Effect of viscoelasticity on the filtration loss characteristics of aqueous polymer solutions

Fluid loss control is generally achieved by increasing the shear viscosity of the fluid and developing an internal/external filter cake using fluid loss control additives. If the viscosifiers and fluid loss control additives are not selected properly, both mechanisms may lead to a significant reduction of permeability. Moreover, increasing the fluid shear viscosity may not be desirable all the time due to the high annular pressure losses (i.e., the ECD limit), in particular, when drilling long horizontal and extended reach wells. In this paper, a new methodology is presented to formulate an ideal well fluid, which effectively reduces the fluid loss into the formation without causing additional frictional pressure losses in the well. Blends of a water-soluble Polyethylene Oxide (PEO) with different molecular weight distributions and similar average molecular weights (Mw) were prepared. The PEO blends were then used to prepare aqueous polymer solutions, which had similar shear viscosities but significantly different elastic characteristics (i.e., normal stress and relaxation time). Core flow experiments were conducted to investigate the effects of viscoelastic fluid rheology on the formation of internal cake (i.e., frictional pressure drop). It was possible to see the effect of fluid elasticity on the frictional pressure losses alone because both fluids had the same shear viscosity but different elastic properties. The resistance of the fluid with higher elasticity to flow through a porous medium was significantly higher than that of the fluid with lower elasticity. The experimental results indicated that the filtration of a polymer-based fluid into a porous medium could be considerably reduced by increasing the elastic properties of the solution through controlling the molecular weight distribution of the polymer, while keeping the shear viscosity and concentration of the polymer constant. Specifically, the formation damage risk of polymer-based drilling fluids could be minimized without inducing additional pressure drop due to fluid flow inside the well. (C) 2010 Elsevier B.V. All rights reserved.