Abstract:
A fluid that is useful in stimulation operations, and in particular, in hydraulic fracturing treatments, comprises a carrier fluid; a solvatable, crosslinkable polymer; a cross-linking agent that does not cause substantial cross-linking of the polymer at temperatures less than about 105° F. and a pH of about 10 or greater; and an organic amine stabilizing agent that has a first pK a  or a pH in water of at least about 9.5. One group of such amines has the formula 
     
       
         H 2 N—(R 1 NH) n —H 
       
     
     where R 1  is C 1 -C 4  alkyl and n is from 1-6. In one embodiment, the cross-linking agent is an organic zirconate, such as bis(hydroxyethyl)glycine zirconate. The organic zirconate is effective to cross-link the polymer when the composition is at a temperature of at least about 105° F., and a pH of about 10 or higher, preferably a pH in the range of about 10.5-12.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This Invention relates to the stimulation of hydrocarbon wells and in particular to fluids and methods for hydraulic fracturing of a subterranean formation. 
     BACKGROUND OF THE INVENTION 
     Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation. This provides a partial flowpath for the oil to reach the surface. In order for oil to be “produced,” that is travel from the formation to the wellbore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the wellbore. This flowpath is through the formation rock—e.g., sandstone, carbonates—which has pores of sufficient size, connectivity, and number to provide a conduit for the oil to move through the formation. 
     Hence, one of the most common reasons for a decline in oil production is “damage” to the formation that plugs the rock pores and therefore impedes the flow of oil. This damage generally arises from another fluid deliberately injected into the wellbore, for instance, drilling fluid. Even after drilling, some drilling fluid remains in the region of the formation near the wellbore, which may dehydrate and form a coating on the wellbore. The natural effect of this coating is to decrease permeability to oil moving from the formation in the direction of the wellbore. 
     Another reason for lower-than-expected production is that the formation is naturally “tight” (low permeability formation), that is, the pores are sufficiently small that the oil migrates toward the wellbore only very slowly. The common denominator in both cases (damage and naturally tight reservoirs) is low permeability. 
     Techniques performed by hydrocarbon producers to increase the net permeability of the reservoir are referred to as “stimulation.” Essentially, one can perform a stimulation technique by: (1) injecting chemicals into the wellbore to react with and dissolve the damage (e.g., wellbore coating); (2) injecting chemicals through the wellbore and into the formation to react with and dissolve small portions of the formation to create alternative flowpaths for the hydrocarbon (thus rather than removing the damage, redirecting the migrating oil around or through the damage); or (3) injecting chemicals through the wellbore and into the formation at pressures sufficient to actually fracture the formation, thereby creating a large flow channel though which hydrocarbon can more readily move from the formation and into the wellbore. The present invention is directed primarily to the third of these processes. 
     Hydraulic fracturing involves literally breaking or fracturing a portion of the surrounding strata, by injecting a specialized fluid into the wellbore directed at the face of the geologic formation at pressures sufficient to initiate and extend a fracture in the formation (i.e. above the minimum in situ rock stress). More particularly, a fluid is injected through a wellbore; the fluid exits the wellbore through holes (perforations in the well casing) and is directed against the face of the formation (sometimes wells are completed openhole where no casing and therefore no perforations exist, so the fluid is injected through the wellbore and directly to the formation face) at a pressure and flow rate sufficient to overcome the minimum in situ stress (also known as minimum principal stress) to initiate and/or extend a fracture(s) into the formation. Actually, what is created by this process is not always a single fracture, but a fracture zone, i.e., a zone having multiple fractures, or cracks in the formation, through which hydrocarbon can more easily flow to the wellbore. 
     Generally speaking, creating a fracture in a hydrocarbon-bearing formation requires a complex suite of materials. In the case of conventional fracturing treatments, four or five principal components are required: (1) a carrier fluid (usually water or brine), (2) a polymer, (3) a cross-linker, (4) a proppant, and (5) optionally a breaker. (Numerous other components are sometimes added, e.g. fluid loss agents, whose purpose is to control leak-off, or migration of the fluid into the fracture face.) Roughly, the purpose of these fluids is to first create/extend the fracture, then once it is opened sufficiently, to deliver proppant into the fracture, which keeps the fracture from closing once the pumping operation is completed. The carrier fluid is simply the means by which the proppant and breaker are carried into the formation. Thus, the fracturing fluid is typically prepared by blending a polymeric gelling agent with an aqueous solution (sometimes oil-based, sometimes a multi-phase fluid is desirable); often, the polymeric gelling agent is a solvatable polysaccharide, e.g., galactomannan gums, glycomannan gums, and cellulose derivatives. The purpose of the solvatable (or hydratable) polysaccharides is: (1) to provide viscosity to the fluid so that it can create/extend the fracture; and (2) to thicken the aqueous solution so that solid particles known as “proppant” (discussed below) can be suspended in the solution for delivery into the fracture. Again, the purpose of the proppant is to literally hold open or prop open the fracture after it has been created. Thus the polysaccharides function as viscosifiers, that is, they increase the viscosity of the aqueous solution by 10 to 100 times, or even more. In many fracturing treatments, a cross-linking agent is added which further increases the viscosity of the solution by cross-linking the polymer. The borate ion has been used extensively as a crosslinking agent for hydrated guar gums and other galactomannans to form aqueous gels, e.g., U.S. Pat. No. 3,059,909. Other suitable cross-linking agents include titanium (U.S. Pat. No. 3,888,312), chromium, iron, aluminum and zirconium (U.S. Pat. No. 3,301,723) compounds. 
     The purpose of the proppant is to keep the newly fractured formation in that fractured state, i.e., from re-closing after the fracturing process is completed; thus, it is designed to keep the fracture open—in other words to provide a permeable path (along the fracture) for the hydrocarbon to flow through the fracture and into the wellbore. More specifically, the proppant provides channels within the fracture through which the hydrocarbon can flow into the wellbore and therefore be withdrawn or “produced.” Typical materials from which the proppant is made include sand (e.g. 20-40 mesh), bauxite, man-made intermediate-strength or high strength materials and glass beads. The proppant can also be coated with resin, which causes the resin particles to stick to one another, to help prevent proppant flowback in certain applications. Thus, the purpose of the fracturing fluid generally is two-fold: (1) to create or extend an existing fracture through high-pressure introduction into the geologic formation of interest; and (2) to simultaneously deliver the proppant into the fracture void space so that the proppant can create a permanent channel through which the hydrocarbon can flow to the wellbore. 
     One problem in fracturing operations is that the polymers often degrade before the operation is completed, as a result of thermal, oxidative/free radical, or acid hydrolysis reactions. This degradation causes the viscosity of the fracturing fluid to decrease correspondingly. Reduction in viscosity can reduce the fluid&#39;s effectiveness in creating fractures and delivering proppant to the desired sites. Two approaches have been used in an attempt to maintain the desired minimum viscosity in the fracturing fluid during the fracturing operation. One is to increase the initial loading of the polymer in the fluid, thus increasing the fluid&#39;s initial viscosity. However, this approach increases the energy required to pump the fluid into and through the wellbore. This and the cost of the additional polymer increases the overall cost of the fracturing operation, and also can lower well performance due to reduced conductivity in the proppant pack. 
     A second approach is to include a stabilizer in the fracturing fluid, to minimize polymer degradation. Commonly used stabilizers include methanol and sodium thiosulfate (Na 2 S 2 O 3 ). Although the mechanism of action of these stabilizers is not fully understood, it is believed that they act as oxygen scavengers, and thus prevent polymer degradation that would otherwise be caused by oxygen dissolved in the fracturing fluid. However, methanol is flammable and therefore is generally avoided. A substantial quantity of sodium thiosulfate is required when it is used as a stabilizer. Neither of these two compounds is sufficiently effective as a stabilizer. 
     The problem of polymer degradation is becoming even more important recently because of the increasing incidence of very deep, hot (e.g., temperature &gt;250° F.) wells. Therefore, there is a need for improved fracturing fluids that are suitable for use at high temperatures. 
     SUMMARY OF THE INVENTION 
     The present invention relates to the use of fluids in hydraulic fracturing operations. One embodiment of the invention is a well treatment fluid composition that comprises a carrier fluid; a solvatable, crosslinkable polymer; a cross-inking agent that does not cause substantial cross-linking of the polymer at ambient temperature (less than about 105° F.) and a pH of about 10 or greater; and an organic amine stabilizing agent that has a first pK a  or a pH in water of at least about 9.5. 
     “Substantial cross-linking” in this context is indicated by a viscosity increase of at least about 300% over the base fluid viscosity. In other words, when a cross-linker of the present invention is combined with the polymer, the viscosity of the composition should increase by less than about 300% as long as the composition remains below about 105° F. Substantial cross-linking will occur at a pH of at least about 10 when the composition is heated to about 105° F. or higher. In one embodiment of the invention, the cross-linking agent is an organic zirconate. Most preferably, the organic zirconate cross-linking agent is effective to cross-link the polymer at a pH in the range of about 10.5-12 and a temperature of at least about 105° F. One particularly preferred cross-linking agent comprises bis(hydroxyethyl)glycine zirconate. 
     In one embodiment, the organic amine stabilizer has the formula 
     
       
         H 2 N—(R 1 NH)n—H 
       
     
     where R 1  is C 1 -C 4  alkyl and n is from 1-6. Preferably R 1  is ethylene and n is 4. Tetraethylenepentamine (TEPA) is a particularly preferred stabilizer. 
     The composition can optionally further comprise a proppant, a delay agent (such as a bicarbonate salt), a viscosity breaker agent, or one or more other additives, such as scale inhibitors, surfactants, biocides, and breaker aids. 
     In one specific embodiment of the present invention, the well treatment fluid composition comprises a carrier fluid; a solvatable, crosslinkable polymer selected from the group consisting of guar, hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxypropyl guar, hydroxyethyl cellulose, carboxymethylhydroxyethyl cellulose, hydroxypropyl cellulose, xanthan, and mixtures thereof; a cross-linking agent that comprises bis(hydroxyethyl)glycine zirconate; an organic amine stabilizing agent that comprises tetraethylenepentamine; and a delay agent that comprises a bicarbonate salt. 
     Another aspect of the present invention is a method of hydraulically fracturing a subterranean formation. The method includes the step of injecting a well treatment fluid composition via a wellbore into a subterranean formation at a flow rate and pressure sufficient to produce or extend a fracture in the formation. The well treatment fluid composition comprises the materials described above. 
     The compositions and methods of the present invention provide several substantial advantages over prior fracturing fluids and methods. At ambient temperature, the fluid can quickly reach a viscosity sufficient to transport proppant (e.g., 40-120 cP), but will not crosslink further until it is heated to about 105 ° F. or higher. Preferably the fluid will exhibit this delay in cross-linking for at least about 10 minutes at ambient temperature. Therefore, the fluid has an initial viscosity that is high enough to carry proppant, but not so high as to make pumping the fluid difficult. When exposed to elevated formation temperature, the fluid can crosslink further, and will be less likely than prior art fluids to suffer reduction of viscosity to excessively low levels. The present invention also is relatively simple and inexpensive to manufacture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a graph of the change in viscosity over time of a fluid that was heated to about 350° F. 
     FIG. 2 is a graph of the change in viscosity over time of a fluid of the present invention that was heated to about 350° F. 
     FIG. 3 is a graph of the change in viscosity over time of a fluid of the present invention at ambient temperature. 
     FIG. 4 is a graph of the change in viscosity as a function of temperature for a fluid of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Components of the Fracturing Fluid 
     While the compositions of the present invention are described herein as comprising certain materials, it should be understood that the composition can optionally comprise two or more chemically different such materials. For example, a composition could comprise a mixture of two or more organic amine stabilizing agents having the characteristics described above. Likewise, two or more organic zirconate cross linkers or other components could be present in the composition. 
     A fracturing fluid of the present invention will comprise a carrier fluid. Water and brine are the most commonly used carrier fluids. Emulsions or other combinations of aqueous and organic fluids can also be used. 
     The fracturing fluid will also comprise a viscosifying polymer that is typically a solvatable polysaccharide. Suitable hydratable polymers include, for example, guar, hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxypropyl guar, hydroxyethyl cellulose, carboxymethylhydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan. Other natural and synthetic polymers can be used as well. 
     The fluid will also comprise an organic zirconate cross-linking agent for the polymer. One particularly preferred crosslinker is bis(hydroxyethyl)glycine zirconate, available from DuPont. (See U.S. Pat. No. 4,808,739.) 
     Preferably the well treatment fluid also comprises a delay agent, to delay the cross-linking of the polymer. This permits the fracturing fluid to be pumped at a lower initial viscosity, while allowing the fluid viscosity to subsequently increase to the desired level after cross-linking begins. Suitable delay agents include, for example, bicarbonate salts. A particularly preferred delay agent is sodium bicarbonate. 
     The fluid also comprises an organic amine stabilizing agent that has a first pK a  or a pH in water of at least about 9.5. The organic amine preferably has from 1-20 carbon atoms, more preferably 1-10 carbon atoms. In one particularly preferred embodiment, the organic amine has the formula: 
     
       
         H 2 N—(R 1 NH) n —H 
       
     
     where R 1  is C 1 -C 4  alkyl and n is from 1-6. Preferably R 1  is ethylene and n is 4. This preferred amine, tetraethylenepentamine (TEPA), is available from Dow Chemical. When TEPA is used as the stabilizer, the fluid will typically have a pH of about 10.8, which is too high for many Zr-based crosslinkers to work effectively. However, it has surprisingly been found that the use of an organic zirconate as described above allows the needed crosslinking to occur despite the relatively high pH. 
     Table 1 below lists a number of organic amines that can be used as stabilizers in the present invention. The pK a  values in the table are from the literature; the pH values in the table were mostly determined experimentally, although some were taken from the literature. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Code or 
                   
                   
               
               
                 Stabilizer 
                 Tradename 
                 pKa 
                 pH 
               
               
                   
               
             
             
               
                 tetraethylenepentamine 
                 TEPA 
                   
                 11.29 
               
               
                 ethylenediamine 
                   
                 10.7, 7.6 
               
               
                 diethylenetriamine 
                 DETA 
                   
                 11.42 
               
               
                 piperazine 
               
               
                 N-aminoethylpiperazine 
               
               
                 triethylenetetramine 
               
               
                 pentaethylenehexamine 
               
               
                 higher ethylene polyamines 
               
               
                 1,4-diaminobutane 
                   
                 11.2, 9.7 
               
               
                 n-butylamine 
                   
                 10.8 
               
               
                 n-decylamine 
                   
                 10.6 
               
               
                 diethylamine 
                   
                 10.5 
               
               
                 diisopropylamine 
                   
                 11   
               
               
                 ethylamine 
                   
                 10.8 
               
               
                 hexamethylenediamine 
                   
                 11.9 
               
               
                 piperazine 
                   
                  9.8 
               
               
                 1,2-diaminopropane 
                   
                  9.8, 6.6 
               
               
                 1,3-diaminopropane 
                   
                 10.9, 9.0 
               
               
                 tetramethylenediamine 
                   
                 10.7 
               
               
                 di-(gamma-aminopropylether) of 
                 DPA-12 
                   
                 11.41 
               
               
                 2-methyl-1,3-propane diol 
               
               
                 di-(gamma-aminopropylether) of 
                 NDPA-10 
                   
                 11.58 
               
               
                 ethylene glycol 
               
               
                 di-(gamma-aminopropylether) of 
                 NDPA-12 
                   
                 11.55 
               
               
                 1,4-butane diol 
               
               
                 N,N′-bis(3-aminopropyl)ethylene- 
                 BAPED 
                   
                 11.72 
               
               
                 diamine 
               
               
                 tris-(2-aminoethyl)amine 
                 TAA 
                   
                 11.25 
               
               
                 Alkoxylated diethylene diamine 
                 ADD 
                   
                 10.68 
               
               
                 N-tallowalkyl-1,3-propanediamines 
                 Duomeen T 
                   
                  9.68 
               
               
                 N,N-diethylhydroxylamine 
                 DHA 
                   
                 11.06 
               
               
                 dodecylamine 
                 DDA 
                   
                 10.22 
               
               
                   
               
             
          
         
       
     
     In addition to DPA-12, NDPA-10, and NDPA-12 as listed in the above table, other similar organic amine stabilizers include other amino analogs of diols, glycols, and poly(propyleneglycol)&#39;s (available from Tomah Products, Inc., Milton, Wis.). Duomeen T, also listed in the above table, is available from Akzo Nobel Chemicals, Inc., Chicago, Ill. 
     The fluid will also typically comprise a proppant. Suitable materials from which the proppant can be made include sand (e.g. 20-40 mesh), bauxite, man-made intermediate-strength or high strength materials, and glass beads. Optionally the proppant can be coated with resin of a type and in an amount that will permit consolidation of the proppant particles into a mass, for example when subjected to the elevated temperatures and pressures of the formation. 
     The fluid will also typically comprise a breaker. The purpose of this component is to “break” or destroy/diminish the viscosity of the fracturing fluid (the matrix carrying the proppant) so that this fluid is more easily recovered from the fracture during clean-up. Examples of breakers suitable for use in the method of the present invention include enzymes such as galactomannanase and oxidizers such as ammonium persulfate. Additionally, the breakers can be encapsulated to delay their release, for example as described in U.S. Pat. No. 4,741,401, which is incorporated herein by reference. 
     Optionally, the fracturing fluid can further contain one or more additives such as surfactants, breaker aids, salts (e.g., potassium chloride), anti-foam agents, scale inhibitors, and bactericides. 
     The proportion of the various components of a composition of the present invention will vary depending on the characteristics of the formation to be treated and other factors well known in the art. Typical concentration ranges for an exemplary composition are as follows (percentages are by weight): 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 water 
                   95-99.5% 
               
               
                   
                 hydratable polymer 
                 0.24-0.72% 
               
               
                   
                 crosslinker 
                 0.05-0.15% 
               
               
                   
                 organic amine stabilizer 
                 0.05-0.40% 
               
               
                   
                 KCl 
                 1-2% 
               
               
                   
                 other additives 
                      0.01-0.5% each 
               
               
                   
                   
               
             
          
         
       
     
     The components of the fracturing fluid can be combined in a mixing tank above ground and then injected into the well and the target formation. Alternatively, one or more of the components, for example the breaker, can be stored by itself and injected into the wellbore and the formation after the fluid has been injected. 
     The composition of the present invention provides useful stability enhancement at temperatures of 250° F. or higher. Preferably the fracturing fluid of the present invention can maintain a viscosity of at least 100 cP at 100 sec −1  for at least 90 minutes at 375° F. 
     Fracturing Procedures 
     Techniques for hydraulically fracturing a subterranean formation will be known to persons of ordinary skill in the art, and will involve pumping the fracturing fluid into the borehole and out into the surrounding formation. The fluid pressure is above the minimum in situ rock stress, thus creating or extending fractures in the formation. See  Stimulation Engineering Handbook , John W. Ely, Pennwell Publishing Co., Tulsa, Okla. (1994). 
     The present invention can be further understood from the following examples. 
     EXAMPLE 1 
     Aqueous polymer solutions were aged in an air oven at elevated temperatures, and their viscosity was measured before and after the aging. The solutions were 50 ppt (pounds of additive per 1,000 gallons of fluid) carboxymethylhydroxypropyl guar (CMHPG) linear gels prepared from a slurry of 51% (wt.) CMHPG (available from Hercules) and 49% diesel oil. This fluid was hydrated in 2% KCl solution by adding just enough aqueous sodium acetate/acetic acid mixture (pH 5.5-6.0) to adjust the pH to 7 while blending at 2,000 RPM on a Waring blender for 15 minutes. To this was added 1 gpt (gallons of additive per 1,000 gallons of fluid) of a bactericide comprising 42.5 weight % propane-1,2-diol, 2-5 wt % sodium hydroxide, and 9 wt % 1,2-benzisothiazolin-3-one in water (referred to hereafter as “bactericide 1”). The base gels were made in 1 liter quantities, and stored in Nalgene-type plastic bottles. The viscosity of each batch of base gel was measured at 70° F. on a Contraves LS-30 viscometer to establish the baseline for that batch. 
     The fluids contained various combinations of tetraethylenepentamine (TEPA) with other materials, and were aged at 325° F. for 2 or 5 hours. The results are shown in Table 2 below. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Concentration 
                   
                 Concentration 
                 % of initial 
                 % of initial 
                   
               
               
                 TEPA 
                 Secondary 
                 secondary 
                 viscosity after 
                 viscosity after 
               
               
                 (gpt) 
                 additive 
                 additive 
                 2 hrs. 
                 5 hrs. 
                 Comments 
               
               
                   
               
             
             
               
                 5 
                 — 
                 — 
                 93 
                 — 
                 pH 11.50 
               
               
                 1 
                 NaOH 
                 2% 
                 63 
                 — 
                 pH 11.52 
               
               
                 2 
                 NaOH 
                 2% 
                 78 
                 — 
                 pH 11.51 
               
               
                 3 
                 NaOH 
                 2% 
                 90 
                 — 
                 pH 11.53 
               
               
                 5 
                 — 
                 — 
                 63 
                 25 
               
               
                 5 
                 MeOH 
                  2 gpt 
                 74 
                 19 
               
               
                 5 
                 MeOH 
                  5 gpt 
                 69 
                  8 
               
               
                 5 
                 MeOH 
                 10 gpt 
                 — 
                  6 
               
               
                 5 
                 — 
                 — 
                 — 
                 76 
               
               
                 5 
                 Na bicarbonate 
                  2 ppt 
                 — 
                 63 
               
               
                 5 
                 Na bicarbonate 
                  5 ppt 
                 — 
                 65 
               
               
                 5 
                 Na bicarbonate 
                 10 ppt 
                 — 
                 66 
               
               
                 5 
                 Na bicarbonate 
                 20 ppt 
                 — 
                 60 
               
               
                 5 
                 — 
                 — 
                 — 
                 25 
               
               
                 5 
                 Na thiosulfate 
                 10 ppt 
                 — 
                  8 
               
               
                 5 
                 Na thiosulfate 
                 20 ppt 
                 — 
                  7 
               
               
                 5 
                 Na thiosulfate 
                 40 ppt 
                 — 
                  2 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 2 
     Changes in the viscosity of fluids as a function of time at elevated temperatures were measured with a Fann 50 viscometer. FIG. 1 shows the viscosity change of a fluid that was heated to 350° F. This fluid comprised 11.3 gpt of a slurry of 51 wt % CMHPG/49% diesel; 2% KCl; 1 gpt an aqueous organo-zirconium complex (available as ZXL-750 from Benchmark Research and Technology, Midland, Tex.); 8.5 gpt of 6.7% aqueous sodium hydroxide; 1 gpt of aqueous sodium acetate/acetic acid mixture (pH 5.5-6.0); 10 ppt sodium thiosulfate; 1 gpt of a surfactant mixture that comprised 20 wt % isopropanol, 20 wt % 2-butoxyethanol (EGMBE), 20 wt % ethoxylated C 11  linear/branched alcohols, 10 wt % ethoxylated C 12 -C 15  linear alcohols in water referred to hereafter as “surfactant mixture 1”); and 5 gpt of 85 wt % aqueous triethanolamine. 
     FIG. 2 shows the viscosity change of another fluid, which contained tetraethylenepentamine (TEPA) as a stabilizer, and was cross-linked with an organic zirconate. This fluid comprised a slurry of 51 wt % CMHPG/49% diesel, 2% KCl, 1 gpt bis(hydroxyethyl)glycine zirconate, 1 gpt of aqueous sodium acetate/acetic acid mixture (pH 5.5-6.0), 1 gpt of bactericide 1, and 5 gpt TEPA. The apparent drops in viscosity for about 45 minutes after the fluids reach the elevated temperature are believed to be due to “bob climb” commonly seen with viscous zirconates in this viscometer geometry. The fluid recovered from the test of FIG. 1 was brown, while the fluid recovered from the test of FIG. 2 was yellow. 
     The fluid containing TEPA and bis(hydroxyethyl)glycine zirconate (FIG. 2) at ambient temperature quickly reached a viscosity sufficient to transport proppant (40-120 cP), but did not crosslink further, even after 10 minutes, until it was heated. 
     FIG. 3 shows the change in viscosity over time at ambient temperature of the same fluid described above with respect to FIG. 2, which comprised 1 gpt bis(hydroxyethyl)glycine zirconate and 5 gpt TEPA. FIG. 4 shows viscosity change, as measured on a Fann 35 viscometer, of a portion of the same fluid from FIG. 3 that was heated above ambient temperature. The true crosslink temperature was about 140° F. 
     Table 3 below shows data from measurements of additional fluids, made with a Fann 50 viscometer at 100 sec −1 . The fluids in this test were heated to 350° F. and viscosity was measured at various times. All of the fluids were prepared in deionized water with 11.3 gpt of a slurry of 51 wt % CMHPG/49% diesel; 1 gpt of aqueous sodium acetate/acetic acid mixture (pH 5.5-6.0) as a buffer; and 167 ppt potassium chloride as a clay stabilizer. Other components of the fluid, as well as the experimental results, are summarized in Table 3. The crosslink temperatures were determined visually. The last four columns in the table show the viscosity at 100 sec −1  at 2, 100, and 240 minutes, and the time in minutes for the viscosity to decrease to 100 cP. 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Cross- 
                   
                   
                 Na 
                   
                   
                 Trieth- 
                   
                   
                   
                   
                   
                   
               
               
                   
                 link 
                 Acid or 
                   
                 bicar- 
                 Na thio- 
                 Addi- 
                 anol- 
                   
                 Cross- 
               
               
                 Run 
                 Temp. 
                 Base 
                 Cross- 
                 bonate 
                 sulfate 
                 tive 
                 amine 
                 TEPA 
                 link pH/ 
                 cP @ 2 
                 cP @ 
                 cP @ 
                 min @ 
               
               
                 Number 
                 (° F.) 
                 (gpt) 
                 linker 
                 (ppt) 
                 (ppt) 
                 (1 gpt) 
                 (1) 
                 (gpt) 
                 final pH 
                 min 
                 100 min 
                 240 min 
                 100 cP 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 2-1 
                 80 
                   
                 1.0 gpt 
                   
                   
                 bacteri- 
                   
                 5 gpt 
                 10.82 
                 &gt;1,000 
                 76 
                 20 
                 96 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 10.31 
               
               
                   
                   
                   
                 bicine 
               
               
                   
                   
                   
                 (2) 
               
               
                 2-2 
                 113 
                 8.5 gpt 
                 1 gpt 
                 12 ppt 
                 30 ppt 
                 surf. 
                 1 gpt 
                   
                 9.52 
                 &gt;1,000 
                 100 
                 1 
                 100 
               
               
                   
                   
                 6.7% 
                 ZXL- 
                   
                   
                 mixture 
                   
                   
                 9.19 
               
               
                   
                   
                 NaOH 
                 750 (3) 
                   
                   
                 2 
               
               
                   
                   
                   
                   
                   
                   
                 (4) 
               
               
                 2-3 
                 79 
                   
                 1.0 gpt 
                   
                   
                 bacteri- 
                   
                 5 gpt 
                 10.82 
                 &gt;1,000 
                 100 
                 14 
                 100 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 10.28 
               
               
                   
                   
                   
                 bicine 
               
               
                 2-4 
                 138 
                   
                 1.0 gpt 
                   
                   
                 bacteri- 
                   
                 1 gpt 
                 10.02 
                 &gt;1,000 
                 10 
                 9 
                 37 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 9.24 
               
               
                   
                   
                   
                 bicine 
               
               
                 2-5 
                 92 
                   
                 1.0 gpt 
                   
                   
                 bacteri- 
                   
                 10 gpt  
                 11.12 
                 &gt;1,000 
                 56 
                 2 
                 65 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 11.03 
               
               
                   
                   
                   
                 bicine 
               
               
                 2-6 
                 123 
                 38 gpt 
                 1 gpt 
                 12 ppt 
                 30 ppt 
                 surf. 
                 1 gpt 
                 5 gpt 
                 8.08 
                 235 
                 1 
                 1 
                 17 
               
               
                   
                   
                 10% 
                 ZXL- 
                   
                   
                 mixture 
                   
                   
                 8 
               
               
                   
                   
                 HCl 
                 750 
                   
                   
                 2 
               
               
                 2-7 
                 158 
                 8.5 gpt 
                 1 gpt 
                 12 ppt 
                 10 ppt 
                 surf. 
                 5 gpt 
                   
                 9.34 
                 &gt;1,000 
                 119 
                 15 
                 103 
               
               
                   
                   
                 6.7% 
                 ZXL- 
                   
                   
                 mixture 
                   
                   
                 9.18 
               
               
                   
                   
                 NaOH 
                 750 
                   
                   
                 1 
               
               
                 2-8 
                 139 
                 11.7 gpt 
                 1 gpt 
                 12 ppt 
                 30 ppt 
                 surf. 
                 1 gpt 
                 5 gpt 
                 9.43 
                 820 
                 5 
                 3 
                 40 
               
               
                   
                   
                 10% 
                 ZXL- 
                   
                   
                 mixture 
                   
                   
                 9.12 
               
               
                   
                   
                 HCl 
                 750 
                   
                   
                 2 
               
               
                 2-9 
                 104 
                   
                 1.0 gpt 
                   
                 10 ppt 
                 bacteri- 
                 1 gpt 
                 5 gpt 
                 10.83 
                 &gt;1,000 
                 90 
                 1 
                 98 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 10.29 
               
               
                   
                   
                   
                 bicine 
               
               
                 2-10 
                 165 
                 8.5 gpt 
                 1 gpt 
                 12 ppt 
                 30 ppt 
                 surf. 
                 1 gpt 
                   
                 8.90 
                 575 
                 330 
                 120 
                 &gt;240 
               
               
                   
                   
                 6.7% 
                 ZXL- 
                   
                   
                 mixture 
                   
                   
                 8.73 
               
               
                   
                   
                 NaOH 
                 750 
                   
                   
                 2 
               
               
                 2-11 
                 124 
                   
                 1.0 gpt 
                   
                   
                 bacteri- 
                   
                 5 gpt 
                 10.86 
                 &gt;1,000 
                 129 
                 204 
                 &gt;240 
               
               
                   
                   
                   
                 Zr 
                   
                   
                 cide 1 
                   
                   
                 10.31 
               
               
                   
                   
                   
                 bicine 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 3 
     Viscosity measurements similar to those described in Example 2 above were made on fluids containing various organic amines. Each of these fluids, which were all heated to 350° F., comprised 50 ppt of CMHPG as the polymer; 167 ppt of potassium chloride as a clay stabilizer; 1.25 gpt of bis(hydroxyethyl)glycine zirconate as a crosslinker, 12 ppt of sodium bicarbonate; 1 gpt of surfactant mixture 1; and 2 ppt of 85 wt % aqueous triethanolamine. The CMHPG was part of a slurry of 51 wt % CMHPG/49% diesel, dispersed and hydrated with 2 gpt (in most runs) of aqueous sodium acetate/acetic acid mixture (pH 5.5-6.0). (The amount of the sodium acetate/acetic acid solution used was 1 gpt in runs 3-8 and 3-9, and 2.16 gpt in run 3-11.) Viscosity was measured on a Fann 50 viscometer at 100 sec −1  after 2, 100, and 240 minutes of heating. Table 4 below summarizes the other components used in the fluids and the data. 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                 NaOH 
                   
                   
                 Initial 
                   
                   
                   
                   
                   
               
               
                   
                 Crosslink 
                 (30% 
                 Na thio- 
                   
                 pH/ 
                   
                   
                   
                   
                 Bob 
               
               
                 Run 
                 Temp. 
                 aqueous) 
                 sulfate 
                   
                 crosslink 
                 cP @ 2 
                 cP @ 100 
                 cP @ 240 
                 min @ 
                 climb 
               
               
                 Number 
                 (° F.) 
                 (gpt) 
                 (ppt) 
                 Additive 
                 pH 
                 min 
                 min 
                 min 
                 100 cP 
                 (min) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3-1 
                 126 
                 1.7 
                   
                   
                 10.72 
                 1,000 
                 20 
                 — 
                  7 
                 0 
               
               
                   
                   
                   
                   
                   
                 10.87 
               
               
                 3-2 
                 139 
                 1.54 
                 25 
                   
                 10.84 
                 1,000 
                 40 
                  8 
                  5 
                 0 
               
               
                   
                   
                   
                   
                   
                 — 
               
               
                 3-3 
                 149 
                 1.3 
                   
                 5 gpt 
                 10.60 
                 1,000 
                 55 
                 26 
                 185  
                 110 
               
               
                   
                   
                   
                   
                 TEPA 
                 — 
               
               
                 3-4 
                 139 
                   
                 25 
                 5 gpt 
                 10.32 
                 1,000 
                 85 
                 14 
                 130  
                 120 
               
               
                   
                   
                   
                   
                 TEPA 
                 10.17 
               
               
                 3-5 
                 138 
                   
                 25 
                 5 gpt 
                 10.37 
                 1,000 
                 120  
                 80 
                 235  
                 185 
               
               
                   
                   
                   
                   
                 TEPA 
                 10.30 
               
               
                 3-6 
                 141 
                 1.02 
                 25 
                 4 gpt 
                 10.79 
                 1,000 
                 75 
                 25 
                 43 
                 0 
               
               
                   
                   
                   
                   
                 DETA 
                 — 
               
               
                 3-7 
                 139 
                 0.84 
                   
                 4 gpt 
                 10.64 
                 1,000 
                 100  
                 60 
                 207  
                 120 
               
               
                   
                   
                   
                   
                 DETA 
                 — 
               
               
                 3-8 
                   
                 1.6 
                 25 
                 4 gpt 
                 10.59 
                 1,000 
                 56 
                 — 
                 &gt;140  
                 120 
               
               
                   
                   
                   
                   
                 ADD 
                  9.67 
               
               
                 3-9 
                   
                 1.62 
                   
                 4 gpt 
                 10.62 
                 1,000 
                 30 
                 — 
                 34 
                 0 
               
               
                   
                   
                   
                   
                 ADD 
                  9.93 
               
               
                 3-10 
                 100 
                 0.72 
                 25 
                 4 gpt 
                 10.72 
                 1,000 
                 45 
                 — 
                 25 
                 0 
               
               
                   
                   
                   
                   
                 BAPED 
                 — 
               
               
                 3-11 
                 152 
                   
                   
                 4 gpt 
                 10.77 
                 1,000 
                 35 
                 — 
                 47 
                 0 
               
               
                   
                   
                   
                   
                 BAPED 
                 10.26 
               
               
                 3-12 
                 137 
                 1.02 
                 25 
                 4 gpt 
                 10.62 
                 1,000 
                 65 
                 27 
                 48 
                 10 
               
               
                   
                   
                   
                   
                 NDPA-10 
                 — 
               
               
                 3-13 
                 144 
                 0.96 
                   
                 4 gpt 
                 10.85 
                 1,000 
                 45 
                 — 
                 15 
                 0 
               
               
                   
                   
                   
                   
                 NDPA-10 
                 10.55 
               
               
                 3-14 
                 141 
                 1.22 
                 25 
                 4 gpt 
                 10.69 
                 1,000 
                 55 
                 62 
                 — 
                 0 
               
               
                   
                   
                   
                   
                 DPA-12 
                 10.61 
               
               
                 3-15 
                 133 
                 1.18 
                   
                 4 gpt 
                 10.65 
                 1,000 
                 70 
                 — 
                  5 
                 0 
               
               
                   
                   
                   
                   
                 DPA-12 
                 10.62 
               
               
                 3-16 
                 125 
                 0.72 
                 25 
                 4 gpt 
                 10.54 
                 1,000 
                 60 
                 34 
                 20 
                 0 
               
               
                   
                   
                   
                   
                 NDPA-12 
                 — 
               
               
                 3-17 
                 144 
                 0.88 
                   
                 4 gpt 
                 10.71 
                 1,000 
                 15 
                 — 
                 15 
                 0 
               
               
                   
                   
                   
                   
                 NDPA-12 
                 — 
               
               
                 3-18 
                 145 
                 0.78 
                 25 
                 5 gpt 
                 10.80 
                 1,000 
                 105  
                 65 
                 102  
                 0 
               
               
                   
                   
                   
                   
                 TAA 
                 — 
               
               
                 3-19 
                 158 
                 1.74 
                 25 
                 5 gpt 
                 10.62 
                 1,000 
                 — 
                 — 
                 19 
                 0 
               
               
                   
                   
                   
                   
                 DHA 
                 10.97 
               
               
                 3-20 
                 169 
                 1.28 
                 25 
                 5 gpt 
                 10.40 
                 1,000 
                 80 
                 35 
                 10 
                 0 
               
               
                   
                   
                   
                   
                 DDA 
                 10.79 
               
               
                 3-21 
                   
                 3.4 
                 25 
                 5 gpt 
                 10.81 
                   790 
                 40 
                 — 
                 12 
                 0 
               
               
                   
                   
                   
                   
                 Duomeen 
                 10.05 
               
               
                   
                   
                   
                   
                 T 
               
               
                   
               
               
                 (The additive abbreviations used in TABLE 4 have the same meaning as defined in the previous examples.)  
               
             
          
         
       
     
     The preceding description of specific embodiments of the present invention is not intended to be a complete list of every possible embodiment of the invention. Persons skilled in this field will recognize that modifications can be made to the specific embodiments described here that would be within the scope of the present invention.