Abstract

Knowledge of in-situ stress magnitudes is important in exploring and developing conventional and unconventional oil and gas resources. Whilst the vertical and minimum horizontal stresses may be derived relatively straight forward, the magnitude of maximum horizontal stress cannot be measured directly and must be indirectly estimated. In this paper, a new semi-analytical poroelastic solution is developed for stress and pore pressure distributions surrounding a borehole with a known breakout geometry. The entire geometry of the stabilized borehole breakout, not just breakout width, is utilized for estimating the maximum horizontal stress magnitude. Breakout tip strength is evaluated by considering several mechanisms perceived to be responsible for breakout stabilization. The maximum horizontal stress magnitude is then estimated from the equilibrium condition of stress and rock strength at the breakout tip which attracts the highest stress concentration. The newly derived maximum horizontal stress estimation model is validated based on several sets of laboratory borehole breakout experiments conducted under three-dimensional stress conditions sourced from literature. Comparison between the model prediction and the experimental results showed that the estimated maximum horizontal stress has a good approximation to the maximum horizontal stress magnitude applied and showed a significant improvement over the existing method.

Introduction

Knowledge of the state of in-situ stresses is important in exploring and developing conventional and unconventional oil and gas resources. It plays a critical role in analyzing wellbore stability, sand/solids production, well trajectory optimization, perforation orientation and hydraulic fracture stimulation. For a petroleum basin with a relatively flat surface topology, the in-situ stress state may be defined by a vertical and two horizonal stresses and their orientations. Whilst the magnitudes of the vertical and minimum horizontal stresses may be derived relatively straight forward, the magnitude of the maximum horizontal stress cannot be measured directly and must be indirectly estimated.

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