Several metals are present in most drilling muds (Table 1). Concentrations of individual metals may vary depending on the composition of the base ingredients and additives. The metals of greatest concern because of their abundance in drilling muds and cuttings and their potential toxicity to marine organisms include arsenic, barium, chromium, cadmium, copper, iron, lead, mercury, nickel, and zinc. Some of these metals are added intentionally to drilling muds as metal salts and organo-metallic compounds, if approved by local regulations. These metals are included in the added metals category. Most metals in drilling discharges are trace impurities in drill cuttings and major mud ingredients, particularly barite, ilmenite, and clay.
The strengthening of environmental regulations around the world has changed the way service companies and their customers view the provision of drilling fluids. Ignoring the effects on the environment from mixing, transporting, cleaning, re-using and disposing of mud and cuttings is no longer an option.
There are three contributing factors of toxicity in drilling waste: the chemistry of the mud formulation, inefficient separation of toxic and non-toxic components and the drilled rock. Typically, the first mechanism is known best because it includes products deliberately added to the system to build and maintain the rheology and stability of drilling fluids. The technology of mud mixing and treatment is recognized as a source of pollutants such as barium (from barite), mercury and cadmium (from barite impurities), lead (from pipe dope), chromium (from viscosity reducers and corrosion inhibitors), diesel [from lubricants, spotting fluids, and oil-based mud (OBM) cuttings] and arsenic and formaldehyde (from biocides).
Centrifugal Cuttings Dryers
One of the international benchmarks for an efficient solids control and waste management system is to incorporate a Centrifugal Cuttings Dryer (VCD) into any environmental management strategy. The VCD (Vertical cuttings dryer) units typically consist of a high-speed vertical centrifuge that achieves maximum liquid solid separation in large volume processing.