Preliminary Assessment of the Resource and Exploitation Potential of Lower Permian Marine-Continent Transitional Facies Shale Gas in the Huainan Basin, Eastern China, Based on a Comprehensive Understanding of Geological Conditions

[Image: see text] The Huainan Basin in eastern China contains abundant shale gas resources; the Lower Permian is an exploration horizon with a high potential for shale gas in marine-continent transitional facies. However, few detailed analyses have investigated shale gas in this area. In this paper, a comprehensive investigation of the geochemical characteristics, physical properties, and gas-bearing capacities of shale reservoirs was conducted, and the resource and exploitation potential were evaluated. The results show that the cumulative thicknesses of the Shanxi Formation (P(1s)) and lower Shihezi Formation (P(2xs)) are mostly greater than 35 and 65 m, respectively. The TOC contents of the P(1s) and P(2xs) shale vary from 0.11 to 8.87% and from 0.22 to 14.63%, respectively; the kerogens predominantly belong to type II with minor amounts of type I or type III kerogens; average R(o) values range between 0.83 and 0.94% and between 0.82 and 1.02% in P(1s) and P(2xs), respectively; the shale samples are primarily at a low maturity, while some shale samples have entered the high-maturity stage. The shale reservoirs have low permeability and porosity in P(1s) and P(2xs), respectively. The pores of the P(1s) shale reservoir are characterized by well-developed micropores and transition pores and poorly developed mesopores, while the pores in the P(2xs) shale reservoir are all characterized by well-developed micropores and transition pores and some well-developed macropores; the different pore types in the shale reservoirs developed in the organic matter, clay minerals, and pyrite, while a few endogenous fractures developed in the organic matter and structural fractures developed in the minerals. The total shale gas contents in P(1s) and P(2xs) are 2.85 and 2.96 m(3) t(–1), respectively. The P(2xs) shale reservoir has a higher hydrocarbon generation potential than P(1s) and has a lower gas generation potential. The total shale gas amounts in P(1s) and P(2xs) are 3602.29–4083.04 × 10(8) and 2811.04–3450.77 × 10(8) m(3), respectively. Further research on shale gas exploration and exploitation for these formations needs to be performed.