Depth issues in the oil patch : a study of wellbore position uncertainty in the Ekofisk Field

Abstract

The understanding of the subsurface geometrical position of the wellbore is crucial. The wellbore positioning data is relied upon by different disciplines or functional groups throughout the life of any given field. For example the geological and reservoir models rely heavily on subsurface geometrical position data. The drilling discipline depends on this data for planning of future injector or producing wells where the main objectives are to navigate through existing wells thus avoiding collision and hitting the target. Therefore the choice of survey tools and the work practices employed in gathering this data are essential. This thesis provides a general overview of directional drilling & applications, survey calculations methods, survey tools and survey errors. The results of position uncertainty analysis performed on two resurveyed wells from the Ekofisk field on the Norwegian Continental Shelf are presented in this thesis. The analysis shows that the use of gyroscopic tools has a lower error rate compared to magnetic tools. Potential improvements in terms of technologies and work practices for planning and drilling of future wells have been suggested.