Millions of tones of oil contaminated drill cuttings are produced every year. By nature the cuttings are contaminated by drilling mud. The level of contamination depends on the efficiency of the mud return system carried out by means of shell shakers. The cuttings may origin from drilling with water based mud (WBM) or oil based mud (OBM). Many different composition of mud and many different properties in the well result in a vast variety of cuttings properties. Defining caracteristics of the cuttings is difficult and it is often not made easier by the drillers and mud suppliers who tend to protect details about their mud.
Drill cuttings have different destinys in different areas. Some is dumped, some is reinjected, sometimes the material is cleaned and parts of the waste are reused in new mud. It appears as if the destiny of drilling wastes often is decided based upon limited input and without overall conciderations. In some cases the decision seems based on unproportional focus in only a few areas like ease of operation, emissions to sea/air, cost, storage, etc. Often the value of oil in the cuttings is not given appropriate attention.
The purpose of this document is to touch upon the different routes OBM cuttings may take and treatment methods in general, then to discuss available thermal separation techniques and finally to describe studies made of oil quality from thermal separation by means of friction based hammermill driers.
Often the oil recovery acceptance criteria are based on a maximum flash point reduction caused by the thermal process, but comparison is made to virgin base oil which not necessarily represents the actual oil in the feed. Tests have shown a measurable shift in distillation curve and flash point from virgin base oil to oil in drill cuttings. This study does not include identification of the scources of degradation of oil before separation, but it is likely that aging and pollution from mud additives or from well formation are factors of significance.
The findings are that the hammermill works for recovery of high quality oil from OBM drill cuttings without degrading oil qualit ard. In fact the thermal separation process can be used to raise the quality of oil compared to the actual feed to the unit by removing oil fractions outside of the virgin base oil specification. Recovery and reconditioning of the valuable base oil justifies the cost of the cleaning process, providing a win/win situation for the drillers, mud companies and for the environment.