Lithofacies Characteristics, Depositional Environment and Sequence Stratigraphic Framework in the Saline Lacustrine Basin-A Case Study of the Eocene Low Member of Xingouzui Formation, Jianghan Basin, China

Abstract

The Jianghan Basin is a lacustrine basin in central China developing multiple salt bearing deposits in the Eocene with the success of shale oil exploration in the Qianjiang Formation. The lower member of the Xingouzui Formation in the Chentuokou Depression has become another exploration target. However, rapid changes in lithofacies and strong sedimentary heterogeneity limit the exploration progress. This study aimed to explore the sequence division, lithofacies characteristics, and sedimentary environment using sedimentological, X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses. The sequence stratigraphic analysis indicates that the low member of the Xingouzui Formation is divided into two third-order sequences, namely SQ1 and SQ2, and four system tracts, including highstand systems tract (HST), lake expanding system tract (EST), early highstand system tract (EHST), and late highstand system tract (LHST). Moreover, a total of nine major lithofacies and five lithofacies associations (LA1-5) were identified. The organic geochemical data show that the laminated argillaceous dolomite in EST and EHST developed the best oil content with an average TOC of 1.18% and S1 of 3.18 mg/g, The laminated argillaceous dolomite deposited in anoxic conditions with a humid climate, moderate salinity, and stratified deep waterbody is a favorable exploration facies for shale oil.

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“…The identification and analysis of the major and trace elements by XRF spectroscopy was possible due to the characteristic behavior of atoms when they interact with radiation [ 20 , 21 ]. When materials are excited by X-rays (high-energy and very short wavelength radiation), they can be ionized.…”

Novel Method for the Classification of Shale Oil Reservoirs Associated with Mobility: Inspiration from Gas Adsorption and Multiple Isothermal Stage Pyrolysis

“…Since the Cretaceous, the following strata, e.g., the Yuyang, Shashi, Xin’gouzui, Jingsha, Qianjiang, and Jingdezhen formations, were deposited orderly (Figure ). Among them, the Paleogene Xin’gouzui formation is recognized as one of the most important oil-bearing strata in the study area. ,, The lower Xin’gouzui formation is deposited in a saline environment, which is dominated by argillaceous dolomite and muddy shale lithology. , The distribution range of vitrinite reflectance ( R o ) is about 0.5–1.07% . Moreover, it can be further divided into the III oil bed, clay interlayer bed, II oil bed, I oil bed, and gypsolyte bed from bottom to top.…”

“…22,46,50 The lower Xin'gouzui formation is deposited in a saline environment, which is dominated by argillaceous dolomite and muddy shale lithology. 49,51 The distribution range of vitrinite reflectance (R o ) is about 0.5−1.07%. 49 Moreover, it can be further divided into the III oil bed, clay interlayer bed, II oil bed, I oil bed, and gypsolyte bed from bottom to top.…”

“…The II oil bed, with a thickness of ∼100 m, is one of the predominant exploration systems for shale oil in the basin. 25,51…”

“…Moreover, it can be further divided into the III oil bed, clay interlayer bed, II oil bed, I oil bed, and gypsolyte bed from bottom to top. The II oil bed, with a thickness of ∼100 m, is one of the predominant exploration systems for shale oil in the basin. , …”