The third annual report of "Improving CO2 Efficiency for Recovery Oil in Heterogeneous Reservoirs" presents results of laboratory studies with related analytical models for improved oil recovery. All studies were designed to optimize utilization and extend the practice of CO2 flooding to a wider range of reservoirs.
Chapter 1 describes the behavior at low concentrations of the surfactant Chaser International CD1045TM (CD) versus different salinity, pressure and temperature. Results of studies on the effects of pH and polymer (hydrolyzed polyacrylamide.HPAM) and CO2 foam stability after adsorption in the core are also reported. Calcium lignosulfonate (CLS) transport mechanisms through sandstone, description of the adsorption of CD and CD/CLS onto three porous media (sandstone, limestone and dolomite) and five minerals, and the effect of adsorption on foam stability are also reported.
In Chapter 2, the adsorption kinetics of CLS in porous Berea sandstone and non-porous minerals are compared by monitoring adsorption density change with time. Results show that adsorption requires a much longer time for the porous versus non-porous medium. CLS adsorption onto sandstone can be divided into three regions: adsorption controlled by dispersion, adsorption controlled by diffusion and adsorption equilibrium. NaI tracer used to characterize the sandstone had similar trends to earlier results for the CLS desorption process, suggesting a dual porosity model to simulate flow through Berea sandstone.
The kinetics and equilibrium test for CD adsorption onto five non-porous minerals and three porous media are reported in Chapter 3. CD adsorption and desorption onto non-porous minerals can be established in less than one hour with adsorption densities ranging from 0.4 to 1.2 mg of CD per g of mineral in decreasing order of montmorillonite, dolomite, kaolinite, silica and calcite. The surfactant adsorption onto three porous media takes much longer than one hour, with Berea sandstone requiring the longest time.
In Chapter 4, comparisons of static adsorption of CLS, CD, and CLS/CD mixtures onto five pure minerals showed that the presence of CLS decreased the adsorption of CD onto the five minerals by 20 to 70%. Dynamic CLS/CD mixture adsorption tests onto Berea sandstone and Indian limestone cores showed that competitive adsorption between CD and CLS generally takes several days to reach equilibrium. Foam stability and interfacial tension tests on both injected and effluent samples were performed which showed that both foam stability and IFT decreased due to adsorption. Also it appears that there is a chromatographic effect on the surfactants in flow through porous media. Progress was realized in developing general equations for stress sensitivity on non-Darcy parameters (permeability and non-Darcy coefficient), and the multiphase flow induced by a high flow rate was confirmed as a mechanism for injectivity loss in CO2 flooding.