P -400 Seismic Expressions of Igneous Flows - Hydrocarbon Prospectivity: Kerala-Konkan Basin, India Ravi Verma, Duggirala Moses Nathaniel, Rabi Bastia, Shashirekha Mahapatra, Megha Saxena Petroleum Business (E&P), Reliance Industries Limited, India e-mail: ravi.verma@ ril.com Summary We present a series of observations denoting various features commonly found in volcanic passive margin set-up. Analysis of such seismic features, both in the deep and shallow section and inferred geology from such an analysis can have deep impact on prospect delineation in volcanic basins. Sill intrusion can generate subtle anticlinal traps that might be valid prospects because thermal effect of sills is relatively limited. Thus, there is less chance of generating an over-mature prospect, unless the sills occur in high numbers. Apart form seismic, filtered gravity and magnetic data may be used to define areas with high amount of large intrusives. Flood basalt regions in volcanic basins which simply blanket sedimentary basins without intrusives in the subsurface are most prospective regions. In this case, basalt thickness estimation and associated burial depth become an important parameter to estimate prospectivity. Clustering of small gas – related amplitude anomalies stacked vertically in footwall or hanging – wall traps along single faults is direct observational evidence that links fault planes to significant fluid flux. Pockmark craters and mounds identified on the sea bottom and within the seismic section, formed due to igneous intrusion and hydrothermal pipes are also discussed for analysis of seal integrity. Introduction Volcanic basins are defined as sedimentary basins significantly affected by flood basalt volcanism. The presence of shallow basalt covering the underlying sediments significantly inhibits imaging of the subsurface. Additionally, the sub-basalt sediments are commonly intruded by sill and dike complexes (e.g., Bell and Butcher, 2002; Smallwood and Maresh, 2002), creating additional seismic imaging problems. Other nonseismic problems include uncertainties in the temperature history of the basin and associated digenetic effects generated by igneous rocks. On the other hand, forced folds formed above saucer-shaped sills may form potential hydrocarbon traps (Figure 1). Seismic evidence of small gas-related amplitude anomalies along single faults connecting deeper seismic with shallow is indicative of hydrocarbon potential that a basin holds despite poor seismic imaging (Figure 2). Volcanic intrusives, expressing itself as discordant amplitude anomalies, help in hydrocarbon maturation and fluid migration. In this article, we briefly review the main igneous rock types encountered in volcanic basins and their seismic expressions as well as explain how to interpret seismic images in volcanic basins from an explorer’s point of view. Forced fold due to sill Figure 1: Jack-up overburden due to sill intrusion