Calibration of Secondary Creep Model for Salt Formation in an Exploratory Well Using Field Data

The drilling of wells in saline formations poses considerable challenges, primarily due to the phenomenon of salt creep, which can compromise stability and the integrity of drilling tools owing to unanticipated salt closure events. This study aims to calibrate the parameters of the secondary creep model (steady state) for a salt formation encountered in an exploratory oil well located in the Campos Basin, Brazil, utilizing field data obtained during the drilling process. The primary objective is to enhance the understanding of the behavior of salt formations under downhole conditions, addressing the discrepancies observed between the modeled behavior during the design phase and the actual performance during drilling operations. The well under investigation is positioned at a water depth less than 1000 meters, with an overburden gradient of 17.07 ppg (pound per gallon) and a temperature of 126.4°C (Celsius) at the top of the salt formation. Caliper logs were registered in four distinct periods (8, 10, 12, and 18 days) during the drilling activities. The calibration process involved a systematic comparison between the real caliper behavior observed in the well and the pre-established predictions from secondary creep, based on a dual mechanism model in which standard parameters taken from laboratory tests of the same lithology but not from the same field were used. Key factors, including confinement, temperature, and time-dependent deformation, were meticulously evaluated. Data analysis techniques and associated interactive numerical simulations, were employed to refine the model parameters and account for the intricate nature of saline creep under in situ conditions. The results indicated significant deviations between the predicted and observed salt behavior within the well, particularly regarding creep rates. The calibrated model demonstrated that variables such as burial depth and elevated temperatures substantially influence the deformation characteristics of the salt, resulting in creep rates that exceeded initial expectations. Furthermore, the study emphasized the critical role of time-dependent well closure, which intensified with prolonged exposure durations. These findings underscore the necessity of integrating more dynamic and region-specific parameters during the initial well design phase to enhance predictions of formation behavior and mitigate operational challenges. The calibrated model provides a more accurate representation of the mechanical behavior of salt formations, thereby facilitating improved planning and execution of drilling operations in analogous geological environments.