Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (2): 418-428.doi: 10.11743/ogg20230213

• Petroleum Geology • Previous Articles     Next Articles

Influence of mantle-derived CO2 on hydrocarbon accumulation in Qinhuangdao 29 tectonic zone, Bohai Sea

Wei LI(), Jianyong XU, Zhifeng LIU, Youchuan LI, Wenqi ZHU   

  1. CNOOC Research Institute Co. Ltd. ,Beijing,100028,China
  • Received:2022-08-08 Revised:2022-12-22 Online:2023-03-17 Published:2023-03-17

Abstract:

Reservoirs of high CO2 content are rarely found in Bohai Sea, offshore of the Bohai Bay Basin, and Qinhuangdao 29 tectonic zone (QHD29) is one of the few typical reservoirs of the type. To study the correlation of hydrocarbon accumulation with the migration and accumulation of high-CO2-content gas is of great significance to oil and gas exploration and the discovery of CO2 gas reservoirs. Based on geochemical analysis of saturated and aromatic hydrocarbons, petrologic characteristics of fluid inclusions, we systematically discuss the interrelationship between CO2 charging and hydrocarbon accumulation in QHD29 tectonic zone and the genetic mechanism of hig-CO2-content reservoirs in the tectonic zone. The results are shown as follows. First, the hydrocarbons sourced from the source rocks of the first and third members of Shahejie Formation (E2s1 and E2s3) mainly accumulate in the E2s1, followed by Dongying Formation (E3d). Second, QHD29 reservoirs underwent two stages of hydrocarbon charging. The early stage features crude oil charging dominated by north-south lateral migration from the Qinnan Sag to the uplift along the sand bodies; and the late stage features instantaneous gas accumulation caused by magmatic-hydrothermal fluid as dominated by vertical migration. The supercritical CO2, fluid rich in hydrocarbons, moved upward along the deep-rooted faults, entered the major oil reservoirs, and then moved laterally from south to north. Third, QHD29 reservoirs obviously experienced gas washing under both early oil and late gas accumulation events, forming a hydrocarbon distribution pattern with heavy oil and bitumen enriched at the bottom, light oil and gas condensate in the middle, and CO2 gas dominating on top of the major reservoirs.

Key words: CO2 gas, gas washing, oil/gas migration, hydrocarbon accumulation by charging, Qinnan Sag, Bohai Sea

CLC Number: