琼东南盆地西区乐东—陵水凹陷梅山组深水海底扇储层是天然气勘探的重点领域.综合应用岩石薄片X衍射、扫描电镜、阴极发光、稳定同位素、流体包裹体等分析方法,系统研究了高温-超压背景下的深水海底扇储层成岩作用及其对孔隙演化的影响.结果表明:①梅山组深水海底扇储层岩石类型以岩屑石英砂岩和长石岩屑砂岩为主,储层物性以低—中孔、特低—低渗为主,具有强非均质性.②储层经历早期压实作用、黏土矿物胶结→第1期低熟油充注→长石溶解,铁方解石及石英次生加大→第2期较高成熟油气充注→(铁)白云石胶结、石英及其次生加大溶解、超压形成→第3期高成熟天然气充注→晚期CO2充注及热液矿物胶结.③储层孔隙演化受控于超压保护的压实-胶结作用和溶解作用,早期压实-胶结是主要的破坏性作用,超压保孔和溶解增孔是主要的建设性作用,并且对深水海底扇不同构造带储层孔隙演化的影响不同,形成现今差异孔隙特征.

The deep-water submarine fans of the Miocene Meishan Formation in Ledong-Lingshui sags in the west area of Qiongdongnan Basin,are the main gas exploration area.A comprehensive analysis is conducted to study the diagenesis and its influence on the porosity evolution of deep-water submarine fan reservoir under the background of high temperature and overpressure,by means of thin section,X diffraction,scanning electron microscopy(SEM),cathodoluminescence,stable isotope,and fluid inclusion analysis.The results show that:(1)The rock types of deep-water submarine fan reservoir in Meishan Formation are mainly lithic quartz sandstone and feldspar lithic sandstone.The reservoir properties are mainly characterized by low-medium porosity and low to ultra-low permeability,with strong heterogeneity.(2)The reservoirs evolved as follows:early compaction and clay mineral cementation→the first phase of low mature oil filling→feldspar dissolution,secondary enlargement of quartz,ferrocalcite cementation→the second phase of higher mature oil-gas filling→(ferrodolomite)dolomite cementation,quartz and its secondary enlargement dissolution,overpressure formation→the third phase of high mature natural gas accumulation→late CO2 charging,hydrothermal action.(3)The reservoir pore evolution is controlled by the compaction-cementation with overpressure protection and dissolution.Early compaction and cementation are the main destructive factors.The pore preservation of overpressure and dissolution are the main constructive factors.The influence degree of diagenesis on the deep-water submarine fan reservoir is different in the different tectonic zones,resulting in the current differential pore characteristics.