Uncertainty Management for Well Planning and Execution; Case Study of New Drills in Tom Boy Field in the Swamp Niger Delta

Abstract

The Tom Boy field is one of the oldest fields in the Niger Delta Basin with more than 30 wells at the time of initiating infill development drilling campaign. The drilling campaign of 11 wells (10 producers and 1 Water Source) was planned to develop reservoirs that have not been produced and to optimize production from developed reservoirs. Numerous challenges were faced in the planning and execution phases for the infill drilling. Key uncertainties include, Structure, Stratigraphy, wellbore placement issues, current fluid saturation/contacts in the reservoirs, and wellbore instability issues as wells drilled through pressure-depleted reservoirs. Thus, this paper addressed how these uncertainties were managed during planning and execution of the drilling program. Through integration of detailed Uncertainty Management Plan (UMP) during execution, the team eliminated the need for drilling pilot well in an instance; and in another scenario, successfully landed a horizontal well in a 10ft thick sand. The methodology used include deployment of improved technologies, proper planning, appropriate mud-weight design, history matched reservoir models, optimizing subsurface target locations for data acquisition and proper well sequencing on the drilling schedule was used to understand the current saturation in some target reservoirs and target the sweet spot in the reservoir. Pre-execution decision tree assisted with making quick real time decisions while drilling the landing and lateral hole sections based on the outcome of each uncertainty identified in the UMP signpost. Decision tree incorporated all information (earth model, seismic data, dips, local pre-drill model etc.) integrated with potential outcomes from real-time reservoir navigation data obtained from geosteering tools to aid well placement in an optimal position within clean sand. All wells were successfully drilled and completed in the sweet spot of target reservoirs to meet pre-drill production targets.