Formation Laws of Inorganic Gas Pools in the Northern Jiangsu Basin

Abstract  In the Northern Jiangsu basin there are high pure CO2 gas pools, low condensed oil‐containing CO2 gas pools, high condensed oil‐containing CO2 gas pools and He‐containing natural gas pools, with the δ13Cco2 (PDB) values ranging from −2.87%o to −6.50%o, 3He/4He 3.71 × 10−6 to 6.42 × 10−6, R/Ra 2.64 to 4.5, 40Ar/36Ar 705 to 734, belonging to typical mantle source inorganic gas pools which are related to young magmatic activity. The gas layers occur in two major reservoir‐caprock systems, the terrestrial Meso‐Cenozoic clastic rock system and the marine Meso‐Palaeozoic carbonate rock‐clastic rock system. Controlled by the difference in the scale of traps in the two reservoir‐caprock systems, large and medium‐scale inorganic gas pools are formed in the marine Meso‐Palaeozoic Group and only small ones are formed in the terrestrial Meso‐Cenozoic strata. Inorganic gas pools in this basin are distributed along the two deep lithospheric faults on the west and south boundaries of the basin. Gas pools are developed at the intersected part of the ENE‐trending faults that control the half graben and the E‐W tenso‐shear faults, mainly distributed near the Es1, Ny1 and Ny2‐Q basalt eruption centres.