Low-pressure accumulation of hydrocarbon recorded by fluid inclusions in T165 reservoir, Tuozhuang area, Dongying Sag

Some fractures filled with calcites were found in the deep reservoirs in Tuozhuang area of the Dong-ying Sag. Large numbers of oil-bearing inclusions were contained in the calcite veins. The calcite veins contain two different morphologic crystals, which are fine xenomorphic crystal and medium-crystalline automorphic crystal, and the features of fluid inclusions in the two kinds of crystals are different. Based on optical observation, microthermometry and PVT simulation, this paper revealed the P-T trapping conditions of fluid inclusions, and also analyzed the characteristics of hydrocarbon accumulation. a) The fluid inclusions only recorded one period of accumulation, mainly during Nm. b) In the early accumulation, the pressure coefficient was less than 1, presenting the characteristic of low-pressure migration and injection. The seismic pumping caused by fault activities was the dominant dynamic force of hydrocarbon injection. In addition, it is not reliable to distinguish different accumulation periods by the petrographic characteristics of authigenetic minerals.