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United States Patent 19 (11) 3,766,983 Chiu [45] Oct. 23, 1973

54 STABILIZED NON ONIC 3,648,770 3/1972 Dreher et al...... 166/275 THICKENED WATER OTHER PUBLICATIONS (75) Inventor: Ying-Chech Chiu, Houston, Tex. Allene Jeanes, “Composition and Properties of a 73 Assignee: Heteropolysaccharide Produced from Glucose by Shell Oil Company, Houston, Tex. Xanthomonas Campestris', Abstract of Papers, 136th 22 Filed: May 15, 1972 Meeting American Chemical Society, Sept. 13-18, 21) Appl. No.: 253,420 1959, page 7D. Primary Examiner-Marvin A. Champion (52) U.S. Cl...... 1661274, 166/270, 166/275, Assistant Examiner-Jack E. Ebel 166/305 R Attorney-H. W. Coryell et al. 51 Int. Cl...... E21b 43/16 58 Field of Search...... 166/244 D, 270, 274, 57 ABSTRACT 166/275, 300, 304 A reservoir oil displacing fluid that is relatively stable 56) References Cited toward multivalent metal ions comprises an aqueous liquid solution of a viscosity enhancing amount of a UNITED STATES PATENTS water soluble nonionic polysaccharide and an effec 3,371,710 311968 Harvey et al...... 166/274 3,508,612 4/1970 Reisberg et al...... 166/275 tive amount of a water soluble metal salt adapted to 3,532,166 10/1970 Williams...... clarify a calcium ion induced turbidity in that solution. ..., 166/275 3,581,824 6, 1971 Hurd...... a - - 166/270 4 Claims, No Drawings 3,766,983 1. 2 STABILIZED NONIONIC POLYSACCHARIDE solution that contains a viscosity enhancing amount of THICKENED WATER a water soluble nonionic polysaccharide, has a rela tively low calcium ion concentration, preferably one of BACKGROUND OF THE INVENTION less than about 360 parts per million, and contains an This invention relates to a well treating process or oil 5 effective amount of a water soluble metal salt capable recovery process in which a relatively viscous aqueous of clarifying a calcium ion induced turbidity in an aque liquid is injected into a subterranean reservoir to dis ous solution of that polysaccharide, and (3) displacing place oil within the reservoir. More particularly, the in the viscosity enhanced aqueous solution through the vention relates to a nonionic polysaccharide (or biopol reservoir to displace the oil. ymer) thickened water which is stabilized against the 10 In certain situations, some or all of the above fluid in viscosity altering effects of the multivalent metal ion jecting steps can be accomplished by injecting a single containing waters that are apt to be encountered in fluid. For example, where the calcium ion concentra such reservoirs. tion of the reservoir water is not excessive and/or the Prior well treating processes or oil recovery pro distance by which the oil is to be displaced is too short cesses have used various natural or synthetic ionic 15 to cause a significant increase in the calcium ion con polymers as water thickeners or viscosity enhancing tent of an aqueous liquid being displaced through the agents. The natural ionic polymers are typified by the reservoir for that distance, no fluid need be injected in polysaccharide B-1459, produced by fermenting a order to effect the step 1 adjustment of the reservoir sugar with a of the Xanthomonas campestris water calcium ion concentration. The calcium ion con NRRL B-1459. Such an ionic polysaccharide contains 20 centration of the portion of the reservoir through which dextroglucose, detromannose and dextroglucuronic the oil is to be displaced is preferably kept below about acid groups along with a significant proportion of ace 1,000 parts per million. Where the distance by which tic acid (in the form of acetyl groups) and pyruvic acid the reservoir oil is to be displaced is relatively short (for (attached through ketal linkages). example, in a well treatment operation for removing a Although the previously used natural ionic polysac 25 water injectivity-impeding concentration of residual oil charide water thickeners are advantageous relative to from around an injection well) the step 3 displacement synthetic ionic polymer water thickeners (in having a of the viscosity enhanced aqueous solution can be ef relatively high thickening efficiency, being relatively fected by simply injecting more of that solution. Thus, stable under reservoir conditions, and being producible in certain situations, all 3 stpes can be effected by sim at lower cost) they tend to agglomerate and form reser 30 ply injecting the specified viscosity enhanced aqueous voir plugging materials when they are mixed with aque solution until the oil has been displaced. ous liquids containing multivalent ions (such as the al Nonionic suitable for use in this in kaline earth metal ions that are commonly present in vention comprise those characterized by a multiplicity waters encountered in subterranean reservoirs). For of D-glucose units attached together in a straight chain example, in U.S. Pat. No. 3,581,824, the agglomerating 35 through beta-1,3 linkages. Such polysaccharides are tendency of an ionic polysaccharide, such as the poly produced when the appropriate molds are incubated in saccharide B-1459, is utilized to selectively plug the a medium containing source materials. most permeable zones in a reservoir being water Suitable polysaccharides and method for their produc flooded. The plugging is effected by preceding an injec tion are described in U. S. Pat. No. 3,301,848. Suitable tion of an aqueous solution of such a polysaccharide by 40 nonionic polysaccharides are commercially available an injection of an aqueous liquid having a relatively under the trade name Polytran from the Pillsbury Com high concentration of divalention. pany. A particularly suitable material comprises Poly tran-FS in the form of a water solution containing SUMMARY OF THE INVENTION about 0.3 to 0.4 percent by weight of the polysaccha This invention relates to a reservoir oil displacing 45 ride. fluid that is relatively stable toward multivalent metal The nonionic polysaccharides are chemically distinct ions and a use of such a fluid to displace oil within a from the ionic polysaccharides (particularly because of subterranean reservoir. The present oil displacing fluid the absence of any anionic carboxyl groups). In gen comprises an aqueous liquid solution containing a vis eral, the nonionic polysaccharide solutions tend to be cosity enhancing amount of a water soluble nonionic 50 strongly pseudoplastic and have viscosities which are polysaccharide and an effective amount of a water sol relatively free of fatigue or hysterisis when subjected to uble metal salt that is capable of clarifying a calcium varying degrees of shear. They also have viscosities ion induced turbidity in that solution (i.e. the specified which are relatively pH and salt insensitive and un aqueous solution of the specified poly-saccharide). dergo no apparent viscosity decrease with temperature The oil displacing process of this invention comprises 55 up to about 400°F. the steps of: (1) injecting an aqueous liquid of low cal In general, in displacing an oil within a subterranean cium ion content, preferably one containing less than reservoir formation by injecting a viscosity enhanced about 360 parts per million calcium ion, into a portion aqueous solution, the effective viscosity (or reciprocal of the reservoir through which oil is to be displaced, of the mobility within the reservoir) should be at least with said injection being continued to the extent re 60 substantially equal to and perferably greater than that quired to reduce the calcium ion concentration of the of the reservoir oil and/or any oil displacing liquid aqueous liquid in that portion of the reservoir to less (such as an aqueous or oil external sur-factant system) than one which could impart a significantly high cal that is injected ahead of the viscosity enhanced solu cium ion concentration, e.g. one greater than about 65 tion. In the present process, the concentration of the 1,000 parts per million, to slug of water which is dis nonionic polysaccharide should be in the order of from placed through that portion of the reservoir, (2) inject about 100 to 1,000 parts by weight of polysaccharide ing into the same portion of the reservoir an aqueous per million parts by weight of solution. Such a concen 3,766,983 3 4. tration provides viscosities in the order of from about Table 1 2 to 50 centipoises at room temperature in water con EFFECT OF ADDING SALT ON POLY TRAN-FS taining about 4,000 ppm total solid. Such viscosities are SOLUTION usually sufficient to provide effective displacements of 5 a reservoir oil. Wiscos- Ge. Although an aqueous solution of a nonionic polysac Total ity, cp Formation Amount (6 pm, Turbidity (after charide is generally salt insensitive, it tends to become of Salt too pH (Visual aging ppm temp.) Obser- OW turbid when mixed with more than about 20 parts per vation night) million of calcium ion. Such a turbidity can be removed 10 by filtration, for example, through a 5 micron millipore O 69.5 4. O O 250 ZnCl, 4.3 2.4 O 8 filter. However, such a filtration requires additional 250 MgCl, 42.6 2.5 O time and expense and causes the viscosity of the aque 50 CaCl, 43.2 2.9 turbid $8 250 FeSO, 44.0 2.2 0 & ous solution to be descreased, particularly when the 250 BaCl, 47.6 4.2 0 salt concentration of the solution is relatively high. 15 12,000 NaCl - 0 The nonionic polysaccharides are uniquely affected * After the addition of salt solution, the total volume increased by 25 by calcium ions. Although ionic polysaccharide solu percent. tions (e.g., Kelzan-M; a form of polysaccharide B-1459 that is commercially available from the Kelco Com The data in Table 2 shows the calcium induced tur pany) are generally more reactive with multivalent 20 bidity reducing effects of adding various metals to a so metal ions, the turbidity of a nonionic polysaccharide lution of about 900 parts per million Polytran-FS and solution (e.g. Polytran-FS) is greater in a synthesized about 100 parts per million calcium chloride in water. reservoir formation water. The synthesized formation Note that the test results indicate three categories of water is an aqueous solution containing the following effectiveness: (1) metals, such as the trivalent metals, 25 which remove the turbidity in a few minutes at room metal ions in about the following concentration (in temperature, (2) metals which remove the turbidity parts per million): sodium, 2,000 parts; chloride, 4,600 after a brief heating at 70°C, and (3) metals which pro parts; calcium, 360 parts; magnesium, 180 parts; and vide some turbidity reduction but do not produce any barium 90 parts. In that water, the turbidity of the non additional effect on prolonged heating at 70°C. ionic polysaccharide solution is about 3 to 5 times that 30 of the ionic polysaccharide solution. Table 2 The present invention is at least in part based on a EFFECT OF ADDING ELECTROLYTE ON discovery that an aqueous solution of a viscosity en CLARIFYING POLY TRAN-FS SOLUTION hancing amount of a nonionic polysaccharide can be 35 Turbid- Turbidity Ge. stabilized against the formation of calcium induced tur ity (after Formation bidity by incorporating in the solution an effective Total Amount (at heating at 70°C (after of Titrant OO for certain aging amount of a water soluble metal salt that is capable of ppm temp.) time) Wet clarifying such a calcium induced turbidity. It was night found that (1) the turbidity clarifying or preventing 40 O 60 60 (100 min) O phenomena is indicative of an involvement of both the 50 FeCl, O --- 6 charge on the metal ions and the specific chemical 50 Al(NO) O w 8 180 FeSO, O s properties of those ions, (2) the existence of a signifi 250 ZnCl 6 O (2 min) 250 MgCl, 14 0 (2 min) cant amount of such a capability in a given metal is in 250 Cr(NO).9HO 26 0 (5 min) & dicated by its capability of clarifying or reducing a cal 45 14,000 NaCl 26 28 (100 min) 8& cium induced turbidity in a water solution of the poly 250 BaCl, 35 33 (100 min) 8& saccharide at least in response to a relatively short time heating at a relatively mild temperature, and (3) the ex The data in Table 3 shows the effects of adding triva istence of an outstanding amount of such a capability lent cations to a Polytran-FS solution containing about in a given metal is indicated by such a turbidity clarifi 50 900 parts per million of the polysaccharide and the fol cation within a few minutes at room temperature. lowing amounts (in parts per million) of the following The data in Table 1 shows the effects of various prop metal ions: 1000 parts sodium; 2300 parts chloride; erties of any various metal ions on a solution of about 180 parts calcium; 90 parts magnesium; and 45 parts 900 parts per million Polytran-FS in water (at which barium. The tested solutions which were clarified by concentration the solution viscosity is about equal to 55 solutions of 17 parts per million ferric ion (50 parts per that provided by 1500 parts per million Kelzan M in million ferric chloride) and 10 parts per million alumi water ). The metal ions were added by dropwise addi nun (80 parts per million aluminum nitrate) were fur ther tested by additions of several hundred parts per tions of water solutions containing about 1000 parts million of calcium chloride. The so-tested solutions re per million of the indicated metal salts. The results of 60 such tests are indicative of the relative immunity of mained clear. aqueous solutions of nonionic polysaccharides to rela Table 3 tively large amounts of multivalent metal ions other EFFECT OF ADDING TRIVALENT CATIONS ON than calcium ions. Note that no gellation occured - POLY TRAN-FS SOLUTION not even after aging over night - in any of the indi cated multivalent metal containing solutions of this Gel nonionic polysaccharide. Total Viscosity Formation Amount (6 rpm, (after 3,766,983 S 6 of Titrant room temp.) pH Turbidity aging of the salt concentration of the water that is present in night)Over the portion of the reservoir through which the oil is to O 54.0 4.3 28 O be displaced. Such a determination can be made by 50 ppm FeCl 51.2 3, O sampling and analyzing a portion of the reservoir fluid, 80 ppm Cr(NO). 9HO 49.3 3.6 turbid or can be based on information obtained from prior op 80 ppm Cr(NO). erations and/or equivalent operations in the same or 9H,O other reservoirs. Where the combination of the con (after heating at 70°C) 48.2 3.5 O s 80 ppm Al(NO) 49.0 2.8 0 s centration of calcium ions in the water in that portion of the reservoir and the amount of distance by which O the oil is to be displaced within the reservoir (and thus In order to determine whether the clarifying effect the distance by which the frontal portion of the slug of could be obtained by a change in pH, a turbid solution the present oil displacing liquid is to be displaced of polysaccharide in multivalent metal-containing through the reservoir) is such that the displacement water (the type used in Table 3) was titrated with a one will significantly increase the calcium ion concentra molar solution of hydrochloric acid. The titration grad 5 tion of the present oil-displacing liquid, the injection of ually lowered the pH of the solution from an initial the present oil displacing liquid should be preceded by value of 4.3 to a final value of 2.3, involving an addition an injection of an aqueous solution having a relatively of 1700 parts per million of hydrochloric acid. low calcium ion concentration, in order to prevent such Throughout the titration, the turbidity of the solution a calcium ion buildup. Such an aqueous solution can be remained unchanged. Heating of the titrated turbid so substantially any aqueous solution of substantially inert lution at 70 and also at 100 for a relatively long time salts. It is preferably an aqueous solution containing did not clear up the turbidity. It is thus apparent that less than about 7,000 parts per million total dissolved the relatively specific effect of calcium ion on inducing salt. turbidity in a nonionic polysaccharide solution is not What is claimed is: significantly effected by the pH of the solution. 25 In general, the oil displacing liquids of the present in 1. In a process for displacing oil within a subterra vention can advantageously be used in oil displacing nean reservoir by injecting a viscosity enhanced aque operations and/or oil recovery operations in conjunc ous liquid into the reservoir, the improvement compris tion with substantially any of the conventionally used ing: water-flooding additives and/or supplemental materi 30 injecting aqueous liquid having a relatively low con als, such as: surface active systems or components; sac centration of parts per million calcium ions into the rifically absorbed solutes, such as carbonates, poly reservoir to the extent required to reduce the cal phosphates, or the like; pH adjusting materials, etc. cium ion concentration of the aqueous liquid in the The liquids of the present invention are particularly reservoir portion through which the oil is to be dis useful in a chemical flood oil recovery process in which 35 placed to not more than about 1,000 parts per mil a slug of surfactant system is injected ahead of (or its lion; surfactant components are dissolved in) a portion of injecting an aqueous solution of a viscosity enhancing the present oil displacing liquid. As used herein, the amount of a water soluble nonionic polysaccharide term "oil displacing liquid' or "the displacing of oil' that has a relatively low calcium ion concentration within a reservoir refers to such an operation where the 40 and contains an effective amount of a water soluble oil being displaced is contacted by either the oil dis metal salt that is capable of clarifying a calcium ion placing liquid or a surfactant that contains or precedes induced turbidity in an aqueous solution of the such a liquid. polysaccharide; and The calcium ion content of the present oil displacing displacing said polysaccharide-containing aqueous liquid is preferably kept below about 360 parts per mil 45 solution through the portion of the reservoir to lion while the total dissolved salt concentration is pref which the oil is to be displaced. erably kept below about 7,000 parts per million. The 2. The process of claim 1 in which said turbidity clari water used in formulating the present oil displacing liq fying salt is a salt of a trivalent metal. uid can be substantially any natural or synthetic water 3. The process of claim 2 in which said salt is an iron or aqueous solution that has such a salt concentration, 50 salt. at it occurs in nature or as a result of a water treatment. 4. The process of claim 2 in which said salt is an alu In the present process for displacing oil within a sub minum. terranean reservoir a determination is preferably made xk 3. k k s

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