ABSTRACT:
The rising world energy demand has led to exploration for oil and gas in increasingly difficult environments. Exploration is now extending into sensitive regions, in particular, offshore fields. Drilling in deep water in increasingly deviated and extended wells and borehole instability in challenging geological formations are some of the obstacles encountered. Oil-based drilling fluids are widely used in drilling, especially in highly technical wells. This is because oil-based drilling mud systems perform much better than water-based muds in bore hole stabilization and providing lubricity thereby give faster rates of penetration. However, they are a cause for environmental concern and with the potential long-term liability for damage caused by mud spills and problems in disposal of the oil-contaminated drill cuttings, changes are afoot. The industry has been replacing highly aromatic oils (e.g. diesel) with low aromatic mineral oils as well as synthetic oils. However, as environmental legislation and controls become more stringent, even the newer and less polluting mineral and synthetic oils in vogue now may be adjudged unsuitable because of their non-biodegradability. Indeed, today, in many parts of the world, including countries like the USA, United Kingdom, Holland, Norway, Nigeria and Australia, the use of diesel and mineral oil-based drilling fluids in offshore operations is already either severely restricted or banned because of their toxicity, persistency and bio-accumulation.
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