Drill cuttings are the small pieces of rock that are broken away by the drill bit and carried to the surface during wellbore construction. Many countries allow controlled discharge of drill cuttings to the marine environment, provided that operators comply with regulations designed to address potential environmental effects. A new document released by the International Association of Oil and Gas Producers (IOGP) provides information on the potential environmental and nonwater-quality effects of controlled drill cuttings discharges and examines the history and rationale behind selected regulations covering drill-cuttings discharges.
Cuttings typically range in size from clay-sized particles (approximately 0.002 mm) to coarse gravel (greater than 30 mm), and their size and physical/chemical properties will depend on the formations being drilled, type of drill bit and assembly used, rate of penetration, and type of drilling fluid and additives used.
Several options exist for managing offshore drill cuttings. These include cuttings reinjection/downhole disposal, shipping the cuttings back to shore for treatment and disposal, or offshore treatment to remove associated nonaqueous drilling fluids before discharge to the marine environment where the cuttings will mostly settle on the seafloor. Seabed effects are the primary environmental concern related to the offshore discharge of cuttings that contain residual drilling fluid. Water-column organisms are at a low risk of harm from drill cuttings discharges because of the rapid dilution and dispersion of drill cuttings as they fall through the water column. For onshore disposal, total containment and safe transfer of these materials to onshore treatment and disposal facilities represent key issues of concern, as well as nonwater-quality environmental impacts (NWQEIs; e.g., energy consumption and air emissions).
Controlled discharge of drill cuttings may be the preferential waste-management option when evaluating combined operational risks, life-cycle considerations, and other environmental exposure risks but may be prohibited or strongly discouraged in other areas because of the need to protect specific marine resources or because of local stakeholder concerns.
The newly released document was prepared by IOGP to provide information on the potential environmental and nonwater-quality effects of controlled drill cuttings discharges once the riser is in place, allowing drilling discharges to be treated and managed from the drilling rig (top side) before discharge or alternative disposal management. It explains why, under some conditions, the discharge of drill cuttings offshore can be the most environmentally preferable option while, in others, discharge is discouraged.
To that end, factors influencing environmental impact, impact modeling, and waste-management options are discussed, and the history and rationale behind offshore discharge regulations are presented as case studies. This background information may help operators, regulators, and other interested stakeholders understand the logic and intent of the different regulatory approaches adopted in different types of receiving environments.