Abstract: A process for recovering viscous heavy oil from a substantially shallow reservoir having a low temperature and pressure. Following a steam flood, liquid carbon dioxide is injected into the reservoir where said carbon dioxide remains in its liquid state. Afterwards, a spacer volume of a vaporizable drive fluid is injected into the reservoir behind said carbon dioxide. Subsequently, steam injection is commenced which causes the drive fluid to vaporize and the liquid carbon dioxide to gasify. Vaporization of the drive fluid along with gasification of the carbon dioxide causes a pressure increase in the formation allowing the thinned oil to be removed therefrom.

Abstract: A method for diverting steam injection in injection wells by the use of perforation ball sealers composed of polymer compounds covered with a thin coating of elastomer of low enough density to float in the injected fluids, yet able to stand the adverse temperatures of steam injection.

Abstract: A method for diverting CO.sub.2 injection in injection wells by the use of perforation ball sealers composed of polymer compounds covered with a thin coating of elastomer of low enough density to float in the injected fluids, yet able to stand the adverse temperatures of CO.sub.2 injection.

Abstract: The permeability of subterranean oil-bearing formations is selectively reduced by the injection into the formation of the non-xanthan, anionic heteropolysaccharide S-130 produced by fermentation with a microorganism of the Alcaligenes species. The polymer forms shear-thinning, viscous solutions which selectively enter the more highly permeable regions of the formation and form a gel plug in them to reduce their permeability. The polymer forms gels which are stable under a wide range of reservoir conditions including high temperatures.