Drill cuttings contaminated with oil-based mud (OBM) are treated to remove excess oil prior to discharge into the environment. Recent European legislation has set the limits of permitted oil associated with discharged rock cuttings to 15%w/w in the UK sector and to 10%w/w in Norway and Holland, with a view to substantially reducing this limit further in the near future. Given the geological conditions encountered in the North Sea, the use of OBM's is virtually essential if drilling is to be cost effective. A reduction in discharge limits to significantly below 10%w/w cannot be met economically by existing cuttings cleaning technology and would mean cuttings being returned to land for disposal. The associated costs in doing this will greatly restrict operators' flexibility in exploiting future reserves.
A cuttings cleaning fluid has been developed and tested which can reduce the level of oil on cuttings from >20%w/w to 2-5%w/w (patent pending). The cleaner neither dissolves nor emulsifies the removed oil. Once the contaminating oil has been displaced from the surface of the rock, cutting, the cleaner and the recovered oil separate under centrifugal force into two distinct phases. This allows recycling of the oil back, to the active mud pit and recovery of the cleaner for re-use.
The cleaner has been tested extensively in the laboratory under pressure filtration and centrifuge conditions. Further it has been successful in deoiling small, relatively highly contaminated drill cuttings in a laboratory scale decanting centrifuge system. Full scale tests are underway.