Fault System And Their Relationship With CO₂ Reservoirs In The Bohai Bay Basin ?Sea Area?

The Bohai Bay Basin?sea area?has abundant oil and gas resources,and is the key oil and gas exploration area in China.After more than half a century of exploration,abundant oil and gas fields?reservoirs?have been discovered,but at the same time,abundant CO₂ had been found in some oil and gas fields?reservoirs?.The gas reservoir that containCO₂,can be used as natural gas resources,has economic value and potential market and used widely.But the existence of CO₂ will lead to increase the costs of oil and gas production,which have an adverse impact on the efficient exploration of conventional oil and gas,and it was also not consistent with the current situation of energy saving and emission reduction.Secondly,the study of the global cycle of CO₂is the key about understanding the global carbon cycle.A comprehensive and thorough understanding of the CO₂ cycle on the basis of the origin and evolution of the earth will contribute to the study of genesis and reservoir formation of CO₂.On the basis of previous research and latest geophysical data,we had identified and studied the distribution of the faults in the Bohai Bay Basin,and completed the distribution map of the main faults in Bohai.Based on 2D/3D seismic data,deep reflection seismic profiles,and drilling data,structural interpretation of fault was carried out.We made a detailed division of the fault combination styles in the Bohai area,and studied the characteristics of fracture system.After that,combining with the characteristics of Bohai faults and deep structure features,the anatomy of typical CO₂gas reservoirs.Through the research,the following conclusions and understandings are obtained:?1?Main fault characteristics of bohai bay basin.The distribution characteristics of main fault in Bohai seawas complex and changeable.There are three main directions trends:NE-NNE,NW,EW,and the dominant trend was NE-NNE.The extensional fault system and the strike slip fault system were interwoven in the plane,forming a variety of complex plane combination styles,which were obviously affected by the strike slip action.According to the fault depth,the fault in Bohai sea was divided into 4 categories,First-level faults:the North East strike slip fault belt with the Tan-Lu fault;Second-level faults:Bo-Zhang fault presenting NW;Third-level faults:NE and nearly EW,NW trending basement faults;Fourth-level faults:the near E-NEE overburden fault.?2?Fault combination styles in Bohai areaThe results show that there were four major types of faults in Bohai area:extensional faults and their combination styles,strike slip faults and their combination styles,inversion structures and their combination styles,extensional and strike-slip compound styles.The combination styles of extensional structures mainly include listric fault,ramp-flat listric fault,X-type fault and Step Faults.The combination patterns of the strike slip structure include negative flower structure,semi-flower structure and positive flower structure.Strike slip-extensional composite style mainly for Y shape semi-flower structure.Reverse structural styles are mainly characterized by fault inversion and fold inversion.?3?Controlling factors of CO₂ in Bohai bay basin?sea area?The the distribution of inorganic mantle CO₂ gas in the Bohai sea was constrained by the source area.The region of Moho upliftwas the source area of CO₂ gas accumulation.Bohai high CO₂ gas reservoir was mainly distributed on the Moho surface uplift gradient zone in the central part of the Bozhong depression.The distribution of inorganic mantle CO₂ gas in the Bohai seawas closely related to the faults.The mantle derived CO₂,migration to shallow part by the deep fault,and transported to the effective traps under the constraint of the shallow fault combination pattern.The region of Moho uplift with Y shape semi-flower structure and negative flower structurewas high risk area for CO₂ accumulate in Bozhong depression.