A comparative study of the water based drilling fluid viscoelasticity versus shear viscosity effects on the filtration loss control

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Drilling fluid shear viscosity and the elasticity are two of the most influential factors controlling the volume of fluid invasion into reservoir and the resultant formation damage. Previous studies were inconclusive regarding individual effects of the fluid shear viscosity vs elasticity, mainly because of the difficulty to separate and measure their impacts independently. In this study, two groups of fluids were formulated: one group with the same shear viscosity and variable elasticity and the other group with the same elasticity and variable shear viscosity. Detailed rheological characterizations were carried out by conducting amplitude sweep and controlled shear rate tests. Viscoelastic properties were quantified in terms of the energy dissipation. Static filtration tests and core flooding experiments were conducted to determine the static fluid loss, pressure drop across the core at different fluid flow rates, and the resultant formation damage induced by each fluid. The observations from this study provided several key insights: i-) The static filtration rate can be more effectively controlled by altering fluid viscoelasticity than the fluid shear viscosity; ii-) Both the shear viscosity and the elasticity strongly influence the pressure drop across the core, however, the effect of the fluid elasticity on the pressure drop is more pronounced; iii-) Increasing the fluid elasticity inhibits fluid invasion into the formation more effectively than increasing the fluid shear viscosity; iv-) The fluid elasticity can be effectively used for developing non-invasive fluids, which would reduce static filtration rate, increase pressure drop, and minimize formation damage by effectively reducing fluid invasion.