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Assessment of wellbore stability involves several parameters for which data that may not be readily available. The rock mechanics input data required for analysis are complicated and costly to acquire. Nevertheless, wellbore stability assessment plays an important role in the design of drilling and production of oil and gas wells; therefore, a methodology for bridging the data gap is needed. This paper presents a methodology for wellbore stability assessment with limited data, using common reservoir data. The methodology provides correlations for estimating in-situ stress regimes based on the regional data and rock mechanics parameters based on its lithology. Afterwards, in-situ stress and rock mechanics parameters are used to investigate the effect of stress anisotropy on the mechanical stability of the borehole for various inclination angles. Three failure criteria are reviewed to assess borehole stability, namely Mohr-Coulomb, Drucker-Prager, and modified Lade criteria. These failure criteria are combined with linear and isotropic rock mechanics behavior. Evaluation of stress behavior of a variety of rock lithologies was performed, using failure criteria. Results indicate that the modified Lade criteria tend to be more realistic than the Mohr-Coulomb and Drucker-Prager criteria for these evaluations. Furthermore, this study confirms that, for any type of rock, an increase in borehole inclination angle increases the risk of borehole instability. Sensitivity analysis, based on various reservoir parameters, is performed and confirms the reliability of the correlations reviewed. The methodology presented here can be used as an indicator of borehole instability risk before drilling. Subsequently, the results can be used to optimize drilling design and enhance safety in drilling operations. |
