Oil and Gas

Biography

Biography: Robert Enick

Abstract

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.