Full-range pore throat radius distribution and fractal characteristics of different types of reservoirs in deep carbonate gas reservoirs:A case study of Deng-4 Member in Gaoshiti-Moxi Area,Sichuan Basin
The typical characteristics of deep carbonate gas reservoirs with diverse reservoir media and complex pore throat structure in deep carbonate reservoirs make it difficult to reveal their full-range pore throat distribution and fractal characteristics.Therefore,the high-pressure mercury injection and constant-rate mercury injection experiments were jointly applied to quantitatively characterize the full-range pore throat size distribution of various reservoir types in deep carbonate gas reservoirs in Sichuan Basin.Subsequently,the complexity and mi-cro-heterogeneity of pore throat structures at different scales were revealed through fractal the-ory.Finally,the relationship between fractal dimension and storage and percolation capacities was revealed,and the controlling factors of fractal dimension were analyzed.The results show that the full-range pore throat radius of four types of reservoirs in deep carbonate reservoirs is in the range of 3.6 nm and 500 μm,and all distribution curves have multi-peak characteristics.Deep carbonate gas reservoirs mainly develop nano-scale pore throats,but the differences in micro-scale pore throats are obvious.The average values of total fractal dimension(DT)of fracture-cavity type,cavity type,fracture type and pore type reservoirs are 2.438,2.509,2.762 and 2.804,respectively,reflecting the differences in micro-heterogeneity among different types of reservoirs.All four types of reservoirs have triple fractal characteristics of small pore—fine throat section(r＜0.027 μm),moderate pore—coarse throat section(0.027μm≤r≤3.431 μm),and large pore—fracture section(r＞3.431 μm).Moreover,the differ-ences between different types of reservoirs are mainly reflected in the small pore—fine throat section,resulting in the micro-heterogeneity of the reservoir being mainly affected by the pro-portion of pore throat volume and the value of fractal dimension in this section.The fractal di-mension of nano-scale pore throats is lower than that of micro-scale pore throats,indicating that the heterogeneity and complexity of micro-scale pore throats are stronger than those of nano-scale pore throats under the effects of fractures and cavities.The correlation between DT and porosity,displacement pressure,skewness,maximum mercury saturation,and sorting co-efficient is good,and the correlation between the fractal dimensions of nano-scale pore throats and small pore—fine throat sectionis relatively strong with these structural parameters,indica-ting that the small pore—fine throats at the nano-scale has a greater impact on the overall pore throat connectivity and heterogeneity of deep carbonate gas reservoirs.
deep carbonate gas reservoirsfull-range pore throat radius distributionfractal characteristicspore throat structurehigh-pressure mercury injectionconstant-rate mercury injection
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