Study On The Productivity Of Fractured Horizontal Wells In Low Permeability Tight Sandstone Gas Reservoir

Whether it is from the perspective of energy consumption structure or resource reserves,low-permeability tight gas reservoirs are still the key targets for development in recent decades.Horizontal wells and fracturing horizontal wells are usually effective methods for developing such kinds of gas reservoirs,and the evaluation of productivity is the key to guiding and optimization of gas well production.Because the flow law of low-permeability tight gas reservoirs is different from that of conventional oil and gas reservoirs,the method used to analyze the productivity of conventional oil and gas reservoirs can't be applied directly to such tight gas reservoirs,which may lead to inaccurate results and deviations in guiding the production and optimization of the mine field.Therefore,it is necessary to study the productivity of horizontal wells and fracturing horizontal wells in low penneability tight sandstone gas reservoirs.In this paper,for the conventional horizontal well in low permeability tight sandstone gas reservoir,the flow splitting method is used to separate the whole flow into two regions.The starting pressure gradient and the stress sensitivity effect are considered in the far well region.In addition to the starting pressure gradient,the stress sensitivity effect,the slippage and the high speed non-Darcy effect are considered in the near well area.The seepage equations in the two parts were combined with the conditions of pressure continuity and flow equality,and the steady productivity model of the horizontal well in the low permeability tight sandstone gas reservoir was obtained.Through the analysis of an example,the starting pressure gradient,the stress sensitivity effect,and the high speed non-Darcy effect were found having important influence on the productivity.For fracturing horizontal wells,a steady-state productivity model for horizontal fracturing wells in low-permeability tight sandstone gas reservoirs considering the nonlinear factors in the formation,the shape of crack wedges and wellbore pressure drops was established based on the distribution function of potential,and various influencing factors were analyzed.Finally,for the closed tight rectangular gas reservoir with low penneability and tight sandstone,the point source concept is used to separate the fracture into several point sources.The planar source function in the closed formation was obtained by mirror reflection and the Poissson summation based on instantaneous point source function in the infinite formation.And the point source function in closed rectangular gas reservoir is obtained by the Newman integral.The coupling of each point source flow equation considering the nonlinear characteristics and the pressure drop equation from the point source to the wellbore considering the fracture flow conductivity was achieved to build the unsteady productivity formula of fractured horizontal wells in closed rectangular tight sandstone gas reservoirs.The influencing factors of unsteady state productivity are also analyzed.The research results in this paper provide strong theoretical support for the development and optimization of low permeability tight sandstone gas reservoirs.