The drilling fluid is related either directly or indirectly to almost every drilling problem. This is not to say that the drilling fluid is the cause or solution of all drilling problems, but it is a tool that can often be used to alleviate a problem situation.
Many have thought that a magic additive would solve all of their problems and that the drilling fluid could somehow make up for poor drilling practices. This is simply not the case. It is a part of the drilling process and should be used to complement all other facets of the operation.
Selection and application of the drilling fluid are key factors in the success of any drilling operation. The first objective in planning a mud program is the selection of a mud that will minimize the amount of lost time in the drilling operation. Such a mud will usually be economical regardless of its cost per barrel.
Generally, a good drilling fluid is simple and contains a minimum number of additives. This allows easier maintenance and control of properties. It is desirable to have a mud system that is flexible enough to allow changes to be made to meet changing requirements as they occur. Each change in the mud should be planned well in advance of the time it is required. This will allow current treatment of the mud consistent with future requirements.
Planning of the mud program begins with acquisition of all pertinent geologic and offset well information. This includes pore pressure and fracture gradient profiles, formation characteristics, intervals of possible borehole instability, location of soluble salt beds, and the possibility of sour gas or saltwater flows. Good information is an absolute necessity for good engineering. This necessitates communication between those persons concerned with the different parts of the operation.
Next, the mud and casing programs should be integrated. The only solution to some problems is to isolate them behind casing. This is especially true when two problems that require opposite mud properties occur at the same time. For instance, a lost-returns zone and a high-pressure sand or sloughing shale open at the same time lead to a conflict that cannot be resolved by the mud alone. The mud program should be planned for each casing interval with a contingency plan for deviations from the casing Program.