Workflow for Slot Re-Utilization Assessment on Offshore Brown Fields to Improve Re-Development Profitability – A Case Study in Nigeria

As fields brown out, opportunities tend to shrink in size and recoverable volumes necessitating the design of innovative cost efficient re-development solutions to address increased surface and subsurface challenges. A prominent surface challenge with in-fill drilling on shallow offshore brown fields is slot availability, since the existing platform slots are typically in active use. Some of the known time and cost efficient means of addressing this issue, includes internal slot add-ons, deck extensions for external slot add-ons and shared wellhead systems – all of which can be accommodated up to the design limit of the existing platform. There is also the option of scaled-down platforms such as conductor supported platforms which present a cheaper alternative to conventional jacket platforms. This paper describes a structured approach applied on a brown field in Nigeria, to determine the re-use potential of existing wells on an offshore platform. The case study starts by identifying shut-in wells and active wells which have expected end of producing lives that precede the planned infill drilling period. These wells are then screened out and evaluated for further immediate to near-term utility such as rigless intervention, stimulation, recompletion and workover. The remaining wells form an inventory of the potential donor wells for sidetrack feasibility assessment, which takes into consideration wellbore architecture, casing sizes/depths, environmental regulatory requirements, P&A complexity, surface equipment constraints and well integrity aspects. The identification and categorization of potential donor wells provides the basis for the final step in the workflow which is trajectory feasibility study against identified subsurface targets. The overall objective is to reduce or eliminate the need for new platforms and consequently improve the economics of infill projects.