Advanced Rock Mechanical Characterization of Giant Cretaceous Carbonate Sequence for Reservoir Development

Abstract Advanced rock mechanical characterization of a giant Cretaceous carbonate field in Abu Dhabi is the focus of this paper, that not only focused on routine triaxial tests for shear strength estimates but also to understand pore collapse, tensile strength, thermal and creep behavior of these rocks. The approach has started with auditing and selection of core intervals from various offset wells. These core intervals are selected to represent lateral and vertical coverage of various sub-units within various reservoir and caprock intervals. Scratch tests and whole core CT scans are conducted for selection of appropriate intervals for extracting core plugs. Specialized techniques are deployed for plugging the core intervals. Pre and post-test photographs and CT scans of all the plugs are taken to identify the role of heterogeneity. The testing program encompasses various triaxial tests such as single stage (SST), multi-stage (MST), and unconfined compressive strength (UCS) tests. They are crucial for understanding rock shear failure, strength parameters like UCS, cohesion, friction angle, and stiffness properties including Young's modulus and Poisson's ratio. Acoustic velocity is also recorded during these tests. Additionally, tests like uniaxial pore volume compressibility (UPVC) and Biot are performed to ascertain the compressibility and poro-elastic coefficients. Hydrostatic compaction tests provide insights into pore collapse onset, while Brazilian tests measure tensile strength, and fracture toughness tests assess resistance to crack growth. We also conduct thermal expansion and creep tests to determine the rocks’ thermal behaviour and time-dependent deformation characteristics. Based on the results of rock mechanics testing program, mechanical rock properties correlations have been developed for various reservoir units and caprock. These correlations demonstrate a relationship between geomechanical and petrophysical properties. The developed bespoke correlations have been successfully used across different wells, demonstrating accurate core-log calibrations of mechanical rock properties. This high-level characterization of carbonate reservoirs and caprocks aid in comprehending rock behavior under various field development conditions: such as reservoir depletion, fluid injection, potential CO2 sequestration, and modeling of thermal and creep phenomena.