Fluid Inclusion Analysis for Constraining the Hydrocarbon Accumulation Periods of the Permian Reservoirs in Northeast Ordos Basin

Geochronology of hydrocarbon accumulation and reconstruction is an important and challenging subject of petroleum geology in multi-cycle superimposed basin. By fluid inclusion (FI) analysis combined with the apatite fission track (AFT) modeling thermal path of the FI host rock, a case study of constraining the hydrocarbon accumulation and reconstruction periods of the Permian reservoirs in Northeast Ordos Basin (OB) has been conducted. The FI homogenization temperatures of the oil-gas-bearing sandstone core-samples from the Lower to Upper Permian reservoirs statistically present two groups with a low and a high temperature peaks in ranges of 90–78 and 125–118 ℃, respectively, corresponding to 2-stage primary hydrocarbon accumulations of the Early-Middle Mesozoic. Besides, there exists another group with a medium-high peak temperature of 98 ℃ in the Upper Permian reservoirs, corresponding to the hydrocarbon reconstruction and destruction of the Late Mesozoic to Cenozoic. According to the projected ages of the FI peak temperatures on the AFT thermal path of the FI host rocks, it is further induced that there experienced 3-stage hydrocarbon accumulations in the Permian reservoirs during the Mesozoic to Cenozoic. These are: (1) all the various primary hydrocarbon Permian reservoirs together developed 2-stage accumulations of 162–153 and 140–128 Ma in agreement with the multi-cycle subsidence burial heating process of the basin; (2) the Upper Permian reservoirs further experienced 1-stage secondary hydrocarbon accumulation and reconstruction at ca. 30 Ma in coincidence with a critical tectonic conversion of the slow to rapid uplifting process from the Late Cretaceous to Neogene.