Reservoir potential of the Campanian sandstone in the Dorado North well on the Mannar Basin, offshore Sri Lanka

Abstract

The Mannar Basin is located offshore in between the west coast of Sri Lanka and the east coast of India. It is a Mesozoic failed rift basin filled with Late Jurassic to recent sediments. The basin is one of the main targeted areas for oil and gas exploration in Sri Lanka. In 2011, the existence of an active petroleum system in the basin was confirmed by discovering natural gas from Dorado and Barracuda wells. Although the petroleum system of the Mannar Basin is known to some extent, the porosity and permeability of potential reservoirs in the basin are little known. Previous basin modeling studies have reported that the Late Cretaceous section in the northern part of the Mannar Basin has potential reservoirs. However, their porosity and permeability have not been investigated in detail due to the lack of availability of well data. The objective of this study was to estimate the porosity of approximately 431 m thick Late Cretaceous (Campanian) sandstone section in the Dorado-North well, located on the northern part of the Mannar Basin. The results show that the Campanian section is mainly composed of shaly sandstone. Almost half of the section shows very good reservoir potential, while the rest of the section has fair to good reservoir potential. The quality of a hydrocarbon reservoir depends on its shale fraction. Shale degrades the reservoir quality. Caving in give rise to uncertain data in petrophysical logs. The Campanian section in the Dorado-North has very good hydrocarbon potential.