煤系致密砂岩长石碎屑溶蚀的显微组构约束效应

There are a lot of secondary pores originated from the dissolution of feldspar in tight sandstone of coal measure strata, which provide important reservoir spaces for the tight gas. Clarifying the constraint mechanism of the feldspar microfabrics on dissolution and development regularity of secondary solution pores under this special diagenetic condition is the key to interpret reservoir formation of tight sandstone gas. Consequently, centring on the scientific issues of “The constraint mechanism of microfabrics on feldspar dissolution of tight sandstone in coal measure strata”, taking the tight sandstone of Carboniferous-Permian in eastern Ordos Basin as the research object, the microfabrics ,including surface density, surface area, crystal order parameter, dislocation density and dislocation type of feldspar in tight sandstone of coal measures will be studied by corrosion experiment simulating diagenetic environment of coal measures strata. The preferential dissolution sites and dissolution pathways of feldspar will be found by establishing the relationship between dissolution and microfabrics parameters using SPSS statistical analysis software. Form the above, the constraint mechanism of the feldspar microfabrics on dissolution and development regularity of secondary solution pores in different diagenetic stages will be clarified, which will provide scientific basis to interpret reservoir formation of tight sandstone gas.

在煤系致密砂岩中，大量发育的长石碎屑次生溶孔为煤系致密气提供了重要的储集空间，揭示这种特殊成岩条件下长石碎屑显微组构对溶蚀的约束机理及次生溶孔发育规律，是阐释煤系致密砂岩气成藏作用的关键。鉴于此，本项目拟围绕“煤系致密砂岩长石碎屑溶蚀的显微组构约束效应”这一核心科学问题，选取鄂尔多斯盆地东缘石炭二叠系致密砂岩为研究对象，通过模拟煤系地层环境的溶蚀实验，结合超显微观测，分析不同成岩阶段煤系致密砂岩中长石的显微组构特征，包括不同方向的面网密度、面网间距、晶体有序参数、位错密度和位错类型等；利用SPSS统计分析软件的主成分分析和因子分析模块，建立长石溶蚀与显微组构特征参数之间的关系，提出长石碎屑的优先溶解部位和长石溶蚀加大途径；明确不同成岩阶段长石碎屑溶蚀的显微组构约束效应，揭示煤系致密砂岩中次生溶孔形成规律，为煤系致密气成藏机理研究提供科学依据。

在煤系致密砂岩中，大量发育的长石碎屑次生溶孔为煤系致密气提供了重要的储集空间，揭示这种特殊成岩条件下长石碎屑显微组构对溶蚀的约束机理及次生溶孔发育规律，是阐释煤系致密砂岩气成藏作用的关键。鉴于此，本项目围绕“煤系致密砂岩长石碎屑溶蚀的显微组构约束效应”这一核心科学问题，选取鄂尔多斯盆地东缘石炭二叠系致密砂岩为研究对象，通过模拟煤系地层环境的溶蚀实验，结合超显微观测，分析不同成岩阶段煤系致密砂岩中长石的显微组构特征，包括不同方向的面网密度、面网间距、晶体有序参数、位错密度和位错类型等。研究认为不同成岩阶段影响长石碎屑溶蚀的不同显微组构特征参数均为面网密度、面网间距、晶体有序参数、位错密度和位错类型。在早成岩环境下，位错密度、位错类型和晶体有序参数是影响溶蚀强度的主要因素；而在晚成岩阶段，面网密度和面网间距对溶蚀具有重要意义。溶蚀发生于晶体内部位错缠结发育的区域。溶蚀出现后，晶体溶蚀的特征随外界环境变化而不同。在早成岩阶段的低温环境下，位错密度和晶体有序参数控制了溶蚀的速率。位错密度越大，晶体有序参数越低，溶蚀越趋于加大。在晚成岩阶段的高温环境下，面网密度和面网间距是控制斜长石不同面朝向的溶蚀差异的主要影响因素。面网密度小、面网间距大的面网，溶蚀作用趋于加大。