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

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 othe 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 P1s and has a lower gas generation potential. The total shale gas amounts in P-1s and P-2xs are 3602.29-4083.04 x 10(8) and 2811.04-3450.77 x 10(8) m(3), respectively. Further research on shale gas exploration and exploitation for these formations needs to be performed.