Study On Permeability Characteristics Of Remolded Sandstone With X-shaped Conjugate Fractures

X-type conjugated fissures are widely distributed in the Cretaceous strata in the Ordos area of western China.The existence of fissures makes the hydrogeological conditions in this area very complicated.The disturbance of groundwater excavation caused by mining excavation disrupts the balance of groundwater,making groundwater in the rock mass and fissure rock.The infiltration flow in the body is intensified,which has a serious impact on the safety construction of the wellbore.Therefore,the permeability characteristics of sandstones with X-type conjugated fractures are the key factors affecting the safety of the wellbore.In this paper,the X-type conjugated cracks and filling cracks in the Cretaceous sandstone strata in the Ordos area were taken as the research objects.The remodeled sandstone samples containing X-shaped cracks were obtained by remodeling.The law of permeability change of type fissure specimens is studied.Designed and processed core remolding sample preparation mold,based on pressure and temperature control reshaping method to obtain remodeled sandstone samples without cracks,and then through 3 factors and 3 levels of orthogonal test for sandstone matrix particle reshaping mix ratio.After the determination,the remodeled sandstone with pore characteristics close to the original sandstone was obtained.On this basis,a method for preparing reshaped sandstone containing X-shaped conjugated cracks is proposed through a crack-preparing mold containing X-shaped core molds.The self-developed fracture rock permeability test system was used to conduct the permeability test on the unfilled fracture samples.The results showed that with the increase of confining pressure,the seepage flow shows the law of “rapidly decreasing and gradually stabilizing”,and the confining pressure of 2MPa is the turning point of the law of the change of the seepage flow.When other factors are the same,the seepage volume increases approximately linearly with the increase of the gap width,but the magnitude of the increase gradually decreases.Similarly,the seepage volume increases approximately linearly with the increase of the seepage pressure.When the confining pressure is constant,with the increase of osmotic pressure,the curve of seepage flow with gap width increases in a "step",but the increase rate gradually decreases.Considering the influences of confining pressure,gap width,filling particle size and filling volume quality,a permeability test for filling cracked samples was conducted.The test results show that: during the confining pressure loading process,the seepage flow is approximately linearly decreasing with increasing confining pressure,while during the confining pressure unloading process,the seepage flow does not change much with the decreasing confining pressure.Through the control variable method,the unit percolation flow increases linearly with the increase of the gap width when other factors remain unchanged.The COMSOL Multiphysics software was used to numerically simulate the permeability of different crack-filled specimens and compare it with some test results.The results show that the percolation rate per unit time of rock sample outlet increases linearly with the increase of permeation pressure,gap width and L / D value,but does not change much with the increase of cross angle.The change law with the seepage pressure and the gap width is consistent with the change law of the average value of the seepage test results of each confining pressure fracture,but the increase of the simulated seepage flow with the increase of the seepage pressure is greater than that of the unfilled fracture seepage test.With the increase of the gap width,the simulated seepage flow of the filled crack is greater than that of the unfilled crack test,and the smallest seepage flow of the filled crack test;from the growth rate,the increased rate of seepage flow of the unfilled crack test is greater than that of the filled fracture,the growth rate of simulated seepage flow in filling cracks is the smallest.The paper has 59 pictures,36 tables,and 106 references.