Abstract:
A method of formulating an organo-zirconium compound is accomplished by combining in solution a dialdehyde such as glyoxal with zirconium carbonate. The reacting solution forms an organo-zirconium compound and carbon dioxide which is evolved as a gas from the solution. This eliminates the need to filter or wash the organo-zirconium compound in order to remove undesirable by-products. The organo-zirconium compound can be used as a crosslinking agent for crosslinking aqueous polymer gels used in fracturing fluids for fracturing subterranean formations of oil and gas wells.

Description:
This application is a divisional of application Ser. No. 08/502,352, filed Jul. 14, 1995, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method of forming an organo-metallic compound, and particularly to an organo-zirconium compound, from a starting material of zirconium carbonate, and to a method of use of such an organo-zirconium compound in crosslinking gelled fracturing fluids used in treating subterranean formations of oil and gas wells. 
     2. Description of the Prior Art 
     Hydraulic fracturing fluids used in fracturing subterranean formations of oil and gas wells are usually formed from aqueous based fluids which are gelled by the addition of soluble polymers. These soluble polymers are often formed from solvatable polysaccharides which include such things as guar, guar derivatives and carboxylated cellulose. With very little addition of these polymers, the viscosity of the aqueous fluid can be increased dramatically. Increasing the viscosity of these aqueous based fluids for use as fracturing fluids is beneficial for various reasons. High viscosity fluids create better, larger fractures within the formation when introduced under high pressure. The higher viscosity fluids are also better able to carry proppants which are dispersed throughout the fluid and forced into the fractures so that the fractures remain open after the fluid is removed. 
     Typically, less than 1% by weight of the soluble polymers are added to water to form these viscous aqueous fluids. At 0.5% polymer concentration, water viscosity can be increased from about 1 cps to about 35 cps at 511 sec -1  as measured using a Fann 50 viscometer. Further enhancement of the fluid viscosity occurs by the addition of crosslinking agents. These additives are able to bind polymer strands together to form a continuous network, thus further increasing the viscosity of the fluid. With the addition of these crosslinker additives, the viscosity of the aqueous fluids can be increased and exceed 500 cps at 170 sec -1 . These crosslinkers are generally formed using metal complexes of titanium, zirconium, aluminum or boron. The ligands associated with these metals are chosen so that once the complex is added to the aqueous polymer sol, the polymer must compete with the ligand for the metal. This is beneficial in that it ensures that the metal complex is homogeneously mixed in the polymer sol before crosslinking occurs. The delayed effect also results in less friction or back pressures while pumping the fluid at higher rates into the oil and gas wells. 
     Zirconium lactate is commonly used as a metallic crosslinker in crosslinking these aqueous polymer fluids. Zirconium lactate can provide delayed gelation and high viscosities at elevated temperatures for periods of time that are practical for hydraulic fracturing treatments in oil and gas wells. Prior art methods of formulating zirconium lactate typically involve mixing lactic acid to either zirconium hydroxychloride or zirconium oxychloride. These compounds react to form zirconium lactate as a white precipitate. To remove chloride by-products, the zirconium lactate product is filtered, washed and redissolved by neutralization with a suitable base. The base is generally sodium, potassium or ammonium hydroxide. This method of formulating zirconium crosslinkers has disadvantages, however. Washing and filtering of the zirconium lactate product usually results in less than 100% yield. As much as 10% Zr, measured as ZrO 2 , may be lost during washing. Wastewater from the washings must be recovered and disposed of properly. The crosslinkers formed in this manner may be polymer specific and difficult to use with other polymers, in particular guar gum. These crosslinkers are also expensive because of the extensive processing and handling of wastewater that is required. 
     A need exists, therefore, for a new organo-zirconium compound for use as a crosslinker for polysaccharide containing fracturing fluids which overcomes many of the difficulties associated with the prior art zirconium lactate compounds. 
     A need also exists for such a new organo-zirconium compound which can be simply and inexpensively manufactured from commonly available starting materials. 
     A need also exists for a simple method of manufacturing an organo-zirconium compound which does not generate waste or loss of product as a result of washing and separating techniques. 
     A need also exists for such an organo-zirconium compound which is capable of more effectively crosslinking guar based aqueous fracturing fluids. 
     SUMMARY OF THE INVENTION 
     An organo-zirconium compound is formulated by combining in solution an amount of an aldehyde or dialdehyde with an amount of a zirconium salt. Most preferably, the aldehyde is selected from the group consisting of dialdehydes having about 2-4 carbon atoms, keto aldehydes having about 3-4 carbon atoms, hydroxyl aldehydes having 2-4 carbon atoms, ortho substituted aromatic dialdehydes and ortho substituted aromatic hydroxyl aldehydes. The most preferred reactants are zirconium carbonate and glyoxal with the molar ratio of zirconium to glyoxal being in the range from about 1:0.5 to 1:20, most preferably about 1:2.5 to 1:7. 
     The solution of glyoxal and zirconium carbonate is allowed to react with carbon dioxide being given off as a by-product. The carbon dioxide is allowed to evolve from the solution as a gas so that the zirconium product does not need to be washed to remove undesirable by-products. 
     The zirconium compound produced can be used as a crosslinking agent for crosslinking viscous polymer gels, such as those used in fracturing fluids. By further neutralizing the aqueous solution, zirconium precipitate is dissolved in solution. The solution can then be added to the polymer fluid. 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A zirconium compound of the invention can be formed in a simple process by the addition of a zirconium salt to an aqueous solution of a selected aldehyde or dialdehyde. Suitable zirconium salts include carbonate, ammonium carbonate, oxychloride, acetate, tetrachloride and o-sulfate. The preferred salt is zirconium carbonate due to the nature of the by-products produced, as will be more fully described. 
     The aldehyde or dialdehyde (sometimes referred to collectively hereafter as &#34;aldehyde&#34;) which is reacted with the zirconium salt is preferably selected from the group consisting of dialdehydes having 2-4 carbon atoms, keto aldehydes having about 3-4 carbon atoms, hydroxyl aldehydes having 2-4 carbon atoms, ortho substituted aromatic dialdehydes and ortho substituted aromatic hydroxyl aldehydes. Preferred aldehydes and dialdehydes include, for example, glyoxal, propane dialdehyde, 2-keto propanal, 1,4-butanedial, 2-keto butanal, 2,3-butadione, phthaldehyde, salicaldehyde, etc. The most preferred co-reactant is glyoxal, a dialdehyde, due to its ready availability from a number of commercial sources. 
     The zirconium carbonate is preferably reacted with the glyoxal in a molar ratio of zirconium ion to glyoxal in the range from about 1:0.5 to 1:20, most preferably in the range from about 1:2.5 to 1:7. 
     The process can be initiated by adding the zirconium carbonate to an aqueous solution of 40% aqueous glyoxal. Because zirconium carbonate is used, the reaction results in a by-product of carbon dioxide. Thus, during the reaction, carbon dioxide is given off as a gas which simply bubbles out of solution so that filtering and washing of the zirconium product is unnecessary. A precipitate is immediately observed. The aqueous glyoxal solution is very acidic, normally with a pH of about 2.5. At low pH, the zirconium product formed appears as a precipitate. If desired, this precipitate can be removed from solution by filtering and dried for later use. 
     By further neutralizing the solution with a suitable base, the zirconium precipitate can be dissolved and used as a crosslinking additive for crosslinking various viscous aqueous gels used as fracturing fluids. The solids can be slowly dissolved by neutralizing with base and heating from about 30 minutes to about 6 hours. The preferred temperature for heating can range from ambient to about 250° F. The most preferred heating temperature is about 200° F. for at least two hours. 
     The base can be added while the solution is still hot or after cooling. After the addition of base, the solution can be cooled or heating can continue. Preferred bases to use for neutralization include the alkali metal hydroxides such as potassium hydroxide or sodium hydroxide. Other bases include the alkanolamines, ammonium hydroxide and alkali metal carbonates and bicarbonates. The most preferred base is potassium hydroxide. 
     The preferred procedure used to make the crosslinker and its performance are described in the non-limiting examples which follow: 
     EXAMPLE 1 
     An aqueous solution of 40% (wt) glyoxal weighing 44.25 gr. was heated to 200° F. Then, 20.0 gr. of zirconium carbonate (40.4% ZrO 2 ) slurried in 20.0 gr. of DI water was slowly added to the glyoxal solution and stirred for 60 minutes. During that time, 30.0 gr of water was added to help suspend the solids. After the 60 minutes, 25.24 gr. of 46% aqueous potassium hydroxide was slowly added to the slurry. The heating continued at 200° F. for another 120 minutes. During this time, the solids slowly dissolved. The dark colored solution was then cooled to ambient. The zirconium content measured as ZrO 2  is 5.5% and the pH was 5.55. 
     EXAMPLE 2 
     A liter of tap water was treated with 20.0 gr. of technical grade potassium chloride to produce a 2% weight per volume (wt/vol) potassium chloride solution. Then, with agitation, 4.8 gr. of a fracturing fluid quality guar gum was added, together with 1.2 gr. of sodium bicarbonate, and hydrated for 60 minutes. Afterward, an aliquot of 250 ml of sol was taken and treated with 0.3 gr sodium thiosulfate and 0.06 ml of 50% (wt) monoethanolamine. Lastly, 0.1 ml of crosslinker prepared in Example 1 was added to the sol and stirred vigorously for 60 seconds. The pH of the sol was 8.85. 
     For the testing, a Fann 50 viscometer (Baroid Testing Equipment) with an R1B5 bob and cup were used. A sample of 48.0 gr was poured into the viscometer cup. The cup was screwed onto the viscometer and pressured to 200 psi with N 2 . The sample was then continuously sheared at 42 sec -1  while heating to 250° F. At temperature, a rate sweep using 105, 84, 63 and 42 sec -1  was made and repeated every 30 minutes. The interim rate between the sweeps was 42 sec -1 . The stresses corresponding to each rate of the rate sweep, together with the rates, were converted to their logarithmic value. The Power Law indices, n&#39; and K, were then determined as described by the American Petroleum Institute&#39;s bulletin RP-39. The n&#39; values presented in Tables 1-14 are unitless whereas the K values have the units of dyne/cm 2  -sec. The Power Law indices were then used to calculate the gel&#39;s viscosity at 105, 85 and 42 sec -1 . These data, over time, are shown in Table 
     
                       TABLE 1______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.06 ml 50% (wt) monoethanol amine, and 0.1 ml crosslinkerpH: 8.85             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 29   246      0.740   13.791 411    434   522 60   247      0.691   15.471 367    392   487 91   248      0.664   14.889 312    335   424122   248      0.652   14.447 286    308   393152   248      0.671   12.524 271    290   366183   248      0.680   11.151 251    269   337214   248      0.714   9.103  241    255   313245   248      0.715   8.506  226    240   293______________________________________ 
    
     EXAMPLE 3 
     The testing of the fluids described in the Examples 3-15 are conducted as stated in Example 2. 
     Another 250 ml aliquot of sol prepared in Example 2 was treated with 0.3 gr of sodium thiosulfate and 0.08 ml of 45% (wt) aqueous potassium carbonate. Then, 0.1 ml of crosslinker prepared in Example 1 was added with vigorous stirring for 60 sec. The pH of the sol was 8.83 and the data from the rheological evaluation are shown in Table 
     
                       TABLE 2______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.08 ml 45% (wt) K.sub.2 CO.sub.3  and 0.1 ml crosslinkerpH: 8.83             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 34   248      0.676   21.613 478    512   644 65   248      0.665   18.521 390    418   530 96   248      0.641   18.057 340    366   472126   248      0.665   14.958 315    338   428157   248      0.663   13.684 285    306   388188   248      0.670   12.760 275    295   372219   248      0.742   8.532  257    271   325249   248      0.727   8.423  236    250   304277   248      0.709   8.6484 223    237   291______________________________________ 
    
     EXAMPLE 4 
     The Example 3 was repeated except that the potassium carbonate buffer was reduced to 0.02 ml and the crosslinker increased to 0.12 ml. The sol pH was 8.55. These test data are shown in Table 
     
                       TABLE 3______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.02 ml 45% (wt) K.sub.2 CO.sub.3  and 0.12 ml crosslinkerpH: 8.55             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 34   248      0.585   35.220 510    557   747 64   248      0.613   27.269 450    489   642 95   248      0.618   23.132 391    424   555126   248      0.632   19.179 346    374   485156   248      0.634   16.792 306    330   428187   248      0.623   15.897 275    298   388218   248      0.621   15.0486                         258    279   365249   248      0.64    12.6557                         237    256   330276   248      0.697   8.6348 211    225   278______________________________________ 
    
     EXAMPLE 5 
     In this next example, a 250 ml aliquot was treated with 0.3 gr of sodium thiosulfate and 0.05 ml of 45% (wt) potassium carbonate. Afterwards, 0.12 ml of crosslinker prepared in Example 1 was added to the vigorously stirred sol. The sol pH was 8.81 and the rheological data obtained at 250° F. are presented in Table 4. 
     
                       TABLE 4______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.05 ml 45% (wt) K.sub.2 CO.sub.3  and 0.12 ml crosslinkerpH: 8.81             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 34   248      0.337   43.733 200    230   367 62   248      0.659   24.222 495    532   677 92   248      0.622   23.972 413    447   584123   249      0.586   25.954 378    412   552154   248      0.554   26.897 337    371   508185   249      0.884   5.4826 320    327   355216   249      0.699   10.1253                         249    266   329247   248      0.689   9.6167 226    242   301278   249      0.728   7.5082 212    224   272309   249      0.73    6.8318 194    206   249340   249      0.760   5.643  185    194   230370   249      0.750   5.636  176    186   221401   249      0.769   5.073  173    182   214432   249      0.773   4.687  163    171   201463   249      0.779   4.290  153    161   188493   249      0.770   4.312  148    155   183524   249      0.748   4.612  143    151   180554   249      0.780   3.825  137    144   168585   249      0.744   4.837  147    155   186616   249      0.763   4.630  154    162   191647   249      0.757   4.560  147    155   184678   249      0.727   4.848  136    144   175709   249      0.725   4.453  124    131   159740   249      0.775   3.263  114    120   141771   249      0.748   3.325  103    109   130802   249      0.733   3.192  92     97    118832   249      0.793   2.231  85     89    103863   249      0.754   2.442  78     82    97894    95      0.542   18.5404                         220    242   335______________________________________ 
    
     EXAMPLE 6 
     Another 250 ml aliquot of sol described in Example 2 was treated with 0.30 gr sodium thiosulfate and 0.08 ml of 45% (wt) potassium carbonate. Then, 0.12 ml of crosslinker described in Example 1 was added to the vigorously stirred sol. The sol pH was 9.00 and the rheological data obtained at 250° F. is presented in Table 5. 
     
                       TABLE 5______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.30 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.08 ml 45% (wt) K.sub.2 CO.sub.3  and 0.12 ml crosslinkerpH: 9.00             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 34   248      0.542   63.259 751    827   1142 65   249      0.541   60.143 710    783   1082 96   248      0.522   60.192 651    720   1008126   248      0.500   61.778 603    670   953157   248      0.498   59.425 575    639   910188   249      0.482   60.0358                         539    601   866219   248      0.469   60.4491                         511    571   831250   248      0.483   54.9207                         495    552   795281   248      0.479   54.3202                         481    537   775312   249      0.482   51.2398                         460    513   739343   249      0.475   50.945 443    494   716374   249      0.477   48.841 428    478   692404   249      0.472   48.797 418    467   678435   249      0.485   44.742 407    454   653444   249      0.480   45.127 401    448   646475   249      0.471   46.581 397    444   645506   249      0.468   45.321 381    426   620537   249      0.473   44.167 380    425   616567   249      0.483   41.667 376    419   603598   248      0.465   44.375 368    412   601629   248      0.470   42.310 359    402   584660   248      0.476   39.888 348    389   563691   248      0.476   38.688 338    377   546722   248      0.489   35.133 326    363   520753   248      0.474   36.299 314    351   508784   248      0.478   35.062 309    345   498815   248      0.480   33.105 294    329   474845    98      0.456   63.1739                         502    564   827______________________________________ 
    
     EXAMPLE 7 
     In this example, a liter of 2% (wt/vol) aqueous potassium chloride was vigorously stirred while adding 4.8 gr of fracturing fluid quality carboxymethylhydroxypropyl guar (CMHPG), a dual derivatized guar gum. Afterward, 1.2 gr of sodium bicarbonate was added as a buffer to accelerate polymer hydration. After adequate dispersing, the stirring rate was slowed and the polymer was allowed to hydrate for about an hour. 
     Then, as in the preceding examples, a 250 ml aliquot was withdrawn and treated with 0.45 gr of sodium thiosulfate. Next, acetic acid was added dropwise until the sol pH declined to 5.70. Afterward, 0.19 ml of crosslinker, prepared in Example 1, was added with vigorous stirring to the sol. The final pH of the fluid was 5.70 and 45.0 gr of the sol was poured into the Fann 50 cup. The rheological evaluation was conducted at 250° F. and as described in Example 2. These data are presented in Table 6. 
     
                       TABLE 6______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. CMHPG, 1.2 gr. NaHCO.sub.3, 0.45 gr.Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O, acetic acid added to adjust pH and0.19 ml crosslinkerpH: 5.70             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 32   248      0.579   56.054 790    864   1162 61   248      0.557   46.181 588    645   882 90   248      0.507   40.588 409    454   643119   248      0.504   29.040 289    321   455148   248      0.520   20.366 218    241   339177   249      0.551   12.402 153    169   232206   248      0.560   8.259  107    117   159235   248      0.562   7.043  92     101   137263   248      0.530   5.347  60     66    92292   248      0.529   4.430  49     55    76321   248      0.591   2.475  37     40    54350   248      0.428   4.082  28     32    48379   248      0.408   3.689  23     27    40408   248      0.456   2.686  21     24    35432   249      0.516   1.856  20     22    30461   249      0.420   2.458  17     19    28490   249      0.363   2.642  14     16    24519   248      0.364   2.339  12     14    22548   248      0.439   1.506  11     12    18577   248      0.440   1.382  10     11    17606   248      0.400   1.461  9      10    16635   248      0.265   2.462  8      9     16663   248      0.548   1.239  8      9     15693   248      0.207   2.882  7      9     15722   248      0.166   3.338  7      8     15751   248      0.239   2.416  7      8     14780   248      0.268   2.136  7      8     14809   248      0.276   2.070  7      8     14838   100      0.672   0.513  11     12    15______________________________________ 
    
     EXAMPLE 8 
     In this example, another 250 ml aliquot was withdrawn from the stock solution prepared as described in Example 2. This sol was treated with 0.3 gr of sodium thiosulfate and 0.10 gr of fumaric acid. The sol pH, after dissolution of the acid, was 5.70. Lastly, with vigorous stirring of the sol, 0.38 ml of crosslinker prepared in Example 1 was added. The sol pH was 5.57 and the data from the rheological evaluation at 250° F. is presented in Table 7. 
     
                       TABLE 7______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.10 gr. fumaric acid and 0.38 ml crosslinkerpH: 5.57             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________32    248      0.708   19.068 490    521   64060    249      0.689   15.292 360    384   47889    251      0.760   6.962  228    240   284118   251      0.786   3.731  138    144   168147   251      0.724   3.238  90     95    115______________________________________ 
    
     EXAMPLE 9 
     Another 250 ml aliquot was withdrawn from the stock solution prepared as described in Example 2. The sol was treated with 0.3 gr sodium thiosulfate and 0.5 ml of a 45% (wt) solution of potassium carbonate. The crosslinker prepared in Example 1 was diluted to 50% (wt) with tap water. Then, with vigorous stirring of the sol, 0.25 ml of the diluted crosslinker was added. The sol pH was 8.50 and the data for the rheological evaluation at 200° F. is presented in Table 8. 
     
                       TABLE 8______________________________________Temperature (° F.): 200Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.05 ml 45% (wt) K.sub.2 CO.sub.3  and 0.25 ml of diluted crosslinkerpH: 8.50             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________34    199      0.647   25.919 501    540   69365    199      0.676   18.865 418    447   56296    199      0.621   21.635 371    402   525127   199      0.592   21.943 329    358   478155   199      0.579   21.185 299    326   439185   199      0.661   13.478 278    299   380216   199      0.648   13.356 260    280   358247   199      0.628   13.914 246    267   346278   199      0.631   12.953 233    251   326308   199      0.633   12.231 222    240   310339   199      0.656   10.562 213    229   292370   199      0.654   10.145 203    218   278401   199      0.665   9.402  198    212   269432   199      0.654   9.439  189    203   259463   199      0.685   7.614  176    188   235494   199      0.689   7.154  168    180   224525   199      0.705   6.622  168    179   220556   199      0.701   6.685  166    177   219586   199      0.680   6.899  156    166   209617   199      0.707   5.938  152    162   199627   199      0.737   5.131  151    160   192658   199      0.724   5.288  146    155   188689   199      0.682   5.982  136    146   182720   199      0.702   5.371  134    143   176751   199      0.727   4.707  132    140   170781   199      0.709   4.917  127    135   166812   199      0.686   5.280  122    131   163843   199      0.718   4.305  116    123   150874   199      0.689   4.7115 111    118   147905   199      0.732   3.831  110    116   141936   199      0.675   4.9115 108    116   146967   199      0.73    3.7031 105    112   135998   199      0.695   4.31   104    111   1381028   85      0.464   32.3876                         267    299   437______________________________________ 
    
     EXAMPLE 10 
     In this example, a liter of 2% (wt/vol) aqueous potassium chloride was vigorously stirred while adding 4.8 gr of fracturing fluid quality hydroxypropyl guar (HPG), a derivatized guar gum and 1.2 gr of sodium bicarbonate. After adequate dispersing, the stirring rate was slowed and the polymer was allowed to hydrate for about an hour. 
     A 250 ml aliquot was withdrawn and treated with 0.3 gr of sodium thiosulfate and 0.08 ml of 45% potassium carbonate. Then, with vigorous stirring, 0.12 ml of crosslinker prepared in Example 1 was added to the sol. The sol pH was 9.04 and the data acquired from the rheological evaluation at 250° F. is presented in Table 9. 
     
                       TABLE 9______________________________________Temperature (° F.): 250Additives: 2% KCl, 4.8 gr. HPG, 1.2 gr. NaHCO.sub.3, 0.3 gr. Na.sub.2S.sub.2 O.sub.3.5H.sub.2 O,0.08 ml 45% (wt) K.sub.2 CO.sub.3  and 0.12 ml crosslinkerpH: 9.04             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________32    248      0.675   16.072 354    379   47761    249      0.580   20.483 290    317   42689    249      0.629   15.632 278    301   391118   249      0.577   17.076 238    261   351145   249      0.617   13.297 224    243   318173   249      0.565   15.686 207    227   309202   249      0.581   13.393 191    208   280231   249      0.571   12.945 176    192   260260   249      0.586   11.859 173    188   252289   249      0.592   11.005 165    180   239318   249      0.661   7.727  160    171   218347   249      0.599   9.329  144    157   208376   249      0.596   9.236  141    153   204405   249      0.650   6.918  136    146   187434   249      0.621   7.377  126    137   179463   249      0.611   7.373  121    131   172492   249      0.597   7.572  116    126   168521   249      0.619   6.385  108    117   154550   249      0.664   5.014  105    113   143579   249      0.689   4.331  102    109   135608   249      0.654   4.854  97     104   133616   249      0.629   5.273  94     101   132645   249      0.613   5.329  88     95    125674   249      0.663   4.124  86     92    117703   249      0.689   3.751  88     94    117732   249      0.661   4.005  83     89    113761   249      0.675   3.766  83     89    112790   249      0.698   3.294  81     86    107819   249      0.702   3.119  78     83    102848   249      0.688   3.2253 76     81    100877   249      0.686   3.1348 73     78    97906   249      0.706   2.8311 72     77    94935   249      0.691   3.0418 72     77    96964   249      0.662   3.236  67     72    91993   250      0.643   3.4503 66     71    911022  249      0.657   3.1647 64     69    881051  249      0.657   3.0802 62     67    851080  249      0.663   2.9762 62     67    841109  249      0.64    3.2035 60     65    831137  100      0.511   19.5655                         201    223   315______________________________________ 
    
     EXAMPLE 11 
     In this example, a 250 ml aliquot of CMHPG prepared as described in Example 7 was treated with 0.3 gr of sodium thiosulfate. Then, with stirring, acetic acid was added dropwise until the sol pH was 5.70. Lastly, with vigorous stirring of the sol, 0.19 ml of crosslinker prepared in Example 1 was added. The final sol pH was 5.70 and the data obtained from the rheological evaluation at 200° F. are presented in Table 10. 
     
                       TABLE 10______________________________________Temperature (° F.): 200Additives: 2% KCl, 4.8 gr. CMHPG, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,acetic acid added to adjust pH, and 0.19 ml crosslinkerpH: 5.70             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 32   205      0.444   70.514 530    596   883 61   202      0.455   70.838 561    629   924 90   202      0.435   76.512 552    622   926118   202      0.425   78.281 539    608   913147   202      0.434   74.248 533    601   895176   202      0.446   68.372 519    583   862205   202      0.466   61.856 515    577   841234   202      0.441   65.286 484    545   808263   202      0.454   59.014 465    522   767292   202      0.444   58.220 438    492   729______________________________________ 
    
     EXAMPLE 12 
     In this example, a 250 ml aliquot of CMHPG prepared as described in Example 7 was treated with 0.3 gr of sodium thiosulfate and 0.06 ml of 45% (wt) potassium carbonate. Then, with vigorous stirring of the sol, 0.15 ml of crosslinker prepared in Example 1 was added. 
     The final sol pH was 9.00 and the data acquired from the rheological evaluation at 275° F. are shown in Table 11. 
     
                       TABLE 11______________________________________Temperature (° F.): 275Additives: 2% KCl, 4.8 gr. CMHPG, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.06 ml 45% (wt) K.sub.2 CO.sub.3  and 0.15 ml crosslinkerpH: 9.00             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 31   274      0.622   47.012 809    877   1145 60   274      0.564   48.740 641    703   955 89   274      0.533   44.902 511    564   784118   274      0.510   41.733 427    473   668147   274      0.546   31.878 385    424   584176   274      0.498   36.050 349    388   552205   275      0.522   30.511 330    365   511234   275      0.535   25.977 298    329   457263   274      0.516   26.552 279    309   435292   274      0.571   18.883 256    281   380321   274      0.558   20.908 267    293   401350   274      0.542   21.471 255    281   388379   274      0.548   19.449 237    261   359408   274      0.532   19.154 217    239   333437   273      0.569   15.422 207    227   308466   274      0.598   12.429 191    208   277495   274      0.527   15.677 173    192   268524   274      0.505   15.872 159    176   250553   274      0.544   12.159 146    160   221582   274      0.535   11.503 132    146   202610   274      0.559   9.375  120    132   180639   274      0.520   10.076 108    119   168668   274      0.566   7.544  100    110   149697   274      0.567   6.818  91     100   135726   274      0.533   7.229  82     91    126755   274      0.562   5.840  76     83    114773   274      0.581   5.025  71     78    105802   274      0.607   4.143  67     72    95831   273      0.558   4.847  62     68    93860   274      0.554   4.5336 57     63    86889   273      0.565   4.123  54     60    81918   274      0.574   3.7038 51     56    75947   273      0.528   4.1565 46     51    71976   274      0.581   3.0997 44     48    65______________________________________ 
    
     EXAMPLE 13 
     In this example, a 250 ml aliquot of CMHPG prepared as described in Example 7 was treated with 0.3 gr of sodium thiosulfate and 0.06 ml of 45% (wt) potassium carbonate. Then, with vigorous stirring of the sol, 0.18 ml of crosslinker prepared in Example 1 was added. The final sol pH was 8.95 and the data acquired from the rheological evaluation at 300° F. are shown in Table 12. 
     
                       TABLE 12______________________________________Temperature (° F.): 300Additives: 2% KCl, 4.8 gr. CMHPG, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.06 ml 45% (wt) K.sub.2 CO.sub.3  and 0.18 ml crosslinkerpH: 8.95             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________30    305      0.728   29.502 832    881   106759    284      0.624   31.910 555    600   78388    298      0.571   30.819 419    458   620117   299      0.539   28.911 338    373   516146   299      0.537   24.060 279    308   426175   299      0.553   18.374 229    252   346204   299      0.568   13.462 180    198   268233   299      0.581   9.721  138    151   203262   298      0.584   7.375  106    116   156291   299      0.618   4.815  81     88    115320   299      0.602   3.859  61     66    87349   298      0.619   2.809  48     52    68378   298      0.630   2.125  38     41    53407   298      0.552   2.526  31     35    47436   299      0.401   4.026  25     28    43465   299      0.314   5.343  22     25    41493   298      0.438   2.767  20     23    34522   298      0.445   2.493  19     21    31551   298      0.438   2.344  17     19    29580   298      0.518   1.456  15     17    24609   298      0.606   0.833  13     14    19638   298      0.667   0.556  12     13    16667   299      0.619   0.615  10     11    15696   298      0.446   1.168  9      10    15725   298      0.397   1.347  8      9     14754   298      0.263   2.300  7      9     15783   298      0.218   2.649  7      8     14812   298      0.207   2.680  7      8     14841   298      0.161   3.2311 7      8     14851   298      0.197   2.7087 6      8     13880   298      0.231   2.2448 6      7     13909   298      0.088   4.2004 6      7     14938   298      0.155   3.0535 6      7     13967   298      0.208   2.515  6      7     13995   298      0.167   2.9336 6      7     131024  298      0.158   2.8262 6      7     121053  298      0.194   2.4537 6      7     121082  298      0.13    3.2029 6      7     121111  297      0.174   2.6641 6      7     121140  297      0.198   2.281  5      6     111169  298      0.162   2.6941 5      7     121198  297      0.093   3.8153 6      7     131227  298      0.119   3.4276 6      7     13______________________________________ 
    
     EXAMPLE 14 
     In this example, another 250 ml aliquot was withdrawn from the stock solution prepared as described in Example 2. This sol was treated with 0.3 gr of sodium thiosulfate. Then acetic acid was added dropwise until the sol pH achieved 5.70. Lastly, with vigorous stirring of the sol, 0.38 ml of crosslinker prepared in Example 1 was added. The sol pH was 5.70 and the data from the rheological evaluation at 200° F. is presented in Table 13. 
     
                       TABLE 13______________________________________Temperature (° F.): 200Additives: 2% KCl, 4.8 gr. guar gum, 0.3 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,acetic acid to adjust pH and 0.38 ml crosslinkerpH: 5.70             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 32   200      0.546   25.628 310    341   470 61   202      0.552   22.357 278    306   419 89   202      0.563   20.055 262    288   392118   202      0.625   14.912 260    282   367147   202      0.529   21.147 236    261   364176   202      0.550   17.726 218    240   330205   202      0.567   15.597 208    228   309234   202      0.559   15.232 196    215   293262   202      0.589   12.378 183    199   266291   202      0.626   9.481  166    180   234______________________________________ 
    
     EXAMPLE 15 
     Another 250 ml aliquot of sol described in Example 2 was treated with 0.30 gr sodium thiosulfate and 0.38 ml of 45% (wt) potassium carbonate. Then, 0.12 ml of crosslinker described in Example 1 was added to the vigorously stirred sol. The sol pH was 8.50 and the rheological data obtained at 275° F. is presented in Table 14. 
     
                       TABLE 14______________________________________Temperature (° F.): 275Additives: 2% KCl, 4.8 gr. guar gum, 0.30 gr. Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O,0.38 ml 45% (wt) K.sub.2 CO.sub.3  and 0.12 ml crosslinkerpH: 8.50             Viscosity             at Rates in Sec.sup.-1TIME  TEMP     n&#39;      K&#39;     105s-1 85s-1 42s-1______________________________________ 32   271      0.603   21.522 339    369   488 61   272      0.575   20.274 280    307   414 90   273      0.595   14.999 228    248   330119   273      0.652   10.192 202    217   278148   273      0.659   8.537  175    188   239177   273      0.692   6.438  154    164   204206   273      0.683   5.891  135    144   180235   273      0.762   3.680  122    128   151264   273      0.720   4.060  110    117   143293   273      0.725   3.473  97     102   124322   273      0.652   4.396  87     94    120351   273      0.663   3.688  77     83    105380   272      0.724   2.731  76     80    97408   273      0.673   3.063  67     72    90______________________________________ 
    
     When using the zirconium compounds of the invention as crosslinking agents for aqueous polymer gels used as fracturing fluids, a gelled polymer fracturing fluid is first prepared by adding between about 1% or less by weight of a soluble polymer such as guar, guar derivative or carboxylated cellulose to water. The zirconium crosslinking agent is then added to the gelled fluid in solution while mixing. The amount of the crosslinking agent used to carry out the method of the invention will vary over a wide range and therefore the amounts will vary according to the formation being treated. Preferably, the amount of crosslinking agent used will be in the range from about 0.005 to in excess of 1.00 weight percent, most preferably about 0.01 to 0.10 weight percent, based on the total weight of aqueous fluid. Additionally, proppants and other additives, such as gel stabilizers, buffers, crosslink delaying agents and surfactants, may be added to the fluid prior to pumping into an oil or gas well. The fluid is then pumped into the well at a sufficiently high rate or pressure to cause fractures within the hydrocarbon bearing areas of the formation. The zirconium compound is particularly useful when treating high temperature wells, i.e. those having temperatures in excess of 200° F., due to the good thermal stability and retained viscosity of the crosslinked polymer gel. 
     An invention has been provided with several advantages. The method of the invention allows organo-zirconium compounds to be formed without producing undesirable by-products that must be removed by washing and filtering procedures. Because zirconium carbonate is used as the starting material, the reaction results in the production of carbon dioxide gas as a by-product. The carbon dioxide merely bubbles from solution as a gas so that no additional separating techniques are required. This eliminates the loss of product that would otherwise occur during the washing and filtering steps. There is also no chloride to be recovered and disposed of. The novel organo-zirconium compounds of the invention overcome many of the disadvantages of the prior art compounds, such as high cost, as well as being more applicable for guar gums utilized in aqueous based fracturing fluids. 
     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.