A Case Against Oil Muds
Very much has been written the past few years on the advantages of oil muds, where oil is in the continuous phase, over the more conventional water-based muds. Oil phase muds have, in fact, greatly improved drilling performances especially in cases of hard-to-drill deviated holes as in the Gulf Coast. Also, this type of mud is used very successfully in field development drilling where formation evaluation is not of prime importance*. However, when drilling with an oil mud in areas where well log evaluation is critical as in a wildcat or field stepout, we must be aware of some of the inherent disadvantages associated with the oil mud. Apart from the fact that the geologist, particularly in the Gulf Coast, dreads to see an oil mud used because of its associated sample and core contamination, the log analyst should be concerned as to the possible dire effects to the logs.
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