Sub Seismic Fault Identification within Carbonate Reservoirs with Borehole Images Logging-While-Drilling: Integrated Approach in Optimizing Well Placement; A Case Study from Offshore Abu Dhabi

Abstract

Reservoirs located offshore Abu Dhabi can be complex in terms of sub-seismic structural features such as faults and localized deformations. With use of high-resolution resistivity image logs, a TST (true stratigraphic thickness) technique, along with 3D structural models, uncertainties related to sub seismic structural ambiguities are resolved and well trajectory is optimized while drilling. In this case study, real-time resistivity image logs were used while drilling. The sinusoid’s shape on images provided cutting down dip or up dip information. Dip trends were analyzed using a dip vector plot and to identify zones-of-interest. Dip attribute along with the log response were compared with the pre-job model and the inclination is adjusted accordingly during drilling. Several high angle features can be characterized as stratigraphic changes, fractures, or faults. The morphology and trend change observed in the dip vector plot of these features lead to the conclusion that these are sub-seismic resolution faults and deformation is associated with the fault. The stratigraphic drilling polarity and the TST were calculated using the formation dip data. Using a TST scale and splitting the logs into stratigraphic drilling polarity domains, the fault throw displacement is estimated. The model is updated to reflect the interpreted data. The fault plunge and trend are extrapolated away from the wellbore and to nearby wells.