Wellbore Stability Analysis Using Acoustic Radial Profiles and an Elastoplastic Model

Abstract

Abstract Wellbore instability during drilling, completion, and production is important and costly issue in many oil and gas fields. Field observations show that stress-related wellbore instability challenges are frequently encountered. Estimating stresses and mechanical properties is a key to the success of drilling, completion and production operations. Knowledge of accurate Unconfined Compressive Strength (UCS) is essential for understanding wellbore stability, perforation efficiency, and sanding tendency. UCS along the wellbore and perforation is a key input of failure criteria and can be best obtained from laboratory core testing that are mostly performed in the reservoir section. Cores from the overburden formation are rarely taken, although most wellbore stability related issues are encountered in this section of the well. In this study, wellbore stability modeling was conducted using Finite Element Modeling (FEM) to predict induced stresses and yielded zone around the wellbore in the elastoplastic media. Elastoplastic models were used in conjunction with the Mohr-Coulomb and modified Lade yield criteria. UCS is calculated by matching the resultant stresses around wellbore with dipole radial profiles from the Acoustic Scanning platform. The damage or yielded zone is interpreted by means of volumetric strain analysis. This damage provides an indication of the potential breakout that might occur during drilling, thereby giving an indication of the risks to wellbore instability. This novel technique is applied to compute wellbore stability in the Khuff and pre-Khuff Formations in Saudi Arabia. The methodology can be applied to other locations using similar approach that combines acoustic radial response and FEM.