The Study Of Productivity And Production Law On Fractured Horizontal Wells In Tight Sandstone Reservoir

Tight oil, which belongs to unconventional resource, is a hot issue in petroleumdevelopment recently. Because of lithology dense, poor reservoir properties and the existenceof threshold pressure gradient, tight oil reservoir is difficult to develop. Fractured horizontalwell is an effective technology for tight oil development because of some advantages: lowresistance, high productivity and economic. Complex fractures, diverse flow patterns bothmake it difficult to develop oil reasonably.In this paper, theoretical method and numerical simulation method were used to studyproductivity and production pattern of fractured horizontal well. A new productivity formulaof fractured horizontal well was derived, using conformal transformation and considering theimpact of threshold pressure gradient. The comparison of results between the new method andseveral empirical formulas has verified the correctness of the new productivity formula. Onthe basis of previous studies, non-steady-state productivity model of fractured horizontal wellwas derived with considering of fracture conductivity changes over time and wellborepressure drop. Factor sensibilities of fractured horizontal well in tight sandstone reservoirwere analyzed using this model. In the part of numerical simulation, conceptual models oftight sandstone reservoir were established, and streamline-pressure superimposed diagramswere used to divide flow stages of fractured horizontal well, including bilinear or linear flow,early radial or elliptical flow, compound formation linear, pseudo radial or elliptical flow,boundary-dominated flow. Then the impact of horizontal well length, fracture half-length,fracture conductivity, reservoir permeability, reservoir heterogeneity, impermeable layerposition and interlayer distribution on initial production capacity were studied to guide theoptimization of parameters in the range. Orthogonal design method was used to determine theimportance of parameters on productivity: horizontal well length> fracture half-length>fracture conductivity> fracture number. The fracture conductivity also affects productivity,which drops faster with considering conductivity changes over time. And under differentconductivity, production pressure difference has different impact on the productivity.Finally, the results of the theoretical researches and numerical simulation studies were applied to a practical tight sandstone oilfield. Production stages of fractured horizontal wellwere divided into three stages: production increaseâ†'production decreaseâ†'production steady.Wells and block production changes are basically in line with the hyperbolic decline withanalysis of fractured horizontal well production decline rule. Using fractured horizontal wellto develop tight oil reservoir, formation pressure drops rapidly, cumulative oil and recoverygrow rapidly in the beginning.