Stress Orientation from Image log and Estimation of Shear Wave Velocity using Multiple Regression Model: A Case Study from Krishna-Godavari basin, India

Formation Micro Imager (FMI) logs from four boreholes located in the Krishna-Godavari (K-G) basin, covering an area of about 3760sq km onshore, arc analyzed to identify natural fractures and breakouts. These features are used to calculate the in-situ maximum and minimum horizontal stress orientation at different depth intervals in the wells. The orientation of maximum principle horizontal stress (S-H) obtained from orientations of breakouts and drilling induced fractures varies from N14.54 degrees E to N21.84 degrees E for the four wells. The dip of natural fracture varies from 4.83 degrees to 29.31 degrees with a dominating mean azimuth N9 degrees E. The orientation of S-H is in close agreement with the regional NNE trend of the horst-graben, the K-G basin. In addition to stress directions, the mechanical properties of the formations, like Young's modulus (Y), bulk modulus (K), shear modulus (G), Poisson's ratio (sigma) and unconfined compressive strength (UCS) are estimated from the density and P-and S-wave velocity (Vp and Vs) log data. Further, correlation between Vp and Vs is examined by multiple regression analyses with squared multiple correlation coefficient (R-2) varying from 0.92 to 0.96. The models developed by multiple regression analysis for Vs can be used to estimate elastic moduli and rock strength for other wells in the K-G basin.