| The application of gelled polymer treatments by injecting gelable crosslinker-polymer solutions to change the flow characteristics of a reservoir is a viable improved oil recovery technique. To design successful treatments, it is necessary to understand the interactions between the injected solutions and the rock materials. These chemical interactions include the dissolution of rock, the changes of pH and composition in the injected solution, and the precipitation of chromium hydroxide due to the increase of solution pH.; The first part of this research was undertaken to investigate the effects of initial pH, common ion, and acetate buffer on the change in the pH and concentrations in the injected solution. A three-stage effluent pH behavior was observed when the pH of the injected solution increased from 1 to 13. Added common ions such as calcium and magnesium depressed the dissolution of dolomite and resulted in a lower equilibrium pH. The presence of acetate ions enhanced the dissolution of dolomite, but reduced the rate of pH increase and buffered the solution on a lower pH level.; The second part of this research studied the chemical nature of chromium hydroxide precipitation from chromium acetate solutions by investigating the effects of pH, salinity, temperature, acetate ligand concentration, the source of chromium, and salt type on the precipitation under constant pH titration. An induction period was observed, which decreased exponentially with the increase of temperature, salinity, or solution pH. The precipitation reactions were accelerated with increase in pH, temperature, salinity, and decelerated with an increase in acetate concentration. A kinetic model was developed to describe both the induction period and the rate of precipitation of chromium from a chromium acetate solution in 1% KCl at 25°C for the pH range of 7–10 with OAc to Cr ratios between 3 and 9.; A mathematical model was developed to simulate the chemical interaction between various solutions and dolomite. The proposed model predicts (1) aqueous electrolyte reactions, (2) dissolution of dolomite, (3) precipitation of chromium hydroxide, and (4) polymer gelation time (in Appendix A). The predicated results compared favorably with both experimental results and published models.; The results of this research lead to a better understanding on the chemical interactions between chromium solutions and dolomite rocks. It provides useful information for gel treatments used for in-depth permeability modification in carbonated reservoirs. |
