Fractal Characteristics Andhierarchical Evaluation of the Tight Gas Reservoir'S Pore Structure in Shanxi Formation of Daning-Jixian Area
The fractal dimension of the pore structure of the tight sandstone reservoir in the Daning-Jixian block of the Ordos Basin's Shanxi formation was calculated using the ideas and techniques of fractal geometry,and its relationship to the reservoir's physical characteristics,pore structure,and other factors was examined based on the experimental data of cast thin sections,field emission scanning electron microscopy,physical properties,high-pressure mercury injection,nuclear magnetic resonance,etc.The tight reservoir's pore structure was then further investigated using a hierarchical evaluation.Based on the findings,it was discovered that the Shanxi formation has an average porosity and permeability of 5.05％and 0.15 mD,respectively,which shows that the reservoir space predominantly consists of intergranular dissolved holes,intercrystalline pores,and residual intergranular pores.With values ranging from 2.11 to 2.87 and an average of 2.5,the porosity,permeability,and pore structure characteristics show a good association with the fractal dimension determined using the mercury saturation technique.The reservoir's pore structure may be divided into Type Ⅰ,Type Ⅱ,and Type Ⅲ using the mercury saturation method.Type Ⅱ and Type Ⅲ pore structure types predominate in the Daning-Jixian block.The complexity of micro-heterogeneity of tight sandstone reservoirs is quantitatively reflected through the evaluation of pore structure classification,which provides an effective geological basis for searching for favorable reservoirs and large-scale exploration and development of tight gas.
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