南堡凹陷1号构造带帚状构造特征及其地质意义

Characteristics of brush structures in No.1 structural belt and their geological significance in Nanpu Sag

由于控制南堡1号构造带的帚状构造的主干断裂和次级伴生断裂组合样式与常见的帚状构造断裂组合样式存在差异,在南堡凹陷多期叠加变形的应力背景下,基底先存断裂的再活动及晚期与新生断裂相互作用使帚状构造的演化过程复杂化,进而难以了解帚状构造成因及其对油气的控制规律。为此,基于三维连片地震资料,应用构造解析理论和相关技术,系统研究南堡凹陷1号构造带的构造样式并恢复其演化过程,重点探讨帚状构造的成因及其与油气成藏的内在联系,以期为渤海湾盆地帚状构造区的油气勘探提供理论依据。结果表明:①南堡凹陷1号构造带帚状构造由主干断裂F_(1)、F_(N)及次级断裂控制。F_(1)在中生代开始活动,新生代再活动并由南向北传播、生长,南部边界断裂F_(N)在Ed3沉积期开始活动,二者夹持的次级断裂在Nm沉积期开始活动。②帚状构造经历了古近纪裂陷Ⅰ幕、Ⅱ幕和新近纪后裂陷期三个演化阶段。古近纪Es沉积期主干断裂分段生长为帚状构造的形成提供了背景,古近纪Ed沉积期应力场转变为帚状构造发育提供了应力机制,新近纪Ng‑Nm沉积期F1的斜向伸展作用和FN的正交伸展作用控制了次级断裂,帚状构造就此定型。③南堡1号构造带帚状构造的发育一方面指示新生代存在一期应力体制转变,另一方面反映了控制帚状构造的主干断裂和次级断裂作为油源断裂控制油气垂向运移,同时控制同向断层圈闭和反向断层圈闭的形成——油气富集部位。

The main and secondary associated fault configuration of brush structures controlling the Nanpu No.1 structure belt is different from the common brush structure fault configuration.For this reason,the evolution process of brush structures is complicated due to the reactivity of pre‑existing basement faults and the interaction between late and new faults under the background of multi‑stage superimposed deformation in Nanpu Sag,and it is difficult to understand the genesis of brush structures and their control law on oil and gas.Therefore,based on three‑dimensional(3D)contiguous seismic data,structural analysis theory and related techniques are applied to systematically study the structural pattern of the No.1 structural belt in Nanpu Sag and restore its evolution process,and the genesis of brush structures and its internal relationship with oil and gas accumulation are highlighted,so as to provide a theoretical basis for oil and gas exploration in the brush structure of Bohai Bay Basin.The results show that:①The brush structure of the No.1 structural belt in Nanpu Sag is controlled by main faults F1 and FN and secondary faults.F_(1) started to be active in the Mesozoic and then reactivated in the Cenozoic.It propagated and grew from south to north.The southern boundary fault F_(N) started to be active in the Ed3 deposition period,and the secondary fault held by F_(1 )and F_(N) started to be active in the Nm deposition period.②The brush structure has experienced three stages of evolution:Paleogene riftingⅠandⅡ,as well as post‑Neogene rifting.The segmented growth of main faults in the Paleogene Es deposition period provides the background for the formation of the brush structure,and the stress field in the Paleogene Ed deposition period provides the stress mechanism for the development of the brush structure;the oblique extension of F1 and the orthogonal extension of FN in the Ng‑Nm deposition period of the Neogene control the secondary faults,and the brush structure is established.③On the one hand,the development of brush structures in the Nanpu No.1 structural belt indicates the stress regime transition in the Cenozoic.On the other hand,the main and secondary faults controlling brush structures as oil source faults control not only the vertical migration of oil and gas but also the formation of synchronous and reverse fault traps,indicating the location of oil and gas enrichment.