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.
Method for efficiently recycling water based drilling fluids has been developed. This recycling is conducted in a way beneficial both for the drilling fluid supplier and the operator. Contaminated fluid (slop) is brought back onshore for treatment and reusable fluids from the slop treatment are brought back into the drilling fluids.
Cutting boxes are the primary method of transporting waste drilling fluid and cuttings to shore around the world. Cuttings boxes were developed as an easy method of collecting and transporting cuttings given the weight restrictions of offshore cranes on earlier drilling rigs. Cutting boxes are typically placed near the solids control equipment, where cuttings can be moved relatively short distances and collected in the box. When a Cutting boxes gets full, it is removed and an empty Cutting boxes is shuffled into position. When a sufficient number of full Cutting boxes are ready, they are backloaded onto a workboat and returned to shore. Empty Cutting boxes from the dock facility replace the returned cuttings boxes.