Abstract:
A preferred novel breaker-crosslinker-polymer complex and a method for using the complex in a fracturing fluid to fracture a subterranean formation that surrounds a well bore by pumping the fluid to a desired location within the well bore under sufficient pressure to fracture the surrounding subterranean formation. The complex may be maintained in a substantially non-reactive state by maintaining specific conditions of pH and temperature, until a time at which the fluid is in place in the well bore and the desired fracture is completed. Once the fracture is completed, the specific conditions at which the complex is inactive are no longer maintained. When the conditions change sufficiently, the complex becomes active and the breaker begins to catalyze polymer degradation causing the fracturing fluid to become sufficiently fluid to be pumped from the subterranean formation to the well surface.

Description:
This is a continuation in part of application Ser. No. 08/640,462, filed May 1, 1996 now U.S. Pat. No. 5,806,597. 
    
    
     BACKGROUND OF THE INVENTION 
     Oil well stimulation typically involves injecting a fracturing fluid into the well bore at extremely high pressure to create fractures in the rock formation surrounding the bore. The fractures radiate outwardly from the well bore, typically from about 100 to 1000 meters, and extend the surface area from which oil or gas drains into the well. The fracturing fluid typically carries a propping agent, or “proppant,” such as sand, so that the fractures are propped open when the pressure on the fracturing fluid is released, and the fracture closes around the propping agent. 
     Fracturing fluid typically contains a water soluble polymer, such as guar gum or a derivative thereof, that provides appropriate flow characteristics to the fluid and suspends the proppant particle. When pressure on the fracturing fluid is released and the fracture closes around the propping agent, water is forced out and the water-soluble polymer forms a filter cake. This filter cake can prevent oil or gas flow if it is not removed. 
     Breakers are added to the fracturing fluid to enable removal of the filter cake. Breakers catalyze the breakdown of the polymer in the compacted cake to simple sugars, making the polymer fluid so that it can be pumped out of the well. Currently, breakers are either enzymatic breakers or oxidative breakers. 
     Oxidative breakers have been widely applied in fracturing applications. Oxidizers react non-specifically with any oxidizable material including hydrocarbons, tubular goods, formation components, and other organic additives. Oxidizers release free radicals that react upon susceptible oxidizable bonds or sites. Free radicals are charged ions with unpaired electrons and are very reactive due to their natural tendency to form electron-pair bonds. Free radicals can be generated from either thermal or catalytic activation of stable oxidative species. The major problem with using oxidative breakers to remove a proppant cake is that reactions involving free radicals are usually very rapid so the proppant cake may become fluid before the pumping treatment is completed. 
     Encapsulated oxidative breakers were introduced to provide a delayed release of the persulfate breaker payload until after the pumping treatment is complete. However, there are several problems related to using encapsulated breakers in hydraulic fracturing treatments. First, premature release of the oxidative payload sometimes occurs due to product manufacturing imperfections or coating damage resulting from abrasion experienced in pumping the particles through surface equipment, tubulars, and perforations. Second, homogeneous distribution of encapsulated breaker is more difficult within the propped fracture. Since the persulfate is confined to individual encapsulated particles, encapsulated breakers must be added throughout the pumping process to achieve adequate distribution. 
     Enzymes are a second type of breaker that exhibits a unique ability to act as a bio-catalyst to accelerate chemical reactions. The catalytic activity does not change the enzyme structure during reaction initiation and thus, the enzyme may initiate another reaction, and so on. A polymer-specific enzyme is an enzyme that will align and react with only that particular polymer. 
     The problem with enzymatic breakers is that they begin catalyzing polymer degradation immediately upon addition. Encapsulating enzymes helps alleviate this problem, but causes the same type of problems described above with encapsulated oxidants. A method is needed to prevent or reduce immediate degradation of enzyme additives, while allowing the enzymes to be evenly dispersed throughout the polymer and to retain their activity. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a gellable fracturing fluid composed of a breaker-crosslinker-polymer complex is provided. The complex comprises a matrix of compounds, substantially all of which include a breaker component, a crosslinker component and a polymer component. The complex may be maintained in a substantially non-reactive state by maintaining specific conditions of pH and temperature. A preferred breaker includes an enzyme more particularly a high-temperature-high-pH-guar-specific enzyme or a high-temperature-high-pH-cellulose specific enzyme. The preferred crosslinker components include any of the conventionally used crosslinking agents that are known to those skilled in the art. For instance, in recent years, gellation of the hydratable polymer has been achieved by crosslinking these polymers with metal ions including aluminum, antimony, zirconium and titanium containing compounds including the so-called organometallics. Transition metals such as zirconium and titanium crosslinkers are preferred. Borate ion donating materials are also preferred as crosslinkers, for example, the alkali metal and the alkaline earth metal borates and boric acid. Crosslinkers that contain boron ion donating materials may be called borate systems. Crosslinkers that contain zirconium may be called zirconate systems. A preferred polymer component includes guar or guar derivatives in particular carboxymethyl-hydroxypropyl guar and cellulose or cellulose derivatives. The polymer must be compatible with the enzyme and the crosslinker. The conditions at which a preferred complex may be maintained in a substantially non-reactive state are about pH 9.3 to 11.0 and temperature of about 70° F. to 300° F. 
     According to another aspect of the invention, a method for using the breaker-crosslinker-polymer complex in gellable fracturing fluid is provided. A preferred method for using the fracturing fluid includes pumping the fluid comprising the complex in a substantially non-reactive state to a desired location within the well bore under sufficient pressure to fracture the surrounding subterranean formation. The complex is then maintained in the substantially non-reactive state by maintaining specific conditions of pH and temperature until a time at which the fluid is in place in the well bore and the desired fracture treatment or operation is completed. Once the fracture is completed, the specific conditions at which the complex is inactive are no longer required. Such conditions that may change, for example, are pH and temperature. When the conditions change sufficiently, the complex becomes active and the breaker begins to catalyze polymer degradation causing the fluid to become less viscous, allowing the “broken” fluid to be produced from the subterranean formation to the well surface. A “broken” fluid is considered as a fluid having a viscosity of less than 10 cps at 511 S-1 . 
     The benefits of using the complex and the method of this invention are that more even distribution of the breaker is achieved, initial or front-end viscosity at temperature of the fracturing fluid is substantially increased, and the filter cake is more efficiently removed. The benefits of this invention may be achieved when the breaker is added to a crosslinker and polymer combination or when the breaker is first combined with the crosslinker and then added to the polymer. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In practicing a preferred method of the invention, an aqueous fracturing fluid is first prepared by blending a hydratable polymer into an aqueous fluid. The aqueous fluid could be, for example, water, brine, aqueous based foams or water-alcohol mixtures. Any suitable mixing apparatus may be used for this procedure. In the case of batch mixing, the hydratable polymer and the aqueous fluid are blended for a period of time sufficient to form a hydrated solution. The hydratable polymers useful in the present invention may be any of the hydratable polysaccharides and are familiar to those in the well service industry. These polysaccharides are capable of gelling in the presence of a crosslinking agent to form a gelled based fluid. Specific examples are guar gum, guar gum derivatives, cellulose and cellulose derivatives. The preferred gelling agents are guar gum, hydroxy propyl guar and carboxymethyl-hydroxypropyl guar (CMHPG), carboxymethyl guar (CMG), or carboxymethylhydroxy-ethyl cellulose (CMHEC). 
     The hydratable polymer may be added to the aqueous fluid in concentrations ranging from about 0.06% to 1.8% by weight of the aqueous fluid. The most preferred range for the present invention is about 0.3% to about 0.96% by weight. 
     In addition to the hydratable polymer, the fracturing fluids of the invention include a crosslinking agent. The preferred crosslinkers include any of the conventionally used crosslinking agents that are known to those skilled in the art. For instance, in recent years, gellation of the hydratable polymer has been achieved by crosslinking these polymers with metal ions including aluminum, antimony, zirconium and titanium containing compounds including the so-called organometallics. Transition metals such as zirconium and titanium crosslinkers are preferred. Borate ion donating materials are also preferred as crosslinkers, for example, the alkali metal and the alkaline earth metal borates and boric acid. See, for instance, U.S. Pat. No. 4,514,309 and U.S. Pat. No. 5,201,370. Zirconium and boron crosslinking agents (zirconate or borate crosslinkers) are the most preferred of this invention. 
     A preferred zirconate crosslinking additive is preferably present in the range from about 0.5% to in excess of 2.0% by weight of the polymer. Preferably, the concentration of crosslinking agent is in the range from about 0.7% to about 1.5% by weight of the polymer. 
     A preferred borate crosslinking additive is preferably present in the range from about 0.5% to in excess of 2.0% by weight of the polymer. Preferably, the concentration of crosslinking agent is in the range from about 0.7% to about 1.5% by weight of the polymer. 
     Propping agents are typically added to the base fluid prior to the addition of the crosslinking agent. Propping agents include, for instance, quartz sand grains, glass and resin coated ceramic beads, walnut shell fragments, aluminum pellets, nylon pellets, and the like. The propping agents are normally used in concentrations between about 1 to 18 pounds per gallon of fracturing fluid composition, but higher or lower concentrations can be used as required. The base fluid can also contain other conventional additives common to the well service industry such as surfactants. 
     Unlike the breaker system of the prior art, a new highly stable breaker-crosslinker-polymer complex has been developed that reduces premature fluid degradation while allowing the breaker to be evenly dispersed throughout the polymer. Such a stable breaker-crosslinker-polymer complex may be prepared by determining specific conditions of pH and temperature at which a specific breaker-crosslinker-polymer forms a stable complex with a matrix of compounds, each compound including a compatible breaker, polymer, and crosslinker. Then, fracturing fluid is maintained at those conditions until the fluid is in place in the subterranean formation. Next, the conditions are allowed to vary such that the complex becomes active and the reaction, in which the polymer is broken down to lower molecular weight fragments, is catalyzed by the breaker. Once the polymer is broken down to lower molecular weight fragments, a fluid consistency develops that allows the polymer to be easily removed from the well. 
     Incredible unexpected rheological properties have been attributed to the use of this breaker-crosslinker-polymer complex. Upon formation of the complex, up to about 50% increase in initial viscosity has been demonstrated when compared to the initial viscosity of fracturing fluids without the complex to which breaker has been added. Tables 2 and 3 demonstrate the high initial viscosity of this invention. This high initial viscosity is believed to be due to a matrix of high molecular weight compounds contained in the complex. It is believed that each of the compounds in the matrix is made up of enzyme, crosslinker and polymer held together in equilibrium as long as specific conditions are maintained. 
     Preferred breaker components of this invention are polymer specific enzymes. A particularly advantageous feature of polymer-specific-enzyme breakers with respect to fracturing applications, is that upon introduction to the aqueous polymer solution, the enzyme will attach to a strand of polymer. The enzyme will then “piggy-back” (bind or stay attached) on that polymer strand until such time as conditions are appropriate for the reaction to occur that completely degrades the polymer. The enzyme will migrate to wherever the polymer travels; i.e., within the primary fracture, into natural fractures, or into high permeability matrices. Thus, the enzyme degradant will be distributed and concentrated homogeneously with the polymer throughout the fracture. 
     Preferred embodiments of the breaker-crosslinker-polymer complex have been demonstrated at a temperature range of about 70° F. to about 275° F. and at a pH of about 9.3 to about 10.5. In this environment, preferred breaker-crosslinker-polymer complexes remain in equilibrium with very little or no dissociation and the breaker does not substantially degrade the polymer. 
     As can be seen in Tables 2 and 3, incredible initial viscosity has been demonstrated with the breaker complex comprising a high-temperature-high-pH-guar-specific enzyme, a diesel slurried CMHPG and a zirconate or guar and a borate crosslinker, respectively. Instead of the usual reduction in viscosity of up to 20% on addition of the breaker, fracturing fluids including the breaker system of this embodiment have exhibited substantially increased viscosity upon addition of the breaker as may be seen by the immediate increase in viscosity demonstrated in Tables 2 and 3. This incredible initial viscosity has been demonstrated whether the enzyme was added to the crosslinker and substrate or the enzyme and crosslinker were added to the substrate. 
     The underlying basis of this invention may be better explained by considering conventional enzyme pathways which may be described by the following reaction: 
     
       
         E+S→[ES]→E+P  (1) 
       
     
     in which E is an enzyme, S is a substrate, [ES] is an intermediate enzyme-substrate complex and P is the product of the substrate degradation catalyzed by the enzyme. The reaction rate of the intermediate enzyme-substrate complex is pH dependent and may be slowed or even virtually halted by controlling the pH and temperature of the enzyme substrate complex. 
     Further explanation may be found in the following equations and explanation from Malcom Dixon and Edwin C. Webb.  Enzymes,  Academic Press, p. 162 (New York 1979). For an explanation of the abbreviations, see Table 1. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 SYMBOLS &amp; ABBREVIATIONS 
               
             
          
           
               
                 SYMBOL or 
                   
               
               
                 ABBRE- 
               
               
                 VIATION 
                 DEFINITION 
               
               
                   
               
               
                 S 
                 Substrate 
               
               
                 ES 
                 Enzyme-Substrate Complex 
               
               
                 E 
                 Enzyme 
               
               
                 P 
                 Product 
               
               
                 E n   
                 Enzyme with n negative charge 
               
               
                 E n S 
                 Enzyme (with n negative charge) - Substrate Complex 
               
               
                 E n S′ 
                 Enzyme (with n negative charge) - Substrate (Intermediate) 
               
               
                   
                 Complex prior to breakdown into Product (P) 
               
               
                 E n+1   
                 Enzyme with n+1 negative charge 
               
               
                 E n+1 S 
                 Enzyme with n+1 negative charge - Substrate Complex 
               
               
                 E n+1 S′ 
                 Enzyme with n+1 negative charge - 
               
               
                   
                 Substrate (Intermediate) 
               
               
                   
                 Complex prior to breakdown into Product (P) 
               
               
                 k +1 ,k +2 ,k +3   
                 Velocity constants of successive forward steps 
               
               
                   
                 in an enzyme reaction 
               
               
                 K 
                 Overall equilibrium constant between E n S and E n S′ 
               
               
                 K′ 
                 Overall equilibrium constant between E n+1 S and E n+1 S′ 
               
               
                 K S   s   
                 Apparent dissociation constant of E n S Complex 
               
               
                 K S   s′   
                 Apparent dissociation constant of E n+1 S Complex 
               
               
                 K e , K es , K es′   
                 Ionization constants of E n ; E n S, E n S′ respectively 
               
               
                   
               
             
          
         
       
     
     Some researchers term such an enzyme-substrate complex that has been virtually halted, a non-productive complex. If a substrate forms a non-productive complex with an enzyme, the pH dependence of V and K m  may give an apparent pK value which diverges from the real value in the productive complex if the ratio of correct to abortive binding changes with the pH. For the scheme:                           
     in which the breakdown of the E n S complex is so slow that the remainder of the system remains in equilibrium, the rate equation becomes              v   =       k   +     2   e           1   +     H   Kes     +     K        (     1   +     H     Kes   ′         )           1   +           K   s   S     S          (     1   +     H   Ke       )         1   +     H   Kes     +       K   ′          (     1   +     H     Kes   ′         )                         (   3   )                                
     and thus the observed pK value obtained from plots of pK m  or log V against pH will differ from the true value by the expression                pK   observed     =     pK   -     log                     1   +   K       1   +     K   ′                     (   4   )                                
     As explained in  Enzymes  at p. 162, other instances of non-productive binding have been discussed. A breaker-crosslinker-polymer complex, however, has not heretofore been described as a component of fracturing fluids. 
     One embodiment of the invention includes a method for determining the final formulation of a gellable fracturing fluid for use in a subterranean formation comprising: 
     (1) identifying the approximate temperature range of the subterranean formation; 
     (2) determining the fluid stability time, which is the amount of time that is required for a gellable fracturing fluid having a breaker component to have that breaker component maintained in a non-reactive state so that the fracturing fluid will be stable long enough to execute a hydraulic fracturing treatment; 
     (3) determining one or more preferred preliminary fluid formulations (this preferred preliminary fluid formulation may be based on a number of variables familiar to one of ordinary skill in the art or it may simply be a customer preference; and 
     (4) determining the pH at which the breaker component can be maintained in a substantially non-reactive state. 
     The approximate temperature of the subterranean formation, the fluid stability time, and the preferred preliminary fluid formulation may be determined by any methods known to one of ordinary skill in the art. Once these three parameters are determined, it is possible to perform analyses on fracturing fluids having a breaker component to determine at what point between about pH of 9.3 to 10.5 that an optimum amount of a non-productive complex forms, which will cause the breaker to be maintained in a 
     substantially non-reactive state for the desired time period. This may be accomplished by using the methods described in the examples presented in this application. In those examples, sets of experiments are described as using an identified temperature and identified preferred preliminary fluid formulation as constants, but varying the pH by varying the amount of pH adjusting material included in the fluid formulation. This procedure is shown, in particular in Table 7, 8, and 9. Viscosity measurements of fracturing fluid samples are taken over time. The more non-productive complex in the system, the more viscous the system will remain because more of the breaker will be maintained in a substantially non-reactive state. Comparing Fann Viscometer results of the samples taken over time allows identification of the optimum pH and for selection of the specific parameters desired for a particular fracturing fluid at a particular temperature. 
     Another embodiment of the invention includes varying the amount of breaker while keeping all other parameters constant to determine the optimum amount of breaker desired in the final fluid formulation. Additional breaker may provide additional viscosity because the additional breaker causes an enhanced non productive complex network. Examples 8 (b) and 9(b) describe analyses based on varying the breaker amount and keeping all the other variables the same. Results for Examples 8(b) and 9(b) are presented in Tables 4(b) and 5(b). 
     Once testing has determined the desired final fluid formulation, that final fluid formulation can be used in the field to practice the invention. 
     The following examples will illustrate the invention, but should not be construed to limit the scope thereof unless otherwise expressly noted. 
    
    
     EXAMPLE 1 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution and 0.3125 ml. of zirconate crosslinker was mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration of rheological measurement at 250° F. No enzyme breaker was added to the system of this example. The results in Table 2, example 1, illustrate the effect of the crosslinker on the polymer at these specific conditions. 
     EXAMPLE 2 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in on liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution, 0.25 ml. of high-temperature-high-pH-guar-specific enzyme with about 30,400 international enzyme units per gram, and 0.3125 ml. of zirconate crosslinker was mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R-1-B5 rotor cup configuration for rheological measurement at 250° F. The results in Table 2, example 2, illustrate the effect of holding this particular fracturing fluid at a pH of about 9.3 and a temperature of 250° F. on the viscosity of the fracture fluid. 
     EXAMPLE 3 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution, 1.00 ml. of high-temperature-high-pH-guar-specific enzyme was mixed with about 30,400 international enzyme units per gram, and 0.3125 ml. of zirconate crosslinker were mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration for rheological measurement at 250° F. The results in Table 2, example 3, illustrate the effect of holding this particular fracturing fluid at a pH of about 9.3 and a temperature of 250° F. on the viscosity of the fracture fluid. 
     EXAMPLE 4 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution and 0.3425 ml. of a composite mixture of a zirconate crosslinker and high-temperature-high-pH-guar specific enzyme with about 30,400 international enzyme units per gram and 0.3125 ml. zirconate crosslinker was mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration for rheological measurement at 250° F. The results in Table 2, example 5, illustrate the effect of holding this particular fracturing fluid at a pH of about 9.3 and a temperature of 250° F. on the viscosity of the fracturing fluid. These results demonstrate that the beneficial effects of increased viscosity of this fracturing fluid was not affected by adding the crosslinker and the enzyme in combination. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 VISCOSITY AT 40 sec −1   
               
             
          
           
               
                 TIME AT 
                 EXAMPLE 
                 EXAMPLE 
                 EXAMPLE 
                 EXAMPLE 
               
               
                 TEMP., 
                 1 
                 2 
                 3 
                 4 
               
               
                 HOURS 
                 (cps) 
                 (cps) 
                 (cps) 
                 (cps) 
               
               
                   
               
               
                 0 
                 691 
                 1048 
                 726 
                 1141 
               
               
                 1 
                 591 
                 983 
                 860 
                 962 
               
               
                 2 
                 633 
                 649 
                 696 
                 577 
               
               
                 3 
                 448 
                 401 
                 503 
                 376 
               
               
                 4 
                 622 
                 217 
                 338 
                 259 
               
               
                 5 
                 514 
                 122 
                 185 
                 201 
               
               
                 6 
                 401 
                 83 
                 111 
                 154 
               
               
                 7 
                 267 
                 60 
                 80 
                 133 
               
               
                 8 
                 182 
                 43 
                 60 
                 112 
               
               
                 9 
                 115 
                 39 
                 39 
                 98 
               
               
                 10 
                 94 
                 34 
                 37 
                 89 
               
               
                 12 
                 42 
                 13 
                 28 
                 74 
               
               
                 14 
                 24 
                 2 
                 12 
                 16 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 5 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 2.50 ml. of 45% potassium carbonate solution and 1.50 ml. of borate crosslinker were added and the solution mixed until gelling was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 250° F. The results in Table 3, example 5, illustrate the effect of the crosslinker on the polymer at these specific conditions. 
     EXAMPLE 6 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 250 ml. of 45% potassium carbonate solution, 1.50 ml. of borate crosslinker, 0.125 ml. of high-temperature-high pH-guar-specific enzyme with about 30,400 international enzyme units per gram was mixed until gelling was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 250° F. The results in Table 3, example 6, illustrate the effect of holding this particular fracturing fluid at a pH of about 10.3 and a temperature of 250° F. on the viscosity of the fracturing fluid. 
     EXAMPLE 7 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried guar polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 2.50 ml. of 45% potassium carbonate solution, 1.50 ml. of borate crosslinker and 1.0 ml. of high-temperature-high-pH-guar-specific enzyme with about 30,400 international enzyme units per gram was mixed until gelling was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 250° F. The results in Table 3, example 7, illustrate the effect of holding this particular fracturing fluid at a pH of about 10.3 and a temperature of 250° F. on the viscosity of the fracturing fluid. 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 TIME AT 
                 VISCOSITY AT 40 SEC −1   
               
             
          
           
               
                   
                 TEMP., 
                 EXAMPLE 
                 EXAMPLE 
                 EXAMPLE 
               
               
                   
                 HOURS 
                 5 
                 6 
                 7 
               
               
                   
                   
               
               
                   
                 0 
                 1021 
                 907 
                 922 
               
               
                   
                 1 
                 716 
                 976 
                 881 
               
               
                   
                 2 
                 462 
                 877 
                 655 
               
               
                   
                 3 
                 342 
                 734 
                 512 
               
               
                   
                 4 
                 246 
                 608 
                 425 
               
               
                   
                 5 
                 185 
                 484 
                 312 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 8a 
     A solution containing 2% (w/v) potassium chloride and 30 ppt guar was hydrated in 2.5 l of tap water for about 2 minutes. The solution was divided into 250 ml aliquots. An aliquot was mixed at 1500 rpm to get a vortex. One fourth of a ml of the galactomannanase solution at an appropriate concentration of hemicellulase units/ml (HCU/ml) was added next. Then 0.25 ml of the crosslinker was added. The solution was mixed until gellation was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 100° F. 
     EXAMPLE 8b 
     A solution containing 2% (w/v) potassium chloride and 30 ppt guar was hydrated in 2.5 l of tap water for about 2 minutes. The solution was divided into 250 ml aliquots. An aliquot was mixed at 1500 rpm to get a vortex. One fourth of a ml of the galactomannanase solution at an appropriate concentration of hemicellulase units/ml (HCU/ml) was added next. Then 0.25 ml of the crosslinker was added. The solution was mixed until gellation was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 100° F. 
     Examples 8(a) and 8(b) (results presented in Table 4(a) and (b)) illustrate the effect of a non-productive complex. A non-productive complex is formed by the process described in Example 8(b), whereas a non-productive complex is not formed by the process described in Example 8(a). Example 8(b) data presented in Table 4(b) shows enhanced long term viscosity. For example, at 40 sec −1 , the data presented in Table 4(b) on range from 1296 at zero minutes to 11 at 450 minutes, whereas the data presented in Table 4(b) ranges from 1034 at 0 minutes to 469 at 450 minutes. The data presented in Table 4(b) shows that a viscous state is maintained over 450 minutes, whereas the data presented in Table (a) shows that a viscous state is not maintained by the procedures of Example 8(b). The parameters that cause the production of the non-productive complex of Example 8(b) include a higher pH (from pH 9.5 in Example 8(a) to pH 9.95 in Example 8(b)). In the process described in Example 8(b), the enzyme is not reactive because it is maintained in a non-productive complex. Because the enzyme is not reactive, the fluid does not lose viscosity. In the process described in Example 8(a), the enzyme is reactive. The reaction of the enzyme with the polymer causes the fluid to become less viscous. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 4(a) 
               
             
             
               
                   
               
               
                 Table 4 (a) Data Based 
               
               
                 On U.S. Pat. No. 5,201,370 
               
               
                 (No Non-Productive Complex) 
               
               
                 ADDITIVES: 30 ppt Guar + 0.75 gpt 45% 
               
               
                 Potassium Carbonate + 1 gpt Borate Crosslinker 
               
               
                 BREAKER: 1 gpt Galactomannanase (30,000 IHU/mL) 
               
               
                 TEMPERATURE: 100° F. 
               
               
                 PH: 9.5 
               
             
          
           
               
                   
                 TIME 
                 511 
                 170 
                 100 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 0 
                 313 
                 578 
                 777 
               
               
                   
                 30 
                 274 
                 490 
                 648 
               
               
                   
                 60 
                 238 
                 415 
                 542 
               
               
                   
                 90 
                 215 
                 365 
                 471 
               
               
                   
                 120 
                 181 
                 299 
                 381 
               
               
                   
                 150 
                 153 
                 246 
                 309 
               
               
                   
                 130 
                 126 
                 196 
                 243 
               
               
                   
                 210 
                 103 
                 156 
                 190 
               
               
                   
                 240 
                 85 
                 124 
                 149 
               
               
                   
                 270 
                 70 
                 99 
                 117 
               
               
                   
                 300 
                 58 
                 79 
                 92 
               
               
                   
                 330 
                 48 
                 63 
                 72 
               
               
                   
                 360 
                 40 
                 50 
                 56 
               
               
                   
                 390 
                 30 
                 36 
                 39 
               
               
                   
                 420 
                 18 
                 21 
                 23 
               
               
                   
                 450 
                 9 
                 10 
                 11 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 4(b) 
               
             
             
               
                   
               
               
                 Table 4(b) Data Collected 
               
               
                 For Present Application 
               
               
                 (Strong Non-Productive 
               
               
                 Complex Present) 
               
               
                 ADDITIVES: 30 ppt Guar + 1.25 gpt 45% Potassium 
               
               
                 Carbonate + 1 gpt Borate Crosslinker 
               
               
                 BREAKER: 1 gpt Galactomannanase (30,000 IHU/mL) 
               
               
                 TEMPERATURE: 100° F. 
               
               
                 PH: 9.95 
               
             
          
           
               
                 TIME 
                 40 
                 170 
                 100 
                 40 
               
               
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
               
               
                 0 
                 1296 
                 746 
                 840 
                 1034 
               
               
                 30 
                 1050 
                 374 
                 500 
                 825 
               
               
                 60 
                 861 
                 264 
                 356 
                 600 
               
               
                 90 
                 732 
                 234 
                 311 
                 509 
               
               
                 120 
                 578 
                 221 
                 290 
                 467 
               
               
                 150 
                 458 
                 215 
                 288 
                 477 
               
               
                 130 
                 351 
                 239 
                 323 
                 545 
               
               
                 210 
                 268 
                 230 
                 298 
                 468 
               
               
                 240 
                 204 
                 239 
                 310 
                 483 
               
               
                 270 
                 156 
                 237 
                 302 
                 458 
               
               
                 300 
                 119 
                 235 
                 300 
                 460 
               
               
                 330 
                 90 
                 234 
                 303 
                 473 
               
               
                 360 
                 68 
                 244 
                 314 
                 485 
               
               
                 390 
                 46 
                 262 
                 335 
                 515 
               
               
                 420 
                 26 
                 235 
                 293 
                 428 
               
               
                 450 
                 11 
                 248 
                 314 
                 469 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 9a 
     A solution containing 2% (w/v) potassium chloride and 30 ppt guar was hydrated in 2.5 l of tap water for about 2 minutes. The solution was divided into 250 ml aliquots. An aliquot was mixed at 1500 rpm to get a vortex. One half of a ml of the galactomannanase solution at an appropriate concentration of hemicellulase units/ml (HCU/ml) was added next. Then 0.25 ml of the crosslinker was added. The solution was mixed until gellation was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 100° F. 
     EXAMPLE 9b 
     A solution containing 2% (w/v) potassium chloride and 30 ppt guar was hydrated in 2.5 l of tap water for about 2 minutes. The solution was divided into 250 ml aliquots. An aliquot was mixed at 1500 rpm to get a vortex. One half of a ml of the galactomannanase solution at an appropriate concentration of hemicellulase units/ml (HCU/ml) was added next. Then 0.25 ml of the crosslinker was added. The solution was mixed until gellation was completed. Forty-two grams of sample solution was transferred to a FANN model 50C with an R1-B1 rotor cup configuration for rheological measurement at 100° F. 
     Examples 9(a) and 9(b) (results presented in Table 5(a) and (b)) illustrate the effect of a non-productive complex. A non-productive complex is formed by the process described in Example 9(b), whereas a non-productive process is not formed in the process described in Example 9(a). The data presented in Table 5(b) shows enhanced long term viscosity. For example, at 40 sec −1 , the data presented in Table 5(a) ranges from 1300 at zero minutes to 9 at 450 minutes, whereas the data presented in Table 5(b) shows that the viscosity is maintained by the change from 672 at 0 minutes to 787 at 450 minutes. The data presented in Table 5(b) shows a maintained viscous state, whereas the data presented in Example 9(a) shows that the enzyme acted to make the fluid less viscous. The parameters that cause the production of the non-productive complex of Example 9(b) include an increased pH (from pH 9.5 in Example 9(a) to pH 9.95 in Example 9(b)). In the process described in Example 9(b), the enzyme is not reactive because it is maintained the non-productive complex so the fluid does not lose viscosity. In the process of 9(a), the enzyme is reactive and causes the fluid to become less viscous. There is twice as much enzyme used in Example 9(a) as in Example 8(b). 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 5(a) 
               
             
             
               
                   
               
               
                 Table 5 (a) Data Based 
               
               
                 On U.S. Pat. No. 5,201,370 
               
               
                 (No Non-Productive Complex) 
               
               
                 ADDITIVES: 30 ppt Guar + 0.75 gpt 45% 
               
               
                 Potassium Carbonate + 1 gpt Borate 
               
               
                 Crosslinker 
               
               
                 BREAKER: 2 gpt Galactomannanase (30,000 IHU/mL) 
               
               
                 TEMPERATURE: 100° F. 
               
               
                 PH: 9.5 
               
             
          
           
               
                 TIME 
                 511 
                 170 
                 100 
                 40 
               
               
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
               
               
                 0 
                 314 
                 580 
                 780 
                 1300 
               
               
                 30 
                 267 
                 474 
                 625 
                 1009 
               
               
                 60 
                 197 
                 336 
                 434 
                 676 
               
               
                 90 
                 153 
                 248 
                 313 
                 470 
               
               
                 120 
                 109 
                 168 
                 207 
                 298 
               
               
                 150 
                 83 
                 121 
                 145 
                 200 
               
               
                 180 
                 61 
                 84 
                 98 
                 129 
               
               
                 210 
                 48 
                 62 
                 70 
                 87 
               
               
                 240 
                 35 
                 42 
                 46 
                 54 
               
               
                 270 
                 28 
                 31 
                 33 
                 36 
               
               
                 300 
                 9 
                 9 
                 9 
                 9 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 5(b) 
               
             
             
               
                   
               
               
                 Table 5 (b) Data Collected 
               
               
                 For Present Application 
               
               
                 (No Non-Productive 
               
               
                 Complex Stronger Than 
               
               
                 That in Example 8(b)) 
               
               
                 ADDITIVES: 30 ppt Guar + 1.25 gpt 45% 
               
               
                 Potassium Carbonate + 1 gpt 
               
               
                 Borate Crosslinker 
               
               
                 BREAKER: 2 gpt Galactomannanase (30,000 IHU/mL) 
               
               
                 TEMPERATURE: 100° F. 
               
               
                 PH: 9.95 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 0 
                 481 
                 544 
                 672 
               
               
                   
                 30 
                 396 
                 526 
                 857 
               
               
                   
                 60 
                 406 
                 492 
                 684 
               
               
                   
                 90 
                 478 
                 596 
                 873 
               
               
                   
                 120 
                 443 
                 563 
                 849 
               
               
                   
                 150 
                 336 
                 426 
                 641 
               
               
                   
                 180 
                 421 
                 535 
                 807 
               
               
                   
                 210 
                 410 
                 513 
                 754 
               
               
                   
                 240 
                 403 
                 506 
                 750 
               
               
                   
                 270 
                 514 
                 633 
                 908 
               
               
                   
                 300 
                 441 
                 545 
                 787 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 10 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution and 0.3125 ml. of zirconate crosslinker was mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration of rheological measurement at 200° F. No enzyme breaker was added to the system of this example. The results in Example 10—Table 6, example 10 illustrate the effect of the crosslinker on the polymer at these specific conditions. 
     The results of Example 10 are presented in Table 6. Example 10 describes a process at initial pH of 9.27. There is no enzymatic breaker added. At 40 sec −1 , the viscosity steadily increases from 313 at 2 minutes to 572 at 218 minutes. Viscosity increases due to the action of the polymer. There is no enzyme present to cause reduction in viscosity. There is no non-productive complex present because the initial pH described in Example 10 is less than the range of pH 9.3-11 at which a non-productive complex will form and there is no enzyme present. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 ADDITIVES: 
                 2% (w/w) Potassium Chloride, 10 
               
               
                   
                 milliliters of diesel slurried CMHPG polymer 
               
               
                   
                 (equivalent to 40 pounds per 1000 gallons), 
               
               
                   
                 0.3125 mL of 45% Potassium 
               
               
                   
                 Carbonate solution, 0.3125 mL of 
               
               
                   
                 Zirconate Crosslinker 
               
               
                 BREAKER: 
                 None 
               
               
                 TEMPERATURE: 
                 200° F. 
               
               
                 INITIAL PH: 
                 9.27 (Slightly Below pH 9.3 and No Breaker 
               
               
                   
                 so No Non-Productive Complex Produced) 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 2 
                 60 
                 110 
                 313 
               
               
                   
                 33 
                 512 
                 590 
                 753 
               
               
                   
                 64 
                 435 
                 498 
                 631 
               
               
                   
                 95 
                 437 
                 509 
                 661 
               
               
                   
                 125 
                 405 
                 483 
                 657 
               
               
                   
                 156 
                 401 
                 481 
                 659 
               
               
                   
                 187 
                 374 
                 452 
                 627 
               
               
                   
                 218 
                 360 
                 426 
                 572 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 11 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.3125 ml. of 45% potassium carbonate solution, 1.00 ml. of high-temperature-high-pH-guar-specific enzyme was mixed with about 30,400 international enzyme units per gram, and 0.3125 ml. of zirconate crosslinker were mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R-1-B5 rotor cup configuration for rheological measurement at 200° F. The results in Example 11—Table 7 illustrate the effect of the crosslinker in the enzyme on the polymer at these conditions. 
     The results of Example 11 are presented in Table 7. Example 11 describes a process at initial pH of 9.27. There is 1 ml of enzymatic breaker added. At 40 sec −1 , the viscosity increases from 288 at 2 minutes to 527 at 122 minutes, then begins to lose viscosity after 122 minutes down to 392 at 215 minutes. This process shows an enzyme breaking the viscosity normally. There is no to only a very sight production of non-productive complex present in Example 11. The pH of 9.27 is less than the range of pH 9.3-11 at which a non-productive complex will form. There is an enzyme present. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 ADDITIVES: 
                 2% (w/w) Potassium Chloride, 10 ml 
               
               
                   
                 of diesel slurried CMHPG polymer (equivalent 
               
               
                   
                 to 40 pounds per 1000 gallons), 0.3125 ml of 45% 
               
               
                   
                 Potassium Carbonate solution, 
               
               
                   
                 0.3125 mL of Zirconate Crosslinker 
               
               
                 BREAKER: 
                 1 mL of high-temperature-high-pH-guar-specific 
               
               
                   
                 enzyme (30,4000 IUH/gram) 
               
               
                 TEMPERATURE: 
                 200° F. 
               
               
                 INITIAL PH: 
                 9.27 (pH below 9.3 so no or only very slight 
               
               
                   
                 Non-Productive Complex present) 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 2 
                 51 
                 97 
                 288 
               
               
                   
                 33 
                 421 
                 492 
                 644 
               
               
                   
                 61 
                 405 
                 454 
                 553 
               
               
                   
                 92 
                 389 
                 433 
                 522 
               
               
                   
                 122 
                 355 
                 411 
                 527 
               
               
                   
                 153 
                 328 
                 359 
                 420 
               
               
                   
                 184 
                 314 
                 339 
                 388 
               
               
                   
                 215 
                 292 
                 326 
                 392 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 12 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.25 ml. of 45% potassium carbonate solution, 1.00 ml. of high-temperature-high-pH-guar-specific enzyme was mixed with about 30,400 international enzyme units per gram, and 0.3125 ml. of zirconate crosslinker were mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration for rheological measurement at 200° F. The results in Example 12—Table 8 illustrate the effect of the enzyme and the crosslinker on the polymer at these conditions. 
     The results of Example 12 are presented in Table 8. Example 12 describes a process at initial pH of 9.1. There is 1 ml of enzymatic breaker added. At 40 sec −1 , the viscosity increases from 424 at 2 minutes to 512 at 30 minutes, then viscosity decreases after 30 minutes down to 206 at 210 minutes. This process shows an enzyme breaking the viscosity normally. There is no non-productive complex described in this Example. The pH of 9.1 is less than the range of pH 9.3-11 at which a non-productive complex will form 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 ADDITIVES: 
                 2% (w/w) Potassium Chloride, 10 ml of diesel 
               
               
                   
                 slurried CMHPG polymer 
               
               
                   
                 (equivalent to 40 pounds per 1000 gallons), 0.25 
               
               
                   
                 ml of 45% Potassium Carbonate 
               
               
                   
                 solution, 0.3125 mL of Zirconate Crosslinker 
               
               
                 BREAKER: 
                 1 mL of high temperature-high-pH-guar-specific 
               
               
                   
                 enzyme (30,4000 IUH/gram) 
               
               
                 TEMPERATURE: 
                 200° F. 
               
               
                 INITIAL PH: 
                 9.1 (pH below 9.3 so no Non-Productive Complex 
               
               
                   
                 even though there is a 
               
               
                   
                 enzymatic breaker present) 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 2 
                 67 
                 132 
                 424 
               
               
                   
                 30 
                 269 
                 341 
                 513 
               
               
                   
                 60 
                 225 
                 265 
                 351 
               
               
                   
                 90 
                 210 
                 246 
                 322 
               
               
                   
                 120 
                 204 
                 235 
                 301 
               
               
                   
                 150 
                 173 
                 203 
                 266 
               
               
                   
                 180 
                 141 
                 170 
                 236 
               
               
                   
                 210 
                 120 
                 146 
                 206 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 13 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.375 ml. of 45% potassium carbonate solution and 0.3125 ml. of zirconate crosslinker was mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration of rheological measurement at 200° F. No enzyme breaker was added to the system of this example. The results in Example 13—Table 9 illustrate the effect of the crosslinker on the polymer at these specific conditions. 
     The results of Example 13 are presented in Table 9. Example 13 describes a process at initial pH of 10.4. There is no enzymatic breaker added. At 40 sec −1 , the viscosity increases from 2839 at 2 minutes and degrades to 279 at 218 minutes. There is no non-productive complex described in this Example because there is no enzyme added. The pH of 10.4 is sufficient to form a non-productive complex if there were enzyme present. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 ADDITIVES: 
                 2% (w/w) Potassium Chloride, 10 ml of diesel 
               
               
                   
                 slurried CMHPG polymer 
               
               
                   
                 (equivalent to 40 pounds per 1000 gallons), 0.375 
               
               
                   
                 ml of 45% Potassium Carbonate 
               
               
                   
                 solution, 0.3125 ml of Zirconate Crosslinker 
               
               
                 BREAKER: 
                 None 
               
               
                 TEMPERATURE: 
                 200° F. 
               
               
                 INITIAL PH: 
                 10.4 (pH sufficient for Non-Productive Complex 
               
               
                   
                 formation, but no Non- 
               
               
                   
                 Productive Complex forms because there is 
               
               
                   
                 no enzymatic breaker present) 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 2 
                 782 
                 1255 
                 2839 
               
               
                   
                 33 
                 1103 
                 1353 
                 1928 
               
               
                   
                 64 
                 950 
                 1181 
                 1722 
               
               
                   
                 95 
                 691 
                 874 
                 1313 
               
               
                   
                 125 
                 492 
                 633 
                 978 
               
               
                   
                 156 
                 319 
                 416 
                 658 
               
               
                   
                 187 
                 195 
                 260 
                 425 
               
               
                   
                 218 
                 124 
                 166 
                 279 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 14 
     A solution containing 2% (w/w) potassium chloride and 10 milliliters of diesel slurried CMHPG polymer (equivalent to 40 pounds per 1000 gallons) was hydrated in one liter of tap water for about 30 minutes. The solution was divided into 250 ml. aliquots. An aliquot was mixed at 1500 rpm to get a vortex. A solution containing 0.75 ml. of 45% potassium carbonate solution, 1.00 ml. of high-temperature-high-pH-guar-specific enzyme was mixed with about 30,400 international enzyme units per gram, and 0.3125 ml. of zirconate crosslinker were mixed until gelling was completed. Forty-six grams of sample solution was transferred to a FANN model 50C with an R1-B5 rotor cup configuration for rheological measurement at 200° F. The results in Example 14—Table 10 illustrate the effect of the crosslinker and breaker on the polymer at these conditions. 
     The results of Example 14 are presented in Table 10. Example 14 describes a process at initial pH of 10.4. One ml of enzymatic breaker is added. At 40 sec −1 , the viscosity is at 2577 at 2 minutes. The viscosity decreases over time, but is maintained at a level of 795 after 215 minutes. This is 3 times as viscous as the results presented in Table 9. This increase is due to the production of a non-productive complex. The enzyme is part of the non-productive complex and therefore cannot react to make the fluid become less viscous. The pH of 10.4 is sufficient to form a non-productive complex and there is an enzyme present. The difference between the data presented in Table 9 and Table 10 is that an enzyme is present in Example 14(Table 10 data) and this enzyme contributes to a non-productive complex. When the enzyme becomes part of the non-productive complex, the enzyme cannot react with the polymer to cause the fluid to become less viscous. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 ADDITIVES: 
                 2% (w/w) Potassium Chloride, 10 ml of diesel 
               
               
                   
                 slurried CMHPG polymer 
               
               
                   
                 (equivalent to 40 pounds per 1000 gallons), 
               
               
                   
                 0.375 ml of 45% Potassium Carbonate 
               
               
                   
                 solution, 0.3125 ml of Zirconate Crosslinker 
               
               
                 BREAKER: 
                 1 ml of high-temperature-high-pH-guar-specific 
               
               
                   
                 enzyme (30,4000 IUH/gram) 
               
               
                 TEMPERATURE: 
                 200° F. 
               
               
                 INITIAL PH: 
                 10.4 (pH between 9.3-10.5 and enzymatic breaker 
               
               
                   
                 present; strong Non-Productive 
               
               
                   
                 Complex present) 
               
             
          
           
               
                   
                 TIME 
                 170 
                 100 
                 40 
               
               
                   
                 (min) 
                 sec −1   
                 sec −1   
                 sec −1   
               
               
                   
                   
               
               
                   
                 2 
                 611 
                 1035 
                 2577 
               
               
                   
                 33 
                 1364 
                 1602 
                 2117 
               
               
                   
                 61 
                 1048 
                 1252 
                 1702 
               
               
                   
                 92 
                 837 
                 1018 
                 1428 
               
               
                   
                 122 
                 690 
                 850 
                 1219 
               
               
                   
                 153 
                 573 
                 714 
                 1044 
               
               
                   
                 184 
                 475 
                 604 
                 915 
               
               
                   
                 215 
                 403 
                 517 
                 795 
               
               
                   
                   
               
             
          
         
       
     
     The preceding description of specific embodiments for the present invention is not intended to be a complete list of every embodiment of the invention. Persons who are skilled in this field will recognize that modifications can be made to the specific embodiments described herein that would be within the scope of the invention.