University of Pittsburgh
Dr. Enick has an active research area in high-pressure thermodynamics, high-pressure phase behavior and membrane separations. Most of his work, including the IAES projects, is related to CO2-rich gas mixtures. For example, Dr. Enick develops strategies for designing novel materials that have very favorable thermodynamic interactions with CO2. Previously, this research led to the identification of novel compounds, including surfactants, chelating agents and thickeners, which were extremely soluble in dense CO2. In the current work, these strategies will be used in an attempt to design high-flux, CO2-selective polymeric membranes. Polymers with specific, relatively strong thermodynamic interactions with CO2 will be cast or pressed into thin membranes. It is anticipated that these favorable interactions between CO2 and the polymer may significantly enhance the solubility of the CO2 in the membrane. Other modifications to the polymer will be incorporated to promote the diffusivity of the CO2 in the membrane. In another application, an attempt will be made to design solvents that absorb significant amounts of only CO2 at high pressure. Unlike conventional solvents that require low pressure during regeneration, all of the absorbed CO2 would be released from these novel materials with a very modest pressure drop. If successful, this solvent would be used to separate high pressure H2-CO2 mixtures into a high pressure H2 stream and a slightly lower (but still high) pressure CO2-rich stream.
The low viscosity of high pressure CO2 injection in oil-bearing formations leads to a host of problems, including viscous fingering, enhanced gravity override, loss of CO2 to thier zones, high produced gas-to-oil ratios, high CO2 utilization rates, and high gas re-compression costs. Water-alternating-gas (WAG) flooding remains the standard technique for reducing CO2 mobility via reduction of CO2 relative permeability, while gels can improve conformance control in stratified formations by diverting flow from thief zones. Surfactant-stabilized CO2-in-brine foams (CO2 is the high volume %, internal phase) remain a promising, low-cost means of mobility control and/or conformance control. A review of the prior use of nonionic, anionic and cationic surfactants in lab tests and pilot trials will be presented, most notably the alternate injection of aqueous surfactant solution and CO2 gas (SAG). A summary of our recent surfactant design developments will also be presented. Surfactant solubility studies, high pressure foam stability tests, static and dynamic adsorption experiments, flow-through-porous media pressure drop (i.e. mobility) results, and CT imaging of foam formation in porous media will be used to illustrate the performance of the surfactants. For example, certain amphoteric surfactants appear to be excellent foaming agents at extreme temperatures (up to ~130oC) when dissolved in high (~250000 ppm) total dissolved solids (TDS) brines, such as those found in Middle Eastern formations. With regard to nonionics, one can employ specific non-ionic surfactants that dissolve appreciably in CO2, but are even more brine-soluble. When a CO2-nonionic surfactant solution enters the formation, the surfactant will partition into the brine and stabilize the foam, thereby facilitating the continuous injection of a CO2-surfactant solution (GS process), or the alternate injection of brine and a CO2-surfactant solution (WAGS). To gain the greatest assurance that foams are generated in-situ, an operator could also inject surfactant in the brine phase and in the alternating CO2 slugs (SAGS). Finally, we will include an assessment of the CO2-soluble and brine-soluble “switchable” surfactants identified by Johnston and co-workers that exhibit a non-ionic to cationic transformation triggered by the carbonic acid that forms in the brine.