Modeling of in-situ horizontal stresses and orientation of maximum horizhontal stress in the gas hydrate-bearing sediments of the Mahanadi offshore basin, India

Horizontal stresses are key parameters of reservoir geomechanics and wellbore stability modeling. For scientific well drilling, where direct measurements are not always available, modeling of horizontal stresses is challenging, especially for highly porous un-compacted gas hydrate-bearing sediments below the seafloor. We have estimated the minimum (S-h) and maximum (S-H) horizontal stresses by using rock poro-elastic models based on three wells data which are situated at the national gas hydrate program (NGHP)-01 sites of the offshore Mahanadi basin. The stress magnitudes are validated by wellbore breakout. We have computed the stress magnitudes using 2D seismic for mapping the gas hydrate-bearing sediments. The average gradients of S-H and S-h (10.58 MPa/km and 10.48 MPa/km) are less than the gradient of vertical stress, S-V (10.67 MPa/km). The present-day stress distribution at the NGHP-01 site is principally a normal faulting (S-V > S-H > S-h) regime as obtained from stress polygons. The breakouts identified from both formation image and caliper data, suggest a NNW-SSE orientation for S-H in the Pleistocene age, which is slightly anti-clock wise relative to the northward oriented of the Indian sub-continent. This change in the orientation of S-H could be due to a local structure/fault system cross-cutting the bottom simulating reflector, and mass sliding/slumping on the seafloor. The orientation of S-H varies from N11.25 degrees W to N25.7 degrees W of D-quality. We have analysed wellbore stability using the Mohr-Coulomb circle and hoop stress techniques. These results will enable numerical modeling of production from gas hydrate reservoirs planned for the future.

Automated summary

Horizontal stresses are important for reservoir geomechanics and wellbore stability modeling. This study analyzes the distribution and characteristics of horizontal stresses in a gas hydrate geological system, and predicts wellbore stability using modeling techniques.