Multidisciplinary Approach in Resolving Aquifer Anomaly Behavior in Major Abu Dhabi Field

Abstract Drilling through the Dammam, Umm Er Radhuma, and Simsima formations in the giant Abu Dhabi field presents challenges due to limited understanding of these aquifer intervals. In one cluster, a water supply well experienced an issue where black thick fluid emerged at the surface. This well, which was extracting water for injection wells, had to be idled due to the fluid invasion. The study aimed to develop an understanding of the shallow aquifer to identify the root cause of the problem and optimize drilling practices, particularly in the aquifer section. A multi-disciplinary integrated approach was utilized to understand the aquifer, using seismic data as the foundational background. Attributes such as spectral decomposition and Gradient Coherency Cube (GCC) were employed to enhance the seismic data to identify geological features. Well logs data, borehole images, cores, and mud losses data were then integrated with the seismic information to characterize the depth of interest and the aquifer properties contributing to fluid invasion. Pressure data and fluid samples from the aquifer were also analyzed to investigate the issue. GCC and spectral decomposition attributes highlighted minor faults between the problematic wells, which were not identified in the original seismic data. Most fractures observed in the borehole images were closed; however, some connected porosities in the aquifer levels could function as conduits for fluid invasion. Additionally, geological features identified in the attributes were located far from the problematic wells and were interpreted as being filled with fine sediments due to the distal environment of deposition. Analysis of mud losses data indicated that loss intervals mainly began at the boundary of the Umm Er Radhuma basal shale and Simsima formation, where friable shale was observed in the core data. Rock physics analysis from the logs also indicated that this interval aligned with friable shale lines, which are geomechanically weak and prone to collapse under vigorous drilling practices. Lab analysis of fluid samples from the aquifer showed high total suspended solids, which decreased over time during flushing. Higher aquifer pressure depletion was also observed in the problematic area, suggesting a lateral gradient towards that location.