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Where offshore discharge of cuttings is not sanctioned by regulatory and environmental agencies, there are many possible disposal options. Waste segregation at the rigsite is a key factor in the success of zero-discharge programs. Drilling-fluid waste, drill cuttings, waste generated by cementing or completion operations, and waste water from the rig must be handled and stored separately. Another option is minimizing the initial volume of cuttings through installation and careful maintenance of high performance solids-control equipment. An effective cuttings-drying process should be established at the rigsite so that any cuttings transported to shore have the lowest possible fluid retention.
At present, thermal desorption is considered one of the most effective methods of processing cuttings. Thermal desorption results in a 0.1 to 0.5% ROC rate and recovers the liquid oil for possible reuse. In thermal desorption, cuttings are heated to a very high temperature so that oil and water are boiled into gases. The water is released as steam and the oil is condensed to liquid.
However, the recovered oil may not have the same properties as the original base fluid because of the possibility of high temperatures breaking the heavier hydrocarbon molecules into lighter compounds. This may lower the oil flash point and alter its rheological properties. Though these changes are generally slight, they are suffi cient to prevent most operators from attempting to reuse the oil in a drilling-mud formulation. The oil is typically used as heating oil or to fuel the thermal desorption process. Salts or heavy metals are not removed from the cuttings.
