Method of using Sophorolipids in well treatment operations

Abstract

Recovery of fluids from a subterranean formation during a well treatment operation is enhanced by injecting into the formation a treatment fluid comprising a sophorolipid.

Claims

1. A method of enhancing recovery of a well treatment fluid from a well comprising: (a) introducing into the well the well treatment fluid, the well treatment fluid comprising at least one sophorolipidic compound selected from the group consisting of: ##STR00008## (b) treating the well with the well treatment fluid during a well treatment operation; and (c) recovering the well treatment fluid containing the sophorolipidic compound from the well after step (b), wherein the recovery of the well treatment fluid is enhanced by the sophorolipidic compound in the well treatment fluid.

2. The method of claim 1, wherein (I) and (II) are in equilibrium with each other.

3. The method of claim 1, wherein the well treatment operation is a hydraulic fracturing operation and further wherein the well treatment fluid is a fracturing fluid and is introduced into the well during the hydraulic fracturing operation, the fracturing fluid inducing a fracture in a subterranean formation penetrated by the well.

4. The method of claim 1, wherein the well treatment operation is slickwater fracturing and further wherein the well treatment fluid is a fracturing fluid introduced into the well during slickwater fracturing, the fracturing fluid inducing a fracture in a subterranean formation penetrated by the well.

5. The method of claim 1, wherein the well treatment operation is a drilling operation and further wherein the well treatment fluid is a drilling mud, the drilling mud being introduced into the well during the drilling operation.

6. The method of claim 1, wherein the well treatment operation is a gravel packing operation and further wherein the well treatment fluid is introduced into the well during the gravel packing operation.

7. The method of claim 1, wherein the well treatment operation is an acidizing operation and further wherein the well treatment fluid is an acidizing fluid, the acidizing fluid being introduced into the well during the acidizing operation.

8. The method of claim 1, further comprising producing hydrocarbons from a subterranean formation penetrated by the well wherein surface tension between the well treatment fluid and the produced hydrocarbons is reduced by the sophorolipidic compound in the well treatment fluid.

9. The method of claim 8, further comprising enhancing the permeability of the subterranean formation to the produced hydrocarbons by the sophorolipidic compound in the well treatment fluid.

10. The method of claim 1, wherein the well treatment fluid comprising the sophorolipidic compound is a matrix stimulation fluid.

11. The method of claim 1, wherein the well treatment fluid comprising the sophorolipidic compound is a drill-in fluid, a workover fluid, or a packer fluid.

12. The method of claim 1, wherein the well treatment fluid is a completion fluid.

13. The method of claim 1, wherein the well treatment operation is a diversion treatment conducted after a subterranean formation penetrated by the well is fractured and further wherein the well treatment fluid comprising the sophorolipidic compound is a diverter fluid.

14. The method of claim 1, wherein the well treatment fluid further comprises underivatized or derivatized guar.

15. The method of claim 14, wherein the well treatment fluid further comprises a crosslinking agent.

16. A method of increasing recovery of a well treatment fluid injected into a well during a drilling, stimulating or gravel packing operation, the method comprising introducing into a well during the drilling, stimulating or gravel packing operation the well treatment fluid, the well treatment fluid comprising at least one sophorolipidic compound selected from the group consisting of: ##STR00009## wherein the amount of the well treatment fluid recovered from the well after the drilling, stimulating or gravel packing operation is enhanced by the presence of the sophorolipidic compound in the well treatment fluid injected into the well.

17. The method of claim 16, wherein the well treatment fluid comprises guar and a crosslinking agent.

18. The method of claim 17, wherein the guar is underivatized or derivatized guar.

19. A method of fracturing a subterranean formation penetrated by a wellbore, the method comprising: (a) pumping a fracturing fluid into the wellbore at a pressure sufficient to create or enlarge a fracture; (b) producing fluid from the created or enlarged fracture; and wherein the method further comprises either: (i) pumping a spearhead fluid into the wellbore prior to step (a), the spearhead fluid comprising at least one sophorolipidic compound; or (ii) pumping a diverter fluid into the wellbore after step (b), the diverter fluid comprising at least one sophorolipidic compound and wherein the sophorolipidic compound is selected from the group consisting of: ##STR00010##

20. The method of claim 19, wherein (I) and (II) are in equilibrium with each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to more fully understand the drawings referred to in the detailed description of the present invention, a brief description of each drawing is presented, in which:

(2) The FIGURE illustrates the compatibility of a sophorolipids in guar based well treatment fluids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) A sophorolipid may be incorporated into a well treatment fluid. The sophorolipid is particularly useful as a flowback additive to enhance the recovery of fluids used in well treatment operations.

(4) Sophorolipids may be manufactured from corn (or other grain-based media) and vegetable oil with variations in the process being dependent on the natural and non-pathogenic yeast strand and production medium. As such, sophorolipids are naturally occurring bio-surfactant glycolipids produced from yeasts. For instance, the sophorolipids are glycolipids produced fermentatively from such yeasts as Candida bombicola, Candida apicola, and Wickerhamiella domercqiae. Sophorolipids are generally composed of a dimeric sophorose sugar moiety (-D-Glc-(1.fwdarw.2)-D-Glc) linked glycosidically to a hydroxyl fatty acid residue. In a preferred embodiment, a sophorose sugar moiety is linked via the glycosidic linkage to the hydroxyl group of a 17-hydroxy-C.sub.18 saturated or monoenoic (cis-9) fatty acid.

(5) Depending on the pH of the system, sophorolipids can assume a circular, lactonic sophorolipid form or a linear, acidic sophorolipid form. Usually the 6-hydroxyl groups of the glucose moieties are acetylated. Depending upon the organism and the fermentation conditions used to produce the sophorolipid, the acidic or lactone form may predominate.

(6) Suitable sophorolipids for use in the disclosure are those set forth in U.S. Patent Publication No. 20170044586 A1 and U.S. Patent Publication No. 20170051197 A1, both of which are herein incorporated by reference in their entirety.

(7) In a preferred embodiment, the sophorolipid is a mixture of sophorolipidic compounds represented by the formulas (I) and (II):

(8) ##STR00004##
wherein R.sup.1 is hydrogen or an acetyl group; and either R.sup.2 is hydrogen or a C.sub.1-C.sub.9 saturated or unsaturated aliphatic group; and R.sup.3 is a C.sub.7-C.sub.16 saturated or unsaturated aliphatic group; or R.sup.2 is hydrogen or methyl and R.sup.3 is a saturated or unsaturated hydrocarbon chain that contains from 12 to 18 carbon atoms, more preferably from about 13 to about 17 carbon atoms.

(9) As illustrated, the hydroxyl fatty acid moiety of the acidic sophorolipids may remain a free acid (I) or form a macrocyclic lactone ring with the 4-OH group of the sophorose lactone form (II). Such sophorolipidic compounds may be prepared by conventional methods known in the art, such as those disclosed in U.S. Pat. No. 5,879,913, herein incorporated by reference.

(10) In an embodiment, the sophorolipid is a mixture of sophorolipidic compounds of the formulas (III) and (IV):

(11) ##STR00005##

(12) As described above, the sophorolipids may be a mixture of acidic-form sophorolipids of formula (Ia), where the sophorolipids may be in the free acid form (R.sup.3COOH); or acidic-form sophorolipids of formula (Ib), where the acidic-form sophorolipids may be in the neutralized form, as a salt or as a sophorolipid anion (as illustrated in formula (Ib) below) and associated cations (i.e. NH.sub.4.sup.+, Na.sup.+, K.sup.+ Ca.sup.2+, Mn.sup.2+, or Fe.sup.3+, typically Na.sup.+ or K.sup.+) that are distributed in the sophorolipid containing composition and n is 1, 2, or 3.

(13) ##STR00006## and ester-form sophorolipids of formulas either (IIa) or (IIb), or mixtures of (IIa) and (IIb), where these ester-form sophorolipids may be in the closed-ring form that may also be referred to as ester sophorolipids, or where the sophorolipids are in the open-ring form but the carboxyl acid moiety is esterified with, for example, a suitable alcohol or other hydroxyl-containing compound (R.sup.3COOR.sup.4, as an ester),

(14) ##STR00007##
wherein R.sup.1 is hydrogen, a C.sub.1 to C.sub.4 hydrocarbon or carboxylic acid group (typically an acetyl group); and either (i) R.sup.2 is hydrogen or a C.sub.1-C.sub.9 saturated or unsaturated aliphatic group; and R.sup.3 is a C.sub.7-C.sub.20 saturated or unsaturated aliphatic group; or (ii) R.sup.2 is hydrogen or a methyl group and R.sup.3 is a saturated or unsaturated hydrocarbon chain that contains from 7 to 20 carbon atoms. Typically R.sup.2 is a hydrogen or methyl or ethyl group, (preferably a methyl group or hydrogen). Typically R.sup.3 is C.sub.7 to C.sub.20 saturated or unsaturated aliphatic group a C.sub.7 to C.sub.20 (preferred is C.sub.15 monounsaturated), and R.sup.4 is hydrogen, C.sub.1-C.sub.9 saturated or unsaturated aliphatic group, monohydroxyl aliphatic group, or polyhydroxyl aliphatic group (preferred is hydrogen group). In one embodiment, the sophorolipid is a mixture of sophorolipids compounds of the formulas (Ia), (Ib), (IIa), and/or (IIb) wherein R.sup.2 is hydrogen or methyl.

(15) In another embodiment, the sophorolipid is a mixture of acidic-form sophorolipids where the acid moiety is at least partially neutralized with a base to form a salt or anion and cation distributed in the sophorolipid containing composition as described above, and ester-form sophorolipids where the carboxylic moiety is a lactone or an open chain ester-form sophorolipid (i.e. where the lactone ring is in open form but the acid moiety is esterified with a suitable hydroxyl containing compound such as, for example, glycerol or some other hydroxyl containing compound, such as mono- and poly-alcohols), or mixtures thereof. In yet another embodiment, all or any combination of the above describe sophorolipids may be in the composition.

(16) Typically, the pH of the well treatment fluid containing the sophorolipid is from about 7.0 to about 13.0, more typically from about 8.5 to about 10.5.

(17) The dry solids of materials made from such processes is typically greater than about 90%, more typically greater than about 95%, sophorolipid. Typically, there are some free fatty acids (preferably no greater than 5%) and a small amount of vegetable oil in the reaction product.

(18) The sophorolipids described herein have particular applicability as flowback additives in a well treatment operation. As flowback additives, the sophorolipids function as biosurfactants in reducing the surface tension between the treatment fluid containing the sophorolipid and the produced hydrocarbons. This enables the recovery of more fluid from the formation and enhances or restores the formation's relative permeability to hydrocarbons.

(19) In addition to being biodegradable, the sophorolipid biosurfactants are non-toxic, biocompatible and are made from renewable resources. The use of sophorolipid biosurfactants in well treatment fluids provides a green alternative to treatment fluids containing conventional flowback surfactants. In well treatment operations, such as hydraulic fracturing, which present environmental concerns, sophorolipid biosurfactants provide an attractive alternative to conventional synthetic surfactants. They further maximize the benefits of a fracturing operation by improving the recovery of the treatment fluid introduced into the formation.

(20) The treatment fluid containing the sophorolipid may be fresh water, salt water, brine or may further be non-aqueous, such as methanol, ethylene glycol, etc. The fluid may further be a foamed fluid especially where it is desired to be used for deeper proppant penetration or in water sensitive zones.

(21) While the sophorolipid may be a component of a well treatment fluid and pumped into the wellbore during a well treatment operation, a fluid containing the sophorolipid may also be pumped into the wellbore prior to or subsequent of such treatment operation. For example, during a well treatment operation (such as a drilling, stimulation or gravel packing operation), a fluid which is later desired to be recovered (a recoverable fluid) may be pumped into the wellbore. This fluid may be, for instance, a fracturing fluid, a matrix stimulation fluid, an acidizing fluid, a hydrocarbon-based treatment fluid, a drilling mud, a drill-in fluid, a workover fluid, a packer fluid or a completion fluid. The sophorolipid may be a component of the recoverable fluid.

(22) Alternatively, a precursor fluid may be pumped into the wellbore prior to the recoverable fluid. This precursor fluid may contain the sophorolipid. As an example, a spearhead fluid containing the sophorolipid may be pumped into the wellbore prior to the pumping of the fracturing fluid.

(23) In another alternative, a post fluid may be pumped into the wellbore subsequent to the pumping of the recoverable fluid. This post fluid may contain the sophorolipid. As an example, a diverter fluid may be pumped into the wellbore subsequent to the pumping of the fracturing fluid. The diverter fluid may contain the sophorolipid.

(24) In an embodiment, the sophorolipid may be a component of a fluid containing a viscosifying agent. The viscosifying agent may be a synthetic or natural polymer as well as a viscoelastic surfactant.

(25) The synthetic or natural polymer may contain one or more functional groups, such as a hydroxyl, carboxyl, sulfate, sulfonate, amino or amido group. Preferred synthetic and natural polymers include polysaccharides and derivatives thereof, polyvinyl alcohols, polyacrylates (including the (meth)acrylates), polypyrrolidones, polyacrylamides (including (meth)acrylamides) as well as 2-acrylamido-2-methylpropane sulfonate and mixtures thereof.

(26) Suitable polysaccharides and derivatives include those which contain one or more monosaccharide units of galactose, fructose, mannose, glucoside, glucose, xylose, arabinose, glucuronic acid and pyranosyl sulfate. These include non-derivatized and derivatized guar gums, locust bean gum, tara, xanthan, succinoglycan, scleroglucan and carrageenan. These polysaccharides include guar gums and derivatives, starches and galactomannan gums. In a preferred embodiment, guar gum may be underivatized guar or a derivatized guar, such as a hydroxyalkyl guar (like hydroxypropyl guar), a carboxyalkyl guar (like carboxymethyl guar) and a carboxyalkylhydroxyalkyl guar like carboxymethylhydroxypropyl).

(27) Further, the polysaccharide may be a cellulose or cellulose derivative such as an alkylcellulose, hydroxyalkyl cellulose or alkylhydroxyalkyl cellulose, carboxyalkyl cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose, hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose, hydroxybutylmethyl cellulose, methylhydroxyethyl cellulose, methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose, carboxyethylcellulose, carboxymethylcellulose and carboxymethylhydroxyethyl cellulose.

(28) When the viscosifying agent is polymeric, the fluid may further contain a crosslinking agent. Suitable crosslinking agents include borate ion releasing compounds, organometallic or organic complexed metal ions comprising at least one transition metal or alkaline earth metal ion as well as mixtures thereof.

(29) Borate ion releasing compounds which can be employed include, for example, any boron compound which will supply borate ions in the fluid upon disassociation from the deformable core. Such compounds include boric acid, alkali metal borates such as sodium diborate, potassium tetraborate, sodium tetraborate (borax), pentaborates and the like and alkaline and zinc metal borates. Such borate ion releasing compounds are disclosed in U.S. Pat. Nos. 3,058,909 and 3,974,077 herein incorporated by reference. In addition, such borate ion releasing compounds include boric oxide (such as selected from H.sub.3BO.sub.3 and B.sub.2O.sub.3) and polymeric borate compounds. Mixtures of any of the referenced borate ion releasing compounds may further be employed. Such borate-releasers typically require a basic pH (e.g., 8.0 to 12) for crosslinking to occur.

(30) Further preferred crosslinking agents are those, such as organometallic and organic complexed metal compounds, which can supply trivalent or higher polyvalent metal ions into the fluid upon their disassociation from the deformable core. Examples of the trivalent or higher polyvalent metal ions include boron, titanium, zirconium, aluminum, yttrium, cerium, etc. or a mixture thereof. Examples of titanium compounds include titanium ammonium lactate, titanium triethanolamine, titanium acetylacetonate, titanium diisopropoxide bisacetyl aminate, titanium tetra(2-ethyl hexoxide), titanium tetraisopropoxide, titanium di(n-butoxy) bistriethanol aminate, titanium isopropoxyoctylene glycolate, titanium diisopropoxy bistriethanol aminate and titanium chloride. Examples of zirconium salts include zirconium ammonium carbonate, zirconium carbonate, zirconium acetylacetonate, zirconium diisopropylamine lactate, zirconium chloride, zirconium lactate, zirconium lactate triethanolamine, zirconium oxyacetate, zirconium acetate, zirconium oxynitrate, zirconium sulfate, tetrabutoxyzirconium (butyl zirconate), zirconium mono(acetylacetonate), zirconium n-butyrate and zirconium n-propylate. The crosslinking agent may optionally be encapsulated. Examples of typical crosslinking agents include, but are not limited to, those described in U.S. Pat. Nos. 4,514,309 and 5,247,995, which are incorporated herein by reference.

(31) Further, the viscoelastic surfactant may be any viscoelastic surfactant known in the art. Preferred are those viscoelastic surfactants containing an anionic surfactant and a cationic surfactant. A most preferred viscoelastic surfactant is the combination of sodium xylene sulfonate, as anionic surfactant, and N,N,N-trimethyl-1-octadecammonium chloride, as cationic surfactant. Such viscoelastic surfactants are set forth in U.S. Pat. No. 6,468,945, herein incorporated by reference. The volume ratio of anionic surfactant:cationic surfactant is from about 1:4 to about 4:1.

(32) Other preferred viscoelastic surfactants are those which contain a C.sub.10 to C.sub.24 alkyl trialkyl quaternary ammonium aromatic salt admixed with an anionic surfactant, such as sodium xylene sulfonate. Such systems include those set forth in U.S. Patent Publication No. 20040138071, herein incorporated by reference. Typically, the volume ratio of cationic surfactant:anionic surfactant of such viscoelastic surfactants is between from about 1:1 to about 3:1. The alkyl group forming the alkylated moiety can be a C.sub.10 to C.sub.24 alkyl group, preferably a C.sub.12 to a C.sub.20 alkyl. In a most preferred embodiment, the alkyl group forming the alkylated moiety is a C.sub.18 alkyl. The aromatic salt is preferably an aromatic salicylate or phthalate. The trialkyl moiety contains preferably from C.sub.1 to C.sub.4 alkyl groups, most preferably methyl. In a preferred mode, the surfactant is a gelled C.sub.18 trimethyl quaternary ammonium phthalate or a gelled C.sub.18 trimethyl quaternary ammonium salicylate. Such C.sub.10 to C.sub.24 alkyl trialkyl quaternary ammonium aromatic salts may be formed by mixing a C.sub.10 to C.sub.24, preferably a C.sub.18, alkyl trialkyl quaternary ammonium chloride with an alkali aromatic salt, such as a sodium salt of either salicylic acid or phthalic acid.

(33) The fluid containing the sophorolipid may further contain a breaker for defragmenting the viscosifying polymer and reducing the viscosity of the treatment fluid. Suitable are enzymatic and oxidative delayed breakers. Examples of suitable materials include, but are not limited to, amines, acids, acid salts, acid-producing materials, etc. The breaker is preferably an acid breaker such as hydrochloric acid, formic acid or sulfamic acid or alternatively a basic breaker such as sodium bisulfate. The oxidizing agent is preferably an alkaline earth peroxide, an encapsulated persulfate, a catalyzed organic peroxide or a hydrochlorite bleach.

(34) In a preferred embodiment, the sophorolipid is used as flowback additive in a drilling fluid to enhance the recovery of the fluid having suspended solids and cuttings out of the wellbore. Such fluids, in addition to the viscosifying agent, typically may contain weighting agents.

(35) In another preferred embodiment, the sophorolipid is used as a flowback additive in a hydraulic fracturing or a sand control operation.

(36) In a preferred embodiment, the sophorolipids may be used in slickwater fracturing, a type of hydraulic fracturing that uses a low viscosity aqueous fluid to induce the subterranean fracture. The fluid containing the sophorolipid for use in slickwater fracturing typically has a viscosity only slightly higher than unadulterated fresh water or brine and typically contains a friction reduction agent. The fluid may further contain a non-crosslinked or linear gel. Typically, the friction reduction agent present in slickwater does not increase the viscosity of the fracturing fluid by more than 1 to 2 centipoises (cP). The slickwater fluid may be crosslinked or may consist of a linear viscosifying agent.

(37) The sand control method may use the well treatment fluid in accordance with any method in which a pack of particulate material is formed within a wellbore that it is permeable to fluids produced from a wellbore, such as oil, gas, or water, but that substantially prevents or reduces production of formation materials, such as formation sand, from the formation into the wellbore. Such methods may or may not employ a gravel pack screen, may be introduced into a wellbore at pressures below, at or above the fracturing pressure of the formation, such as frac pack, and/or may be employed in conjunction with resins such as sand consolidation resins is so desired.

(38) A fracturing fluid containing a sophorolipid may further contain a proppant. Such proppants include conventional proppants such as sand, glass beads, walnut hulls, and metal shot as well as resin-coated sands, intermediate strength ceramics, and sintered bauxite as well ultra lightweight proppants (ULW) having an apparent specific gravity less than or equal to 2.45. Such proppant include those disclosed in U.S. Pat. Nos. 6,364,018, 6,330,916; 6,059,034; 7,426,961; 7,322,411; 7,528,096; and 7,931,087, herein incorporated by reference.

(39) The fluid may further contain one or more well treatment agents such as corrosion inhibitors, surfactants, biocides, surface tension reduction agents, friction reducers, scale inhibitors, clay stabilizers and iron control agents.

(40) The sophorolipid may be combined with the other components of the fluid in a batch process performed at the wellsite using mixing vessels or may be batched mixed away from the wellsite and transported to the wellsite. In a preferred embodiment, the fluid containing the sophorolipid is prepared on the fly using continuous mixing methods at the wellsite.

(41) The following examples are illustrative of some of the embodiments of the present invention. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the description set forth herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow.

(42) All percentages set forth in the Examples are given in terms of weight units except as may otherwise be indicated.

EXAMPLES

Example 1

(43) Fluid recovery was used to check the initial response of a sophorolipid biosurfactant by packing a column with 20/40 Ottawa sand. Nitrogen gas pressure was used to simulate production and flowed at a controlled rate to recover the fluid from the column. A flow meter was calibrated to get the desired flow rate of the fluid to be 8 cc/sec at 20 psi. The biosurfactant was tested at 1 gallon per one thousand gallons of tap water (gpt) and 2% KCl. The biosurfactant was also tested at 0.5 gpt in tap water at a pH of 5.0 and 11.0. The recovered amount of fluid from the column was captured and divided by the initial, known volume and a percent recovered volume calculated. Base fluid recovery without addition of surfactants gave fluid recovery below 60%. The results are set forth in Table I wherein Biosurfactant A is a sophorolipid comprising a mixture of formulas (III) and (IV). Biosurfactant B is a 50:50 v/v mixture of Biosurfactant A and ethylene glycol (as winterizing agent).

(44) TABLE-US-00001 TABLE I Base Fluid- Base fluid- 1 gpt, 0.5 gpt, 0.5 gpt, water 0.5 gpt, water, Tap water 2% KCl Product 1 gpt, water 2% KCl water pH of 5.0 pH of 11.0 54.2% 54.6% A 87.0% 84.4% 85.9% 86.0% 89.0% B 87.1% 77.6% 87.8% 84.4% 89.5%
Table 1 demonstrates that as little as 0.5 gpt of a 1% solution of Biosurfactant A and Biosurfactant B produces a favorable recovery of base fluid.

(45) Fluid recovery was then tested on two non-lipid synthetic fluid loss recovery additives, commercially available from Baker Hughes Incorporated. The results are shown in Table II and illustrate that the biosophorolipid additives exhibit the approximate percent fluid loss recovery as non-lipid additives.

(46) TABLE-US-00002 TABLE II Product 1 gpt, water 1 gpt, 2% KCl C 88.5% 87.0% D 88.6% 86.3%

(47) Example 2. Into 1 1 of water was added, with vigorous stirring, 6.25 gpt of an underivatized guar having an intrinsic viscosity of about 16.3 dl/g, 1.5 gpt of a borate crosslinker, commercially available as XLW-30 from Baker Hughes Incorporated, and 1.5 gpt of a potassium containing buffer capable of adjusting the pH of the fluid to a range of about 11.0, commercially available as BF-9L from Baker Hughes Incorporated. After gelation, the compatibility of two sophorolipids containing compounds of formulas (III) and (IV) with a 25 ppt of the guar based fluid was rheologically tested on a Fann 50 viscometer. The crosslinked fluid was tested at a constant shear rate of 100 sec.sup.1 with a shear rate ramp of 100, 80, 60, 40 sec.sup.1 at 75 F. initially and then every 30 minutes at 200 F. for 3 hours. The Fann 50 bath was pre-heated to a 200 F. The results, set forth in, the FIGURE demonstrate the compatibility of the biosurfactants with the guar based fluid.

(48) From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concepts of the invention.