Geochemical Characteristics and Hydrocarbon Generation Potential of Different Lithologic Source Rocks in the Second Member of Funing Formation in Qintong Sag, Subei Basin

doi:10.19657/j.geoscience.1000-8527.2023.049

Abstract

Abstract:

The second member of Paleogene Funing Formation (E₁f₂) is the main target interval of shale oil exploration and has good prospects of oil and gas exploration in Qintong Sag.Predecessors have studied the hydrocarbon generation potential and geochemical characteristics of source rocks in the E₁f₂ in the study area systematically, but the study on the geochemical characteristics and forming environment of source rocks in different sub-members and lithology of the E₁f₂ is still relatively weak, which brings difficulties to the prediction of shale oil sweet spots and resource potential evaluation, as well as the correlation of oil-sources in the E₁f₂ in the study area.In this paper, some representative shale samples of the E₁f₂ in typical wells are selected, and the geochemical characteristics, hydrocarbon generation potential and formation environment of different sub-sections and lithologic source rocks of E₁f₂ in the study area are compared by using geochemical experimental techniques.The results show that the source rocks of E₁ $f 2 4$ and E₁ $f 2 5$ in the study area have the highest abundance of organic matter, mainly type Ⅱ₁ organic matter.The abundance of organic matter in E₁ $f 2 2$ and E₁ $f 2 3$ source rocks is high, mainly type Ⅱ₁ and Ⅱ₂ organic matter.The abundance of organic matter in E₁ $f 2 1$ is relatively low, and the type of organic matter is Ⅱ₂.The lithology of source rocks in the E₁f₂ in the study area is relatively complex, mainly including mudstone, calcareous mudstone and calcareous shale.Mudstone is mainly distributed in E₁ $f 2 4$ and E₁ $f 2 5$ , with the highest abundance of organic matter, mainly type Ⅱ₁ and type Ⅰ organic matter, deposited in weak oxidation-weak reduction freshwater environment, mixed source organic matter dominated by lower aquatic organisms.The calcareous shale and calcareous mudstone are mainly distributed in E₁ $f 2 1$ , E₁ $f 2 2$ and E₁ $f 2 3$ .The organic matter abundance of calcareous shale is higher, and the organic matter type is mainly type Ⅱ₁, a few Ⅱ₂, which is deposited in a strongly reducing saline water environment and mixed source organic matter source.The organic matter abundance of the calcareous mudstone is low-medium, and the type of organic matter type is mainly Ⅱ₂, with a small amount of Ⅱ₁ and Ⅲ, which is deposited in the reducing environment of brackish water and is the source of mixed source organic matter.The source rocks of E₁f₂ are in low mature-mature stage.According to the distribution characteristics of Pr / Ph, Ga / C₃₀H, C₂₄TeT / C₂₆TT and ααα20RC₂₇ sterane / ααα20RC₂₉ sterane, the source rocks of three different lithologies in the E₁f₂ can be distinguished.These understandings can provide geochemical basis for the evaluation of oil and gas resource potential, oil-source correlation and shale oil exploration in different intervals and lithologic source rocks of the E₁f₂ in the study area.

Key words: Subei Basin, Qintong Sag, argillaceous shale, hydrocarbon generating potential, geochemical characteristic, depositional environment

CLC Number:

P618.13

LI Zhipeng, YU Qiling, ZAN Lin, YU Wenduan, ZHANG Zhihuan. Geochemical Characteristics and Hydrocarbon Generation Potential of Different Lithologic Source Rocks in the Second Member of Funing Formation in Qintong Sag, Subei Basin[J]. Geoscience, 2023, 37(05): 1345-1357.

Figures/Tables 13

Fig.1 Regional geological structure map of Qintong Sag, Subei Basin and stratigraphic map of the second member of Funing Formation ((c) modified from reference[1])

Fig.2 Logging response characteristic of lithology identification in the second member of Funing Formation, Qintong Sag

Fig.3 Lithologic combination profile of source rocks of typical wells in the second member of Funing Formation, Qintong Sag

Fig.4 Plot of TOC versus S1+S2 of source rock samples from the second member of Funing Formation, Qintong Sag

Fig.5 Plot of Tmax versus HI of source rock samples from the second member of Funing Formation, Qintong Sag

Fig.6 Plot of TOC versus HI of source rock samples from the second member of Funing Formation, Qintong Sag

Fig.7 Triangular diagram of macerals of source rocks in the second member of Funing Formation, Qintong Sag

Fig.8 Plot of Ro versus burial depth (a) and the contour map of Ro (b) in the second member of Funing Formation, Qintong Sag

Fig.9 Characteristics of partial biomarker spectra of different types of source rocks in the second member of Funing Formation, Qintong Sag

Fig.10 Plots of Ph/nC18 versus Pr/n C 17 [ 23 - 25 ] (a) and C29ααα(20R)/C27ααα(20R) versus Pr/Ph [25?-27] (b) of different source rock samples from the second member of Funing Formation, Qintong Sag

Fig.11 C27-C29 regular sterane triangulation of different types of source rocks in the second member of Funing Formation, Qintong Sag[25,28-29]

Fig.12 Plots of Pr/Ph verses Ga/C30 hopene[36] (a)and Pr/Ph verses DBT/PHE[37-38] (b) of different types of source rocks in the second member of Funing Formation, Qintong Sag

Fig.13 Box diagrams of biomarker parameters comparison of different types of source rocks in the second member of Funing Formation, Qintong Sag

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