Designing drill in fluids which can guarantee minimum invasion into the reservoir rock is a must for open hole completion wells. The industry has proposed several ideas to deal with the problem, most of them based on adding bridging agents to the fluid formulation. Such agents would block pores near the well bore and, consequently, prevent additional fluid to invade the rock, but often require acid treatment for their removal.

A different concept is proposed for controlling invasion in this article: designing a polymer based fluid which would generate extremely high friction losses when flowing through a porous media without generating extra losses while flowing in the well. In this case the fluid would present proper flow and solids transport properties in the well and would not invade the rock formation.

Experimental results obtained with the flow of different polymer solutions through consolidated inert porous media show that the viscoelastic behavior of fluids can be a major restriction to fluid invasion. Based on a viscoelastic resistive force proposition for the porous media, flow characterizarion maps defining viscous flow, elastic flow and viscoelastic flow regions are obtained

This article deals with the optimization of the drilling fluid viscoelastic parameters, such as the first normal stress difference and the extensional viscosity, aimining the minimization of fluid invasion through oil reservoirs. The arrival of this rheology controlled invasion concept brings to the polymer manufacturers a new challenge: the development of a highly viscoelastic polymer with non damaging behavior and adequate wellbore properties.

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