Drilling progress. Pt. 2. How fluid properties affect drilling variables

Drilling fluids should be selected based on anticipated conditions that will be encountered while drilling. Within a given class, drilling fluids may have drastically different effects on drilling rates, hole stability, and formation evaluation. A graph is included which compares the effective individual mud properties on penetration rate. Density and solids content are the most severe rate reducers and are interdependent. Densities should be kept as close to the formation pressure gradient as practical, and solids should be controlled in the optimum range. Extremely high bottomhole temperatures encountered in the ultra deep and geothermal drilling makes temperature stability of a mud system an important factor. Drilling fluids are categorized in tabular form by their ability to maintain hole stability in various types of troublesome formations. An important function of a drilling fluid system-other than mechanically making a stable hole at an economic rate--is to make positive identification of the presence of water, oil, gas or steam possible while maintaining original well productivity.