Abstract: 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.

Key words: Calcite-cemented strip, controlling factor, spatial distribution, close well-spacing, Huaqing area