Permeability Modification of Diatomite During Hot Fluid Injection

Abstract

Abstract One area of concern that has accompanied steam injection into diatomite for oil recovery is the evolution of permeability and porosity as silica dissolves in hot steam condensate and is redistributed on rock surfaces as condensate cools. Since grain size is quite fine and typical pore throat dimensions in diatomite range from roughly 1 to 6 m, dissolution of silica near pore throats should increase permeability drastically. Likewise, a small amount of deposition at pore throats will cause clogging. Our goals are to improve understanding of the effects of mineral dissolution/reprecipitation in diatomite and to formulate permeability versus porosity relationships necessary for reservoir simulation. We employ a network model to gauge how evolving pore topology affects permeability and porosity. Hence, we calculate macroscopic trends by incorporating pore-level physics. The model is anchored to real rock through actual pore-throat and pore-body size distributions. Results indicate that plugging of the network and a corresponding decrease in permeability occur when moderate amounts of silica precipitate. Plugging is most severe for small values of network connectivity and large values of the pore-body to pore-throat aspect ratio. When porosity change from 0 to 10 % is examined closely, it is found that permeability decrease correlates with porosity decrease according to a power-law expression with power-law exponents in the, range of 8 to 9. Such a power-law dependence has been measured previously by experiment. These values confirm the strong dependence of permeability on deposited silica. The dissolution process displays an equally strong dependence on porosity change and again permeability increases most dramatically for dissolution in networks with small values of connectivity and large values of the pore-throat to pore-body aspect ratio. Again, power-law expressions adequately describe permeability increase as a function of porosity for a moderate range of dissolution.