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 is a continuation of application Ser. No. 08/502,352, filed Jul. 14, 1995, now 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 1. 
     
                       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, 0.06ml 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   52260    247      0.691   15.471 367    392   48791    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 Theological evaluation are shown in Table 2. 
     
                       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, 0.08ml 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   64465    248      0.665   18.521 390    418   53096    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 3. 
     
                       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 ml45% (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   74764    248      0.613   27.269 450    489   64295    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 ml45% (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   36762    248      0.659   24.222 495    532   67792    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 ml45% (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   114265    249      0.541   60.143 710    783   108296    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    584   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   116261    248      0.557   46.181 588    645   88290    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  1l     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,0.5 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   88361    202       0.455  70.838  561   629   92490    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   114560    274       0.564  48.740  641   703   95589    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  1.166   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   47061    202       0.552  22.357  278   306   41989    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   48861    272       0.575  20.274  280   307   41490    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.