Quartz Origins and Paleoenvironmental Controls on Organic Matter Accumulation of Marine Shale in the Ordovician Wulalike Formation, Northwestern Ordos Basin, China: Significance for Shale Gas Exploration

Yanni Zhang, Rongxi Li (), Shengli Xi, Jianwen Gao, Lei Chen (), Hexin Huang (), Bangsheng Zhao and Ahmed Khaled
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Yanni Zhang: School of Earth Science and Resources, Chang’an University, Xi’an 710054, China
Rongxi Li: School of Earth Science and Resources, Chang’an University, Xi’an 710054, China
Shengli Xi: PetroChina Changqing Oilfield Company, Xi’an 710018, China
Jianwen Gao: Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi’an 710018, China
Lei Chen: School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
Hexin Huang: School of Earth Science and Resources, Chang’an University, Xi’an 710054, China
Bangsheng Zhao: School of Earth Science and Resources, Chang’an University, Xi’an 710054, China
Ahmed Khaled: School of Earth Science and Resources, Chang’an University, Xi’an 710054, China

Energies, 2023, vol. 16, issue 14, 1-23

Abstract: The Ordovician Wulalike marine siliceous shale is a notable hydrocarbon source rock in the Northwestern Ordos Basin. However, the causes of quartz and organic matter enrichment are still a mystery to experts. In this study, the organic geochemistry (maceral compositions, R bitu , and TOC) and elemental geochemistry (major and trace elements) with mineralogy (XRD) and petrography were jointly acquired to systematically investigate the quartz origins and the paleoenvironment, and the main controlling factors for organic matter enrichment in the Wulalike shale. The results show that the organic matter is type I kerogen with low TOC concentrations (average 0.51%), and that the thermal evolution has reached mature and high mature stages (mean R equ is 1.08%). Three types of quartz are developed in Wulalike shale: biogenic quartz (average 63%) is the most dominant, followed by clastic quartz (average 31%) and microcrystalline quartz (average 6%). Babio and Ba/Al values indicate the low paleoproductivity, which is the primary cause for the low TOC found throughout the area. Redox indexes show the anoxic or dysoxic to oxic conditions from the bottom to the top of the section. Paleoclimate and paleowater depth proxies also changed from the bottom to the top. Various paleoenvironments and sedimentological evidence show that Wulalike shale went through the changing environments, and the early sedimentary environments were conducive to organic matter enrichment, leading to a relatively high TOC. The paleoproductivity and preservation conditions have an impact on organic matter enrichment. Based on the results of biogenic quartz distribution and sedimentary environments, it is considered that the bottom of the Wulalike Formation is the most favorable for shale gas exploration and development.

Keywords: Ordos Basin; Wulalike Formation; biogenic quartz; paleoenvironments; organic matter accumulation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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