23.8Ma±的构造事件在南海北部深水砂岩储层成岩演化过程中的响应及其对储层储集性能的影响

Several obvious tectonic activity events recorded at 32 Ma, 23.8 Ma, 16 Ma respectively, occurred in the northern South China Sea, and they have had a profound impact on the depositional environment, provenance, the sea level change, geothermal gradient, sedimentation processes, petrologic and geochemical characteristics of the sediments, as well as the hydrocarbon pool formation of the Paliegen. The preliminary research result shows that the elevated geothermal attributed to the tectonic activities, has a distinct impact on diagenetic evolution of the deep-water sandstone reservoir in the South China Sea. Nevertheless, few related research results has been reported. This project will select the Zhuhai Group (32.0-23.8 Ma) and Zhujiang Group (23.8-16.5 Ma) deep-water sandstone reservoirs in the Baiyun Sag, northern South China Sea as the research targets, the comparative research of the petrologic composition and texture, diagenesis and burial-diagenetic- hydrocarbon filling process in the vertical and N-S horizontal direction in high geothermal gradient and high heat-flow background caused by the tectonic activities will be carried on. The quantitative damages and contributions of the major diagenesis on the deep-water sandstone reservoir quality will be analyzed. Moreover，response of the tectonic activity in the diagenetic evolution of the deep-water sandstone reservoirs, the secondary pore developing and the relatively high quality sandstone reservoir forming mechanism in the high geothermal gradient and high heat-flow background will be discussed.

南海盆地在32 Ma、23.8 Ma、16 Ma发生过几次较大规模的构造活动事件，其对南海盆地古近纪沉积环境、物源、海平面变化、地温梯度、沉积作用及其产物的岩石学与地球化学特征、油气藏的形成等产生了深远的影响。初步研究结果显示，这些构造事件导致的地温梯度的升高对南海北部深水砂岩储层的成岩演化过程也产生了较明显的影响，但目前鲜有这方面研究成果的报道。本项目拟以南海北部白云凹陷32-23.8Ma的珠海组与23.8-16.5Ma的珠江组砂岩储层为目的层，通过由构造活动导致的高地温热流背景下深水砂岩储层岩石学组分与结构特征、成岩作用、埋藏-成岩-烃类充注演化过程在纵向上及南北方向上的对比研究，分析主要成岩作用对深水砂岩储层储集性能的破坏与贡献，探讨构造活动在深层碎屑岩储层成岩演化过程中的响应，以及高地温热流背景下砂岩储层次生孔隙发育与相对优质储层形成机制。

本研究发现了南海北部深水区与构造热事件及高热流背景相关的岩石学、矿物学与碳、氧、锶同位素地球化学与成岩响应证据。研究了深水区砂岩储层中碳酸盐胶结作用期次、胶结物类型、物质来源与成因机理。根据受热机制的不同，将南海北部深水区划分为低地温梯度区（≤4℃/100m）、高地温梯度区（>4℃/100m）和受异常热影响三个区域，讨论了以上三个地区储层的差异性成岩-孔隙演化过程。认为三个区域由于升温速率与受热机制不同储层的成岩-孔隙演化路径有差别，地温梯度与升温速率影响压实作用的强度、黏土矿物及碳酸盐等胶结物的类型及其分布特征，最终导致储层物性的差异。低地温梯度区储层属于正常成岩演化过程；高地温梯度区和受异常热影响区储层显示出异常热成岩演化特征，深部热流体参与了储层的成岩演化过程，热压实作用是高地温梯度区和热异常区储层原生孔隙丧失的主要成岩作用，粘土矿物的热异常转化对储层孔隙度、特别是渗透率产生了较大影响。在以上研究基础上，建立了三个地区储层的差异性埋藏-烃类充注-成岩-孔隙演化历史。研究成果与认识可为不同热流背景下储层次生孔隙发育带及有效储层预测提供科学依据。