辽东凸起北段走滑断层特征及对油气成藏的控制

Characteristics of strike-slip faults in the northern part of Liaodong salient and their control on hydrocarbon accumulation

渤海海域锦州23-2大油田的发现标志着辽东凸起北段新近系油气勘探获得重大突破,但其油气成藏主控因素尚不清楚。以锦州23-2油田为例,运用地层厚度差异对比法刻画走滑断层位移量,提出油气运移指数定量评价断-砂耦合关系,探讨了辽东凸起北段走滑断层对油气成藏的控制作用。结果表明,研究区发育辽东1号和辽中2号两条走滑断层,走滑断层特征差异较大,对油气成藏具有明显的控制作用,主要体现在:①压扭性走滑断层走滑强度控制了油气保存条件,辽东1号走滑断层压扭特征明显,馆陶组沉积时期断层走滑位移量大,走滑速率快,侧封能力强,为油气富集提供良好保存条件;②走滑转换带释压段断-砂耦合控制了油气运移条件,研究区位于辽中2号S形走滑转换带释压段,晚期调节断层发育,断层发育程度、活动性及其与砂体耦合关系决定了油气运移条件,导致不同区块油气富集程度差异较大。本文研究结果对于推进辽东凸起北段的油气勘探具有指导作用,对渤海类似地区的油气成藏研究也具有借鉴意义。

The discovery of JZ23-2 giant oilfield in Bohai sea area marks a significant breakthrough in Neogene oil and gas exploration in the northern part of Liaodong salient.However,the main controlling factors of hydrocarbon accumulation are still unclear.Taking JZ23-2 oilfield as an example,the displacement of the strike-slip fault is described by comparing the thickness difference of stratum.The oil and gas migration index is proposed to quantitatively evaluate the coupling relationship between fault and sand body and the control effect of strike-slip fault on hydrocarbon accumulation in the northern part of Liaodong salient is discussed.The results show that Liaodong No.1 and Liaozhong No.2 strike-slip faults were developed in the study area and with quite different characteristics,they have obvious control effects on hydrocarbon accumulation,especially in the following aspects:①The strike-slip intensity of the torsional strike-slip fault controls the hydrocarbon preservation conditions.The Liaodong No.1 strike-slip fault is torsional strike-slip fault,which has a fast strike-slip rate,large strike-slip displacement in Guantao Formation period and strong side sealing ability,which provides good preservation conditions for hydrocarbon enrichment.②The fault-sand body coupling of the pressure-relief section of the strike-slip transition zone controls the hydrocarbon migration.The study area is located in the pressure-relief section of the LZ2 S-shaped strike-slip transition zone,and the late regulation faults were developed.The degree of fault development,activity and its coupling with sand bodies determine the conditions of hydrocarbon migration and cause large difference in hydrocarbon enrichment in different blocks.The study results can serve as a guide for promoting oil and gas exploration in the northern part of the Liaodong salient and can also be used as a reference for the study of hydrocarbon accumulation in similar areas of Bohai sea.