The dissolution of calcite in hydrochloric acid was studied with the aid of a rotating disk system at 800 psig in the temperature range-156-25°C. At 25°C the dissolution process is mass transfer limited even at high disk rotation speeds whereas at-156°C both mass transfer and surface reaction rates limit the dissolution rate. The multicomponent coupled ionic diffusive fluxes of reactants and products were defined by using the gradient of the electrochemical potentials as driving forces for the diffusion. The activity coefficients used in calculating the multicomponent diffusivities of the diffusing species were estimated by Hamed's rule. The concentration protiles of the ions in the boundary layer were then determined by numerically integrating the system of coupled convective diffusion equations. The effects of variable density, viscosity, and high mass fluxes on the fluid velocity in the boundary layer were taken into account. The rate of the surface reaction was found to be proportional to the 0.63 power of the surface hydrochloric acid concentration. Analysis of the experiments suggests that the absorption of hydrogen ion (described by a Freundlich adsorption isotherm) on the solid calcite surface and subsequent reaction of the adsorbed hydrogen ion with the solid calcite matrix is the reaction mechanism. lNTRODUC'IlON

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A novel technique has been developed for obtaining permeability-porosity relationships in naturally consolidated porous media. The results show that the local change of permeability with porosity is an order of magnitude greater than previously reported. The method may also be used for determining mass transfer coefficients in naturally consolidated systems where the acidization rate is diffusion controlled.

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This paper describes the design and use of a rotating disk apparatus for studying reactions between fluids and solid surfaces. The apparatus is capable of operation in extremely corrosive liquid environments under controlled pressures and temperatures up to 70 atm and 150°C. The design includes a unique magnetic drive assembly that allows the disk to be rotated in the high pressure reactor vessel without the need of a stuffing box seal. All parts that contact corrosive fluids are fabricated from Hastelloy alloys and Teflon. A special feature of the reactor vessel is its ready conversion to a high pressure visual cell.