The Lochranza Field was developed using seismic amplitude analysis, evolving conceptual geological models and the implementation of horizontal well technology, built on the knowledge gained from the adjacent Donan Field redevelopment. Subtle depositional and structural complexities were, however, encountered in the Lochranza development wells. These had the potential to impact on the successful targeting of reservoir sands.

Thinning sands and erratic lateral sand pinch-outs at the margins of the deep-water Balmoral Fan complex, small-scale sand injection and subtle structural complexity across the Lochranza Field were identified in the first phase of development. These introduced greater interpretation uncertainty and made further development challenging. This highlighted the importance of considering alternative geological scenarios, whilst these insights aided the identification of infill well opportunities.

These uncertainties were partially mitigated by the planned development well trajectory, the data acquisition programme and the ability to geosteer based upon the geology encountered. It proved important to be mindful of different geological scenarios whilst geosteering, guided by the real-time dataset, keeping the 3D geological model peripheral to decision-making to limit the impact of anchoring bias.

Identification of infill targets used a pragmatic approach based upon empirical data that showed that well recovery efficiency could be characterized by net pay length, stand-off from the oil–water contact (OWC) and connected hydrocarbon volume. Infill opportunities were defined probabilistically and subsequently supported by 3D reservoir simulation. This assessment was helped significantly by additional appraisal being undertaken as part of development well drilling.