Abstract: A system and method are provided for treating biodegradable waste material in a landfill by aerobic degradation. Waste material is deposited in the landfill and covered. The moisture content in the landfill is increased from about 40% to about 70% and a source of oxygen is injected into the landfill to drive and maintain primarily aerobic degradation of the waste material. The temperature in the landfill is increased to substantially eliminate pathogens from the waste material. The temperature in the landfill is controlled within a range of about 130.degree. F. to about 150.degree. F. to sustain the primarily aerobic degradation. Any combination of oxygen content, moisture content, and temperature in the landfill is monitored and varied to sustain and maintain the primarily aerobic degradation in the landfill.

Abstract: A method for carrying out a well treatment in a well (e.g. fracturing, sand control, etc.) wherein a high-viscosity treatment fluid containing a gel (e.g. a polymeric gelling agent) is flowed down the well along with a bacteria selected from the generic classes of Enterococcus and Corynebacterium or a mixture of the two, which is capable of digesting and/or cleaving the gel to reduce the viscosity of the gel at the conclusion of the well treatment.

Abstract: This invention relates to a deep remediation injection system for in-situ remediation of contaminated soil and ground water capable of progressive penetration both vertically and horizontally in contaminated soil and ground water having a soil penetrating lance for injecting air and oxygen and liquid with suspended biologicals into the contaminated soil as said soil penetrating lance is inserted for penetration in the soil, an air compressor for compressing air and delivering the air under pressure to the soil penetrating lance on one end, a liquid pump for pressurizing the liquid and suspended biologicals and delivering said liquid and suspended biologicals under pressure to the soil penetrating lance on one end, a gas connector control for connecting the gas compressor to the lance and for controlling the compressed gas flow, and a liquid connector means for connecting the liquid pump to the lance and controlling the pressurized liquids; and the method of developing a treatment grid both as to the depth of

Abstract: In a method of remediating contamination in soils of the vadose zone at least one injection well and at least one extraction well are established in the soil. Oxygen-containing gas such as air is injected into the injection well. A vacuum is applied to the extraction well for extracting the air together with volatile contaminants through the extraction well. The air and volatile contaminants are returned into the injection well. A biological medium containing microbes is continuously added to the air to be returned into the injection well for introducing the biological medium into the soil. The apparatus for remediating contamination in soils of the vadose zone includes at least one injection well and at least one extraction well to be placed in the soil. The apparatus has a device for injecting air into the injection well. A device for applying a vacuum to the extraction well for extracting the air together with volatile contaminants is provided.

Abstract: A method for introducing materials into a medium including creating passages in the medium with a blast of a pure preselected compressed gas that encourages activity of a preselected entity within or introduced into the medium and maintaining the passages with preselected materials for maintaining the passages.

Abstract: A process for remedying polluted soil which comprises the steps of injecting a liquid agent containing a microorganism into the polluted soil, and injecting a gas into a region wherein the water content of the soil became 0.6 or more times its saturation water content after the injection of the liquid agent. Using this method bioremediation of contaminated soil can be economically and efficiently carried out.

Abstract: The present invention relates to a method of removing contaminating hydrocarbons from regions which are subjected to extreme temperatures. The temperatures are generally outside the range of optimum growth of hydrocarbon-degrading microorganisms. The method can involve the steps of contacting the region with hydrocarbon-degrading microorganisms, and adjusting the temperature of the region contacted with the microorganisms to optimize their growth.

Abstract: An in situ thermally enhanced microbial remediation strategy and a method for the biodegradation of toxic petroleum fuel hydrocarbon and halogenated organic solvent contaminants. The method utilizes nonpathogenic, thermophilic bacteria for the thermal biodegradation of toxic and carcinogenic contaminants, such as benzene, toluene, ethylbenzene and xylenes, from fuel leaks and the chlorinated ethenes, such as trichloroethylene, chlorinated ethanes, such as 1,1,1-trichloroethane, and chlorinated methanes, such as chloroform, from past solvent cleaning practices. The method relies on and takes advantage of the pre-existing heated conditions and the array of delivery/recovery wells that are created and in place following primary subsurface contaminant volatilization efforts via thermal approaches, such as dynamic underground steam-electrical heating.

Abstract: A method used for in situ remediation of contaminated subsurface ground and subsurface water using chemically or biologically reactive sheets. The reactive or active sheets contain one or more selected compounds capable of recovering, destroying, degrading and immobilizing contaminants in the soil or water. The compounds that will be selected depends on the contaminants to be treated. The compound may be diatomaceaous earth pellets or other porous materials inoculated with selected non-pathogenic microbes, a zero-valent metal such as iron, tin, aluminum and zinc, a leachable compound such as sodium percarbonate or an adsorptive compound such as activated carbon and zeolite. The contaminants may be petroleum hydrocarbons, chlorinated hydrocarbons and other hazardous chemicals.

Abstract: A process for microbial remediation of soil polluted with a pollutant by introducing into the polluted soil a decomposing microorganism, a nutrient and/or an inducer necessary for the expression of a decomposing activity in the microorganism, wherein a coefficient of permeability of the polluted soil is controlled to be small and uniform so that the introduced substance may be uniformly distributed over a soil area to be remedied. Also a process for treating soil which comprises a step of controlling the coefficient of permeability of the soil so that a peak at the substantially smallest coefficient of permeability may comprise the largest percentage in the distribution of coefficient of permeability.

Abstract: There is provided a bio-remediation system and a method associated therewith for remediating a spilled hydrocarbon-based fluid from soil effectively and without causing migration of the fluid to previously uncontaminated areas. The bio-remediation system removes hydrocarbon-based fluid from a subterranean location using microbes which are immersed in a nutrient-rich medium. The microbes biologically remediate the hydrocarbon-based fluid by consuming the hydrocarbon-based fluid. The bio-remediation system ensures that the microbes and the nutrient-rich medium do not extend below the water table thus producing further contamination by monitoring moisture levels and levels of respiratory gases in the soil. When the microbes descend too deep, an air pump is actuated to dry a buffer zone between the water table and the spilled hydrocarbon-based fluid, thus halting progression of the microbes in the nutrient-rich medium.

Abstract: A method and apparatus for achieving in situ bioremediation of volatile contaminants in the vapor phase and dissolved or dispersed contaminants in the groundwater phase at a contaminated site. The apparatus of this invention is configured to be used within a remediation well of the type employed with vapor extraction and dewatering techniques, and serves to biologically treat soil contaminants in situ with microbes and any suitable microbial nutrients. As such, the present invention is adapted to be employed in conjunction with vapor extraction and dewatering remediation techniques to treat vapor and water-borne contaminants more effectively. The apparatus securely retains the microbes in a manner that serves to prevent leaching into the surrounding soil while simultaneously protecting the microbial population from predatory, competitive and inhibitory microorganisms.

Abstract: A system for in-situ bioremediation of contaminated soil and ground water wherein porous inorganic support spheres such as diatomaceous earth pellets are treated by inoculation with selected non-pathogenic microbes, ie. bacteria, for destroying or converting the contaminate. The contaminates may be hydrocarbons, sulphides, cyanides, nitrates, heavy metals and other chemicals. The porous cells of the diatomaceous earth pellets provide a home not only for the microbes but also for oxygen, water and other nutrients to help sustain the life of the augmented colonies of microbes introduced in the pellets. The contaminated soil is prepared for treatment by creating fractures and fissures therein using fluid pressure introduced through spaced apart holes drilled to selected depths. The depth of the drilled holes and the hole spacing will depend on the area of contamination.

Abstract: A method and apparatus are disclosed for reducing or eliminating non-naturally occurring, subsurface, liquid contaminants from one or more soil formations, which involves the steps of pneumatically fracturing the soil formation to produce a fracture network; simultaneously or subsequently inserting into said fracture network and throughout adjacent portions of the soil formation, a pressurized gas stream, and introducing into the pressurized gas stream a mixture of one or more liquid amendments, wherein said pressurized gas, in conjunction with said liquid amendments, has an oxygen or other electron acceptor content sufficient to promote the growth of aerobic or other microorganisms in said fracture network, and wherein the pressurized gas has a sufficiently high gas to liquid ratio to atomize the liquid amendments, whereby the amendments are distributed throughout the soil formation.

Abstract: An apparatus and method for delivery of remediation material to treat underground contaminated soils and water having a hollow cylindrical pipe through which both to apply water under air pressure and to deliver the remediation materials. Tanks of water, nutrients, and bacteria are typically mounted on the platform of a flat-bed truck or on a trailer which is transported by means of a hitch. A compressor is connected to the tanks of water, nutrients, and bacteria to provide pressurized air to create flow of water, nutrients, and bacteria from the tanks to the underground contaminated soils and water.

Abstract: Methods and apparatuses for removing contaminants. At least one injection well is drilled through the vadose zone to a depth below the water table defining the upper boundary of the aquifer. A plurality of venting wells or venting laterals are established to a depth above the water table sufficient to discourage fouling by contaminated water or condensate, and oxygenated substances are injected under pressure through the injection wells. Additional biochemical cleansing may occur at ground level prior to venting of contaminated air. Microbes natural to the contaminated site may be extracted, analyzed, fermented, and reintroduced to enhance biodegradation, and nutrients, food, or both, may be supplied to the microbial population to sustain high levels of degradation activity. Relatively pure liquid contaminant may be separated from other fluids, such as water.

Abstract: The use of a dextrin as the carbon source for achieving a complete nutrient medium capable of sustaining microbial activity in subterranean formations is disclosed.

Abstract: A novel process for sustaining microbial activity in subterranean formations which comprises introducing in addition to microbial nutrients, a sequestering anion. This process may include the sequential injection of sources of individual nutrient components which are deficient in said subterranean formation, whereby the injected phosphorus source is more readily transportable due to the presence of a sequestering agent in the formation.

Abstract: The present invention provides a process for sustaining microbial activity in subterranean formations which comprises introducing as a microbial nutrient, an organic phosphate, This process may include the sequential injection of sources of individual nutrient components which are deficient in said subterranean formation, whereby the injected phosphorus source is an organic phosphate.

Abstract: The novel heteropolysaccharide BM07, useful, e.g., as a thickening/stabilizing/suspending agent for a wide variety of industrial applications, is produced by fermenting a nutrient medium containing at least one source of assimilable carbon with a strain of Agrobacterium tumefaciens I-736, or recombinant or mutant thereof.

Abstract: The present invention provides a process for injecting microbial nutrients into a subterranean formation wherein microorganism are provided a phosphorus nutrient source, and said phosphorus nutrient source into said formation under acid conditions.

Abstract: A novel process for sustaining microbial activity in subterranean formations which comprises introducing as a microbial nutrient, a scale inhibitor. This process may include the sequential injection of sources of individual nutrient components which are deficient in said subterranean formation, whereby the injected phosphorus source is selected from the group consisting of an organic phosphate and an organic phosphonate.

Abstract: A novel process for sustaining microbial activity in subterranean formations which comprises introducing as a microbial nutrient, a phosphite salt. This process may include the sequential injection of sources of individual nutrient components which are deficient in said subterranean formation, whereby the injected phosphorus source is selected from the group consisting of a phosphite salt and a phosphorous acid.

Abstract: A method for simultaneously heating the subsurface and imaging the effects of the heating. This method combines the use of tomographic imaging (electrical resistance tomography or ERT) to image electrical resistivity distribution underground, with joule heating by electrical currents injected in the ground. A potential distribution is established on a series of buried electrodes resulting in energy deposition underground which is a function of the resistivity and injection current density. Measurement of the voltages and currents also permits a tomographic reconstruction of the resistivity distribution. Using this tomographic information, the current injection pattern on the driving electrodes can be adjusted to change the current density distribution and thus optimize the heating. As the heating changes conditions, the applied current pattern can be repeatedly adjusted (based on updated resistivity tomographs) to affect real time control of the heating.

Abstract: The invention relates to an improved method for injecting and transporting small particles in a natural porous medium. The method is characterized in that, in a first step, the porous medium is conditioned by means of an aqueous solution containing a hydrocarbonaceous compound, polymers or surface-active agents, in a second step, a plug of suspended particles is injected in the aqueous medium containing at least one hydrocarbonaceous compound, polymer or surface-active agent and, in a third step, the plug of particles is pushed by an appropriate aqueous medium. The method is particularly useful for implantation of bacteria in a porous medium.

Abstract: This invention relates to the preparation of new, modified organisms, through challenge growth processes, that are viable in the extreme temperature, pressure and pH conditions and salt concentrations of an oil reservoir and that are suitable for use in microbial enhanced oil recovery. The modified microorganisms of the present invention are used to enhance oil recovery and remove sulfur compounds and metals from the crude oil.

Abstract: Disclosed is a process for improved removal of contaminants including oily wastes and other organic hydrocarbonaceous materials from ground waters and areas adjacent to or in the vicinity of ground water locations. Ground and ground water contamination due to its unique nature, as being below ground and often not readily removable, has presented unique challenges to efforts seeking to render contaminated sites safe for habitation and/or contain and prevent contaminants to other, non-contaminated areas. The present process presents a viable solution to the problem of removing hydrocarbonaceous contaminating materials from ground and ground water. The process includes the use of at least two injection wells and at least one extraction well. One of the injection wells is being used for introduction of steam into a subsurface saturated zone.

Abstract: Methods and apparatuses for removing contaminants. A plurality of injection wells are drilled through the vadose zone to a depth below the water table defining the upper boundary of the aquifer. A plurality of venting wells or venting laterals are established to a depth above the water table sufficient to discourage fouling by contaminated water or condensate, and oxygenated gas is injected under pressure through the injection wells. Additional biochemical cleansing may occur at ground level prior to venting of contaminated air. Microbes natural to the contaminated site may be extracted, analyzed, fermented, and reintroduced to enhance biodegradation, and nutrients, food, or both, may be supplied to the microbial population to sustain high levels of degradation activity. Relatively pure liquid contaminant may be separated from other fluids, such as water.

Abstract: Methods are provided for remediating subsurface areas contaminated by toxic organic compounds. An innocuous oil, such as vegetable oil, mineral oil, or other immiscible organic liquid, is introduced into the contaminated area and permitted to move therethrough. The oil concentrates or strips the organic contaminants, such that the concentration of the contaminants is reduced and such contaminants are available to be either pumped out of the subsurface area or metabolized by microorganisms. Microorganisms may be introduced into the contaminated area to effect bioremediation of the contamination. The methods may be adapted to deliver microorganisms, enzymes, nutrients and electron donors to subsurface zones contaminated by nitrate in order to stimulate or enhance denitrification.

Abstract: J-1 which is a strain of cyanobacteria is used to form and excrete a material useful as an emulsifying agent for forming emulsions of hydrocarbons and oils in liquids such as water.Method of separating and culturing the cyanobacteria under conditions necessary to achieve a maximum formation and excretion of the emulsifying agent into solution.Method of purifying and separating excreted as well as intracellular material from cyanobacteria.Method of removing stains with a material excreted by cyanobacteria, and particularly strain J-1.Method of effecting the secondary recovery of petroleum through the use of a material excreted by cyanobacteria, and particularly strain J-1.Extracellular polymeric material which is greater than 200,000 Daltons in molecular weight, and contains sugar, fatty acid, and protein moieties, and amide, carboxylic and amino groups.

Abstract: A variant strain of Agrobacter radiobacter has been found to produce a unique heteropolysaccharide containing D-galactose, D-glucose and pyruvic acid in approximate molar ratios of 2:15:2 in a seventeen member repeat unit having the structure shown below, wherein Glc represents D-glucose, Gal represents D-galactose and Pyr represents pyruvic acid, with the numerals indicating the positions of linkage in these ring structures. The heteropolysaccharide is useful in mobility control in oil reservoir formations, especially when crosslinked with trivalent metal cations (Cr.sup.3+, Al.sup.3+, Fe.sup.3+ or Ti.sup.3+) to form a gel which preferentially fills high permeability zones in such reservoirs.

Abstract: Methods and apparatuses for removing contaminants from soil and an associated subsurface groundwater aquifer. An injection well(s) is drilled through the vadose zone to a depth below the water table defining the upper boundary of the aquifer. An extraction well is established to a depth above the water table. Oxygenated gas is injected under pressure through the injection well while a vacuum is applied to the extraction well. Contaminants are removed from the groundwater aquifer and from the vadose zone by a combination of physical, chemical, and biochemical processes. Additional biochemical cleansing may occur at ground level prior to venting of extracted, contaminated air. Relatively pure liquid contaminant may be extracted simultaneously with cleansing of the soil above the aquifer. Microbes natural to the contaminated site are extracted, analyzed, fermented, and reintroduced to enhance biodegradation.

Abstract: An improved gravel packing process is provided in which a gravel pack slurry is thickened with succinoglycan and the slurry further comprises an amount of breaker effective to result in 80 percent settlement of sand from the slurry after a time period larger than about one hour and shorter than about three hours.

Abstract: A microbial system is provided for selective plugging of permeable regions of a subterranean formation, for use in conjunction with injection of surfactant-containing foams. Bacteria indigenous to the target formation are isolated, and selected for ability to degrade the surfactant of interest. Small, non-adherent ultramicrobacteria, or UMB, are prepared from the selected culture by starvation. The UMB and the surfactant-containing foam are then injected into the target formation. The surfactant allows the foam to penetrate into the formation. The UMB then revive to their vegetative state, degrade the surfactant and produce exopolymer, thus plugging the formation.

Abstract: A method of microbial enhanced oil recovery for recovering oil from an oil-bearing rock formation. A population of aerobic bacteria is introduced into the formation at a position spaced from a production borehole. The micro-organisms are adapted to use oil as a carbon source. Pressurised injection water is introduced into the formation via an injection borehole, the water including a source of oxygen and mineral nutrients. The bacteria multiply using the oil as their main carbon source and the oxygen in the injection water as their main oxygen source. In so doing, they dissociate the oil from the rock formation and the dissociated oil is removed via the production borehole by the injection water.

Abstract: A process is provided for reducing the porosity/permeability of a subsurface geological formation. The process generally involves the precipitation of minerals from an aqueous system. The minerals are precipitated in the presence of microorganisms. The process may be suitably utilized to enhance the recovery of oil from oil reservoirs or to control the flow of a spilled contaminant in a reservoir.

Abstract: A system and method for establishing, maintaining or enhancing microorganisms utilized to remediate contaminated soil or groundwater which includes of a direct push rod or cylinder equipped with a fluid or gas delivery system. The system also includes computer-based monitoring capabilities which can monitor or control the subsurface events. Microorganisms, nutrient solutions, or gases such as air can be introduced into the subsurface environment of predetermined locations. The delivery device is a long rod or cylinder which is pushed into the ground via applied pressure at the surface. The internals of this device contain tubing or other means to deliver fluid through openings in the rod or cylinder to the surrounding environment. The fluid may be driven into the environment by surface pumps or gas pressure. The delivery rod or cylinder may be withdrawn for reutilization or left in place for continuous service.

Abstract: A process and device for decontamination of contaminated soil wherein contaminated soil is precleansed by a pressurized flushing and cutting jet of a cutting device located in a borehole. The soil is removed from the existing soil structure and flushed so intensely that is largely freed from adhering pollutants. The fine particles of the flushed and precleansed soil, together with the pollutants, are sluiced as a slurry in a return flow through a preventer. For decontamination, they are conveyed to a decontamination plant where the remaining pollutants are extracted. The coarse particles of soil remain in the ground. Finally, the cleansed soil, together with a bonding agent, is flushed back into the borehole where it forms a soil structure capable of bearing loads.

Abstract: The present invention provides a method of injecting nutrients into a subterranean formation in order to achieve a desired in-situ microbial objective. Sources of individual nutrient components which are deficient in the formation are sequentially injected so that a complete nutrient medium capable of sustaining substantial microbial activity is formed in the formation upon injection of the last of said sources. Said sources are preferably injected into the formation in order of decreasing quantitative formation retainability.

Abstract: This invention relates to a process for recovery of oil from oil reservoirs with assistance from microorganisms. More particularly, the present invention contemplates a method for recovering oil from a reservoir comprising increasing the population of endogenous microorganisms in said reservoir, said microorganisms having surface active properties, to a level sufficient to effect enhanced oil recovery.

Abstract: A method of microbial enhanced oil recovery includes introducing, into an underground carbonate-containing rock formation that defines an anaerobic environment, denitrifying microorganisms, water, and a source of nitrate ion. The microorganisms reduce the nitrate and produce sulfuric acid which dissolves the rock formation, releasing oil. The microorganisms can be denitrifying Thiobacilli, such as T. denitrificans.

Abstract: In treating oil well down hole bores, a method of treating subterranean formations by fracturing by utilization of a fluid loss additive (FLA) comprising starch or a mixture of natural and modified starches plus an enzyme which degrades the alpha linkage of starch and does not the degrade the beta linkage of guar and modified guar where used as a viscosity modifier. Natural/modified starches are utilized in a preferred ratio of 3:7 to 7:3 or 1:9 to 9:1 with optimum at 1:1, and the mix is used in the dry form for application from the surface down the bore hole.

Abstract: A method is provided for in situ decontamination of contaminated subsurface area by injection of steam into injection wells and withdrawing liquids and vapors from extraction wells under subatmospheric pressure whereby steam is passed through the contaminated area in an essentially horizontal direction. After a substantial portion of the contamination has been removed in this manner, the injection of steam is ceased, but the extraction at subatmospheric pressure is continued, to volatilize and remove the residual water and contaminants trapped in the pores of the soil. The steam injection may be periodically resumed to reheat the area and to replenish the water in the pores.

Abstract: The present invention is a process for in situ biodegradation of spilled hydrocarbons. The process involves drawing oxygen into a hydrocarbon contaminated zone. A borehole is drilled into the contaminated zone and gas is evacuated at high rates out of the borehole to thereby draw oxygen from the earth's surface and through the contaminated zone. Surprisingly, the carbon dioxide concentration in the evacuated gas remains high even at the high flow rates. The rate of gas evacuation in the present process is maintained sufficiently high so that the hydrocarbon biodegradation rate is within at least 50% of the maximum hydrocarbon biodegradation within the zone. The process can be applied to both porous and nonporous soils having relatively low water and gas permeability.

Abstract: Novel deacetylated polysaccharide biopolymers having improved viscosity/filtrability/injectability, well adopted for the secondary and tertiary recovery of oil deposits, are conveniently prepared by (i) acidifying an aqueous polysaccharide composition, e.g., a carbohydrate fermentation broth, with nitric acid to a pH of from about 2 to 0.1, (ii) heat-treating said acidified composition at a temperature of from about 50.degree. to 100.degree. C. for from about 5 to 60 minutes, and (iii) cooling said heat-treated composition and adjusting the pH thereof to a value of from about 5 to 7.

Abstract: This invention relates to a process for recovery of oil from oil reservoirs with assistance from microorganisms. More particularly, the present invention contemplates a method for recovering oil from a reservoir comprising increasing the population of endogenous microorganisms in said reservoir, said microorganisms having surface active properties, to a level sufficient to effect enhanced oil recovery.

Abstract: The present invention is a phosphate compound for use in a bacterial nutrient medium. The medium is injected downhole in a petroleum formation along with a bacteria (or its spore) and provides the bacteria with growth nutrients. The nutrient solution contains a phosphate compound which: will not precipitate out of solution under ambient conditions; will chelate alkaline earth, rare earth, transition and heavy metal ions; and provide a nutrient source for the bacteria.

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.

Abstract: A method is provided for microbial enhanced oil recovery, wherein a combination of microorganisms is empirically formulated based on survivability under reservoir conditions and oil recovery efficiency, such that injection of the microbial combination may be made, in the presence of essentially only nutrient solution, directly into an injection well of an oil bearing reservoir having oil present at waterflood residual oil saturation concentration. The microbial combination is capable of displacing residual oil from reservoir rock, which oil may be recovered by waterflooding without causing plugging of the reservoir rock. Further, the microorganisms are capable of being transported through the pores of the reservoir rock between said injection well and associated production wells, during waterflooding, which results in a larger area of the reservoir being covered by the oil-mobilizing microorganisms.

Abstract: Process for treating a xanthan gum in order to improve the filterability of its aqueous solutions, comprising an enzymatic treatment of an aqueous solution of xanthan gum containing, as dissolved salts, a proportion of alkali and/or alkaline-earth metals of at least 10.sup.-2 equivalent/liter, said treatment being performed by means of two enzyme extracts of different types, a so-called PG enzyme having as main activity a polygalacturonase activity and a so-called P enzyme extract whose main activity is a protease activity, in conditions compatible with the activity of said enzyme extracts. The obtained xanthan gum powder or solution can be used as enhanced oil recovery agent.