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Ervironmental friendly drilling fluid management offshore Norway

Bilstad T., Jensen B., Toft M.

AGH Drilling, Oil, Gas

2014

Vol. 31, no. 2

191--197

Types and amount of fluids utilized when drilling a well determine to which extent the drilled cuttings are legally considered hazardous waste. The main categories of drilling fluids are oil based (OBM), water based (WBM) and synthetic based mud (SBM). The purpose of adding fluids to the drilling operations is to cool and lubricate the drill bit, to stabilize the well bore, to control subsurface pressure, to control formation pressure, to control well stability. to control corrosion, and to carry cuttings to the surface. Historically, cuttings from drilling sub-surface wells have been depositeddirectly from the platform to the seabed. However, environmental laws and regulations for the Norwegian offshore sector prohibit such practice when the oil on cutting exceeds 1 % by weight. Re-injection of cuttings as a slurry into subsurface formations is still practiced. Due to migration, leaks, re-entering of slurry onto the seabed, and collapsing formations this disposal method is on a decline. Transport of oily cuttings to shore for final treatment is the preferred Norwegian practice. However, cutting treatment on platforms is also continuousl yevaluated. For logistics and cost reasons, as well as health, safety and environmental (HSE) and working environment reasons, emphasis is put on offshore waste minimization, reuse and recycle.Ten onshore locations in Norway are currently receiving cuttings for further treatment and fluid recovery. The treated cuttings are for the most part disposed in landfills.

Offshore drilled cuttings management

Bilstad T., Stenberg E. S., Jensen B., Larsen T., Toft M.

AGH Drilling, Oil, Gas

2013

Vol. 30, no. 1

47--50

The search for offshore fossil fuels generates large volumes of drilled cuttings which under certain conditions are defined hazardous, negating disposal at sea. Much of the cuttings end up in onshore landfills. The types of fluids used in well drilling operations determine to which extent the cuttings are considered hazardous. The three main types of fluids are oil based mud (OBM), water based mud (WBM) and synthetic based mud (SBM). The purpose of adding fluids or mud in the drilling operations is to cool and lubricate the drill bit, to stabilize the well bore, to control subsurface pressure, formation pressure, well stability and corrosion, and to carry cuttings to the surface. OBM is based on either diesel or mineral oil. One advantage of OBM is enhanced drilling performance, especially in technical challenging environments. A drawback, however, is the toxicity of OBM, prohibiting discharge of cuttings to the marine environment. Drilled cuttings are rocks produced during drilling operations, becoming coated with drilling fluids. Historically, cuttings have been disposed to sea. However, recent environmental laws and regulations prohibit such practice. Re-injection of cuttings as a slurry into subsurface formations has also been discontinued due to leaks and re-entering of slurry into the bottom waters. Transport of cuttings to shore is therefore the choice. For logistics and cost reasons emphasis is put on offshore waste minimization and reuse/recycle. Total fluid management (TFM) leads to environmental impact reduction (EIR). Minimization of drilling fluids and reuse of fluids lead to cost reduction. Volume of cuttings is reduced through directional drilling and by drilling smaller diameter holes. Synthetic based drilling fluids (SBM) are replacing OBM. Drilling wastes are further separated into a fluid and a solid phase. The solids may be used for road and other construction purposes, whereas the OBM is burned for energy recovery. The purpose of the thermo-mechanical cuttings cleaner (TCC) is to convert hazardous oily cuttings into useful products. TCC facilities are only available onshore in Norway. However, offshore TCC units will in due time be introduced, negating the need for transport of cuttings to shore. Cuttings are allowed disposed to sea when no toxic fluids are attached. TCC separation is accomplished by generating temperatures of 240-300 degrees of Celsius sufficient for evaporation of oil and water from the mineral solids.