In spite of their wide use in hydraulic fracturing and gravelpack operations, the complex flow behavior of surfactant-based fluids in straight tubing is least investigated. Accurate prediction of friction-pressure is essential for proper treatment design. Previous correlations from small tubings data and using simple power-law fluid model parameters alone do not scale-up to large tubing sizes for field application.
The properties of one of the most popular surfactants, Aromox APA-T, are thoroughly investigated. It is a highlyactive surfactant used as gelling agent in aqueous and brine solutions. Commonly used surfactant concentrations (1.5, 2, 3, and 4% by vol.) are studied. Rheological and viscoelastic measurements are conducted using Bohlin rheometer. Flow tests are conducted using ?-, 1?-, 2?-, and 2?-in. tubings.
The results show SB fluid exhibiting a non-Newtonian pseudo-plastic behavior. Fluid concentration and pipe shear have a significant effect on fluid elasticity. The conventional Fanning friction factor versus Reynolds number correlation is improved by including a new dimensionless group that accounts for both fluid elasticity and pipe diameter. A new definition of Deborah number is introduced. Thus, a new correlation for predicting friction factors of SB fluid in straight tubing is developed. The scale-up problem is thus alleviated with the present analysis and it provides more accurate friction-pressure estimates.
In the petroleum industry processes, a variety of fluids are pumped through straight tubing during operations such as hydraulic fracturing, acidizing, wellbore cleanup, cementing and drilling which usually are executed under turbulent flow conditions. Turbulent flow regime is characterized by rapid fluctuations of velocity, pressure, and shear stress. The fluctuation is a function of time and position in the flow. They lead to development of high unsteady vortices and eddies which increase fluid resistance to flow. Therefore, high friction pressure losses are encountered which limits their pumping capacity. Adding small amount of specific high molecular weight polymers known as "Drag Reducers" under turbulent pipe flow condition can drastically decrease friction pressure gradient and thus, increase pumping capacity. Surfactant, the newly developed fluid requires less energy to pump than more conventional polymer fluids, effectively reducing wellsite pump-horsepower requirements[1,2,3]. Surfactants offer numerous advantages over conventional polymers. As drag reducers, the entangled micelles have much more resistance to mechanical degradation. Also, after disruption, surfactant molecules can reconstruct themselves to recover their drag reducing ability once the shear stress returns below a critical value while in polymer molecules, the disruption is irreversible. As hydraulic fracturing fluids, surfactant based fluids are viscous, non-polymer, water based, and have low molecular weight. Therefore, they do not leave much residue in the formation. Furthermore, they alleviate the need of various additives conventionally used with polymers. They can be used as carrier fluids for either hydraulic fracturing or gravel pack application and can be prepared with a variety of fluids including fresh water, brines and produced water as long as there is no hydrocarbon contamination[4,5].
Flow data gathered using lab tubing size are conventionally used to develop friction factor correlations to predict friction pressure loss in larger tubing sizes.
