密井网条件下钙质胶结条带空间展布研究

综合应用铸体薄片、物性分析等资料，以鄂尔多斯盆地华庆地区长8油组为例，对密井网条件下低渗致密砂岩内部的钙质胶结条带进行了研究，明确了其基本特征，阐明了不同位置胶结条带的发育控制因素，建立了密井网条件下钙质胶结条带的空间展布模式。研究表明，华庆地区长8油组砂岩中，钙质胶结条带广泛发育，主要成分为晚期铁方解石。不同发育位置的钙质胶结条带发育主控因素不一，整体胶结式发育主要受控于粒度，中部式主要受侧向临近泥页岩和长石溶蚀影响，顶底式则主要受到粒度和泥页岩发育程度配置关系影响。不同沉积微相组合和构型界面控制了钙质胶结条带的垂向分布，平面上钙质胶结条带主要呈团块状、条带状分布于研究区中部远离物源的分流河道末端及其附近河口坝中部。总体上，密井网条件下钙质胶结条带在空间上呈厚层粗粒砂体内部"顶底胶结厚延伸远中部胶结薄延伸近"和薄层砂体"整体胶结薄延伸近"的展布模式。

Study on Spatial Distribution of Calcite-cemented Strips Under Close Well-spacing Conditions

Using data from casting sheet images and physical property analyses, this study investigates calcite-cemented strips in compact sandstones of low-permeability under close well-spaced conditions, as exemplified by the Chang-8 oil formation in the Huaqing area of the Ordos Basin. Specifically, their basic characteristics are analyzed, the controlling factors for the development of them at different locations are identified, and a spatial distribution model for calcite-cemented strips under close well-spacing conditions is built. The results of the study show that calcite-cemented strips were widely developed in the sandstones of the Chang-8 oil formation in the Huaqing area, and mainly comprise late-stage ferrous calcites. The primary controlling factors for their development vary with the location of development. In particular, their development is primarily controlled by granularity, lateral adjacent mud shales and feldspar corrosion in the middle, and by the dispositional relationship between granularity and degree of mud shale development at the top and bottom. Their vertical distribution is controlled jointly by a combination of sedimentary microfacies and a configurational interface. Horizontally, they mainly take on a crumby structure and have a zonal distribution at the end of the distributary river way, far away from the provenance in the middle of the study area, and in the middle of the nearby estuary dam. Overall, the spatial distribution of calcite-cemented strips under the close well-spacing condition is characterized as follows:(1) in the thick-layer coarse-grained sands, calcite cementation is thick and far-stretching at the bottom and top, but thin and near-stretching in the middle; (2) in the thin-layer sands, calcite cementation is thin and near-stretching.