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Overpressure and its positive effect in deep sandstone reservoir quality of Bozhong Depression, offshore Bohai Bay Basin, China

Wang, Xiao; He, Sheng; Jones, Stuart J.; Yang, Rui; Wei, Ajuan; Liu, Changhai; Liu, Qiang; Cheng, Chunyang; Liu, Weimin

Overpressure and its positive effect in deep sandstone reservoir quality of Bozhong Depression, offshore Bohai Bay Basin, China Thumbnail


Authors

Xiao Wang

Sheng He

Rui Yang

Ajuan Wei

Changhai Liu

Qiang Liu

Chunyang Cheng

Weimin Liu



Abstract

Bohai Bay Basin is a Meso-Cenozoic terrestrial sedimentary basin in eastern China. Its offshore regions, including Bozhong and Liaodongwan Depressions, are favourable exploration targets which provide near a half of the petroleum reserves in the basin. Eocene Shahejie (Es) Formation and Oligocene Dongying (Ed) Formations are two important exploration targets in Bozhong Depression, and overpressure is commonly seen in Es and Ed Formations in this area. Our research examined the distribution characteristics of overpressure in the formations and suggest the main mechanism of overpressure is compaction disequilibrium due to the rapid sedimentation rates (~500 m/Ma) of fine-grained sediments in this area. Also, oil and gas generation within the thick mudstones of the two formations has added the magnitude of overpressure. We investigated the reservoir quality especially primary porosity in Es and Ed formations, and their relationship with overpressure. The positive effect of overpressure on reservoir porosity preservation was validated through microscopic observations and vertical effective stress (VES) analysis. We established a quantitative model for evaluating the relationship of overpressure, pore structures, porosity, and VES. The result suggests the overpressure in the targeted formations were primarily originated from undercompaction. The overpressure kept VES from increasing and helped preserve the primary intergranular porosity. The porosity preserved by overpressure can be significantly higher than normally compacted porosity under the same condition of depth and temperature.

Journal Article Type Article
Acceptance Date Aug 8, 2019
Online Publication Date Aug 9, 2019
Publication Date Nov 30, 2019
Deposit Date Sep 5, 2019
Publicly Available Date Aug 9, 2020
Journal Journal of Petroleum Science and Engineering
Print ISSN 0920-4105
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 182
Article Number 106362
DOI https://doi.org/10.1016/j.petrol.2019.106362
Public URL https://durham-repository.worktribe.com/output/1293995

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