Bonga Northwest Subsurface Development – Planning, Execution and Uncertainty Management

Abstract

The Bonga North West (BNW) field is located in Shell operated Oil Mining Lease (OML) 118, a deepwater development in Nigeria. This paper presents the BNW subsurface development strategy and the associated uncertainty management both at planning (Field Development Plan -FDP) and execute phase. The first development in the OML 118 acreage is the Bonga Main field which came on stream in November 2005 via a Floating, production, storage and offloading (FPSO) vessel. The development strategy of the block is to maximize value from the asset, ensuring that the hub is kept full by developing reservoirs in the nearby fields while optimizing production from the block. In pursuant of this strategy, detailed subsurface evaluations were carried out to estimate expected recovery of the nearby fields as potential tie-backs to the Bonga Main FPSO. The size of nearby discoveries and proximity to the FPSO were two key parameters used to develop the OML 118 development strategy. BNW was discovered in 2003 following the detailed interpretation of 3D seismic acquired in 1995 on the acreage. Integrated evaluation across key disciplines established commercial viability of the project. This, coupled with a detailed geo-hazard study, formed the basis for the 2011 BNW FDP. The FDP proposed the field being developed with nine wells in two phases of drilling. The development phasing was driven by the requirement to manage the field uncertainties by gathering additional data. The first phase development involves six wells (four oil producers and two water injectors). BNW leveraged on its close proximity to the existing Bonga Main infrastructure and was approved as a subsea tie back development to existing Bonga Main FPSO. The FDP enabled a robust management of challenges such as shallow gas occurrence, structural/depth uncertainty, stratigraphic/reservoir development, reservoir connectivity, fluid prediction in the shallow horizons, bore hole stability and overburden shale issues encountered in the execution phase. Also a new technology that targeted managing of impairments in water injection wells experienced in the operation of Bonga Main field was also successfully deployed in the BNW field development. All Phase 1 development wells have been successfully drilled and several learnings from this project have been documented and will be used on projects going forward.