Hydrocarbon generation from Carboniferous-Permian coaly source rocks in the Huanghua depression under different geologic
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ORIGINAL PAPER
Hydrocarbon generation from Carboniferous‑Permian coaly source rocks in the Huanghua depression under different geological processes Jin‑Jun Xu1,2 · Qiang Jin1 Received: 13 March 2020 © The Author(s) 2020
Abstract Natural gas and condensate derived from Carboniferous-Permian (C-P) coaly source rocks discovered in the Dagang Oilfield in the Bohai Bay Basin (east China) have important implications for the potential exploration of C-P coaly source rocks. This study analyzed the secondary, tertiary, and dynamic characteristics of hydrocarbon generation in order to predict the hydrocarbon potentials of different exploration areas in the Dagang Oilfield. The results indicated that C-P oil and gas were generated from coaly source rocks by secondary or tertiary hydrocarbon generation and characterized by notably different hydrocarbon products and generation dynamics. Secondary hydrocarbon generation was completed when the maturity reached vitrinite reflectance (Ro) of 0.7%–0.9% before uplift prior to the Eocene. Tertiary hydrocarbon generation from the source rocks was limited in deep buried sags in the Oligocene, where the products consisted of light oil and gas. The activation energies for secondary and tertiary hydrocarbon generation were 260–280 kJ/mol and 300–330 kJ/mol, respectively, indicating that each instance of hydrocarbon generation required higher temperature or deeper burial than the previous instance. Locations with secondary or tertiary hydrocarbon generation from C-P coaly source rocks were interpreted as potential oil and gas exploration regions. Keywords Hydrocarbon generation · Thermal simulation · Coaly source rocks · Carboniferous-Permian · Huanghua depression
1 Introduction Huanghua Depression is one of the most petroliferous depressions in the Bohai Bay Basin of east China, and the main source rocks for accumulations are Paleogene lacustrine source rocks that generate large amounts of oil and gas (Hao et al. 2007; Li et al. 2015; Liang et al. 2018). Coaly source rocks were deposited under the basin during the Edited by Jie Hao * Jin‑Jun Xu [email protected] 1
Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, Shandong, China
Pilot National Laboratory for Marine Science and Technology, China University of Petroleum (East China), Aoshanwei Wenhai Road 1, Qingdao 266237, Shandong, China
2
C-P period, leading to the discovery of gas and condensate in drilling wells within the C-P sandstone reservoirs and buried-hill reservoirs in deep parts of the basin (Liu et al. 2017; Zhao et al. 2018). For example, gas and condensate produced from well Gbg1 in the Zhanhua sag and well Su20 on the Suqiao-Wenan slope of the Jizhong sag both originate from C-P coaly source rocks (Dai and Xia 1990; Liu et al. 2017; Gong et al. 2018). In 2017–2018, large quantities of crude oil (30.2 m3/d) and gas (8 × 104 m3/d) were produced at depths of 4956.8–4984.9 m in sandstones from well Yg1, and at depths of 3836–3841 m in Ordovician buried-hill carbonate
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