Proppant Transport of Fracturing Gels is Influenced by Proppant Type

Abstract

Fracturing gels are formulated to have a high viscosity sufficient to generate fracture geometry and transport proppant materials. Fracturing fluids are subjected to extensive QA/QC testing on high-temperature rheometers to ensure they have adequate viscosity to perform the intended task and break within a time frame suitable for the operation performed. Although most rheological tests incorporate only the gelled fluid without proppant materials, it is assumed that the fluid will transport proppants to their desired location.A field location reported that treatments containing certain proppants were screening out more frequently. Tests were performed on a slurry viscometer (SV). It was discovered that not all proppant materials of the same nominal size and density were transported equally when added to a fracturing gel. The typical properties of the borate gels were measured, but no significant differences were found that would account for differences in transport. All the proppants had nominal 20/40 mesh size. A laser analysis of the particles indicated small differences in the distribution of sizes. However, the size analysis did not fit the trend that "bigger settles faster."Scanning electron micrographs showed differences in surface roughness between the ceramic materials and sand. The proppants were coated with a tacky substance to neutralize any chemical absorption effects. The coated proppants then settled in a manner consistent with their physical characteristics (size and density), but the tacky material caused agglomeration and faster settling than before. The coated proppants were treated chemically to temporarily disable the tackiness, and it was observed that all the materials settled in a manner consistent with their physical characteristics.It was found that certain 20/40-mesh proppants were suspended twice as long as other proppants in the same gel environment. The proppant effect was measured with the SV. The trend from the SV instrument correlated well with the screenout rate observed in the field.Analysis indicated a surface catalytic effect of ceramic proppants causing faster decomposition of oxidizing breakers and accelerated gel breaking. This effect was absent in fluids with uncoated sand. Some resin-coated proppants were found to also accelerate breaking because of leaching of chemical compounds from the coatings. Therefore, it is not correct to assume that all proppants added to fracturing gels will be transported equally. Viscosity measurements of gels without proppant might not give accurate information about the behavior of gels with proppant if the proppant interacts with the gels. IntroductionThe majority of oil and gas wells in the Unites States, and a large number of international wells, are stimulated by hydraulic fracturing. A great deal of study and effort goes into the development and production of fluids that are able to withstand the temperatures and duration of fracturing treatments for subterranean formations. The fracturing fluid must generate fracture geometry and carry p...

Investigating the Dominant Factors Influencing Well Screenouts for Crosslinked Fracturing Fluids in Shale Plays

“…Quantitative measurements for proppant suspension and transport were performed on the metal and borate crosslinked fluid systems using the proppant transport measuring device developed by Harris et al (2005) and Harris and Heath (2009), which measures slurry viscosity of a crosslinked proppant-laden fluid. The instrument uses specially designed geometry in a rotational viscometer to determine the rate of proppant settling.…”

Effects of Alternative Water Sources on Formation and Proppant Pack Damage Reduction Properties of Near-residue-free Fracturing Fluid

“…Effects on a fluid's ability to support dynamic proppant transport was studied using a proppant transport measuring device developed by Harris et al (2005) and Harris and Heath (2009), which measures slurry viscosity of a proppant-laden fluid. This slurry viscometer instrument uses a specially designed geometry coupled with a rotational viscometer to determine the rate of proppant settling.…”

“…This slurry viscometer instrument uses a specially designed geometry coupled with a rotational viscometer to determine the rate of proppant settling. The device combines a vane bob and coquette with flagged wall, which mimics the fluid conditions encountered in a typical fracturing application (Harris et al 2005;Harris and Heath 2009;Loveless et al 2011). Fluid was crosslinked and prepared with a sand loading of 8 lbm/gal (20/40-mesh Ottawa sand) and loaded into the viscometer.…”

Residue-Free Fracturing Fluid Provides Superior Cleanup and Exceptional Proppant Transport

“…To examine the ability of the res-free fluid to transport fluid, the dynamic viscosity was investigated using a conventional highpressure/high-temperature (HP/HT) viscometer, as shown in the previous section. However, understanding that the dynamic viscosity is a bulk measurement that does not give the full indication of the molecular forces that enable proppant transport (Loveless et al 2011), a slurry viscometer developed by Harris et al (2005Harris et al ( , 2009) was used to relate the dynamic viscosity and the onset of proppant settling. Measurements and flow curve rheology experiments were also conducted to gain greater understanding of the fluid's behavior at different shear rates.…”

“…This procedure employed a vane bob and flagged wall couette to mimic the fluid conditions encountered during a typical fracturing treatment (Harris et al 2005(Harris et al , 2009Loveless et al 2011). In a typical experiment, 8 lbm/gal of 20/40-mesh Ottawa sand proppant was added to a prepared fracturing fluid formulation and loaded in the viscometer.…”