Texaco Inc.

Timothy N Tyler

Joseph T Carlin

Melvin E Mills, Jr

John A Wells

James W Ware

Jack H Park

Disclosed is a novel sulfated biopolymer, a method for synthesizing the sulfated biopolymer and an oil recovery method employing an aqueous fluid containing the material. The sulfated biopolymer is made by reacting polysaccharides with sulfuric acid in the presence of an aliphatic alcohol at a temperature of from 35.degree. to 75.degree. F., in order to avoid degradation of the polymer by the sulfuric acid. The polymer produces a viscous solution which is less prone to increasing viscosities as shear rate is decreased, which makes it especially suitable for use as a viscosifying polymer in a polymer flooding enhanced oil recovery process.

Sulfated biopolymers for use in recovering petroleum from a subterranean

Disclosed is an improved surfactant waterflooding enhanced oil recovery process employing a fluid containing as substantial in the only anionic surfactant, an ethoxylated and sulfated or ethoxylated and sulfonated surfactant. The degree of ethoxylation of the surfactant is determined by determining the degree of ethoxylation which produces the first inflection point in the electrical conductivity of a fluid as the degree of ethoxylation is increased from a value below that which causes solubility of the fluid in the aqueous environment in which it is tested to a value slightly greater than borderline solubility. Optimum results are obtained if the average degree of ethoxylation of the ethoxylated and sulfated or ethoxylated and sulfonated surfactant is from n-0.2 to n+0.1 and preferably from n-0.15 to n+0.05, where n is the degree of ethoxylation corresponding to the first inflection point in electrical conductivity.

Surfactant waterflooding enhanced oil recovery process

Disclosed is an oil recovery process for recovering oil from subterranean formations containing relatively high salinity water, said process employing an aqueous surfactant fluid containing at least two surfactants, one primary anionic surfactant such as petroleum sulfonate and a solubilizing cosurfactant such as an alkyl or alkylaryl, polyethoxy sulfate or sulfonate. The process comprises injecting a plurality of slugs of surfactant fluids followed by a low salinity fluid containing a viscosifying amount of a hydrophilic polymer. The salinity and concentration of solubilizing cosurfactant of each surfactant slug are both decreased from the maximum level in the first slug of the surfactant fluid and in successive slugs to a minimum level at the last slug of the surfactant fluid.

Double tapered surfactant waterflood oil recovery process

Disclosed is a novel aqueous surfactant-containing fluid suitable for use in surfactant flooding oil recovery processes, and an oil recovery process using the fluid. The fluid contains petroleum sulfonates alone or in combination with solubilizing co-surfactants such as ethoxylated alkyl or alkylaryl compounds, alkyl or alkylaryl polyethoxy sulfates, or alkyl or alkylaryl polyethoxy sulfonates. The petroleum sulfonate is a mixture of petroleum sulfonates of varying equivalent weights ranging from 250 to 700, with an average equivalent weight between 325 and 425 and preferably between 350 and 400. Additionally, the distribution of equivalent weights is relatively uniform, with from 40 to 70 percent being less than 400 and from 60 to 30 percent of the petroleum sulfonates having equivalent weights being 400 or greater; and preferably from 15 to 35 percent of the petroleum sulfonates having equivalent weights less than 350, and 30 to 50 percent having equivalent weights from 350 to less than 500 and from 10 to 40 percent of the petroleum sulfonates having equivalent weights of 500 and above. The especially preferred embodiment employs a mixture of petroleum sulfonates in which 5 to 15 percent have equivalent weights less than 300, from 25 to 50 percent have equivalent weights the range of from about 300 to less than 400, from 15 to 25 percent fall in the range of from about 400 to less than 500 and from 5 to 20 percent have equivalent weights greater than 500.

Surfactant flooding oil recovery process

In the recovery of oil from an oil-bearing formation having a high salinity connate water wherein an aqueous surfactant slug containing a commercially available petroleum sulfonate is injected followed by the injection of an aqueous drive agent, improved recovery is obtained, if a cosurfactant and a mono-unsaturated secondary alcohol are added to the surfactant slug.

Surfactant oil recovery process usable in a formation having high

Primary anionic surfactants such as organic sulfonates, specifically petroleum sulfonates as well as synthetic alkyl or alkylaryl sulfonates are effective for recovering oil from subterranean, oil-containing formations only if the salinity and/or concentration of divalent ions in the formation water is relatively low. Many petroleum formations contain water whose salinity is in excess of the tolerance level of organic sulfonates, and either the high salinity water must be displaced by a preflush or the primary anionic organic sulfonate surfactants must be used in conjunction with an effective solubilizing co-surfactant in order to increase the solubility of the organic sulfonate in the high salinity and/or hard water. Suitable solubilizing co-surfactants include ethoxylated alcohols, alkyl phenols, and alkyl or alkylaryl thiols, as well as sulfated or sulfonated, ethoxylated alcohols or alkyl phenols. Optimum performance in any particular field is achieved if the ratio of primary anionic surfactant to solubilizing co-surfactant is carefully chosen so the surfactant combination exhibits borderline solubility in the particular formation water in which the surfactants are to be employed. The concentration ratio of primary and solubilizing surfactants which results in the desired borderline solubility may be identified by preparing a number of samples in the formation water using different ratios of primary surfactant concentration to solubilizing co-surfactant concentration, measuring the electrical conductivity of the samples and choosing the concentration ratio corresponding to the sample which produced the minimum electrical conductivity, or at which point the conductivity vs. concentration ratio curve exhibited an inflection point.

Salinity tolerant surfactant oil recovery process

Disclosed is an aqueous, saline surfactant-containing fluid and an oil recovery process using the fluid for recovering oil from formations containing high salinity and/or high hardness water, the fluid comprising an anionic surfactant such as organic sulfonate especially petroleum sulfonates as well as synthetic alkyl or alkylaryl sulfonates and a solubilizing co-surfactants such as an ethoxylated alcohol, alkyl phenol, or alkyl or alkylaryl thiol, or sulfated or sulfonated, ethoxylated alcohols or alkyl phenols. Optimum performance in any particular field is achieved if the ratio of primary anionic surfactant to solubilizing co-surfactant is carefully chosen so the surfactant combination exhibits borderline solubility in the particular formation brine in which the surfactants are to be employed. The concentration ratio of primary and solubilizing surfactants which results in the desired borderline solubility may be identified by preparing a number of samples in the formation water using different weight ratios of primary surfactant to solubilizing co-surfactant concentration, and visually noting the minimum co-surfactant needed to avoid separation of the surfactant fluid into separate phases, or which gives the surfactant fluid a pearlescent, a swirl-silver appearance which is characteristic of fluids having the proper balance of primary anionic surfactant and solubilizing co-surfactant.

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Houston, TX, United States of America

Timothy N Tyler