Approximately 70% of the muds in use in coastal Louisiana are calcium treated, and the majority of these are of the recently introduced, more highly inhibited type. The terminology of inhibition is reviewed. Examples of South Louisiana well records and their mud costs are given for the different types of mud. A curve for flow properties vs. mud weight is presented. Centrifuge economics are discussed. Special muds, mud additives and techniques are described.

At the invitation of the Evangeline Section, Society of Petroleum Engineers of AIME, this paper was prepared to present a brief review of recent innovations and current mud practices along the Gulf Coast of Louisiana. The authors feel that the last two years have been significant ones for the drilling mud industry, in that mud costs have been drastically reduced and practical field muds and techniques have been developed which enable the drilling of deeper wells with less trouble than has heretofore been possible.

Mud Types Currently in Use

First in order of interest is a survey of the types of mud currently being used in South Louisiana (Table I).

As indicated statistically in the survey, the low pH red mud is the most economical type for drilling wells which do not require a heavily weighted mud or anticipate salt water contamination. The cost of chemicals for maintaining deflocculation of the mud is very low in the absence of inhibiting ions. The non-inhibited mud has little tolerance for solids, however, and the flow properties become costly to manage at mud densities in excess of 12.0 ppg. The wells which can be drilled in South Louisiana with this type of mud are in the minority.

At the time this survey was taken, 70% of the muds in use were calcium treated — either with lime, calcium chloride, gypsum, or seawater. These more or less inhibited muds have proven themselves very practical for Gulf Coast drilling, where good filtration and flow properties are required at heavy mud weights and in the presence of contaminants.

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