Characteristics and lower limits of physical properties of reservoirs in Middle Permian Maokou Formation,central Sichuan Basin
The lower limit of physical properties is a key parameter for identifying effective reservoirs and determining their net pays,as well as a necessary subject in estimating gas in place(GIP).The lower limits of physical properties of effective reservoirs in the Middle Permian Maokou Formation,central Sichuan Basin,are often in analogy to those of carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing Formations,eastern Sichuan Basin.However,the Maokou Formation reservoirs are sig-nificantly different in regional geological conditions,sedimentary environments,diagenesis,and rock types,seriously impacting the accuracy of GIP estimation and restricting the exploration and development.The reservoir characteristics of the Maokou Formation were systematically analyzed based on drilling,logging,core,and analytic data.And then the lower limits of physical properties were determined by utilizing the methods of minimum flow pore-throat radius,productivity simulation,and single-layer gas testing.The results show that,(i)the Maokou Formation reservoirs are composed of fine-crystalline dolomites,as well as a small amount of psam-mitic dolomites,limy dolomites,and dolomitic limestones;(ii)the reservoir spaces in the study area are dominated by various disso-lution pores/vugs,with fractures and throats acting as key flow pathways;such spaces are diverse in types and complex in geometry,with strong heterogeneity;(iii)considering the development of dissolution pores/vugs and microfractures,the experimental results of full-diameter samples were used to reflect the physical properties,showing generally low porosity and permeability and locally high porosity and permeability;and(iv)by using the above-mentioned three methods,the lower limits of porosity and permeability are de-termined as 1.97%and 0.009 0 mD,respectively.The study provides a reference for identifying effective reservoirs,determining net pays,and estimating GIP.
Central Sichuan BasinMaokou FormationReservoir rock typeReservoir-permeation spacePhysical propertyLower limit of physical property of effective reservoir
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