When formulated with clean water, fracturing fluid systems consisting of organometallic-crosslinked derivatized polysaccharides performed very well at temperatures above 300 degF. However, the fluid viscosity of some fluids is significantly reduced if hard water is used as the make-up base. The extent of viscosity loss is related to the degree of hardness in the water, and in many instances, renders low-polymer-loading fluid systems ineffective for moderate- to high-temperature applications. A number of "conventional wisdom" techniques were tried to mitigate the damage caused by the water hardness, but without consistent success. These methods included, for example, changing the crosslinking package, changing the buffer system, or using surfactants. A simple-to-use and universally effective method has therefore been highly desirable and sought after to solve the hardness damage problem for the fluid systems.
A method was identified recently that mitigated nearly 100% of the viscosity loss due to water hardness. In one example, a stabilizing additive (stabilizer) at the weight percentage of as low as 0.012% was observed to effectively stabilize fracturing fluid systems comprised of organometallic-crosslinked derivatized polysaccharides in fluid prepared using hard water with at least 200 ppm of Ca2+ ions. In the presence of the stabilizing additive, the fluid formulated with the hard water showed viscosity nearly comparable to that of the baseline fluid prepared with soft water. A number of other viscosity-stabilizing additives were identified with similar capability for mitigating the hardness damage to the fluid systems.
The new viscosity-stabilizing technology for low-loading, organometallic-crosslinked derivatized polysaccharides and treating method will be discussed, and the field-related laboratory test results will be presented.