Tomographic imaging of sub-basalt Mesozoic sediments and shallow basement geometry for hydrocarbon potential below the Deccan Volcanic Province (DVP) of India

Abstract

Summary A shallow 2D tomographic P-wave velocity image is obtained in the Deccan Volcanic Province (DVP) of India using first-arrival seismic data along a 90 km long N-S trending profile in the Deccan Syneclise region. The tomographic image depicts smooth velocity variations of Quaternary (2.0-2.5 km/s) sediments, basalt (5.0-5.5 km/s) and sub-basalt Mesozoic sediments (4.0-4.5 km/s) as well as basement (5.8-6.0 km/s) configuration down to a maximum depth of 5.0 km. Due to late Cretaceous volcanism with outpouring of basaltic lava flows, this region is affected by numerous dyke intrusions and thick basaltic trap forming sills with the presence of horst and graben structures due to deep basinal faults. Although imaging below the basalt is a major challenge for the oil industry, with the help of tomographic imaging technique of long-offset seismic refraction data, we are able to image sporadic sub- and intra-trappean Mesozoic sediments (<0.75 km) deposited below thick columns (0-3 km) of basalt flows above the basement. The imaged Mesozoic sediments are expected to contain hydrocarbon due to their wide extension and suitable trapping mechanism of basaltic sills. The robustness of the velocity image is assessed through numerous tests like velocity perturbations, χ 2 estimates, RMS residuals of traveltime fit, resolution and uncertainty estimates through computation of ray-density or Hits.