Permeability Damage in Diatomite Due to in-situ Silica Dissolution/Precipitation

It has been observed in Mobil's California diatomite thermal recovery projects that water injectivity decreases gradually with time. Several factors, such as reservoir fill-up or high suspended solids concentration in the injection fluid, may effect such decrease. Due to the inherently low permeability of diatomite, small amounts of in-situ silica dissolution and/or precipitation can also have a drastic effect on the matrix permeability and consequently the injectivity. In this study, we outline an experimental program designed to ascertain such behavior and to elucidate qualitative and quantitative results to further our understanding of the problem. Furthermore, transient flow experiments were performed to obtain silica dissolution/precipitation data at various temperatures. It is shown that the silica reaction can be modeled approximately as first-order kinetics. Numerical model results indicate that this kinetic data can be used to model diatomite permeability damage data obtained in the laboratory. Our current effort to simulate field-scale permeability damage using the experimentally-derived silica kinetic model will also be discussed.