The potential for using lignosulfonate as a sacrificial agent to reduce adsorption of the primary foaming agent in CO2 flooding was evaluated in laboratory experiments. Circulation and flow-through methods were used to measure adsorption to assess the loss of surfactants for economic evaluation and to design an optimum surfactant injection scheme.
Results show that lignosulfonate could reduce the adsorption of a primary foaming agent by 24–60% in Berea sandstone and 15–29% in Indiana limestone core samples. The selective adsorption behavior of lignosulfonate and surfactant gives rise to various adsorption results with different injection schemes. Preflushing the core with lignosulfonate proved to be more effective in reducing the loss of primary foaming agent than coinjecting both foaming agents together. Considering the cost savings as well as the effectiveness of foams in improving oil recovery, an effective surfactant injection design with lignosulfonate shows significant potential for economically improving the CO2-foam flooding process.
Foam is a promising mobility controlling agent for gas flooding in improved oil recovery processes. Aqueous foam is a dispersed gaseous phase within a continuous aqueous phase comprised mainly of films known as lamellae. The lamellae are stabilized by adsorption of surfactant at the gas/liquid interfaces. When foam is generated and propagated in the porous media, the foam bubbles are as large as pore bodies and the lamellae span the pores that reduce the gas mobility. To be effective in controlling the gas mobility in gas flooding process, surfactant or foaming agent needs to propagate deeply enough into the reservoir for a persistent foam generation and displacement result. Since surfactant is adsorbed on the rock surface, the loss of surfactant due to adsorption affects the propagation of surfactant and its effectiveness to stabilize the lamellae. Frequently, to overcome problems of surfactant loss, a sufficient amount of surfactant is pre-injected into the reservoir to satisfy the surfactant adsorption prior to injection of gas or pre-generated foam.1–4 Such an approach may not be very economically sound when an expensive foaming agent is used. Therefore, use of a lower cost sacrificial agent may become economically necessary to minimize the loss of costly foaming agent and ensure a satisfactory foam displacement.
Lignosulfonate, an inexpensive byproduct of the paper industry, has been used as a sacrificial agent in surfactant flooding processes.5,6 Because lignosulfonate carries anionic charges in solution, it can reduce surfactant adsorption sites of reservoir rock and act to protect the primary surfactants from adsorption in surfactant flooding process. The use of lignosulfonate as a sacrificial agent in CO2-foam application was first reported in a recent patent by Kalfoglou, et al.7 They found lignosulfonate reduced a foaming agent's adsorption onto limestone crushed rock samples by 16 to 35%. While a better sacrificial effect was reportedly achieved by using synthetic lignosulfonate-acrylic acid graft copolymer, the effect of using lignosulfonate or the new copolymer as a sacrificial agent in oil recovery was not completely evaluated.