Effects of reservoir combination in carbonates with strong heterogeneity on productivity
Several reservoirs,including Sinian,Cambrian and Permian,have been explored in deep marine carbonates,Anyue gasfield,Si-chuan Basin.And they feature buried depth ranging from 4,600 m to 5,200 m and strong heterogeneity.Among which,the intra-platform gas reservoirs in the fourth member of the Sinian Dengying Formation(simply as Dengying 4 Member)are a bit thin and multiple superimposi-tion in the vertical while generally exhibit low porosity and permeability.And some of them are improved in their quality owing to natural fractures or dissolution pores and vugs induced from karstification.The reservoirs are divided into three types of fractured-vuggy,vuggy,and porous reservoirs based on pore-vug-fracture combination and its genesis.Given the difference in pore-throat structure and fracture-vug extension scale,they show exclusive seepage characteristics.Thus,numerical simulation on well productivity was conducted under various reservoir combination.Results show that(i)the combination and reservoir planar or spatial distribution exert a great impact on the pro-ductivity;and(ii)near or far from the wellbore and in the transitional zone,the best productivity is achieved under the first combination of fractured-vuggy+vuggy+porous reservoirs(fractured-vuggy-porous reservoirs),followed by the second combination of vuggy+porous+fractured-vuggy reservoirs(vuggy-porous-fractured reservoirs),and the third combination of porous+fractured vuggy+vuggy reservoirs(porous-fractured-vuggy reservoirs)still with smaller productivity and longer stable production period.Consistent with real practice in nu-merous wells targeted Dengying 4 Member,GM block,these results provide important theoretical basis for well deployment and production performance adjustment in such member or similar carbonate gas reservoirs with strong heterogeneity.
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