One of the factors affecting the economics of CO2-foam flooding is the loss of the foaming agent by adsorption onto reservoir rocks. As a practical approach for reducing the loss of costly surfactants, the use of sacrificial agents is evaluated in this paper.
Several tests were designed to investigate the feasibility of using lignosulfonate as a sacrificial agent in CO2-foam flooding. Foam durability tests were conducted to assess the compatibility of lignosulfonate with a primary foaming agent and the resulting foam properties. Flooding experiments were conducted on a composite core containing well defined high and low permeability regions to evaluate the mobility reduction of foam and the oil recovery efficiency. Adsorption experiments were conducted to assess both the loss of the primary foaming agent and the lignosulfonate for further economic evaluation.
The results showed that lignosulfonate is a weak foaming agent. When used with a strong or primary foaming agent, it enhanced the properties of foams that favorably reduce the mobility of CO2 to correct the nonuniform flow pattern in heterogeneous porous media. In composite core sample experiments, foams were effective in diverting CO2 from the high permeability region to the low permeability region and increasing oil recovery efficiency. When lignosulfonate was used as a sacrificial agent, comparable incremental oil recovery could be achieved with concentration of the primary foaming agent reduced by as much as 80 percent. Considering the cost of reduction and the effectiveness of foams in improving oil recovery, an effective experimental design using lignosulfonate with another primary foaming agent shows potential for economically improving the CO2-foam flooding process.