Millions of tonnes 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 characteristics 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 for competitive reasons.

Drill cuttings have different destinies 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 upon limited input and without overall considerations. In some cases the decision seems based on un-proportional 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.

High surface temperatures and long retention time can degrade the oil. For applications where the OBM oil is of high quality and high value, it could make a significant impact on the business case if all or parts of the output oil from the process can be re-used in new OBM or used as fuel for diesel engines.

Heat generated by friction is a well known phenomenon and evaporation by friction heat in the Thermomechanical Cuttings Cleaner (TCC^®) has been available in the drilling waste market for approximately 10 years. This method offers the best quality of recovered oil and is also the safest method to use.

Base oils used for drilling mud are well defined, low sulphur, low aromatics oils within the diesel range of distillation. Among the quality specifications for the base oil are density and flash point. In addition HSE requirements like low aromatics, BTEX and low sulphur applies.
 
Fingerprint
This Example with oil from a TCC^® site shows a GC MS profile of virgin base oil (top) and base oil recovered in the hammermill (bottom).
 
The recovered oil has the same fingerprint as virgin base oil. The recovered oil is directly re-usable as base oil in new mud.
 
The recovered oil is cleaned in several stages before it is discharged in two different fractions; the main fraction comes directly from the oil condenser and a small fraction is separated from the water which is evaporated in parallel with the oil.
 
BTEX
Despite the virgin base oil being low on BTEX GC analysis sometimes demonstrates small BTEX concentrations in the feed. In cases where the total BTEX is higher than spec one can separate it out by keeping the smallest fraction of recovered oil separate from the larger. BTEX will, if present, accumulate in the oil fractions separated from recovered water.
 
Flash point
Often a maximum flash point reduction is used as a quality assurance in thermal desorption of OBM drill cuttings, but if the flash point specified for virgin base oil in the MSDS is used as reference this may lead to misleading conclusions. It is important to compare flash point of the actual oil in cuttings and recovered oil. The TCC^® unit does not change flash point of oil.
 
Conclusions
The hammermill is used for recovery of high quality oil from OBM drill cuttings without degrading oil quality. 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. Compared to other drying methodologies TCC^® friction driers offer a gentle evaporation, low residence time in the reactor and low required process temperature. These, in addition to the homogenous mixing, are all factors that ensure the best possible oil recovery.

Click here to watch our animation of the TCC process

In the same way as any other thermal technology, the capacity of a TCC^® is depending on the energy input and the content of the waste. Therefore, any capacity indication for thermal desorption processes has to be based on the composition of the waste.

The energy required to heat and evaporate the various components in the waste is defined by thermodynamics.

In particular, capacity is depending on the amount of water in the waste. When Thermtech gives an indication of the processing capacity this is based on assumptions regarding the content. A "3 ton per hour" unit will have that capacity with 70/15/15 solids/water/oil ratio (by weight) and will have a main motor/engine of approx. 700kW. If the water content is lower, the capacity of the same unit will be higher than three tons per hour. Up-scaling the equipment, also above 4-5 tons per hour is probably doable, but that may leave less flexibility than what multiple units will give.