Effects of salinity on the hydraulic characteristics of welan gum fluids in straight and coiled tubing

Abstract

At low concentrations, welan gum fluids have high viscosity, excellent suspending properties, shear thinning (pseudoplastic) rheological properties, viscosity retention at high temperatures and provides excellent friction pressure reduction. Hence, they are used in oilfield operations including hydraulic fracturing, wellbore cleanup, cementing and drilling for viscosity enhancement and friction pressure reduction purposes. In drilling and completion operations, brine solutions are commonly used as base fluids, therefore it is essential to quantify the effects of salinity on the rheological and hydraulic properties of welan gum.

In this work, the effects of salinity on the rheological and hydraulic properties of welan gum fluids of various concentrations (0.5, 1, 2 and 3 lb bbl) in fresh water, 2% and 4% KC1 has been evaluated through experimental studies. The experimental set-up includes a 1/2-in. OD flow loop with a 15-ft straight section and 18-ft coiled tubing with curvature ratio of 0.019. From the experimental data gathered, it is confirmed that rheology of welan gum fluids is sensitive to the concentration of salt. The sensitivity is seen as a reduction in viscosity of fluid as the concentration of salt is increased.

For flow in straight tubing, it is observed that at low concentrations of 0.5 and 1.0 lb/bbl, welan gum fluids in brine solutions exhibit lower drag reduction compared to that in fresh water. The opposite effect is observed at higher concentrations of 2.0 and 3 .0 lb/bbl. It is also observed that in coiled tubing, the drag reduction characteristics of welan gum fluids in brine solutions increased when compared with those prepared with fresh water. The friction pressure data for welan gum fluids in straight and coiled tubing as observed in the experimental investigation are correlated using the following dimensionless parameters - Fanning friction factor and generalized Reynolds number. These correlations are found to provide good accuracy for prediction purposes when compared to the experimental data from larger tubing sizes.