Abstract
Inverted oil muds have the ability to control the expansion of water-sensitive clays, and they must be used whenever wellbore stability is unattainable with water-based muds. However, the initial production rate of a well drilled with inverted oil mud is often lower than expected.
The prevalent damage mechanisms have been found to be: Inversion of wettability of the rock matrix from water-wet to oil-wet, and formation of stable emulsions inside the porous medium. Reductions to the mobility of oil between 60 % and 98 % have been found.
A process, with the trade name ULTRAMIX™ was developed which includes a mixture of surfactants and solvents, each one having a specific function against the effects of the components of the inverted oil mud filtrate, and a procedure for the proper placement of this mixture in the porous medium surrounding the wellbore.
Laboratory tests of this process showed a damage removal up to 96 %. Full scale field treatments conducted over 5 years yielded production increases ranging from 60 to 300 %, sustained over long periods.
