Waste treatment and disposal is the process of management and disposal of waste generated by drilling fluid and drill cuttings, after the solids collection and control phase. Depending on the mud system used and initial treatment, the water content in cuttings and its toxicity may still be high and further treatment could be required, prior to final disposal. This stage is not always present and there are instances when non-toxic waste is disposed immediately. Oil-based mud and synthetic-based mud are considered to be toxic and must go through a treatment and disposal process. There are various options to treat and dispose the waste and the selection criteria are driven by 1) regulations; 2) costs, 3) type of waste, and 4) what equipment is available. The options available are:
- Cuttings Re-injection (CRI) is used for re-injecting drill cuttings back to the reservoir through separate disposal wells, old non-producing wells or existing production wells. This process returns drill cuttings to its native environment and does not produce any pollution. This is the only on-site, permanent disposal method that is in full compliance with environment standards. In certain applications, cuttings re-injection is a more cost-effective solution, when compared to skip-and-ship and onshore treatment and disposal.
- Thermal desorption is a process of indirectly heating the waste to increase volatility of contaminants that frees them from solids matrix and evaporates them from the cuttings. This in turn removes oil and other toxic materials from the processed cuttings and provides less than 0.1% of oil-on-cuttings content, to allow further disposal (landfill and land farming) or recycling (road spreading, construction materials or restoring coastal wetlands). Thermal treatment is the most effective technology to process waste generated by oil-based mud systems. Current days, technology allows in-situ processing using TCC RotoMill technology with full disposal offshore, given the space and power capacity on the drilling rig allows installation of the equipment. This completely eliminates the requirements of transporting waste to shore for further processing. Two major types of technology are used: 1) Thermomechanical, whereby friction is the source of heat and 2) Thermal Phase Separation, where propane, natural gas or diesel, combusts in the burners to heat up the cuttings.
- Fixation / Stabilization / Encapsulation used mainly with water-based mud. The technology converts liquid and slurry waste into dry and solid materials with high structural integrity. Materials and chemicals such as calcium oxide, cement, fly ash, mica and lime are used to treat drill cuttings and encapsulate them. Stabilized drilling waste has been used as a material for road foundations and backfill for earthworks. Although there are some limitations, this method has been approved and successfully used in various locations. Because of the equipment footprint, it has never been used in offshore locations.
- Dewatering is a chemical and mechanical process that is used to recover water from the mud and return it back to the drilling fluid.