Research On Meso-pore Structure Characteristics Of Salt Rock

The rock salt is the best energy storage medium by internationally recognized, and the change of the internal pore network is an important factor in salt rock gas storage leak. Subtle changes will lead to a substantial increase in gas permeability. In order to better provide a theoretical basis for the design of the salt rock gas storage, improve gas storage security, the rock salt internal study of the microscopic pore structure is particularly important. In this paper, experimental methods like (constant) pressure mercury and gas adsorption (N2) used for the meso-structure test on rock salt, combined with fractal theory to derive the average pore throat ratio, average pore radius, pore size and distribution geometry, permeabilitycontribution rate, as well as micro-uniformity coefficient parameter distribution law of micro-structural features characterize of the internal porosity of the rock salt. Then, according to the test parameters, combined with mercury injection capillary pressure curves,numerical simulation and theoretical methods to reconstrut pore three-dimensional model,and then derive mathematical relationship between the model of the pore structure and permeability of the rock salt. Now Detailed below:(1) Conventional pressure mercury was used to study the salt rock mesoscopic structural features, we can see the pore structure of the rock salt is less than lμm sub-pore-based. And then analyze the relationship between the physical properties of salt rock porosity and pore throat distribution which is closely related to the characteristic parameters of the pore throat.(2) Based on fractal theory, using controlled mercury to analyze the distribution characteristics of the meso-structure of the salt rock. The derived characterization using fractal dimension of a single throat penetration contribution rate, the average radius of the throat as well as the expression of the microscopic uniformity coefficient. The results show that the distribution of rock salt in the pore throats belong to two different systems, throat distributions in fractal structure, and the channels do not meet, and the correlation of throat distribution fractal dimension and permeability is poor. Small-throated occupy pore permeability of rock salt contribution rate, most of the salt rock specimen throat fractal dimension increases, the stronger of its heterogeneity.(3) Based on the the cylindrical equivalent model theory and the combination of gas adsorption method,we analze the meso-structure of the poreof rock salt. Using the the BET algorithm to calculate the ratio of the pore surface area, BJH algorithm to calculate the aperture, and compare with pressure mercury experiments. It shows that the throat radius of10-50nm and belong to a normal distribution, three adsorption of the sample-desorption isotherms drawed is class IV curve,it proved desorption is not complete. There is a relatively large hole and desorption hysteresis curve. The curve shape between the sample is not the same,it prove that the pore’s distribution Characteristics is complex and differences.(4) Conventional mercury intrusion, constant pressure mercury and gas adsorption three experimental methods were compared and analyzed, it was found that the constant pressure mercury more accurate than the conventional pressure mercury.The gas adsorption can be measured by mercury intrusion experiments can not be measured. There is a complementary relationship between the both.(5) Capillary pressure curve and Wall formula were respectively estimated the penetration of the salt rock, and then base on the theory of fractal geometry, establish the theoretical relationship model of salt rock permeability and porosity. Then based on the Carman-Kozeny model, in addition to consideringsalt rock porosity micro-pore throat characteristics, but also consider the connectivity of the pore the curvature permeability, establish the permeability estimation model and permeability fractal model and use it to verify the test results. The results show that the theoretical models built and experimental data are more reasonable, and according to the permeability and porosity model that the permeability of the rock salt is jointly controlled by the meso-structure of the pore curvature and pore throat, bending and permeability. Simple Ascending Descending relationship does not exist between the meso-structure and permeability of pore throat, a complex analytical relations exist between the three joint function of the size of the penetration.(6) Using pressure mercury experimental to study the pore structure of the rock salt and base on fractal theory to characterize the pore structure characteristics. Experimental data on the various parameters of rock salt pore distribution were analyzed positioning, then use the MAT-lab software to build Voronoi diagram and establish a two-dimensional pore network model. Then drawn for visualization of three-dimensional modeling of salt rock pore meso-structure parameters established based on the previous experimental data such as theoretical number of porosity and pore throat radius, coordination number. Analyze the salt rock porosity distribution law, and finally utilize the ADINA and VB programming established the three-dimensional visualization model of salt rock pore.