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Abstract
Partially hydrolyzed polyacrylamide (HPAM) as the main component of slickwater fracturing fluid is a shear-sensitive polymer, which suffers from mechanical degradation at turbulent flow rates. Five different concentrations of HPAM as well as mixtures of polyacrylamide/xanthan gum were prepared to investigate the possibility of improving shear stability of HPAM. Drag reduction (DR) measurements were performed in a closed flow loop. For HPAM solutions, the extent of DR increased from 30% to 67% with increasing HPAM concentration from 100 to 1000 wppm. All the HPAM solutions suffered from mechanical degradation and loss of DR efficiency over the shearing period. Results indicated that the resistance to shear degradation increased with increasing polymer concentration. DR efficiency of 600 wppm xanthan gum (XG) was 38%, indicating that XG was not as good a drag reducer as HPAM. But with only 6% DR decline, XG solution exhibited a better shear stability compared to HPAM solutions. Mixed HPAM/XG solutions initially exhibited greater DR (40% and 55%) compared to XG, but due to shear degradation, DR% dropped for HPAM/XG solutions. Compared to 200 wppm HPAM solution, addition of XG did not improve the drag reduction efficiency of HPAM/XG mixed solutions though XG slightly improved the resistance against mechanical degradation in HPAM/XG mixed polymer solutions.
Highlights
Due to the development of horizontal drilling and hydraulic fracturing technology in recent years, oil and gas production from unconventional resources such as shale formations has played an important role in supplying energy in the USA (Larch et al 2012; Palisch et al 2010)
Since various hydrolyzed polyacrylamide (HPAM) and xanthan gum (XG) molecules with different molecular weights are available in the market, we study the behavior of single polymer solutions, so that we can compare them with binary solutions and assess the degree of improvement in shear stability
It was observed that the difference between turbulent friction factors of 200, 500, and 1000 wppm solutions was very small, which is in agreement with the results shown in Prandtl–Karman coordinates, indicating that at the studied range of Reynolds numbers, Drag reduction (DR) efficiency was close to its maximum value (MDR); further increase in concentration did not change friction factors
Summary
Due to the development of horizontal drilling and hydraulic fracturing technology in recent years, oil and gas production from unconventional resources such as shale formations has played an important role in supplying energy in the USA (Larch et al 2012; Palisch et al 2010). Creation of openings in the reservoir rock involves pumping fracturing fluids into the wellbore at elevated flow rates and pressures. The main component of low-viscosity fracturing fluids is water and low concentrations of polymer ranging from 0.25 to 10 lb per thousand gallons (Bunger et al 2013; Palisch et al 2010). Because of the relatively low viscosity of slickwater, cleanup problems and damage associated with using viscous fluids are minimized, which makes slickwater suitable for fracturing low-permeability reservoirs (Wu et al 2013; Palisch et al 2010). As a result of lower viscosity, slickwater cannot suspend and transport proppants as effectively as gelled fluids. To overcome poor proppant transport, higher pumping rates are applied, which in turn
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