Ultra-Deep LWD-Resistivity is Essential to Map Reservoir Structure and Fluid Contacts in a Two-Branched Horizontal Producer
Authors: Antonsen Frank , De Oliveira Maria Emilia , Hermanrud Kristine , Luna Carlos Aizprua , Petersen Steen Agerlin , Metcalfe Richard William , Constable Monica Vik , Alme Arvid , Vee Torill , Salim Diogo , Denichou Jean-Michel , Seydoux Jean , Omeragic Dzevat , Thiel Michael , Etchebes Marie 
Published: April 2018

The Byrding asset on the Norwegian Continental Shelf (NCS) successfully drilled a two-branched horizontal producer in a structuraly complex area with many faults, changes in reservoir properties laterally, and an uncertainty on oil-water contact (OWC) levels along the trajectories. The key inputs for optimal well placement of the two branches were measurements to map the reservoir top while drilling and the OWC up to approximately 20 - 30m TVD from the wellbore.

Before deploying the ultra-deep directional resistivity tool, it was critical before drilling to evaluate how top reservoir and OWC would be mapped by inversion of electromagnetic measurements. The reservoir conditions were challenging with a low resistivity contrast towards reservoir top and a gradually changing resistivity towards the OWC. It was, therefore, critical in the pre-job phase to help all involved in the future geosteering operation to get familiar with using the ultra-deep resistivity real-time interpretation to meet the objectives and to update the geomodel after drilling.

To plan the well placement job a new workflow was applied to build a realistic geomodel based on geological understanding, legacy offset wells measurements, and seismic interpretations. Then potential scenarios generated from this geomodel were used to simulate synthetic ultra-deep directional resistivity responses and inversions results, synthetic standard LWD-data, and seismic. Finally, an updated geomodel was built after the drilling campaign, validated through "Model-Compare-Update" traditional iterative process using synthetic and real data.

In conclusion, the pre-job analysis was important to understand how to interpret reservoir top and OWC. This knowledge was used in real-time while drilling and post-operation to update reservoir top interpretation and the OWC position. This case study describes the importance of having a workflow to build a realistic high resolution geomodel that is validated with all the subsurface measurements at different scales. Deployment of such highly integrated workflow open new horizon for the collaboration between service company and operator for improved pre-job planning, real-time decisions and post-job integrated interpretation. Furthermore, integrated interpretation of data from the two wells with seismic performed over the post drilling analysis is proven to be essential to ensure future production steering of the two-branched horizontal producers.

An alternative ultra-deep azimuthal resistivity inversion algorithm was successfully used while drilling along with the standard inversion to better interpret reservoir top in the context of low resistivity contrast from this case study. An important, and unprecedented effort of pre-job planning was conducted to select optimal LWD real time dataset required. IT and "cross-platform-data-exchange" challenges were overcome to allow an extensive and innovative use of realistic geomodel scenarii for multiple measurements simulation, including from synthetic ultra-deep resistivity inversions results, standard LWD-data, to seismic interpretation.