Advanced Geomechanical Laboratory Characterization of Principal Reservoir Formations in Faihaa Field, Iraq

Abstract The Faihaa Field encompasses multiple hydrocarbon-bearing formations at varying stages of development. The carbonate formations (A and B) currently serve as the primary production zones with the C and D formations along with the carbonate E and clastic G reservoirs undergoing phased development. A full-scale waterflood strategy is planned for the A and B formations to provide pressure support and maximize sweep efficiency. Concurrently, the carbonate E and clastic G reservoirs are being strategically developed with the drilling of border wells, aimed at enhancing production and competing with adjacent fields. The pace of these development activities is expected to intensify significantly. To address the associated risks of these aggressive plans, a comprehensive geomechanical study has been initiated. A preliminary screening utilizing Heterogeneous Rock Analysis (HRA) was performed to determine optimal depth intervals for representative geomechanical testing across the three main reservoir formations. This assessment identified 27 key depth intervals spread across 8 wells. A thorough suite of geomechanical tests was conducted on more than 160 core plug samples. These tests included Uniaxial Compressive Strength (UCS), Triaxial Compression Testing (TXC) in both single and multi-stage formats, Biot's coefficient determination, Uniaxial-strain Pore Volume Compressibility, Brazilian tensile strength, proppant embedment analysis, thermal expansion coefficient measurement, fluid sensitivity analysis, acid reactivity testing, scratch tests, and an array of ancillary measurements (e.g., ultrasonic velocities, density profiling, porosity evaluation, mineralogical analysis, CT-imaging, and pre/post-test photos). To evaluate the risk of pore collapse, geomechanical tests were performed on representative reservoir intervals, accounting for rock heterogeneity through the integration of well logs and continuous core data. Tests such as uniaxial-strain compression (far-field compaction), triaxial compression (near-wellbore compaction), and hydrostatic compaction (compactant cap) were utilized. The acquired data was synthesized to differentiate between shear failure and compaction failure mechanisms within the shear stress versus effective mean stress domain. Additionally, reservoir depletion scenarios were simulated, tracing stress evolution from pre-production in-situ conditions to projected abandonment pressures across 10 distinct reservoir zones, each with variable porosity profiles. This advanced geomechanical characterization will deliver pivotal insights into the in-situ stress field orientation, a critical factor for optimizing the drilling of complex wells in the Faihaa Field. These initial findings lay the groundwork for future phases of study, which will further enhance the understanding of reservoir mechanical behavior under production stresses and optimize long-term development and management strategies for the field.