渤海湾盆地歧口凹陷滨海断鼻断-砂组合模式与油气成藏

Fault-sand combination modes and hydrocarbon accumulation in Binhai fault nose of Qikou Sag, Bohai Bay Basin, East China

基于地震、测录井等资料,以渤海湾盆地歧口凹陷滨海断裂下降盘的滨海断鼻为对象,开展断裂特征、砂体展布及断-砂组合与油气成藏分析,揭示断陷湖盆断裂发育区的油气富集规律。研究结果表明,滨海断鼻新生代构造特征具有东西分带性,西段断裂主体区构造简单,东段帚状断裂区构造复杂,发育多组断裂。断裂演化的差异控制了砂体的空间展布,砂体在断鼻中段顺港东断裂下降盘的断槽带呈大面积连片分布,形成顺向型断-砂组合模式,而断鼻东段断裂活动时期较晚,砂体受古地貌控制呈多期次北南向指状展布,与断裂匹配形成垂向型断-砂组合模式。断裂与砂体、油源及盖层的配置关系决定了油气的垂向输导能力、平面展布及纵向分布特征,在断鼻中段及东段分别形成了单条主断裂供烃-断砂顺向匹配-多层系立体含油和断裂系复式输导-断砂垂向匹配-条带状叠置含油两种油气成藏模式,控制了滨海断鼻油气分布和富集程度的差异。

Based on seismic and logging data, taking the downthrow fault nose of Binhai fault in Qikou Sag as the object of study, we analyzed fault characteristics, sand body distribution, fault-sand combinations and hydrocarbon accumulation to reveal the hydrocarbon enrichment law in the fault-rich area of fault depression lake basin. The results show that the Binhai Cenozoic fault nose is characterized by east-west zoning, the main part of the western fault segment is simple in structure, whereas the broom-shaped faults in the eastern segment are complex in structure, including several groups of faults. The difference of fault evolution controls the spatial distribution of sand bodies. The sand bodies are in continuous large pieces in the downthrow fault trough belt along the Gangdong Fault in the middle segment of the fault nose, forming consequent fault-sand combination;whereas the fault activity period of the eastern part of the fault nose was later, and the sand bodies controlled by paleogeomorphology are distributed in multi-phase north-south finger-shaped pattern, forming vertical fault-sand combination pattern matching with the fault. The configuration between faults and sand bodies, and oil sources and caprocks determine the vertical conductivity, plane distribution and vertical distribution of oil and gas. Two oil and gas accumulation modes, i.e. single main fault hydrocarbon supply-fault sand consequent matching-oil accumulation in multi-layers stereoscopically and fault system transportation-fault sand vertical matching-oil accumulation in banded overlapping layers occur in the middle and eastern segments of the fault nose respectively, and they control the difference of oil and gas distribution and enrichment degree in the Binhai fault nose.