Friction reducers (FRs) are used to decrease the amount of horsepower required to move a hydraulic fracturing fluid through a formation at a fixed flow rate. Though FR viscosity is not a crucial consideration in proppant transport when used before the perforations in slick water applications, FR viscosity becomes a greater consideration in proppant transport from the perforations into the formation and an important qualifying criterion with the advent of High Viscosity Friction Reducer (HVFR) systems that require higher loadings than traditional FRs. Consistent viscosity measurement can vary greatly depending upon a number of factors, for example temperature, hydration approach, polymer concentration, brine composition, and additive interaction. A study was developed and implemented to determine the influence of HVFR by concentrated particulate and bead settling.
This study investigated the viscosities of five HVFRs applying eight variables using response surface methodology. Initial study criteria were establishing consistent hydration with unique apparatus design and viscosity measurement verification. Once established, this method examined the effects of 1:1, 2:1, and 2:2 salts, singularly or in various concentrations and combinations. Experimental designs under fresh water conditions were also conducted with varied HVFR loadings (1.0 to 6.0gpt), blender RPM (600 to 12,000), and blender mixing times (0.5 to 8.7 minutes). Viscosities were measured from 200 to 6000 (1/sec). Static settlement testing in ranges of 0.87 to 3.50 pounds per gallon in 0 to 140,000 total dissolved solids (TDS) brines was conducted. Single bead settling measurements were performed in fresh water and API brine.
Specific HVFR and salt matrix combinations tested resulted in highly correlated response surfaces exhibiting consistent trends. The TDS and hardness had a minor to major influence on viscosity based upon the specific HVFR examined. Brines were predominately antagonistic with respect to viscosity with few synergistic results. The influences of HVFR dosage and mixing correlated highly to the viscosity of all HVFRs, and extended mixing time durations had no influence on some HVFR combinations indicating a viscosity reduction limit. In certain regions of the design space, settling rates were related to viscosity.
Selection of an HVFR system precisely tailored for a specific brine composition guaranteeing maximum friction reduction and proppant transportation performance was vital. The influence of pumping and tubular transport on the HVFR viscosity is continuous and quantifiable. Additionally, the viscosity of the HVFR in a downhole brine environment provides discernable data for assessing far end well bore proppant transport and damage potential. This study established a reliable method for gauging performance and examining measurable field variables of HVFR systems.