Crosslinked, borate

Hydroxypropylguar gum gel can be crosslinked with borates [1227], ti-tanates, or zirconates. Borate-crosslinked fluids and linear hydroxyethyl-cellulose gels are the most commonly used fluids for high-permeability fracture treatments. This is for use for hydraulic fracturing fluid under high-temperature and high-shear stress. 

These parameters have significant effect on the final viscosity of gel in the fracture. Correlations to estimate friction pressures in field size tubulars have been developed from laboratory test data. In conjunction with field calibrations, these correlations can aid in accurate prediction of friction pressure of borate-crosslinked fluids. 

Static leak-off experiments with borate-crosslinked and zirconate-cross-Unked hydroxypropylguar fluids showed practically the same leak-off coefficients [1883]. An investigation of the stress-sensitive properties showed that zirconate filter-cakes have viscoelastic properties, but borate filter-cakes are merely elastic. Noncrosslinked fluids show no filter-cake-type behavior for a large range of core permeabilities, but rather a viscous flow dependent on porous medium characteristics. 

Borate-crosslinked fracturing fluids have been successfully used in fracturing operations. These fluids provide excellent rheologic, fluid loss, and fracture conductivity properties over fluid temperatures up to 105° C. The mechanism of borate crosslinking is an equilibrium process that can produce very high fluid viscosities under conditions of low shear [336]. 

Adding a borate crosslinking agent to the gel to crosslink the polymer [783]... 

Drying the borate-crosslinked polysaccharide formed in step 2... 

A borate crosslinking agent can be boric acid, borax, an alkaline earth metal borate, or an alkali metal alkaline earth metal borate. The borate source, calculated as boric oxide, must be present in an amount of 5% to 30% by weight. 

Elevated Temperatures. Borate-crosslinked guar fracturing fluids have been reformulated to allow use at higher temperatures in both freshwater and seawater. 

Rheologic measurements conflrmed that a soluble delayed-release acid could be used to convert a borate-crosslinked fluid into a linear gel [1353]. 

B. R. Ainley and S. B. McConnell. Delayed borate crosslinked fracturing fluid. Patent EP 528461,1993. 

B. R. Ainley, K. H. Nimerick, andR. J. Card. High-temperature, borate-crosslinked fracturing fluids A comparison of delay methodology. In Proceedings Volume, volume , pages 517-520. SPE Prod Oper Symp (Oklahoma City, 3/21-3/23), 1993. 

P. C. Harris and S. J. Heath. Delayed release borate crosslinking agent. Patent EP 594364, 1994. 

K. H. Nimerick, C. W. Crown, S. B. McConnell, andB. Ainley. Method of using borate crosslinked fracturing fluid having increased temperature range. Patent US 5259455,1993. 

S. N. Shah, P. C. Harris, and H. C. Tan. Rheological characterization of borate crosslinked fracturing fluids employing a simulated field procedure. In Proceedings Volume. SPE Prod Technol Symp (Hobbs, NM, 11/7-11/8), 1988. 

Shah, S.N. Harris, P.C. Tan, H.C. "Rheological Characterization of Borate Crosslinked Fracturing Fluids Employing A Simulated Field Procedure" SPE Paper 18589, 1988 SPE Production Technology Symposium, Hobbs, N.M. 

In 1949, Deuel and Neukom [131] sug sted that the origin of cro links in aqueous poly(vinyl alcohol)/borate gels is the complexation shown in Fig. 48. This concept of didiol type complexation was adopted by authors in more recent times [130,184-193]. Schultz and Myers [185] measured the dynamic moduli G and G" of polyfvinyl alcohol)/borate gels (at small deformation amplitudes in order not to disturb the gel [185]). At low frequendes, the gels showed Uquidlike behaviour this means that the borate crosslinks are dynamic in nature. Such results were also reported by Beltman [7]. He measu the dynamic moduli of a gel formed in a 4 wt% PVA98.5 solution with 2.5 wt% of borax (=0.0069 mol/1, which is equivalent to 0.0276 mol/1 of borate) at various temperatures (15-75 °C). Results are shown in Fig. 49. 

Fig. 48. Schematic view of a network fonKd by borate crosslinking of pd vin alcohol). Reproduce from Mak-romol Chem [Ref. 131] by the courtesy of Huthig Wepf Ver-lag PuUishers, Zug, Switzerland...

Harris, P. C. and van Batenburg, D. A Comparison of Freshwater- and Seawater-Based Borate-Crosslinked Fracturing Fluids International Symposium on Oilfield Chemistry, Houston, TX, February 16-19, 1999 (SPE 50777). 

Brannon, H. D., Ault, M. G. New Delayed Borate-Crosslinked Fluid Provides Improve Fracture Conductivity in High Temperature Applications 66th Annual Technical Conference and Exhibition of SPE, DaUas, Texas, October 6-9, 1991 (SPE 22838). 

Nimerick, K. H., Temple, H. L., and Card, R. J. New pH-Buffered Low Polymer Borate Crosslinked Eluidsfor Hydraulic Eracturing, Gas Teehnology Conference, Calgary, Alberta, Canada April 28-May 1, 1996 (SPE 35638). 

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