Real-time geological interpretation while drilling can be achieved with high-resolution borehole images; however, the use of different drilling fluids, telemetry-related limitations, and non-optimal depth control on rigs often leave geoscientists with limited and poorquality data, leading to inconsistencies over a field's life cycle. This study from offshore Norway presents applications of new measurements and algorithms to address such challenges providing consistent borehole imaging for geological interpretations while drilling complex subsurface.
New multi-physics high-resolution LWD (logging while drilling) technology was deployed for real-time imaging in boreholes drilled with nonconductive fluids, addressing technology gaps that earlier allowed such services only in conductive aqueous fluids and providing much-needed independence to drill various well trajectories in any mud configuration without limiting high-resolution imaging for geological, petrophysical, and geomechanical interpretation. Correspondingly, real-time data transmission challenges were addressed with improved mud-pulse telemetry and wired drill-pipe. Furthermore, new application algorithms were developed to compensate for inadequate depth control impacting the integrity of high-resolution data.
We present results from field development operations in the Utsira High region of the Norwegian North Sea, including examples of pilot and lateral sections drilled with conductive and nonconductive fluids. Conventional evaluation of the encountered heterogeneous mix of alluvial fans, plains, and aeolian dune facies is difficult, even more in horizontal drains where standard logs are often featureless across problematic conglomerates. Real-time dips picked on high-definition images helped with geosteering as well. Examples of geological features from different wells are presented with unique resistivity images from new LWD borehole imager for nonconductive fluid, comparing with image data acquired in conductive mud for consistent interpretation. Structural elements of sub-seismic faults and fractures were interpreted with consistency to provide geologists with confident feature-picks for updating their reservoir models.
Borehole images have long been used by geologists and log analysts for various aspects of reservoir characterization and well-operations support. However, most of these applications were earlier possible only with e-line logging after drilling operation was complete and the open-hole needed to be left for wireline operations. Logging while drilling (LWD) imagers often provided lower resolution data compared to Wireline, that too in recorded mode whilst the real-time data streamed while drilling often lacked the quality to pick the subtle features with confidence to subject the data for further interpretation. Technology advances in LWD imaging brought higher resolution imagers to operations and resistivity and ultrasonic images were made available compared to the legacy photo-electric (PEF), density and gamma-ray (GR) images (Fig 1). The recorded mode (memory) data started to approximate wireline imaging quality in water-base mud (WBM). Oil-base mud (OBM) LWD imaging for geological interpretation remained a challenge till Maeso (2018) presented a new dual physics imager. Shrivastava (2019, 2020) presented a brief account of borehole imaging journey, and the multiphysics LWD imager that overcame the barrier of OBM imaging.