Perfect Infill Drilling and Geosteering with Hybrid Rotary Steerable System and Novel Ultra-Deep Resistivity High-Definition Mapping Technology – A Case Study from Offshore Australia
Authors: Hoeyland Henning , Bakar Aida , Iliani Nur Shahera , Yeoh Xiao Qi , Fadjarijanto Ari , Gallagher Brian , Wang Haifeng , Singam Chandrasekhar Kirthi , Liu Yang , Rigden Matthew , Jiang Xiaohu , Mirto Ettore 
Published: October 2023

Stag field in the northwest shelf of offshore Australia has been in production since 1998 and recently two horizontal infill wells were planned to recover unswept oil. Well A was planned in the west part of the field in perpendicular direction to several existing wells, and well B was planned as an Extended-Reach-Drilling (ERD) well towards the east part of the field. Drilling challenges for these wells included the poorly consolidated formation in reservoir, the unstable overburden Muderong shale, the anti-collision risk for well A, and extended reach drilling operation for well B. Both wells required geosteering operation, which had the associated challenges of the depth uncertainty of top reservoir at landing, the undulating reservoir top with glauconite erosional features, the movable OWC, and the low resistivity in reservoir. A systematic approach for drilling, geosteering, and completion was required to ensure the success of this infill campaign.

A new hybrid Rotary Steerable System (RSS) with the capability of delivering high-build rate with greater precision and ROP with less formation restrictions, was chosen to tackle these drilling challenges. Geosteering operation adopted a new generation Ultra-Deep Resistivity High-Definition (UDR-HD) mapping tool that can provide larger depth of investigation and higher resolution at the same time, through innovations on the measurements and inversion method. This new tool is capable of providing high-definition mapping even for reservoir with low resistivity and limited contrast with overburden shale. This capability helped the operator address challenges of landing, geosteering, and OWC mapping. The combination of the hybrid RSS and the UDR-HD tool provided a fit-for-purpose solution for these two challenging infill wells.

The execution of the drilling and geosteering for both wells went smoothly. The two wells were drilled with 100% operation efficiency, achieving approximately 3km reservoir exposure in total, without issue with anti-collision and completion run. Landing was optimized thanks to remote detection of top reservoir while drilling in overburden. The clear reservoir boundaries depicted by UDR-HD mapping tool enabled the operator to make informed geosteering decisions to maximize production, while the hybrid RSS implemented these decisions accurately and reliably without compromising wellbore quality.

The hybrid RSS and UDR-HD tools were used in both the 8.5-inch intermediate section and the 6×7-inch reservoir section and delivered the desired performance for both sections. The hybrid RSS was capable of delivering required build rate regardless of formations. Even with limited resistivity contrast, the UDR-HD tool could still provide clear reservoir mapping no matter it was from inside or outside the reservoir. Further study the UDR-HD tool data also deliver more insights of features like OWC, glauconite pods, and locations of well crossings.