Abstract

Present study has identified a previously unknown carbonate buildup withinin the Mahuva Formation in the Tapti Daman Block, Western Offshore Basin of India. Thin carbonate beds within shales are found to be hydrocarbon bearing in this area, which has produced small volumes of oil and gas in the Dahanu and adjacent structures. The carbonate buildups can represent a significant new play type in the Tapti Daman sub Basin, where shales and limestones are known source rock. The present carbonate buildup, imaged as a lens like event in three-dimensional seismic data, forms an eliptical feature in the isopach, amplitude, impedance and velocity maps. It is characterized by generally high but variable seismic amplitude, and its thicknesses (30 to 40 m) exhibit a complex pattern, suggesting weathering and/or localized carbonate growth. A relationship between impedance and porosity was derived. Using this relationship the seismically derived impedance values were converted to porosities. The derived porosities, perhaps, qualitatively demarcate the areas of better porosity developments within the build up. The lateral and vertical seals for this limestone reservoir are likely to be provided by the shales of Mahuva Formation. Considering the nature of anomaly, paleostructural disposition, thickness maps, seismic attribute studies, impedance/porosity analysis, fairly large size of the builup, located within established Mahuva play, appears to be interesting from hydrocarbon point of view.