Source rock distribution and geochemistry of hydrocarbons in Mandapeta area of East Godavari sub-basin, Krishna-Godavari Basin, India

摘要

Mandapeta area in the East Godavari sub-basin of Krishna-Godavari (K.G.) Basin, India, hosts commercial accumulation of gaseous hydrocarbons in two major reservoir units i.e. Mandapeta Sandstone and Gollapalli Sandstone. Major source rock in this area is Kommugudem Formation with localized contribution from Raghavapuram Shale. Kommugudem Formation, comprising good volume of Type Ⅲ organic matter, is presently at maturity regime of peak oil window to gas generation stage. Raghavapuram Shale also comprises good volume of mainly gas/condensate prone Type Ⅲ organic matter and is generally at the threshold of oil window. Chemical and isotopic composition of the gases of both Mandapeta Sandstone and Gollapalli Sandstone represent a maturity regime ranging from late 'oil window' to gas/condensate stage indicative of their origin dominantly from Kommugudem source rocks and supplemented by localized beds observed in Gollapalli Formation. Gas pool encountered in Tirupati Formation in Mandapeta west area might have been sourced from Raghavapuram Shale which is adequately mature in this area. Regional distribution of source rocks indicates this area to be mainly gas/ condensate prone. However the areas where Kommugudem Formation is in peak oil window stage, such as north of Draksharama high, may hold some promise for liquid hydrocarbons.