Characterizing the Structural and Mechanical Properties of a Geological Fault Zone for Geomechanical Assessment: A Case Study in the Recôncavo Basin (Brazil)

ABSTRACT: This work presents a case study of a highly depleted oil and gas reservoir in the Recôncavo Basin (NE Brazil) that was the object of a massive waterflood project. One of the main risks appointed by assurance teams was the chance of fault reactivation and leakage to other reservoirs. At the time of the project design, the datasets of stress state and rock properties were quite poor. From that, the project team designed a robust data acquisition program. A significant part of the new dataset comes from cores that sampled both hanging and footwall blocks and the fault core of one of the geological faults that compartmentalise the accumulation. Reservoir and cap rocks were also sampled. CT imagery, HD structural description and Scratch Testing reveals the different architectural elements of the fault zone and, most importantly, evidenced that fault rocks in the fault core have a mechanical strength three times higher than the country rock. Using this data in the geomechanical assessment gave greater confidence to the subsequent risk analyses and project implementation.