The presentation ”Overcoming Coring Challenges in a New Unconventional Play Offshore by Integration of Formation Evaluation Data” will be given by Thomas Bradley, Baker Hughes.
The meeting will be under strict guidelines given by FHI/NIPH: https://www.fhi.no/en/
A well was drilled into a prospective new unconventional mudstone play offshore Norway. Two of five coring runs were successful while the rest yielded little to no core recovery. Investigations attributed the poor recovery to sub-optimal coring practices, equipment failure and operational errors. Recently, the accompanying petrophysical logs and seismic data were revisited, and upon detailed investigation several unusual responses were observed to correspond with intervals of poor core recovery. Subsequent investigation of the core itself substantiated that the coring issues largely had natural causes. This understanding is being applied to two imminent coring operations and has driven selection of drilling, coring and wireline technology and procedures, in addition to informing casing design.
Wireline nuclear magnetic resonance (NMR) and cross dipole acoustic data, logging whilst drilling(LWD) density (including azimuthal images), neutron porosity and resistivity was acquired over the interval of interest for standard formation evaluation purposes. This interpretation was conducted immediately after the initial drilling and showed the formation to be a series of highly porous oil bearing mudstones. However, no in depth advanced interpretation was conducted at the time. Recently, advanced analysis including high resolution log enhancement, NMR 2D porosity and saturation analysis, acoustic azimuthal anisotropy, near wellbore imaging, fracture interpretation, and borehole image interpretation were performed on the log data, and new and improved 3D seismic data was interpreted.
When interpreted in detail it could be observed that unusual responses in the logs showed a close correspondence to the intervals of poor core recovery. In particular, high azimuthal anisotropy was observed, and when this was compared to the near wellbore reflection image a significant planar reflecting feature was identified which is determined to be a fault. Indications of this feature was subsequently found in seismic data. When then compared to the azimuthal density image after resolution enhancement was applied, although the image is still of too low resolution to directly image the fault, disturbed bedding was observed which is commonly associated with faulted intervals. Several core fragments proved to have extensive small-scale fracturing not noticed previously, and slicken lines were found along several larger fractures previously presumed to be drilling induced.
The investigations of the log data revealed that a previously unknown sub-seismic fault was present right below the depth where coring problems were encountered. The detailed interpretation was able to determine the precise location of the fault and its extent in the formation. Knowledge of this subsequently explained the coring problems encountered and helps to optimize imminent coring in the same formation. Lessons learned and the methodology likely also applies to similar formations.
Thomas Bradley is a Senior Technical Advisor for Formation Evaluation and Energy Transition with Baker Hughes. After graduating from The Royal School of Mines, Imperial College, London with a degree in Geology with Engineering Geology in 1996, he started his career in 1997 as a Wireline Data Processor with Western Atlas International. Since then he has worked in a variety of technical and supervisory roles in a variety of countries with Baker Hughes and is currently based in Oudkarspel, the Netherlands. His main interests are openhole petrophysics, acoustic logging, nuclear magnetic resonance and geothermal energy. He has been an SPWLA member since 2005, and is a former President of the Dutch Petrophysical Society. He currently serves on the Dutch Petrophysical Society board as Vice President of Communications and Publications