The use of thermal desorption technology or thermal desorption units (TDUs) to recover oil from drill cuttings has been well documented in the industry and a detailed study of all available technology and processes was published by Halliburton in 2004.3
In summary, thermal desorption of oil from drilling cuttings for environmentally acceptable disposal of the cuttings was identified as an option in the early 1990s. The technology used for this purpose evolved significantly in the intervening years. In Europe and South America, the processed cuttings typically measure less than 1% of Total Petroleum Hydrocarbons (TPH) before disposal in landfills and this was the target selected for the subject project.
Regulatory agencies in other areas have also set standards for the levels of TPH in cuttings prior to disposal or discharge to the environment. Some processes do not require thermal desorption technologies. For example, in the Gulf of Mexico the discharge of cuttings with TPH levels of either 6.9% or 9.4% by weight, depending on the synthetic oil selected, is allowed if other toxicity and biodegradation standards are met or exceeded.
These levels of oil on cuttings can be attained with mechanical systems. However, the trend in environmental regulations is toward greater stringency and therefore an increased demand for minimal TPH levels in treated cuttings will drive the development of more oil-removal technologies.
All thermal desorption processes evaporate the oil and water from the cuttings. The heat required to evaporate the oil and water provides enough energy to remove and separate emulsified oil as well. Free and emulsified oil and water are removed by distillation, and in the process, water evaporates first to produce steam. Oil has a higher boiling point and evaporates after the water. The production of steam can also assist in lowering the boiling point of oil.
The goal is to produce oil-free (or ultra-low TPH) solids for disposal by distilling off oils from the cuttings and recovering oil to be re-used for drilling fluid.