Abstract
To investigate the effect of siliceous cementation on the densification of sandstone and the forming process of tight sandstone, based on cathodoluminescence, scanning electron microscopy and thin section analysis, the growth mechanism and characteristics of quartz particles in tight sandstone formations are explored. Meanwhile, combined with conventional core analysis and X-ray diffraction experiments, the factors affecting the crystallization of quartz particles, including the chlorite content, grain size and clay mineral, are analyzed, respectively. The entire siliceous cementation is divided into two processes. The first part is the process in which the weathered and rounded particles in the formation are restored to the hexagonal dipyramid crystal by siliceous cementation. The second part is the process of coaxial growth that the hexagonal dipyramid crystal continues to increase with the form of micro-quartz film. As siliceous cements continue to increase, the petrological characteristics of sandstones are constantly changing. The tight sandstone developed in the study area is composed of lithic sandstone and quartz lithic sandstone. Based on the analysis results, 2D and 3D evolution models are established for densification of two different lithic sandstones. When the content of siliceous cement in the study area is less than 17%, the porosity of tight sandstone increases with the increase of cement. When the content of cement is more than 17%, the porosity of tight sandstone is negatively correlated with the content of cement. When the cement content is greater than 10%, the reservoir permeability is negatively correlated with it. Furthermore, the particle size mainly affects the permeability of reservoir, and the particle size is negatively correlated with the permeability of tight sandstone. The most high-quality tight sandstone reservoir in the study area is in the first cementation stage when siliceous cements are distributed in porphyritic texture with the content of 10–15% and a grain size of 0.2–0.3 mm. In addition, the relatively high-quality reservoir is the one developing clay mineral film with a content of cementation about 5–12%.
Highlights
In recent years, tight sandstone reservoirs have gradually become a hotspot of natural gas exploration and development in the world
The growth form is a large amount of microcrystalline quartz randomly that after the quartz particles restored to hexagonal dipyramid crystals, the whole crystal would growing on the surface the The crystal
The first part is the process in which the weathered and rounded particles in the formation are restored to the hexagonal dipyramid crystal by siliceous cementation
Summary
Tight sandstone reservoirs have gradually become a hotspot of natural gas exploration and development in the world. The reservoir physical property is the key factor that determines the type of gas reservoirs and the difficulty of development The geological elements such as rock composition, cementation type, content, and skeleton particle characteristics of coal measures should be studied emphatically. He8, Shan and Shan sections are the main reservoir of tight sandstone gas in the study area. The geological factors such as reservoir rock composition, cement type, content, and skeleton particle characteristics are bound to affect reservoir physical properties [11,12,13]. The formation mechanism of siliceous cementation in the tight sandstone, the evolution mode of tight sandstone and its influencing factors are explored, respectively
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