Study on the permeability calculation method of carboniferous carbonate reservoirs in the Coastal Caspian Basin based on the characteristics of pore-throat combination

Permeability is a key parameter for finding effective reservoirs and evaluating reservoir production capacity, but accurate evaluation of permeability in carbonate reservoirs has always been a challenge. This study proposes a new method for calculating the permeability of carbonate reservoirs. This study focuses on the Carboniferous carbonate reservoirs in the Pre-Caspian Sea Basin and uses high-pressure mercury injection experiments to measure the micropore structure of the reservoirs. According to the distribution of pore throats, it is divided into macropores, mesopores, small pores, and nanopores. Based on Multi-Resolution Graph-based Clustering, a reservoir permeability calculation model is established. The following understandings were obtained: (1) The pore throat radius of small pore is 0.27 μm, and the contribution rate to permeability is 13.8%; (2) The pore throat radius of mesopores is 0.83 μm and a contribution rate of 28.9% to permeability; (3) The pore throat radius of macropore was 3.78 μm, and the contribution rate to permeability was 57.4%; and (4) The model established using MRGC method has good performance. The innovation of this article is to propose a new permeability modeling method for carbonate reservoirs, which can be used for calculating the permeability of reservoirs in other regions.