Recent studies have found that the viscosities of borate gels at actual downhole pressure conditions may be 80% less than those from standard high-pressure/high-temperature rheometer measurement (which uses 400-psi top pressure). A proposed mechanism for this phenomenon is a pressure-induced shifting of the crosslink/temperature stability near the “melt temperature” of borate-crosslinked gels, leading to a reversible thinning. This paper poses a novel approach to exploit the pressure effect by capturing the pressure-thinned fluid in a thin state and irreversibly breaking the gel viscosity.
The chemistry of most crosslinked-gel fracturing fluids has been optimized carefully over the years, yielding a base chemistry that has remained mostly consistent for 20 years with incremental innovations. These fluids include either metal-crosslinked polymer solutions or borate-crosslinked guar, which is used for the largest percentage of crosslinked-gel fracturing treatments.
While widely used in both crosslinked and hybrid fracture designs, several performance issues have been noted in optimization and execution of these fluids. Slow shear recovery has been identified in many nondelayed borate-crosslinked fluids, which varies on the basis of shear rate, gel salinity, and additives....
An Innovative Approach to Gel Breakers for Hydraulic Fracturing
01 March 2017