It is proposed within this paper that the use of Less Toxic Oil Based mud (LTOBM) with an oil to water (o/w) ratio of 50/50 (as opposed to the more conventional 75/25 o/w ratio) significantly reduces mud costs and may also reduce the volume of oil retained on cuttings and hence reduce the volume of oil dumped into the sea along with the cuttings.

Mud properties from two Field Trials of the 50/50 LTOBM in the UK sector of the North Sea are presented and the oil on cuttings retention figures are discussed theoretically.

Techniques suitable for investigating water in oil emulsions (to see what physical changes are brought about by varying the oil/water ratio and other parameters) are reviewed, and Optical Microscopy, Laser Light Scattering and Electron Microscopy results are presented.

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