Petroleum Potential of the Cauvery Basin, Sri Lanka

Abstract

The Cauvery Basin is located between the southeastern region of India and the north and the northwestern region of Sri Lanka. It is a pericretonic rift basin evolved due to the crustal extension between the Indo-Lanka landmasses. The rifting has given rise to northeast-southwest trending horst/ basement ridges subdividing the basin into four distinct sub basins/depressions. The Pesalai-Palk Bay depression and a part of the Ramnad-Palk Bay-Nagapattinam depression, separated by the Mandapam-Delft ridge, constitute the Sri Lankan sector of the Cauvery Basin. The Indian sector of the basin is producing both oil and natural gas. Six exploration wells drilled in the Sri Lankan sector of the Cauvery Basin during 1972-1981 was dry. Little further exploration has taken place in the Sri Lankan sector of the Cauvery Basin since 1981. In 2011, three exploration wells were drilled in the Mannar Basin, which is located immediately south of the Cauvery Basin, and discovered natural gas in two wells. These maiden hydrocarbon discoveries in Sri Lanka confirmed the occurrence of an active petroleum system in the Mannar Basin. The resumption of hydrocarbon exploration in the Sri Lankan sector of the Cauvery Basin has been taken into consideration since the maiden hydrocarbon discovery. However, the petroleum potential of the Sri Lankan sector of the Cauvery Basin is little known. The objective of this study was to evaluate the petroleum potential of the Cauvery Basin under the Sri Lankan jurisdiction based on a limited dataset, which include seismic, lithostraigraphy and biostratigraphy data and Rock Eval Pyrolysis, maceral composition analysis, total organic carbon and vitrinite reflectance data. The results of the study show that the stratigraphic thickness in the Sri Lankan sector of the Cauvery Basin is smaller compared that in the Mannar Basin. In the Sri Lankan sector, the potential hydrocarbon source could be Albian and older claystones, the Late Cretaceous sandstone, and Paleogene carbonate rocks could be the potential hydrocarbon plays, and Faults, anticlines, channel fills, and stratigraphic pinch outs could act as hydrocarbon traps. There is a possibility that an active petroleum system exists in the Sri Lankan sector of the Cauvery Basin. One of the reasons for not finding hydrocarbon deposits during 1972-1981 exploratory drilling could be due to the location of most wells on structural highs. The lack of understanding of the stratigraphic thickness, thermal and burial history, and hydrocarbon entrapment amidst tectonic activities that lead to larger hiatuses have to be clearly understood to reduce the exploration risk in the Sri Lankan sector of the Cauvery Basin