As environmental regulations tighten, operators are faced with limited options for oil- and synthetic-based mud and cuttings disposal.
For shallowwater offshore and some onshore drilling operations, cuttings slurrification and reinjection often is the least expensive disposal alternative. However, sometimes well location, formation constraints or local regulations do not permit injection.
Other commonly used treatment and disposal options include:
• bioremediation and landfarming, which require large amounts of land, dilution and long periods of time; and
• encapsulation or fixation, which require addition of a stabilization agent to trap liquids and can be susceptible to leaching due to poor mixing or weak matrix formation.
Each of these options may leave the operator with inherent long-term liability, and none offers the opportunity to recover or recycle any of the hydrocarbons, which are lost to the environment. Water-based mud systems are sometimes an alternative, but directional or difficult straight-hole operations may require oil- or synthetic-based mud to provide better borehole integrity and lubricity to reduce drilling time and costly drilling problems.
Brandt, a Varco company, recently developed and patented the Thermal Oil Recovery (Thor) system, which eliminates future environmental liability, reduces land requirements and provides for waste reduction and recycling. The system has successfully processed cuttings containing diesel-oil or mineral-oil muds for BP in Colombia for nearly 3 years.
Contaminated cuttings with up to 30% oil and 30% water by volume are fed into a hopper by means of a loader. A variable-speed auger under the hopper feeds wet cuttings into the high-temperature, stainless-steel dryer shell, which rotates within an enclosed, insulated firebox with multiple burners. As the drill cuttings move through the dryer, the slurry is heated to between 300°F and 900°F (149°C and 482°C), vaporizing the oil and water. The clean, dry, inert cuttings are discharged from the dryer and sent to a landfill. The processed cuttings typically contain less than 10 ppm total petroleum hydrocarbons and can be used in a variety of construction projects such as high-tensile-strength bricks.
A variable-speed blower keeps a constant negative pressure on the dryer shell, pulling the oil and water vapors through a shell-and-tube condenser. A closed-loop cooling tower provides the cooling water for the condenser and eliminates the need for additional water treatment. The condensate is pumped through an oil-water separator. The recovered water can be used for cooling and rehydration of the discharged cuttings, while the clean oil is recovered and returned to the client. A relatively small portion of the oil is used to fuel the Thor burners.
The system in Colombia works 24 hours a day with regularly scheduled maintenance shutdowns and is capable of processing 6,000 to 8,000 tons of wet, undiluted drill cuttings per month. The system has processed more than 600,000 bbl of cuttings and recovered more than 96,000 bbl of clean oil valued locally at about US $52/bbl, which equates to about $5 million in recovered oil. BP recycles the recovered oil to make new drilling mud, but it also can be used to fuel other processes or even run a diesel engine. Gas chromatograph testing of the oil has shown no significant degradation or formation of new hydrocarbon chains during the thermal process, so it is suitable for recycling.
BP said it saves about $2 million per well in Colombia with this new technology because of better wellbore stability inherent with oil-based mud, less time to total depth and process cost savings compared to other treatment and disposal alternatives.
Using this technology, BP Colombia has reduced the amount of waste transportation and land requirements and eliminated long-term liability while complying with the strictest environmental regulations. BP also has realized better community relations with the creation of new job opportunities.
While the system in Colombia is a large fixed system with cuttings brought to the Thor unit, Brandt also has developed smaller, trailer-mounted treatment systems, with new installations planned for the Middle East and other areas. Treatment systems for offshore use may be viable, but due to space limitations they are limited to low throughput of 2 tons/hour to 3 tons/hour.

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