Permeability of salt-crystal interfaces to brine

Abstract

To investigate the movement of brine along grain boundaries in pobrrystalline salt, measure ments have been made of the radial flow of brine through the interface between cylindrical salt crystals under axial stresses to 140 bar and temperature to 80°C. For constant conditions, the total flow of brine showed a linen dependence on the logarithm of time, end the reciprocal permeability increased linearly with time. Loss of salt from the interface by pressure solution effects was more than enough to account for the decrease in the apparent thkknes» of the interface (i.e., that which r. ay be estimted for an interface of the same permeability formed by plane parallel surfaces). This apparent thickness, initially as large as 10 /un, decreased to as little as 0.2 pm with exposure to stress and flowing bn.ie. It decreased quickly with sudden increases in axial stress and usually increased, though not reversr'bly, with decreases in stress. The rate of increase in the reciprocal per meability with time was roughly proportional to the stress and to the square of the hydraulic pres sure drop. Assuming similar apparent thicknesses for the grain boundaries in polycrystalline salt, permeabilities are predicted that are quite consistent with the low values reported for stressed core specimens.

Brine flow in heated geologic salt.

“…Several laboratory brine and gas permeability tests have observed decreasing permeability during tests (Reynolds and Gloyna, 1960;Sutherland and Cave, 1980;Gilpatrick et al, 1982;Baes et al, 1983;Peach et al, 1987). This observed decrease has been attributed to the following proposed mechanisms:…”