Improved Reservoir Characterization Using Advance LWD Sensor Measurements and Innovative Integrated Workflows- A Case Study from Norwegian North Sea
Authors: Chakraborty S. , Ahmed S. , Sarquez C. , Tosi G. , Javid S. , Straith K. R. , Durand O. , Aarseth N. 
Published: April 2024

An oil field on the Norwegian North Sea has recently experienced oil production decline, following the break-through of injected water in several wells. To mitigate these challenges an infill well campaign was executed, consisting of three oil producers. This study, focusing on one of the wells, shows how an integrated interpretation workflow confirmed intervals of bypassed oil and water flooded zones by integrating a suite of logging-while-drilling (LWD) and surface measurements with pre-drill estimates from static model and 4D seismic data.

An advanced rotary-steerable system was deployed, with an LWD system comprising ultra-deep azimuthal resistivity (UDAR), triple combo, nuclear magnetic resonance (NMR), high-resolution ultrasonic imaging, and a formation pressure tester, to gather quality data, provide subsurface mapping, and to steer the well safely in the area of bypassed oil. In addition, real-time X-ray fluorescence (XRF) data from drill cuttings formed part of an integrated interpretation approach, supporting Geosteering in reservoir area. Additionally, rush interpretations were made which correlate well with existing 4D seismic & static model, further helped to plan desired completions in real time.

The well was successfully placed in the area of by-passed oil and water flooded zones were mapped from UDAR inversion and FE logs interpretation. The overall reservoir mapping and quality proved to be in good alignment with the pre-drill geological model, giving confidence in the overall well placement strategy. Real time data integration furthermore was used for completion placement, defining potential borehole enlargement in the zones identified for packer setting.

Comparisons between NMR T1 porosity and density porosity showed presence of Hydrocarbon in this reservoir. In addition, distinct NMR T1 spectrum observed against waterflooded zones helped to improve understanding of reservoir fluid movement. Formation pressure measurements were integrated with FE interpretations, which confirms the presence of attic oil in the upflank of nearby well. The reservoir and non-reservoir facies were also confirmed by real time XRF data and helped to steer the well. Overall, a holistic approach of data gathering and integrated interpretation in real time helped to design suitable completions and placement of swell packers and screens with good confidence. All these results are also supported by early phase production data where low initial water cut is observed.

Integrating multi scale, real time LWD data with geological model and 4D seismic proved to be an important tool contributing to meet the objectives of the well. The integrated approach strengthened the validity of the subsurface model since the early phase of landing in the reservoir. Although difficulties with data interpretation and geosteering led to sub-optimal well placement over some particularly challenging segments, the multi-disciplinary approach to data integration contributed to optimization of the well placement and real-time decisions.