Rock-Eval analysis of the Lower Cretaceous (Middle Aption-Early Albian) Shahezi Formation in the Xujiaweizi Rift Depression, Songliao Basin, NE Asia

Description

Well SK-2, drilled as a part of the International Continental Scientific Drilling Program (ICDP), is located at the Xujiaweizi Rift Depression, Songliao Basin, northeastern Asia. The Lower Cretaceous (Middle Aptian-Early Albian) Shahezi Formation was entirely recovered by SK-2, spanning a depth range from 3337 m to 5960 m. Rock Eval pyrolysis was performed on 247 core pieces of whole rock shales and mudstones from the Shahezi Formation, following the Chinese National Standard (GB/T 18602 2012, Rock-Eval analysis). The Rock-EVAL 6 was employed to measure the pyrolysis parameters at the Experimental Research Center of Wuxi Research Institute of Petroleum Geology of SINOPEC. Samples were first heated at 300 ℃ to release volatile hydrocarbons (S1) and then temperature programmed to 600 ℃ at 25/min to release pyrolytic hydrocarbons (S2). The Tmax is the temperature corresponding to the maximum yield of S2 hydrocarbon, which can indicate the thermal maturity of kerogen. CO2 released from the thermal degradation of organic matter (S3) is trapped and measured. The hydrogen index (HI, mg HC/g TOC) is obtained by dividing S2 × 100 by TOC. Dividing S3 × 100 by TOC yields the oxygen index (OI, mg HC/g TOC).

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