Abstract
Well logs from ATG- field wells ATG-10 and ATG-11 were calibrated to develop Mechanical Earth Model (MEM) based on elastic parameter, failure parameters, in-situ stresses, pore pressure using well logs to predict wellbore failure. Poisson’s ratio derived from compressional and shear velocities interval transit time and density logs (RHOB), showed that the values ranges from 0.17 to 0.48 and 0.09 to 0.49, and the dynamic Young's Modulus derived from the Compressional and Shear velocity Logs, ranges from 6.0 GPa to 7.8 GPa and 3.6 GPa to 6.6 GPa, the dynamic shear modulus derived from dynamic young’s modulus and Poisson’s ratio which ranges from 3.8 GPa to 5.1 GPa and 2.1 GPa to 5.4 GPa, while the dynamic Bulk modulus ranges from 0.25 GPa to 1.67 GPa and 0.43 GPa to 1.18 GPa for wells ATG-10 and ATG-11 respectively. The calibrated failure parameters or rock strengths derived from compressional velocity logs include: the internal friction angle (Ï•) from Plumb’s correlation, these ranges from 20.869o to 65.5o and 20.869o to 45.61o, Unaxial compressive (UCS) strength ranges from 757.837 psi to 2505.836 psi and 4577.099 psi to 10512.876 psi, cohesion Strength (C) ranges from 205.697 psi to 355.308 psi and 70.652 psi to 390.32 psi and Tensile strength (To) varies from 17.141 psi to 29.609 psi and 5.885 psi to 32.527 psi for well ATG-10 and ATG-11 respectively. The elastic and rock strengths properties vary in a similar trend to the sonic logs as they are derived based on these values. These properties show increasing values with increasing depth, as a result of larger overburden stress, hence lower porosity or high compressional velocity of the formations. However, the elastic properties and formation strength may vary in different formations. Â
Highlights
Maintaining a stable borehole is one of the major task and challenges encountered during exploration of hydrocarbon and it poses serious problems and challenges during exploration and production of hydrocarbon (Cheng, Tan & Detournay, 2003)
Mechanical earth model (MEM) will be constructed using the existing relevant logs, data from the offset well describing the formation mechanical properties pore pressure, stress magnitudes from two offshore wells of ATG field, Niger Delta, and the wellbore instability are analyzed based upon the developed model and the Mohr-Coulomb failure criterion
Geomechanical characterization and state of in-situ stress were characterized using two wells namely ATG-10 and ATG-11 obtained from ATG Field offshore Niger Delta
Summary
Maintaining a stable borehole is one of the major task and challenges encountered during exploration of hydrocarbon and it poses serious problems and challenges during exploration and production of hydrocarbon (Cheng, Tan & Detournay, 2003). Mechanical earth model (MEM) combines geomechanical properties such as in-situ stress states, Poisson’s Ratio, pore pressure, Young’s Modulus, shear modulus, bulk modulus and rock strengths parameters or failure parameters such as the unconfined compressive strength (UCS) and angle of internal friction (Φ), cohesion strength (C), and tensile strength (To) of sedimentary rocks (Iqbal, Ahmad, & Abd Kadir, 2017) These key parameters needed to address a range of geomechanical problems ranging from limiting wellbore instabilities during drilling (Moos et al, 2003), to assessing sanding potential and quantitatively constraining stress magnitudes using observations of wellbore failure (Zoback et al, 2003). Mechanical earth model (MEM) will be constructed using the existing relevant logs, data from the offset well describing the formation mechanical properties pore pressure, stress magnitudes from two offshore wells of ATG field, Niger Delta, and the wellbore instability are analyzed based upon the developed model and the Mohr-Coulomb failure criterion
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