Overcoming the Late-Stage Development Challenges of Bonga Turbidite Reservoirs via Geosteering Technology Deployment

Abstract

The Bonga field is in its late stage Phase-3 development. Infill wells are drilled to target oil in the bypassed or unswept areas of the reservoirs. Unlike the earlier phases of development, the current wells have complex trajectories and are hooked up via crowded subsea manifolds. Because oflimited availability of drilling centers, most of the new wells are extended reach with narrow drilling margins. The target reservoirs are relatively thinner, poorly developed, and more limited in extent and size compared to targets in the earlier phases, increasing inherent subsurface uncertainties. With an expected low case ultimate recovery per well of roughly 10–15 MMstb, and average deepwater well cost of +/- $40 million, the stakes were high and hence critical to get it right the first time. If net-sand is poor or short because of suboptimal landing or well placement in the reservoir, the well objective (recovery and rate) can easily be compromised and could require drilling a sidetrack with additional attendant cost. Longer exposure length of drain hole (reservoir section) was known to improve well production rates hence an essential component of the well plan. To address these challenges and ensure the wells achieve their objectives and deliver their economic value, a geosteering technology (Reservoir Mapping While Drilling tool—GeoSphere) was adopted for optimal landing above the target reservoir(s) and placement within the reservoir channel sands using the Multilayer Distance to Boundary technology (PeriScopeHD). The deployment of geosteering technology was considered to be a success in enabling better sand exposures of the wells in the target sections, thus achieving the well objectives. This paper discusses the implementation of geosteering technology and learnings from two case studies in the Bonga infill campaign.