Evolution and mechanism of permeability of unconsolidated sandstone under high hydrostatic pressure compaction

Abstract

The unconsolidated sandstone in hydrothermal geothermal field in Jianghan basin is taken as the research object. The hydrostatic pressure is applied to a geostress equal to 12.5 MPa. After the deformation of sample is stabilised, the evolution and mechanism of the permeability of unconsolidated sandstone under the compaction of high hydrostatic pressure are studied, which can provide some suggestions for the selection of equipment operating parameters for the tailwater recharge process in the hydrothermal geothermal field. The results indicate that under high hydrostatic pressure compaction, the permeability of unconsolidated sandstone samples tends to be a constant valued of 4.0×103 m2 within the current range of 0.5 mL/min to 3.0 mL/min. The pressure difference between the two ends of the sample increases nonlinearly with time and the degree of nonlinearity gradually increases with the increase of flow rate, but eventually tends to be stabilised. In addition, the sample of unconsolidated sandstone forms a tubular erosion channel in the direction of penetration, extending to about 2/3 of the sample. Based on the stop time of particle transportation and the extension length of tubular erosion channel in the penetration direction, the average migration velocities of particles under different flow rates are determined. It is found that the particle migration velocity increases exponentially with the increase of flow rate, and the amount of microparticle migrated per unit time increases. When the pressure difference exceeds about 1/2 of the hydrostatic pressure, the sample presents erosion damage and upstream diameter shrinkage.

Keywords

• high hyrostatic pressure
• unconsolidate sandstone
• permeabilty
• suffusion
• particle migration