Drilling operations at a new oil and gas field will produce a significant amount of drilling waste. In the Norwegian part of the North Sea, oil contaminated cuttings have not been discharged to sea for the last 20 years because of the OSPAR requirement for max 1 % oil on cuttings. The most frequently used option when drilling with oil based fluids is to send cuttings onshore for treatment. The affiliated volumes of hydrocarbons are distilled off using different methods. On older fields it is not uncommon to recomplete a well to become a waste reinjection well.
In the later years, technology has been developed to treat oil contaminated cuttings to below 1 %. This technology has been in use on drilling rigs on the UK shelf for several years, discharging cuttings from exploration wells drilled with oil based fluids. The technology for cuttings cleaning has been improved in later years, and several operators in the Norwegian sector are now investigating the possibility for cleaning and discharge of drill cuttings when using oil based drilling fluids. The three options for handling oil contaminated cuttings, transport to shore for treatment, discharge to sea and reinjection show different environmental impacts. In the current paper, environmental aspects such as the CO2 and NOx emissions from all these three options will be presented in detail. The consequences of drilling with different rate of penetrations are outlined. The economical consequences of selecting one of these options will also be discussed.
The current analysis is based on a realistic example. The example is the development of a thought field in the North Sea area that can be drilled with a jack-up rig. The consequence of using a semi-submersible rig will be outlined. However, there will be no detailed calculation of those cases.