Page 264 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 240

[ ] Well Programming
2.5.9

increase would require addition of oil. This would dilute the mud so
more weighting material and chemicals would be needed. This would
also increase the volume.

Table 2-2 Lowest OWR Recommended by Density Range (courtesy of Baroid)

Mud weight, ppg Lowest recommended OWR

7-9 60/40
9-11 65/35
11-14 70/30
14-16 75/25
16-19 80/20
19+ 85/15 to 95/5

2.5.9. Environmental Aspects of Oil Muds

Seabed studies of multiwell sites in the North Sea by the mid-eight-
ies (after three or more years of usage of low-aromatic mineral oils)
showed cuttings piles below platforms where in some zones there were
incomplete benthic populations. The problem was the vast amount of
hydrocarbon material in the cuttings piles, and in some cases or some
parts, anaerobic conditions persisted. Subsequently, legislation
required that the amount of oil on cuttings discharged to the seabed be
reduced. Permitted levels of oil on cuttings were persistently reduced.
This required improvements in primary shaker equipment and eventu-
ally the reintroduction of cuttings wash systems. In some offshore areas
(e.g., spawning grounds) the discharge of cuttings from oil muds based
upon low-aromatic mineral oils was banned irrespective of how little
the oil content was on the cuttings.

2.5.10. Oil Mud Additives

Emulsifier. The droplets of brine are held in an invert emulsion in
the oil phase because they are coated by emulsifiers. Emulsifiers are
surfactants that have an organophylic end(s) and a hydrophylic end to

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