Patent Application: US-55378906-A

Abstract:
a controlled - gelation aqueous solution is proposed . the solution contains a hydrophobically - aggregating gelling agent , and an effective amount of an inhibitor which suppresses hydrophobic aggregation of the gelling agent . the inhibitor is soluble in water so that when the controlled - gelation aqueous solution contacts aqueous media the inhibitor disperses and gelation occurs . however , the inhibitor is substantially insoluble in hydrocarbons so that when the controlled - gelation aqueous solution contacts hydrocarbon media the inhibitor continues to suppress said hydrophobic aggregation and gelation is suppressed . the solution may be used to control the flow of water into oil wells , making it possible to reduce the water cut .

Description:
in order for the physical gel formed by the controlled - gelation solution of the present invention to have sufficient mechanical properties , hydrophobically modified polymers may be used as the gelling agent . in one embodiment these polymers are water - soluble co - polymers comprising hydrophilic and hydrophobic monomer units . the hydrophobically modified polymers should comprise a sufficient amount of groups with pronounced hydrophobic properties , which groups are capable of providing reliable cross - linkage of the polymer chains by forming hydrophobic aggregates , or complexes of such hydrophobically associating polymers with a surfactant . one of the possible types of hydrophobically modified polymers is based on polyacrylamide and has the following formula : wherein r is a c 5 - 20 ( preferably c 7 - 15 ) saturated or unsaturated aliphatic alkyl group , x is — o — or — nh —, and y is — h or — ch 3 . typically r is saturated . typically r is linear . in one embodiment , r is a —( ch 2 ) n ch 3 group where n is 8 or 11 . x may be in the range 0 . 5 to 5 ( preferably 1 to 3 ), and y may be in the range 2 to 25 ( preferably 5 to 15 ). the “ x ” monomer unit is hydrophobic and the “ y ” monomer unit is hydrophilic . q is a group which forms charged species in aqueous solution . for example , q may be a carboxylate , sulphate , sulphonate , monophosphate , monophosphonate , xanthate , or ammonium group . the group may be in the form of a salt or the corresponding acid / base . the ammonium group may be primary , secondary , tertiary or quaternary ammonium group . in one embodiment q is a — coona group , although the na atom can be replaced by a hydrogen atom , a different alkali metal , such as k , or any other suitable cation - forming species . r ′ links q to the polymer backbone chain . r ′ may be a covalent bond or a relatively small organic ( preferably hydrocarbyl ) group , e . g . one containing 1 , 2 , 3 , 4 or 5 carbon atoms . preferably r ′ is a covalent bond . however , in one embodiment , r ′ is a — nh — c ( ch 3 ) 2 — ch 2 — group , with the — nh — group being connected to the polymer backbone chain and the — ch 2 — group being connected to q which is e . g . a sulphonate group . the proposed associating gelling liquid ( which may be a controlled - gelation aqueous solution ) and method for selectively inhibiting gelation of the gelling liquid may be used for the selective blocking of the inflow of water into an oil - producing well from subterranean water - bearing formations while maintaining the flow of oil unchanged . the inhibitor makes it possible to suppress hydrophobic association which is responsible for gelation . therefore , prior to and as the liquid is pumped into the well , the viscosity of the liquid is insignificant , which facilitates handling and placement of the liquid . furthermore , the presence of the inhibitor in the gelling liquid can improve the wettability of the liquid with downhole formations , which promotes more effective penetration of the liquid into the “ working section ” of the oil producing well . after a period of time , the liquid forms blocking gel plugs at those places in the well where the liquid is in contact with aqueous media . however , at places of contact between the liquid and oil , gelation continues to be suppressed by the inhibitor and gel plugs are not formed . 0 . 2 g of terpolymer i comprising 84 . 4 mol . % of acrylamide , 1 . 5 mol . % of n - dodecylacrylamide and 14 . 1 mol . % of sodium acrylate , synthesized by the method of micellar polymerization with a concentration of sodium dodecylsulfate of 1 . 5 wt . % and a total concentration of the monomers of 3 . 0 wt . %, was dissolved in 10 ml of a mixture of ethanol ( 60 vol . %) and water ( 40 vol . %) with continuous stirring for 2 hours . in order to model the contact of the polymer solution with formation water , 1 ml of the ready polymer solution was added to 20 ml of an aqueous salt solution containing 30 g / l of sodium chloride and 3 g / l of calcium chloride . in order to model the contact with oil , 1 ml of the polymer solution was added to 20 ml of n - heptane . after two weeks the frequency relationships of the complex modulus of elasticity of the polymer solutions in contact with the aqueous salt solution and the n - heptane were measured . these are presented in fig1 and fig2 . for the sample in contact with water , the modulus of elasticity in the frequency range of from 0 . 01 to 10 hz was higher than the modulus of losses , i . e ., the sample was a physical gel . in contrast , for the sample in contact with the n - heptane , the modulus of elasticity in the frequency range of from 0 . 01 to 10 hz was lower than the modulus of losses , i . e ., in this sample gelation did not take place . the values of the modulus of elasticity measured at a frequency of 0 . 1 hz , and also the viscosity of the initial polymer solution , are presented in table 1 . 0 . 060 g of terpolymer i ( composition as defined in example 1 ) was dissolved in 3 . 8 ml of a mixture of methanol ( 53 vol . %) and water ( 47 vol . %). the change of the rheological properties of the solution upon contact with an aqueous salt solution and n - heptane was studied in the same way as described above in relation to example 1 . the measurement data are presented in table 1 . 0 . 3 g of terpolymer ii comprising 88 . 8 mol . % of acrylamide , 1 . 5 mol . % of n - dodecylacrylamide and 9 . 7 mol . % of sodium acrylate , synthesized by the method of micellar polymerization with a concentration of sodium dodecylsulfate of 3 . 0 wt . % and a total concentration of the monomers of 3 . 0 wt . %, was dissolved in 10 ml of a mixture of ethanol ( 40 vol . %) and water ( 60 vol . %) with continuous stirring for 2 hours . the change of the rheological properties of the solution upon contact with an aqueous salt solution and n - heptane was studied in the same way as described above in relation to example 1 . the measurement data are presented in table 1 . a gelling mixture based on terpolymer i was prepared as described in example 1 , with the exception that 70 μl of a 0 . 020 mol / l aqueous solution of the surfactant cetylpyridinium chloride was additionally added to 4 ml of the mixture . the change of the rheological properties of the solution upon contact with an aqueous salt solution and n - heptane was studied in the same way as described above in relation to example 1 . the measurement data are presented in table 1 . thus , similar results ( the formation of a physical gel upon contact with water and the absence of gelation contact with n - heptane ) are obtained for different hydrophobically modified polymers , and also for hydrophobically modified polymer / surfactant complexes , in the presence of different inhibitors . while the invention has been described in conjunction with the exemplary embodiments described above , many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure . accordingly , the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting . various changes to the described embodiments may be made without departing from the spirit and scope of the invention . 1 . bailley b ., crabtree m ., tyrie j ., elphick j ., kuchuk f ., romano c ., roodhart l ., water control . in oilfield review , spring 2000 , pp . 30 - 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