CO2 Mobility Control

As early as 1955, surfactants were recognized for their effectiveness in lowering gas mobility in reservoir cores by in-situ foam generation. For commercial field application a specific surfactant must have several important characteristics. It must be (1) highly effective with low cost, (2) chemically stable, soluble, and surface active in oilfield brines, and (3) unaffected by contact with crude oil or reservoir minerals. A static foam generator, an adaptation of a conventional blender, was used to screen more than 150 candidate surfactants. Promising additives were then ranked in a unique dynamic test, developed at New Mexico State U., that involves sequential liquid/gas flow in a vertical tube packed with glass beads. Conventional flow tests in tight, unconsolidated sandpacks show good correlation with the dynamic and static screening tests, especially those data obtained in the dynamic experiment. Some synergism exists between additives with amine oxides and amides having the most beneficial effect on foam stability and gas mobility control. The utility of cosurfactant stabilization was demonstrated in linear, two-phase flow tests through tight, unconsolidated sandpacks involving brine and gas. A solution containing 0.45% Alipal CD-128 /SUP TM/ and 0.05% Monamid 150-AD /SUP TM/ can decrease gas mobility over 100-fold. The effectmore » appears to be time independent, indicative of good foam stability. Alipal CD-128 alone reduces gas mobility even more, usually by a factor of two. The moderating influence of a cosurfactant could be beneficial in avoiding ''overcontrol'' of mobility, especially in low-permeability reservoirs.« less