Core-based horizontal or highly inclined well stability analysis for unconsolidated formations

The prediction of a safe mud weight is important when drilling highly inclined or horizontal wells through permeable, poorly consolidated formations. If the mud weight used to drill these types of wells is too high, differential sticking of the drill string will occur. If the mud weight is too low, it is possible that the well bore will collapse. The standard linear elasticity borehole stability analysis methods used by many in industry predicts an unnecessarily high mud weight to prevent borehole collapse,while the safe mud weight is significantly lower. This paper describes a new core-based well stability analysis for horizontal or highly inclined wells in weak formations. New procedures to measure core strength and deformation and the numerical procedure to calculate the well stability for a highly non-linear formation are discussed. Field data and experiences are also included to validate the non-linear borehole stability analysis.