46th U.S. Rock Mechanics/Geomechanics Symposium,
2012. American Rock Mechanics Association
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We develop finite-element models to simulate stresses around salt bodies, and use these results to calculate wellbore stability and optimal mud weights for a vertical wellbore near these salt bodies. In the finite-element models, salt bodies are simulated by viscoelastic material, sediments are elastic, and pore pressure is assumed to be hydrostatic in sediments. We show that near-salt stresses are perturbed; near-salt wellbore instability tends to happen at the places with low minimum principal stress and high shear stress; in these locations, safe mud weight window is narrow. Near a salt sphere, wellbore instability tends to occur above and below the salt sphere due to low minimum principal stress, and at the lateral edges of the salt sphere due to high shear stress. Near an irregular salt sheet, wellbore instability tends to occur at the convex curves of the salt body; if shear stress is very high and minimum principal stress is very low in these locations, safe mud weight window may be impossible. These results show changes of stresses, optimal mud weights and safe drilling window around salt bodies, and provide some insights into the drilling and mud weight programs near salt bodies.
Salt bodies behave viscously and can not sustain deviatoric stresses over geological time scales. In sedimentary basins, where salt bodies are present, stresses are perturbed near salt as the differential stresses in the sediment are redistributed in order for there to be no shear at the salt-sediment interface [1-5]. Abrupt decreases in minimum principal stress above and below salt have been reported [1, 3, 6, 7] and these are consistent with geomechanical modeling results [2, 4, 8]. These stress perturbations may induce wellbore instability such as wellbore breakouts when a wellbore is drilled through.
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