The Origin of Overpressure in the Pinghu Tectonic Zone of Xihu Depression and Its Relationship with Hydrocarbon Accumulation

Jian Li, Dewen Qin, Wensun Yin, Xiaopei Wang, Yong Dai, Hui Shi and Changyu Fan ()
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Jian Li: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Dewen Qin: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Wensun Yin: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Xiaopei Wang: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Yong Dai: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Hui Shi: Shanghai Branch of CNOOC (China) Co., Ltd., Shanghai 200335, China
Changyu Fan: Department of Geology, Northwest University, Xi’an 710069, China

Energies, 2023, vol. 16, issue 24, 1-13

Abstract: Clarification of the cause of overpressure is of great significance for the study of hydrocarbon generation, migration and accumulation processes under an overpressure environment, and the prediction of predrilling pressure. The cause of overpressure in Xihu Depression is still controversial. This study, based on mudstone compaction research and organic matter correction of logging data, ascertained the causes of overpressure in the Pinghu tectonic zone, Xihu Depression. A modified discrimination method for overpressure genesis was used and the overpressure–hydrocarbon distribution relationship was explored. The results show the following: (1) Vertically, overpressure is located in the lower section of the Pinghu Formation, with a pressure coefficient of 1.1–1.7 and a pressure relief feature. On the plane, the pressure coefficient in the Pingzhong area exceeds that in the Pingbei area. (2) The main causes of abnormal high pressure in the research area are undercompaction and fluid expansion. The fluid expansion mechanisms include overpressure transmission and hydrocarbon charging within the reservoir as well as hydrocarbon generation pressurisation and overpressure transmission within the source rock. (3) In the surge section of kaolinite, under fluid pressure, kaolin migrates toward the low-pressure areas, decreasing the porosity in low-pressure areas and preserving pores in high-pressure areas. The evolution of fluid pressure can be divided into two stages: pressurisation; and both pressurisation and pressure relief. Pressurisation and pressure relief drive hydrocarbon charging, but hydrocarbons are more enriched in overpressure layers.

Keywords: overpressure; mudstone compaction; hydrocarbon accumulation; Xihu Depression (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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