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.
