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

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.

Citation

Wang, X., He, S., Jones, S. J., Yang, R., Wei, A., Liu, C., …Liu, W. (2019). Overpressure and its positive effect in deep sandstone reservoir quality of Bozhong Depression, offshore Bohai Bay Basin, China. Journal of Petroleum Science and Engineering, 182, Article 106362. https://doi.org/10.1016/j.petrol.2019.106362

• 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