Assessment of Sub-Basalt Petroleum System in the Kerala-Konkan Basin, India

Shah, Jyoti¹; Fainstein, Roberto²; Mishra, Somen³; Wygrala, Bjorn⁴
¹DCS, Schlumberger, Mumbai, India.
²WesternGeco, Schlumberger, Al-Khobar, Saudi Arabia.
³SIS, Schlumberger, Dehradun, India.
⁴SIS, Schlumberger, Aachen, Germany.

Mesozoic sediments on the western flank of India are covered by flood basalts that were prevalent around the time of the Tertiary-Cretaceous boundary and impact petroleum exploration in offshore western India. Deccan basalt blankets Kutch, Saurashtra, Bombay, and Kerala-Konkan basins along the western flank of the Indian peninsula. The Kerala-Konkan basin has neither undergone extensive structural deformation nor has it been greatly influenced by the post-basalt fluvial sediment deposition systems. Gravity modeling studies rule out any large-scale underplating or thicker magmatic crust and indicate that the volcanism decreases to the south. Plate-reconstruction studies suggest restricted environment of deposition and favorable thermal domains during the early rift phase that were conductive for deposition and maturation of source rocks. Kerala-Konkan basin is an ideal basin to evaluate the sub-basalt trap concept and study the thermal effect of flood basalts on the pre-existing Mesozoic sediments and potential hydrocarbon accumulations.

Analyzing sub-basalt sediments by seismic or drilling was always challenging due to the massive nature of the basalt so any additional knowledge that can be derived from existing data will have substantial value. In this study, we took an integrated approach using seismic and gravity interpretation, as well as petroleum systems modeling, to assess the sensitivity of the hydrocarbons and their properties to the thermal impact of the Deccan basalt in Kerala-Konkan deepwater basin. Different scenarios are analysed to account for the variation of factors, including reservoir and source rock properties and thermal effects to improve understanding of the nature of possible sub-basalt hydrocarbon leads and prospects.

The results of simulations and diverse scenarios indicate the possibility of sizable volumes of gaseous hydrocarbons that could be trapped against structural highs or stratigraphic pinch-outs against basalt.

This study analyses specific elements and geologic processes of sub-basalt petroleum system in the basin. Even with the limited available data, hypotheses can be more rigorously tested to determine the likelihood of hydrocarbon generation and preservation and the resulting prospectivity and hydrocarbon type distributions. This regional study of the Kerala-Konkan basin provides an improved assessment of key risk factors related to the development of subbasalt potential petroleum systems through geologic time.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012