Intra-Fault Drilling/Completion in York Gas Field Development: An Economics Improvement Strategy

Abstract

The York gas field is located in the Southern North Sea (SNS) area of the United Kingdom Continental Shelf (UKCS). Structurally the field is interpreted as having a good number of intra-faults. Of particular interest to this paper is the intra-fault located south-west of the field. Due to the presence of this fault there are two separate crests in the southern area of the field. Each of these two crests was targeted by a horizontal well in the initial development plan of the field. A third horizontal well was to be drilled and completed in the eastern flank of the field. Recent subsurface studies involving petrophysical, geological and reservoir engineering re-interpretation and analysis carried out in the field confirmed the well count, but not the well type, required for development of the field as compared to previous development plan. Furthermore, it was established that by drilling and completing across the aforementioned south-western intra-fault, instead of avoiding it as done in the previous development plan, the total well count for developing the field is reduced by one. Two optimal development scenarios, both having similar recoveries, have been identified for the development of the field. Option 1 has two development wells and requires drilling and completing across an intra-fault. Option 2 requires three development wells and no across fault drilling/completion. Economic analysis of the two development options shows that option 1 has better economics indices. Thus, though option 1 is deemed challenging because it requires drilling/completing across a fault the cost savings to be realised from implementing a two well development, instead of the three wells required in option 2, makes it more attractive, nevertheless. The paper presents the basis and merits of adopting option 1 as the preferred development option for the field. It further discusses the challenges and issues associated with drilling/completing across a fault and way-forward plans to be adopted for a successful implementation of the option 1 development plan. The paper concludes by presenting option 2 as a contingency option to be implemented in the event that option 1 is not successful with regards to drilling/completing across the aforementioned intra-fault.