| In recent years,in-situ leaching mining method is the main mining method for glauberite ore.In the process of solution mining of glauberite,the pore size,shape and connectivity of glauberite are easy to be changed,and then the dissolution rate of glauberite salt is affected by temperature,stress and concentration,reduce the efficiency of production.In addition,glauberite is also a common interlayer in layered salt rock gas storage.During the construction of solution cavity,the interlayer is immersed in solution solution for a long time,and the change of its internal meso-structure will lead to the connection of pores,thus becomes one of the gas leakage channels,and then affects the safe operation of the gas storage.Therefore,it is significant to study the pore-fissure evolution and seepage law of glauberite under the coupling action of temperature-concentration-stress in meso-view,which can improve the production efficiency of glauberite and seal gas storage in layered salt rock.In this paper,physical experiment,numerical simulation and theoretical analysis are combined,taking glauberite as the research object,constructing a three-dimensional pore model of glauberite under different temperature-concentration-axial stress coupling effects,and quantitatively characterizing the mesoporous fissures of glauberite.Two-dimensional structural features and three-dimensional structural features reveal the effects of temperature,concentration,and axial stress on the evolution of glauberite mesopores and cracks.Based on the constructed three-dimensional model,seepage simulation and absolute permeability calculations under different conditions are carried out.The pressure distribution and velocity distribution law in the process of fluid migration are analyzed.The main results of this paper are as follows:(1)Based on the two-dimensional microstructure distribution of glauberite under different conditions,it is found that the porosity of the micro-pores(D?50 ?m)of glauberite increases first and then decreases with the increase of axial stress,the porosity,total porosity and permeability of small pores(0.05 mm<D?0.1 mm),large pores(0.1 mm<D?0.5 mm),microcracks(0.5 mm<D?1 mm)and fractures(D?1 mm)all increased non-linearly.(2)Based on the three-dimensional pore model of glauberite under the coupling action of different temperature-concentration-stress,it is found that the connectivity of the sample is positively correlated with the axial stress,the connectivity of the specimen is increasing.With the increase of temperature,the connectivity of glauberite increased slightly,but the increase was small.Under the condition of the same temperature and axial stress,the connectivity of glauberite in fresh water is the biggest,and the connectivity of glauberite decreases with the increase of concentration.(3)Based on the equivalent connected pore network model of glauberite under the conditions of 8 MPa and 9.6 MPa,it is found that under the combined action of axial stress,temperature and solution,the main coordination number of glauberite pore is 0?20.The proportion of high pore coordination number(coordination number> 20)of glauberite in fresh water solution is 15%,and the connectivity is best.With the increase of solution concentration,the proportion of high pore coordination number decreases gradually.Compared with 8 MPa,at 9.6 MPa,the ratio of high pore coordination number of glauberite increases from 8?10% to9?12%,which has better connectivity and easier permeability.(4)According to the distribution of pressure area,velocity and the connectivity of flow line,the relationship of permeability of the pore model of glauberite under different conditions can be deduced by comparing the pressure distribution map and velocity distribution map obtained by seepage simulation,it is also found that the permeability is determined by the dominant channel in the pore model. |
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