Comparison of Evaporite-Related Source Rocks and Implications for Petroleum Exploration: A Case Study of the Dongying Depression, Bohai Bay Basin, Eastern China
Author:
Chen Yong12ORCID, Han Yun1, Zhang Pengfei3, Wang Miao1, Qiu Yibo3, Zhu Xuelei1, Zhang Xuejun3
Affiliation:
1. School of Geosciences, China University of Petroleum, Qingdao 266580, China 2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China 3. Shengli Oilfield Company, SINOPEC, Dongying 257015, China
Abstract
The Dongying Depression (Bohai Bay Basin, eastern China) was widely filled with evaporite (anhydrite and halite) layers during the Paleogene period, especially the middle of the fourth member of the Shahejie Formation (Es4). Most evaporite layers are interbedded with mudstone strata. The strata of Es4 are divided into three sections, referred to as the upper layers, evaporite layers, and lower layers, respectively. The analysis of elemental concentrations, elemental ratios, and Pr/Ph suggests that the lower layers were deposited in an intermittent saline lake environment within a relatively dry climate. The evaporite layers were formed in a highly saline lake environment, whereas the upper layers were formed in a brackish-saline to fresh-water environment. Organic matter (OM) abundance indices, including total organic carbon (TOC), chloroform extracts, total hydrocarbon content (HC), hydrocarbon generation potential (S1 + S2), and OM type, show that the source rock potential for petroleum generation in the upper layers is best, that in the evaporite layers is fair, and in the lower layers it is poor. Carbon isotopes (δ13C) of hydrocarbons in the evaporite and lower layers were heavier than those in the upper layers. Thermal maturity parameters show that the thermal evolution process of OM in the upper layers was faster where evaporite were present compared with evaporite-free areas, while the thermal evolution of OM in the lower layers was slower in these regions. The high thermal conductivity of evaporites may have accelerated the thermal evolution of source rocks in upper layers and allowed hydrocarbon generation at a shallower burial depth. This resulted in the earlier appearance of the petroleum generation window compared to in evaporite-free areas. Meanwhile, the thermal evolution of OM in the lower layers was restrained, and consequently the hydrocarbon generation window was widened, which implies the potential for petroleum exploration in deep strata under the evaporite sequence. This is a common phenomenon in evaporite-bearing basins, according to previous and present studies.
Funder
National Natural Science Foundation of China Shandong Provincial Natural Science Foundation Key Research Projects of Shandong Province
Subject
Energy (miscellaneous),Energy Engineering and Power Technology,Renewable Energy, Sustainability and the Environment,Electrical and Electronic Engineering,Control and Optimization,Engineering (miscellaneous),Building and Construction
Reference82 articles.
1. Advance of allochthonous salt sheets in passive margins and orogens;Hudec;AAPG Bull.,2006 2. Terra infirma: Understanding salt tectonics;Hudec;Earth Sci. Rev.,2007 3. Warren, J.K. (2006). Evaporites: Sediments, Resources, and Hydrocarbons, Springer. 4. Organic geochemical, isotopic, and seismic indicators of fluid flow in pressurized growth anticlines and mud volcanoes in modern deep-water slope and rise sediments of offshore Brunei Darussalam; implications for hydrocarbon exploration in other mud- and salt-diapir provinces (in Shale tectonics);Warren;AAPG Mem.,2010 5. Salt diapirs and thermal maturity: Scotian Basin;Keen;Bull. Can. Petrol. Geol.,1983
|
|