Emmanuel E. Uzuegbu from Schlumberger
Ahmed Zarroug EL Sedeq, Mohamed Gamal Fawzy; Schlumberger. Rutger Van der Vliet, Lead Reservoir Geophysicist, Neptune Energy. Sylvain Clerc, Lead Operations Geologist , Neptune Energy
State-of-the-art measurement-while-drilling (MWD) directional surveying coupled with the latest 3D reservoir mapping technology were run simultaneously for the first time globally in the North Sea, Norwegian sector. The goal of the Duva development project was to bring unparalleled value to the client’s developmental campaign in the complex reservoir structure of the Duva field in the northern part of the North Sea.
The Duva oil and gas field, Neptune Energy’s first discovery in the Norwegian North Sea, is located 14 km northeast of the Neptune-operated Gjøa field in 340-m water depths. To maximize synergies, the Duva development project was performed in parallel with Gjøa P1. The Duva field is being developed as a subsea installation with three oil producers and one gas producer in a tieback to Gjøa. The field will be operated from the Gjøa semisubmersible platform by means of a dedicated umbilical.
Method, Procedures, Process
The three Duva oil producers were planned as horizontal wells with significant focus on subsurface mapping to maximize production. The subsurface structure complexity posed major challenges to the reservoir and drilling teams because the reservoir units consisted of deep marine turbidites of the Early Cretaceous Agat formation, deposited in a confined environment. Two main units were identified: a lower reservoir with poor reservoir properties and an upper reservoir with good to very good reservoir properties.
The challenge was to place the well deeper in the upper reservoir unit for better oil recovery and avoid the lower reservoir unit, which had inferior properties. Hence, drilling three horizontal oil producers in such a complex structure required a step change in methodology and use of new technologies. Two new technologies were used jointly for the first time globally to achieve optimal well placement. One technology was high-frequency surveying using the Schlumberger definitive dynamic survey-while-drilling service and the other one was the 3D Ultra-Deep Azimuthal Resistivity Technology (3D UDAR), that provided fluid volumes, reservoir structures (dips interpretation), and fault delineations.
Results, Observations, Conclusions
The actual drilling operation was made even more challenging than anticipated due to unexpected wellbore instability. As a result, the value of the two technologies became more evident. What were initially planned to be three horizontal sections turned into a sidetrack on each of the wells.
The interpretations from the 3D UDAR service helped drill the sidetrack trajectories and provided improved confidence in identifying the reservoir boundaries vertically and laterally. During landing, the 3D UDAR inversions revealed the reservoir geometry and the reservoir dip, including the sand and shale layers within the reservoir , which helped avoiding longer shale exposure during the landing. In the horizontal sections, the 3D UDAR service continuously mapped the top and the base of the sand bodies within the upper reservoir, facilitating placing the wellbore within the planned targeted zone. Also, the 3D UDAR inversions revealed the sands and reservoir geometry for the entire drilled sections.
High-frequency surveys by the definitive dynamic survey-while-drilling service enabled more accurate wellbore placement in TVD and in the lateral position. Having the definitive dynamic survey-while-drilling service added additional data reliability and confirmed bottom hole assembly location downhole with accurate and smooth trajectory (minimum tortuosity). In addition, real-time data streaming on mud telemetry was achieved with no compromises due to the high bit rate and wider bandwidth that dynamic survey while drilling tool is cable of delivering. There was no issue for including the 3D UDAR dataset, formation pressure while drilling and triple combo formation evaluation high density data in the real-time data stream.
This project was world’s first drilling operation in which these two technologies were deployed simultaneously on same bottomhole assembly. The Duva field project is an excellent example of successfully integrating the latest drilling and LWD technologies to help the client achieve remarkable strategic and financial results. The technology enabled the client to maximize net recoverable hydrocarbons and deliver the project on time below budget, regardless of all the drilling challenges, resulting in a sidetrack on each of the wells.
Emmanuel Uzuegbu is currently a Senior Geosteering and Reservoir Mapping Engineer with Schlumberger Norway, responsible for geosteering and reservoir mapping services for various Operators in Norwegian Continental Shelf. He received a B.Sc. degree in Geological Sciences from Nigeria in 2006 and M.Sc. degree in Petroleum Geosciences Engineering from University of Stavanger, Norway (2012). He is an active member of society of exploration geophysicists (SEG). He started his career in 2007 as a Reservoir Geologist/Geomodeller and has worked in different roles previously within Schlumberger including Data /Information Management Engineer, Exploration Geoscientist and E&P workflows Consulting. His current interest is in Ultra Deep Azimuthal Resistivity (UDAR) services and Integration of deep EM data in reservoir modelling.