| Water based muds are the most widely used of the three
general types of drilling fluids. This results from the universal
distribution of water, its low cost, its compatibility with human life
and its generally satisfactory nature. In most wells, a water base
mud is used during the entire drilling operation. However, in many
wells where the primary fluid is oil or invert emulsion, only part of the
drilling operation may be done with a water based mud.
Fresh water mud, which at one point was the most widely
used has now been supplanted with other mud types because of the adverse
affects created by the fresh water. Some of these are:
-
High viscosity and gels resulting from hydration and dispersion
of the drilled clays.
-
High viscosity and gels resulting from the high solids content
of weighted muds.
-
High gels and fluid loss resulting from drilling salt, anhydrite,
and cement.
If the viscosity becomes too high, usually a dispersant such
as a phosphate or tannin type will reduce the viscosity sufficiently.
Fresh water muds, however, resulting from the sensitivity of montmorillonite
to salt, cement, gypsum and high solids content reach the limit of their
use at mud weights of 12ppg or higher. |
