As part of the planning for development drilling on the North Sea Catcher fields in 2015, Premier Oil sought technology solutions that would aid in drilling the complex injected sand reservoirs. Due to the highly variable and potentially discontinuous nature of injected and remobilized sand reservoirs, operators have historically had to drill multiple sidetracks and the utility of drilling pilot holes to reduce depth uncertainty was of particular concern. Pilot holes in injectite reservoirs have seen variable success, as the positional information obtained can only be extrapolated over short distances due to rapid changes in reservoir form and stratigraphic position. The complex 3D architecture of injectites also poses challenges in drilling horizontal wells, leading to difficulties in optimizing well placement, with an increased risk of having to carry out a geological sidetrack, and an increased risk of sidetrack failure due to missing reservoir or shale instability. Moreover, pilot holes and sidetracks come with their own drilling challenges, be it technical or financial.
To help de-risk these challenges, Premier Oil selected the Deep Directional Resistivity (DDR) logging while drilling tool to map and to help understand these complex injectite reservoirs. With a depth of investigation of up to and in excess of 30m (100ft) TVD from the wellbore, the service enabled the Premier Oil and Schlumberger Well Placement team to map the injectites complex external geometries and internal architectural features in real-time. Being able to resolve the form of the injectite reservoir in real-time provided the team the ability to use this wellbore-to-reservoir scale information to tie the position of the reservoir to the seismic data. From this it has been possible to forward project wellpaths and make informed geosteering decisions as wells drill ahead and new data is acquired. This ability to map and proactively geosteer, both on landing and within reservoirs in real-time, has helped Premier Oil to avoid both pilot holes and geological sidetracks.
In this paper three case studies are showcased. The first case demonstrates how the requirement of a pilot hole was eliminated by using the DDR technology. The second and third case studies illustrate the quantitative assessment of sidetrack risking and how data collected during drilling enabled optimum well placement via azimuthal geosteering and hence the avoidance of a possible sidetrack during the horizontal reservoir sections.