Hydrocarbon generation from lacustrine shales with retained oil during thermal maturation
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ORIGINAL PAPER
Hydrocarbon generation from lacustrine shales with retained oil during thermal maturation Xin‑He Shao1,2 · Xiong‑Qi Pang1,2 · Mao‑Wen Li3,4 · Zhi‑Ming Li4 · Yi Zhao1,2 Received: 7 January 2020 © The Author(s) 2020
Abstract Thermal maturation in the shale oil/gas system is inherently complex due to the competitive interplays between hydrocarbon generation and retention processes. To study hydrocarbon generation characteristics from shales within different stages of thermal maturation under the influence of retained oil, we performed Micro-Scale Sealed Vessels (MSSV) pyrolysis on a set of artificially matured lacustrine shale samples from the Shahejie Formation in the Dongpu Depression in Bohai Bay Basin, China. Experimental results show that hydrocarbon yields of shale samples with or without retained oil at various thermal maturities follow different evolution paths. Heavy components ( C15+) in samples crack at high temperatures and generally follow a sequence, where they first transform into C6–14 then to C2–5 and C1. Methane accounts for most of the gaseous products at high temperatures in all samples, with different origins. The cracking of C 2–5 is the main methane-generating process in samples with retained oil, whereas the source of methane in samples without retained oil is kerogen. In the studied shales, retained oils at early-mature stage retard the transformation of liquid to gaseous hydrocarbon and prompt the cracking of C2–5 to C 1 to some extent. TSR reaction related to gypsum in the studied samples is the primary reason that can explain the loss of hydrocarbon yields, especially at high temperatures. In addition, transformation of volatile hydrocarbons to gas and coke also accounts for the loss of generated hydrocarbon, as a secondary factor. Keywords MSSV pyrolysis · Hydrocarbon generation · Lacustrine shales · Thermal maturation · Retained oil
1 Introduction Hydrocarbon generation has been a topic of long-standing interest of petroleum geologists, and researchers have earned a lot of achievements in the last few decades (Tissot and Edited by Jie Hao * Xiong‑Qi Pang [email protected] 1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
2
College of Geosciences, China University of Petroleum, Beijing 102249, China
3
State Key Laboratory of Shale Oil and Shale Gas Resources and Effective Development, SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China
4
SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi Institute of Petroleum Geology, Wuxi 214126, Jiangsu, China
Welte 1978; Lewan and Roy 2011; Sondergeld et al. 2013). The general scheme proposed by Tissot and Welte (1978) describing hydrocarbon formation during burial of source rocks has been widely accepted, and numerous studies were carried out on this basis. In addition, techniques have been improved greatly these years to analyze hydrocarbon generation from source rocks. Rock–Eval pyrolysis
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