尼日尔三角洲E背斜顶部断裂演化机制及封闭性

尼日尔三角洲深水区E油田背斜顶部发育大量密集断层，多数断层倾向一致呈多米诺式排布，活动机制和期次不清楚，对油水的分隔作用不明确。基于构造解析思想，通过构造平衡剖面和古构造图回剥技术研究E背斜的轴面迁移过程，结合断裂成核理论明确断裂活动期次和机制，进而划分断裂系统，指导断裂的封闭性评价。提出深水背斜顶部正断层重力滑动的演化机制，确定多米诺式正断层与背斜轴面迁移的多期次对应关系。E构造共分为4个演化阶段，发育7类断裂系统，其中三个期次的重力滑动断阶（阶梯式）断层为本区独有的特殊构造，在古背斜背景下受控于重力作用变形。逆冲断层和多期活动断层的封闭趋势强，重力滑动断阶断层具有潜在封闭性，而晚期伸展断层不具有封闭能力，筛选出16条潜在封闭断层。确定本区断层弱封闭SGR临界值为8%，完全封闭临界值为20%，评价结果显示：其中8条断层完全封闭，能够将断层两盘分隔为不同油水单元，4条断层具有弱封闭能力，不分隔油水，仅影响注水受效，从而指导油田的钻井和注采方案设计。

Structural evolution mechanism and sealing of faults on the crest of anticline E in Niger Delta

Numerous faults were developed on the crest of anticline E in deep water of Niger Delta.They were observed to dip mostly in the same direction and arrange in a domino style.Uncertainties remain in such domains as what their me-chanism is,how many stages they had experienced,and what role they played in dividing oil from water.Based on structural analysis,we studed the axial plane migration of E anticline through structural balanced sections and back-stripping of pa-leotectonic maps.Guided by the theory of fracture nucleation,we identified the active stages and mechanisms of the faults and then categorized the faulting systems to further perform assessment of sealing capacity of the faults.Gravitational sli-ding was identified as the evolution mechanism of the normal faults at the crest of the anticline.A correspondence of multiple stages between the domino-style normal faults and the anticline axial plane migration was also established.We proposed that the E structure had experienced four evolution stages and developed 7 types of faulting systems,among which,3 were gravitational sliding step-faults -quite unique in the area-and were controlled and deformed by gravity against a paleo-anticline setting.Thrust faults and faults with multi-stage movement are the best sealing faults,gravitational sliding step-faults have sealing potential,and later extensional faults have no sealing capacity.About 16 faults were selected as potential sealing faults.The results show a critical SGR value of 8% for weak sealing,and 20% for fully sealing.There were 8 fully-sealed faults that could form different oil/water units in its hanging and foot walls,respectively.There were 4 weakly-sealed faults that could not separate oil from water but only influence responses to water flooding.The study can be used to guide drilling and injection-production planning of oil fields in the area.