Abstract
Based on micro-scale casting thin sections, nano-scale SEM images, and the pore distribution map identified through a binary image in Matlab, the pore size distribution and pore throat coordination number of the strata of Upper Paleozoic He8 section tight sandstone in the southeastern Ordos Basin were quantitatively analyzed with the above experimental data. In combination with a high-pressure mercury injection experiment, the pore throat distribution, the pore throat ratio, and the relationships between the characteristics, parameters, and pore permeability were investigated clearly. The results show that the tight sandstone pore space in the study area is dominated by micron-sized intergranular pores, dissolved pores, and intragranular pores. The nano-scale pore throat consisted of clay minerals, intercrystalline pores, and the flake intergranular pores of overgrowth quartz grains. Kaolinite and illite intercrystalline pores occupy the pore space below 600 nm, while the ones above 800 nm are mainly dominated by the intergranular pores of overgrowth quartz grains, and the 600–800 nm ones are transitional zones. The permeability of tight sandstone increases with the average pore throat radius, sorting coefficient, median pore throat radius, and average pore throat number. The porosity is positively correlated with the average pore radius and the average pore throat coordination number, and negatively correlated with the median pore throat radius.
Highlights
The microscopic pore structure of a reservoir refers to the geometry, size, distribution, and mutual connectivity of the pores and throats in the reservoir rock [1,2], which directly affects the development of the reservoir pore space
According to the routine analysis of cores, the reservoir porosity of the He8 section of the study area ranges from 2.26%
As nano-scale intergranular pores and dissolved pores mainly constitute tight sandstone reservoir spaces, their pore size, distribution, and quantity influences the entire tight sandstone reservoir capacity, and as micron-scale intercrystalline pores and intergranular pores of overgrowth quartz grains, their distribution, number, and shape affect the permeability of tight sandstone
Summary
The microscopic pore structure of a reservoir refers to the geometry, size, distribution, and mutual connectivity of the pores and throats in the reservoir rock [1,2], which directly affects the development of the reservoir pore space. The pore space of tight sandstone reservoirs is divided into three levels: millimeter pore, micron-scale pore, and nano-scale pore. Zou et al discovered nano-scale pores for the first time in a study of unconventional reservoirs in China by applying field emission scanning electron microscopy and X- CT (X-ray computed tomography) reconstruction techniques [3]. From the millimeter pore to the nano-scale pore, many analytical methods, including experiments and numerical simulations, have been applied to the pore structure and characterization of tight sandstone. Nuclear magnetic resonance logging techniques [4,5,6], fluid injection experiments [6,7,8], and image observation method are the
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