Abstract
The fracturing fluid is the essential part of any hydraulic fracturing treatment. A borate-crosslinked guar-based fluid is one of the most commonly used types of fluid. The first mention of guar derivatives crosslinked with boron can be traced back to 1977. Scientific papers that describe boron equilibria as a function of the fluid pH can be trackedback to 1966.
Comprehensive studies of the rheological behavior of borate-based fluids were performed in 1980s and 1990s, and for almost 30 years, it has been considered as a well-known topic.
Recently, a few authors reported a significant decrease in viscosity of the fluid at elevated pressure. This decrease was reversible (i.e., as soon as the pressure values are moved back to the normal, the viscosity is recovers). Such effect can significantly affect the stimulation design and outcome because most of the time the slurry is affected by elevated temperatures and pressures.
Still, many questions remained unanswered. One of them is the effect of crosslinker concentration/composition on the stability of the fluid at highpressure. Another is the comparison of the fluid viscosity under the ISO 13503-1 ramp at standard conditions and elevated pressure. The last one concerns the actual values of the fluid rheological parameters, n and K’, under different pressures.
In this paper, we investigate the fracturing fluid behavior under high pressure. For the first time in the industry, we compare the results of ISO fluid stability testing, and the fluid shear recovery under 400-psi pressure and up to 10,500 psi.
Finally, using a novel hydraulic fracturing simulator, the effect of the pressure-sensitivity of the fluid on the proppant transport, fracture geometry, and, subsequently, well productivity will be demonstrated.
The findings of this paper will have noticeable impact on the design of the hydraulic fracturing treatment where borate-crosslinked fluids are used.
