Page 164 - Drilling Technology in Nontechnical Language

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DRILLING FLUIDS

Overview

A drilling fluid is a combination of liquids, solids, and sometimes gases

that is pumped around the well.
The drilling fluid plays many functions in drilling wells. If the mud

properties (physical, chemical, and rheological) are incorrect, safety and

economics are affected. (Rheology refers to the study of fluids in motion,
and rheological properties such as viscosity can impact several key mud

functions.) Properly designed drilling fluid is essential to safe, efficient,

and economic drilling. It is also not well understood by nonspecialists. In
some companies, the relationship between the quality of the mud and the
final result is ignored simply in order to find the cheapest, rather than the

most appropriate, mud system. This likely leads to a higher overall cost of
the well and possibly lower productivity, too.

Functions of the Drilling Fluid

The drilling fluid has to carry out all of the functions listed here at
some point in every well drilled:
▪ Control formation pore pressures to assure proper well control.
▪ Minimize drilling damage to the reservoir. (This damage reduces

the amount of oil or gas that can flow out of the well.)
▪ Stabilize the wellbore so that the hole diameter remains equal to
bit diameter, or at least minimizes hole enlargement.
▪ Remove cuttings from under the bit while drilling.

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