Rates of Evaporite Deformation: The Role of Pressure Solution

摘要

Evaporite sequences were studied for hazardous waste disposal and hydrocarbon development and storage. Rates of deformation are important in evaluating the long-term performance of different evaporites. Rates are controlled by temperature, differential stress, and active mechanism of deformation for each specific type of evaporite and setting. Strain rates are estimated through in-situ measurements and the integration of geometric strain analysis and stratigraphic arguments for the time required for the observed deformation to occur. An inherent problem in such calculations is the large extrapolation of rates through time. Specific mechanisms can be determined from petrofabric study, as at the WIPP site, SE New Mexico, where textures indicating that pressure solution was active are observed. Calculations based on experimental data are limited by the relatively poor data on diffusion in intergranular fluids. A variety of grain boundary diffusion models have been used. For gravity-driven deformation near the WIPP site, geometric-stratigraphic integration predicts a naturally occurring strain rates of 10 sup -14 s sup -1 to 10 sup -16 s sup -1 . Strain rates of 10 sup -15 to 10 sup -16 s sup -1 are predicted using models for dislocation creep and pressure solution. The rates using two approaches, geometric-stratigraphic and constitutive, are basically in agreement. These rates for the gravity-driven flow structures near WIPP reflect lower temperatures and stresses than salt domes. At the temperatures and stresses estimated for the WIPP flow structures, pressure solution is probably the dominant mechanism, rather than dislocation creep. It remains to be determined where in the transition from transient to steady-state response to an underground excavation in rock-salt pressure solution becomes a major mechanism. 39 refs., 4 figs., 8 tabs. (ERA citation 12:049429)