Where severe drilling conditions exist, especially the combination of water-sensitive sloughing shales, abnormal formation pressures and high bottom-hole temperatures, several operators in South East Asia regularly use "invert emulsion" oil muds to drill and complete trouble-free gauge holes.

This paper will review oil mud operations in the South-East Asian region, and a case history will be presented to illustrate the succesful use of oil mud in the development of a major Indonesian gas field.

Some misconceptions still surround the use of oil muds. Modem oil muds are stable, practical and relatively simple drilling fluids which may be scientifically formulated to match the most severe drilling conditions. This paper will attempt to clarify some of the misunderstandings commonly associated with oil muds.

The range of application and advantages of an oil mud will be demonstrated, and the physical and chemical properties of a typical invert emulsion oil mud will be discussed.

Finally, the key to an efficient oil mud program lies in the planning stage. Using examples from one Indonesian operator's extensive experience, the various economic and logistic factors to be considered when using oil mud will be discussed.

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