RIASSUNTO
Abstract
Total E&P Norge is an EMAS registered and ISO 14001 certified company. With a commitment to continuous improvement and minimizing footprint from activities, an internally defined zero harmful impact objective for the drilling of an exploration well in the Norwegian Sea was set. Deep water coral structures were identified in the vicinity of the well location driving the focus on potential physical impact in addition to chemical impacts on these structures and the sediment fauna.
To verify if the objective is met, the environmental impact level on the marine environment associated with the drilling activities has to be assessed and the effects verified. Three hole sections were discharged and the effects associated with these discharges were investigated. Cuttings size distribution, chemicals composition of the mud, and volume discharged were collected during the drilling of these sections. These data was applied in a risk modelling tool developed within the joint industry project ERMS providing estimation of risk associated with drilling discharges on the sea floor and in the water column. This model is still under qualification/verification and the presented drilling operation represented an excellent case study where the output of the model in term of risk for particles and chemicals can be tested towards field observations. Sea floor observations were performed before, during and after drilling operation in order to evaluate the extent of the cuttings deposition and dispersion.
This paper discusses the risk associated with the chemicals and particles present in the mud, in the water column and in the sediment as estimated by the model. The cutting distribution simulated by the model is compared with observations of the sea floor. From these results and existing knowledge from monitoring and exposure studies, ""zero harmful?? impact level on sediment fauna, coral and water column is discussed. For the sediments impact from physical deposition and change in grain size were observed only in the close vicinity of the well. No chemical contamination could take place based on chemicals discharged and as modelled by the risk modelling tool. Impact to the water column was also considered insignificant and related to physical impact from particles in upper part of the water column and only in the close vicinity of the discharge. Also for the water column no chemical contamination could take place based on chemicals discharged and as confirmed by the risk modelling performed. The conclusion from this study is that the objective was met. The paper proposes that physical impact is considered acceptable within certain distance from the well bore location. The size for such an area should be decided upon based on a case by case evaluation depending upon the extent of the drilling activity and the area.
Introduction
""Hans?? was a gas prospect located in 350 m of water in the Norwegian Sea (figure 1). The exploration drilling started in October 2006 and was completed in April 2007.
In the announcement for the block award in the area, special conditions concerning environment applied. For the first time it was a requirement in the announcement for license applications to conduct mapping for presence of the cold water corals (Lophelia Pertusa) in the area to be drilled to ensure that possible occurrences would not be harmed by the planned drilling activity, amongst others. Cold water corals are listed in CITES appendix II as an endangered species (1). Cold water corals, firstly believed to be very rare, are frequently observed during exploration and pipeline laying activities.