Integrated geomechanical analysis of shear failure wellbore instability in abnormal and normal pore pressure zones using diverse input data: A case study

Abstract

The analysis of data obtained from previous drilled wells play a crucial role in enhancing the operational safety and reducing drilling expenses. A pivotal aspect of this lies in employing a geomechanical model, offering valuable insights into predicting pore pressure, ensuring borehole stability, and optimizing casing placement. This study centers on developing an integrated geomechanical model for three wells within an oil field, especially focusing on pore pressure variations in two distinct formations. An abnormal pressure is observed at overburden zone, while the reservoir zone is characterized by a normal pressure behavior. All relevant data sources including full set logs, dipole shear sonic imager reports, image logs, drilling operation data, and leak of tests are combined as an input to the geomechanical model. The main purpose of this study is to examine the geomechanical behavior of rocks within both abnormal and normal pore pressure zones. Identification of breakout points is achieved through image logs and caliper log data, which results in providing the direction of the minimum horizontal stress. Subsequently, the entire geomechanical model undergoes adjustment and validation based on these identified points. Moreover, the calibration of minimum horizontal stress is accomplished by analyzing the leak of test data. The main finding of this study indicates that the direction of the horizontal stresses varies across different points of the reservoir. Based on the results of the image log interpretation, the minimum horizontal stress direction in well#1 is 145°, in well #2, 125°, and in well# 3, 115°. Moreover, the presence of abnormal pore pressure results in a shift in the stress regime from a normal to strike slip or reverse stress regimes. In Well#1 conforms to a strike-slip regime with wellbore stable azimuths at 30, 70, 210, and 250°. Well#2 and Well#3 exhibit a reversed regime. The well's most stable state aligning with the azimuth of maximum horizontal stress. Lastly, it is determined that the Mogi-Coulomb and the modified Lade failure criterion exhibit superior accuracy in identifying shear failure of rocks when compared to the Mohr-Coulomb criterion. By integrating diverse input data and employing comprehensive validation methods, our model emerges as a robust tool for understanding and predicting geomechanical instability in drilling operations.