Abstract
Abstract The characterization of pore throat structure in tight reservoirs is the basis for the effective development of tight oil. In order to effectively characterize the pore -throat structure of tight sandstone in E Basin, China, this study used high-pressure mercury intrusion (HPMI) testing technology and thin section (TS) technology to jointly explore the characteristics of tight oil pore throat structure. The results of the TS test show that there are many types of pores in the tight sandstone, mainly the primary intergranular pores, dissolved pores, and microfractures. Based on the pore throat parameters obtained by HPMI experiments, the pore throat radius of tight sandstone is between 0.0035 and 2.6158 µm. There are two peaks in the pore throat distribution curve, indicating that the tight sandstone contains at least two types of pores. This is consistent with the results of the TS experiments. In addition, based on the fractal theory and obtained capillary pressure curve by HPMI experiments, the fractal characteristics of tight sandstone pore throat are quantitatively characterized. The results show that the tight sandstones in E Basin have piecewise fractal (multifractal) features. The segmentation fractal feature occurs at a pore throat radius of approximately 0.06 µm. Therefore, according to the fractal characteristics, the tight sandstone pore throat of the study block is divided into macropores (pore throat radius > 0.06 µm) and micropores (pore throat radius < 0.06 µm). The fractal dimension D L of the macropores is larger than the fractal dimension D S of the micropores, indicating that the surface of the macropores is rough and the pores are irregular. This study cannot only provide certain support for characterizing the size of tight oil pore throat, but also plays an inspiring role in understanding the tight pore structure of tight sandstone.
Highlights
As an unconventional oil and gas resource, tight oil and gas has received more and more interest in researchers [1,2]
Some of the muddy rock fragments are rich in organic matter and the compacted deformation is pseudo-matrix
In tight sandstone reservoirs of E Basin, the SW gradually decreases as the frequency of macropores increases and the SW gradually increases as the frequency of small pores increases (Figure 9)
Summary
As an unconventional oil and gas resource, tight oil and gas has received more and more interest in researchers [1,2]. In order to accurately characterize the distribution characteristics of multiscale pore throat structures in tight sandstones, a technique capable of testing the full range should be proposed. The test range is from nanometer to micrometer, which can describe the distribution characteristics of tight sandstone pore throat radius This technology has been widely used in the study of rock pore throat structures and numerous successful applications of HPMI technology have already shown its efficiency for pore throat characterization [30,31,32]. In the pore throat size classification method proposed by the International Union of Pure and Applied Chemistry, micropores are less than 2 nm in width, mesopores in the range of 2 to 50 nm in width, and width of the macropores is greater than 50 nm [41] This classification method is widely used in the pore throat radius distribution of shale. Based on the HPMI experiment, this paper used the fractal theory to quantitatively characterize the pore throat structure of tight sandstone
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