渤海湾盆地莱州湾凹陷南部斜坡带中生界火山岩裂缝特征及分布规律

Characteristics and Distribution of Fractures in Mesozoic Volcanic Rocksin Southern Slope of Laizhou Bay Depression, Bohai Bay Basin

渤海湾盆地莱州湾凹陷南部斜坡带垦利16构造的火山岩储层裂缝发育,对储层品质影响显著,但其形成期次和分布规律还不清晰,制约了储层的深入认识。本文基于岩心、成像测井和野外露头资料开展垦利16构造中生界火山岩裂缝类型、形成期次和分布规律研究。取得如下主要认识:识别出6类裂缝,包括炸裂缝、隐爆缝、冷凝收缩缝、风化缝、构造缝和溶蚀缝;裂缝以中高角度为主;冷凝收缩缝以中等尺度为主,构造缝以大尺度为主;裂缝开度由高到低分别是火山碎屑岩、火山碎屑熔岩、沉火山碎屑岩和熔岩。裂缝形成期具体可划分为5个,走滑应力体系下形成了大量的构造缝。各岩性的裂缝面密度由大到小分别是熔岩、火山碎屑熔岩、火山碎屑岩和沉火山碎屑岩;各岩相的裂缝面密度由大到小分别是熔岩流亚相、热碎屑流亚相、热基浪亚相和崩塌再搬运堆积亚相;露头区熔岩的断裂破碎带宽度可达2 m,裂缝多呈开启状态;火山碎屑岩的断层发育擦痕,形成分米级致密带,降低了岩石渗透性。

The reservoir fractures of volcanic rock of Kenli 16 structure on the southern slope of Laizhou Bay depression in Bohai Bay Basin are developed,which has a significant effect on reservoir quality.However,its formation period and distribution law are not clear,which restricts the in-depth understanding of the reservoir.Based on core,imaging logging and outcrop data,this paper studies the fracture types,formation stages and distribution of Mesozoic volcanic rocks in Kenli 16 structure.The main results are as follows:Six kinds of cracks are identified,including explosion cracks,crypto-explosion cracks,condensation shrinkage cracks,weathering cracks,structural cracks,and corrosion cracks.The fractures are mainly of middle to high angle.The condensation contraction fractures are mainly of medium scale,and the structural fractures are mainly of large scale.The fracture opening degree descends from pyroclastic rock,pyroclastic lava,and sedimentary pyroclastic rock to lava.The fracture formation period can be divided into five stages,and a large number of structural fractures are formed under the strike-slip stress system.The fracture surface densities of each lithology descend from lava,pyroclastic lava,and pyroclastic rock to sedimentary pyroclastic rock.The fracture surface densities of each facies descend from lava flow subfacies,hot clastic flow subfacies,and hot foundation wave subfacies,to collapse retransported accumulation subfacies.In the outcrop area,the fracture zone width of lava can reach 2 m,the cracks are mostly open,and the fault of the pyroclastic rock develops scratches,forming a decimeter-dense zone,which reduces the permeability of the rock.