Geomechanics Considerations for Through- and Near-Salt Well Design

Willson, S.M.; Fredrich, Joanne T.

doi:10.2523/95621-ms

Cited by 18 publications

(16 citation statements)

References 19 publications

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“…His current research interests include wellbore stability analysis, poromechanical modeling in stress and pore pressure of sedimentary basins, numerical modeling in salt tectonics, and finite-element modeling in geodynamic processes of crust and lithosphere. and Fredrich, 2005). One reason is that stresses and fluid pressures adjacent to salt may be highly perturbed relative to their regional values (e.g., Bradley, 1978;Whitson and McFadyen, 2001;Rohleder et al, 2003;Dusseault et al, 2004).…”

Section: A U T H O R Smentioning

confidence: 96%

“…One reason is that stresses and fluid pressures adjacent to salt may be highly perturbed relative to their regional values (e.g., Bradley, 1978;Whitson and McFadyen, 2001;Rohleder et al, 2003;Dusseault et al, 2004). Predicting the magnitude of these anomalies is also challenging (e.g., Rohleder et al, 2003;Willson et al, 2003;Willson and Fredrich, 2005).…”

Section: A U T H O R Smentioning

confidence: 98%

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Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Luo¹,

Nikolinakou²,

Flemings³

et al. 2012

Bulletin

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We compare four approaches to geomechanical modeling of stresses adjacent to salt bodies. These approaches are distinguished by their use of elastic or elastoplastic constitutive laws for sediments surrounding the salt, as well as their treatment of fluid pressures in modeling. We simulate total stress in an elastic medium and then subtract an assumed pore pressure after calculations are complete; simulate effective stress in an elastic medium and use assumed pore pressure during calculations; simulate total stress in an elastoplastic medium, either ignoring pore pressure or approximating its effects by decreasing the internal friction angle; and simulate effective stress in an elastoplastic medium and use assumed pore pressure during calculations. To evaluate these approaches, we compare stresses generated by viscoelastic stress relaxation of a salt sphere. In all cases, relaxation causes the salt sphere to shorten vertically and expand laterally, producing extensional strains above and below the sphere and shortening against the sphere flanks. Deviatoric stresses are highest when sediments are assumed to be elastic, whereas plastic yielding in elastoplastic models places an upper limit on deviatoric stresses that the rocks can support, so stress perturbations are smaller. These comparisons provide insights into stresses around salt bodies and give geoscientists a basis for evaluating and comparing stress predictions.

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Section: A U T H O R Smentioning

confidence: 96%

Section: A U T H O R Smentioning

confidence: 98%

Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Luo¹,

Nikolinakou²,

Flemings³

et al. 2012

Bulletin

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show abstract

“…Another common assumption is that the porepressure parameter in wellbore stability equations for the salt interval is assumed to be equal to the overburden gradient (Willson and Fredrich, 2005). In thicker salt, this is taken as a linearly increasing average between the pore pressure in the sediment just above the salt body and that below the salt body (Zhang et al, 2008).…”

Section: Wellbore Stability In Salt Formationsmentioning

confidence: 99%

Predicting the depth of viscous stress peaks in moving salt sheets: Conceptual framework and implications for drilling

Weijermars¹,

Jackson²

2014

Bulletin

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Peak-stress zones and pressure anomalies around wellbores through moving salt bodies threaten well integrity. Our study provides a conceptual framework to identify the depth of peak zones of shear stress in moving salt sheets, whether autochthonous or allochthonous. We use analytical methods to determine the principal stress magnitudes and stress-trajectory orientations caused by ductile creep in crystalline salt. The four basic flow types analyzed are Couette, Poiseuille, no-slip squeezing, and free-slip squeezing flow. The analytical formulae specify velocity gradients, shearstress profiles, and principal stress trajectories. The analytical results are compared with detailed flow visualizations in numerical and physical models of salt tectonics to test our generic conclusions. We offer guidelines to optimize drilling operations in moving salt bodies. The study suggests that stress trajectories and zones of viscous stress peaks in salt layers should be mapped routinely during well planning, in addition to the traditional analysis of elastic stresses and safe mud-pressure windows for controlling wellbore stability.

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“…Deepwater areas in the Gulf of Mexico, offshore Brazil, Angola, and other places throughout the world, contain oil and gas deposits underlying thick salt formations [17,18,34,35]. Drilling wells in these regions can be challenging because of the water and reservoir depths, tectonics, and environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic analysis of borehole closure for through-salt well design

Fossum

Fredrich

2007

Acta Geotech.

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Probability levels, in the form of marginal cumulative distribution functions, are determined for the time it takes salt to contact a casing, which penetrates a salt canopy, and the time it takes the casing to yield once salt has contacted the casing, in support of through-salt well design activities required for deep-water, sub-salt environments. The finite-element method coupled with an advanced reliability method is used to perform the analyses. Randomness caused by uncertainties in salt properties, lithostatic stress, drilling-mud pressure, production temperature, and borehole ellipticity is handled by including statistics and probability distributions for each of these random variables. The advanced reliability method takes full account of the random variables and processes without Monte Carlo simulation, by using a method for assessing reliability statistics that computes response probabilities in a direct and efficient manner. This advanced reliability method falls under the general category of fast probability integration schemes.

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Geomechanics Considerations for Through- and Near-Salt Well Design

Cited by 18 publications

References 19 publications

Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Geomechanical modeling of stresses adjacent to salt bodies: Part 1—Uncoupled models

Predicting the depth of viscous stress peaks in moving salt sheets: Conceptual framework and implications for drilling

Probabilistic analysis of borehole closure for through-salt well design

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