渤海湾盆地济阳坳陷中生界火山岩储层宏观裂缝充填作用及其对次生孔隙发育的影响

Being an important unit of the cross study of diagenesis and tectonism, study on fracture fillings in low temperature environment has aroused people's attention. Previous studies mainly focus on clastic rocks or carbonate rocks, but little on volcanic rocks. Fractures have more important effect on the reservoir properties and formation mechanism of volcanic rocks than on those of clastic rocks and carbonate rocks. In this project，the Mesozoic volcanic rocks in Jiyang depression will be studied. Based on the analysis of lithology, petrologic facies，reservoir space and macrofracture geometry, the mineral species of macroscopic-fracture fillings and their structures and generations are analyzed. Referring to the difference of mineral generations, C、O、Sr isotopes and fluid inclusion of calcite as well as quartz ESR dating are to be carried out to determine the time of mineral fillings and the relavent fluid properties. Fracture-filling mechanism is to be revealed in combination with the structural evolution of the basin and its burial thermal evolution history.Based on the above investigation, the forming time of fractures and the process of fractures' space alteration are to be further studied. Additionally，according to the information of mineral fluid in the fractures, the effect of fluid flow in factures on the mechanism of secondary pore development will be explored in combination with volcanic sequence of diagenetic evolution and typical authigenic mineral inclusion test. Ultimately, the relevance between volcanic reservoirs' macroscopic-fractures filling and secondary pore formation will be revealed.

作为构造前沿领域-构造成岩交叉研究理想单元之一，低温成岩环境下裂缝充填研究愈来愈受重视，已有工作主要集中于碎屑岩或碳酸盐岩区，对火山岩区裂缝充填研究还很少，而与碎屑岩和碳酸盐岩相比，裂缝对火山岩储集性能及成储机理有着更重要的影响和制约作用。本项目以济阳坳陷中生界火山岩为对象，在岩性岩相、储集空间及宏观裂缝几何学分析基础上，以宏观裂缝充填研究为切入点，分析充填矿物类型、结构及世代性，针对不同世代矿物开展碳氧锶同位素、流体包裹体分析及石英ESR测年，确定矿物充填时间、期次及流体性质，结合盆地构造演化及埋藏-热演化史特征，揭示裂缝充填机理。在此基础上，分析裂缝发育期次、时间及裂缝张开充填变化过程；同时以裂缝内矿物流体示踪信息为纽带，结合火山岩成岩演化序列研究及典型自生矿物包裹体测试，探讨裂缝中流体活动对次生孔隙发育的机理影响，最终揭示火山岩储层宏观裂缝发育、充填与次生孔隙发育的关联性。

围绕火山岩宏观裂缝充填特征及其对火山岩成储影响这一关键科学问题，本项目以济阳坳陷孤西地区中生界火山岩为对象，首先分析了火山岩岩性、岩相、储集空间及物性特征，并运用磷灰石裂变径迹方法进行了研究区构造热演化史恢复；然后在分析火山岩宏观裂缝发育特征基础上，重点运用扫描电镜、阴极发光等分析了裂缝充填显微结构，并结合方解石脉碳、氧、锶同位素、微量元素及流体包裹体测试，分析了裂缝内矿物生长方式、充填序次及相应的流体性质；其次，分析了火山岩成岩作用特征；最后综合以上各项研究，构建了火山岩储层孔隙发育演化模式。研究表明，研究区火山岩主要为自碎角砾熔岩、粗面安山岩和粗面玄武岩及火山角砾岩、凝灰岩等，储集空间主要为次生溶蚀孔隙和裂缝。孤西地区中生界地层早期最大古埋深在孤北地区约800m，为浅埋藏，向南显示出增大趋势。裂缝主要发育有自碎缝、构造缝和风化淋滤缝，普遍被高岭石、蛋白石、石英、方解石等矿物充填，脉体显示出对向式、纤维状和块状生长方式，脉体可示踪出至少5期流体活动，最主要成矿温度60-85℃，成脉流体以火山岩地层内部流体为主，但存在与大气淡水的交换作用。火山岩经历了冷却固结、岩浆期后热液及一次埋藏作用、构造抬升、表生风化淋滤、二次埋藏充填、二次埋藏溶蚀等6个主要成岩期次。构造演化过程直接控制着火山岩储层的发育过程，K1期火山喷发，形成原生孔隙；K1晚期-K2早期，火山岩遭受一次浅埋，部分原生气孔被热液或碳酸盐充填；晚白垩世晚期-古新世，区域构造抬升，火山岩遭受风化淋滤，形成构造缝、风化淋滤缝，同时酸性环境下早期碳酸盐和长石遭受溶蚀；始新世-渐新世，区域构造沉降，火山岩遭受二次埋藏，碱性环境下碳酸盐充填裂缝；随后（东营期），在有机酸影响下，部分碳酸盐和长石进一步遭受溶蚀，形成现今储层面貌。相关认识一方面可以为济阳坳陷中生界火山岩油气藏的下一步勘探部署提供地质依据，同时对于深化认识中国东部中基性火山岩的成储成藏机理具有重要的理论意义。