by producing pressure drop.When the producing pressure drop gets bigger,the effect of coefficient of deformation on productivity gets bigger while the coefficient of deformation is about 0—0.4MPa-1.The horizontal well productivity increases slow down as reservoir thickening.However,horizontal well productivity increases in lineal with the length extending.So it is proved that the effect of threshold pressure gradient on productivity can be abated by lengthening horizontal well.