Drill Cuttings Thermal Desorption

Wed, 01/25/2012 - 08:42

The growing importance given to environmental issues in the oil and gas industry has moved waste handling, treatment and recycling to high on the priority list of drilling companies and their suppliers. When drill cuttings come into contact with hydrocarbons during the drilling of a well, they absorb these hydrocarbons and retain them after being removed from the well.

Across the global oil and gas industry, increasingly stringent environmental regulations require both onshore and oshore drilling operations to clean drill cuttings before they are disposed, because of the potentially adverse eects of discharged drill cuttings on the environment. Especially in anaerobic conditions, such as those found oshore and particularly in deepwater, oil-based drilling fluids have very poor biodegradability, resulting in a drill cuttings build-up on the seafloor. To remove the hydrocarbon contaminants from drill cuttings, a technique called thermal desorption has been employed for decades. This technology is designed to produce hydrocarbon-free solids, or solids with ultra-low hydrocarbon content, for disposal while the recovered hydrocarbons are re-used in drilling fluid. Industry regulation in Europe and South America states that thermally processed drill cuttings should typically have less than 1% of hydrocarbon content before disposal.

Following the registration of a number of patents, Qmax constructed its first drill cuttings thermal desorption plant in Mexico in 2011. Developed and constructed by GEA Process Engineering, requiring an investment of US$8.5 million including equipment, installation and start-up costs, this prototype is now operational in Comales, Tamaulipas, and has the capacity to process 10 tonnes of drill cuttings per hour.

The thermal desorption process starts by mixing the drill cuttings with an agglomerant to produce a pre-treatment mixture. An agglomerant is a mixture of agglomerating agent and a carrier liquid. The agglomerating agent, a cluster of two or more particles held together by physical, chemical or physicochemical interactions, should be stable at temperatures ranging from about 200°C to about 400°C. In Qmax’s drill cuttings thermal desorption process, the pre-treatment mixture is fed to a pressurized desorption chamber where a hot heating gas of 204°C to 316°C is pumped into the chamber to heat the drill cuttings by convection. Within this temperature range, the agglomerating agent should not thermally decompose and caking of the drill cuttings is inhibited. A mixture of drilling fluid, vapour and heating gas is then discharged through an overhead vapour outlet and cleaned cuttings are removed through an underflow cuttings outlet.

Compared to conventional processes, the unique features of Qmax’s patented thermal desorption process are that recovered drill cuttings have a reduced hydrocarbon content and can thus be disposed of more safely. The plant leaks zero discharges into the air, water or ground and recovers 100% of the hydrocarbons for re-use. The reduced particulate content in condensed recovered hydrocarbons enhances the recycling process, and the required space for thermal desorption equipment is reduced both for onshore and oshore applications.

The application of a cost-eective process is an important component in the optimization of the economics of any drilling operation, but the impact is significantly greater oshore. Oshore drilling operators stand to gain the greatest benefits, as it enables them to overcome the current shortcomings of oshore treatment of drill cuttings which results in their collection and transportation to shore for treatment and disposal, or worse, the drill cuttings are simply injected into a disposal well and none of the ‘reduce, reuse, recycle’ principles are adhered to.

Following implementation, thanks to the recovery and re-use of hydrocarbons and water, these companies are transporting lower volumes of drilling fluids and drill cuttings to and from their drilling operations, which results in a substantial reduction in costs as well as in a decrease of the risk of accidental release of drill cuttings into water during transportation.