煤系砂砾岩储层致密化机理--以准噶尔盆地AH5井区八道湾组为例

Densification mechanism of coal-bearing glutenite reservoirs:An example from Badaowan Formation in AH5 well area,Junggar Basin

在埋藏史-热史指导下,利用铸体及荧光薄片、扫描电镜、黏土矿物分析、激光拉曼分析、流体包裹体分析、碳氧同位素测试、物性及含油饱和度等分析手段,对准噶尔盆地AH5井区八道湾组煤系砂砾岩储层致密化机理进行分析.煤系砂砾岩储层的成岩序列为:压实(压溶作用)-石英次生加大-菱铁矿、方解石胶结-伊蒙混层、绿泥石胶结-长石的溶蚀-自生石英、高岭石胶结-菱铁矿、铁白云石胶结-自生石英、伊利石胶结.研究结果表明:储层内胶结物类型多样,整体具有多期、多源的特征,受煤层排酸以及有机酸溶蚀的影响,主要形成于中成岩阶段.除煤系沉积环境外,成岩作用中压实作用是研究区目的储层致密化的关键因素,对砂质储层和砾质储层物性影响最大;胶结作用是砂质和砾质储层进一步致密化的关键因素,溶蚀作用对砂质储层物性改变影响较大,对砾质储层影响有限.在上述研究成果基础上,认为砾质油藏主要为“先致密后成藏”型,砂质油藏主要为“边致密边成藏”型.

Under the guidance of burial-thermal history,densification mechanism of coal-bearing glutenite reservoirs in AH5 well region,Junggar Basin,has been searched by using casting thin section,fluorescence thin section,scanning electron microscope,clay minerals analysis,laser raman analysis,fluid inclusion,stable carbon isotope composition of diagenetic mineral,physical property and oil saturation.It is revealed that diagenetic sequence in coal-bearing glutenite reservoirs include:early compaction(pressure solution),secondary overgrowth of quartz,siderite and calcite cementation,mixed-layer illite and chlorite cementation,corrosion of feldspar,authigenic quartz and kaolinite cementation,siderite and ankerite cementation,illite and authigenic quartz cementation.The result shows that many cementation types occur in reservoirs and have characters of multi-period and multi-sources,a lot of which formed in the middle digenetic phase and affected by corrosion of organic acid.Compaction(except of coal measures environment)is the key factor that make reservoirs densification,which makes most influential on physical property of sand and conglomerate reservoirs;Cementation is the key factors that makes reservoirs further densification;Corrosion have a large effect on physical property of sand reservoirs,while have small effect on conglomerate reservoirs.According to the above results,the conglomerate reservoir is a type of densification before the hydrocarbon accumulation,and sand reservoir is a type of densification with the hydrocarbon accumulation.