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Abstract

A secondary oil recovery process is disclosed involving the injection of a polysaccharide polymer naturally produced by certain bacteria in a solubilized form into the oil sand or horizon. When such polymer is injected, it is solubilized in alkali solution such as sodium hydroxide. Within the formation, the polysaccharide polymer may be precipitated by the later injection of an acid solution or carbon dioxide. The order of injection of the acidic materials and the solubilized polymer is not critical, except with respect to carbon dioxide injection, which must follow the solubilized polymer injection. The gelling or the precipitation of polymer in the formation takes place preferentially in the higher permeability zones, such perhaps already wet with water. By such precipitation, the high permeability zones are selectively blocked off, giving sweep access primarily to the lower permeability zones containing mostly oil. The solubilized polymer may be used as a secondary recovery sweep liquid, per se. The solubilized precipitatable polymer solution may also be used as a consolidator (upon gelling or precipitation) of eroding or loose wellbores and such like oil sands surrounding wellbores. By alternating acidic solution/CO.sub.2 injection with further injection of basic solution or basic polymer solution the polymer body injected into the oil sand can be precipitated in a particular zone, thereafter resolubilized and then re-precipitated elsewhere and so forth. Sequential slugs of acid/solubilized polymer may be injected in any order.

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First Claim