Numerical simulation of multi-scale coupled flow in ultra-deep fractured tight sandstone gas reservoirs
The Cretaceous gas reservoirs in Kelasu gas field of the Tarim Basin are rare ultra-deep fractured tight sandstone gas reservoirs with low porosity.Such reservoirs are remarkably characterized by multi-scale storage and seepage space,with the matrix having the permeability contrast of 5-6 orders of magnitude to the multi-scale fractures and fault media.Conventional seepage theory cannot accurately describe the flow behaviors and development mechanism of these reservoirs.Based on the results of single-fracture flow physical experiments and the fluid mechanics theory,together with the geometric information of multi-scale fractures,the multi-scale media were divided into five flow systems according to the homogenization theory and the volume average scale upgrade method,and the flow equation was established for each flow system.Thus,a multi-scale coupled flow model considering the unsteady crossflow between media was built.Furthermore,the coupled flow model was numerically solved using the finite volume method,and numerical well testing analysis was conducted.The results are obtained in three aspects.First,various flow behaviors are observed in the fractures of different scales.As the fracture width increases,the flow velocity rises,and the flow pattern changes.Second,the multi-scale coupled flow model yields very different results from the dual-medium model,and provides the derivative curve with different trends.Third,the multi-scale coupled flow model is used to successfully interpret the actual well testing data of the gas reservoir,and it can reflect the flow process in actual formations.In conclusion,the proposed multi-scale coupled flow model of ultra-deep fractured tight sandstone gas reservoir reveals the development mechanism of stepwise recovery and coordinated gas supply among multi-scale fractures and tight matrix.The study provides references for the development of similar gas reservoirs.
Tarim BasinKelasu gas fieldCretaceousFractured tight sandstone gas reservoirMulti-scale fracturesFlow patternCoupled flow modelNumerical simulation
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