46th U.S. Rock Mechanics/Geomechanics Symposium,
2012. American Rock Mechanics Association
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Two major aspects in the description of a stress pattern are the effective stress ratio and tectonic factor. This paper presents two case studies focusing on the stress pattern around salt bodies in the deepwater. The salt body geometries are modeled on the basis of a set of sectional seismic data. The geometry of the geomechanical model used in the calculation for a field at the Gulf of Mexico is a block with a height, width, and thickness of 10 km. An inclined cake-shaped salt body with a diameter of 6927 m is embedded in the model. A similar geometric scale is used for the second case study from the Campos basin of offshore Brazil. [n this case, a salt body with an irregular geometry has a thickness of 6024 m along the trajectory of wellbore. An anticline structure wa modeled at the bottom surface of the salt body. umerical re ults obtained with the FEM for each study include: 1) sectional views for the distribution of both the effective stress ratio and tectonic factor, and 2) diagrams of the distribution of the effective tres ratio and the tectonic factor along specific paths below and above the salt body, respectively.
For the I-dimensional (ID) prediction of the mudweight window (MWW), the following input is required: I) pore pressure (PP), overhurden gradient (OBG), and effective stress ratio and/or Poisson''s ratio; 2) cohesive strength (CS), friction angle, (FA) and/or uniaxial compression strength (UCS), and tectonic factor. The first part of the input data is required for the prediction of the upper bound of the MWW, which is the so-called fracture gradient (FG); the second part of input data is used for the prediction of the lower bound of MWW, which is shear failure gradient (SFG).
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