Porosity Mapping of Shallow Subsurface Sediments using Post-Stack Seismic Data From Mahanadi Offshore Basin, India

Petrophysical properties like permeability, porosity and impedance are of utmost importance in identification, delineation and characterisation of reservoir and its appraisal for gas hydrate occurrences. 2D seismic reflection data is used to explore such properties from Mahanadi Offshore Basin, India. The seismic profile presented in the study, constrained with velocity and density well log information, passes through the Sites NGHP-01-09A and NGHP-01-19B. The density based porosity varying from 50% to 75% within a depth interval of 1935 to 2258 m at Site NGHP-01-9A and 1475 to 1680 m at Site NGHP-01-19B, has been used as an input parameter for approximation of porosity by direct inversion of post-stack seismic data. A lithology dependent empirical relation between acoustic impedance and porosity has been used to estimate the properties constrained with well log and available geological information. The cross-plot between acoustic impedance and porosity exhibits a linear relationship with a high correlation of 0.8 (NGHP-01-9A) and 0.82 (NGHP-01-19B). Using this relationship, we have imaged the lateral extent of porosity formation, which varies from 51% to 78% at Site NHP-01-9A and 64% to 80% at Site NGHP-01-19B. The observed results along the studied 2D seismic line are likely supported by the available lithological information at the drilled sites. It is also found that extremely good match exists between seismically derived porosity and those derived from the porosity log.