Abstract:
Cauvery Basin is located between the southeastern onshore areas of India and the
northwestern onshore areas of Sri Lanka. The basin has evolved due to crustal
extension between India and Sri Lanka as a result of the breakup of East Gondwana.
The rifting began in the Hauterivian and continued until the Cenomanian. The Indian
side of the basin accommodates commercially viable oil and natural gas deposits.
Hydrocarbon exploration in the Sri Lankan sector of the basin commenced as early as
1957. Six exploration wells were drilled in Sri Lanka during 1972 to 1981. None of
these wells encountered any economically viable hydrocarbon deposits. Little further
exploration took place in the Cauvery Basin in Sri Lanka to this date. However, the Sri
Lankan government has indicated its plan to resume hydrocarbon exploration in the
Cauvery Basin after the discovery of natural gas deposits in the Mannar Basin in 2011.
The Mannar Basin is considered to be the southern extension of the Cauvery Basin.
Only a handful of studies is available on the Sri Lanka sector of the basin in the public
domain, though plenty is available on the Indian counterpart. The objective of this
study is to understand the burial and thermal history of the Sri Lankan part of the
Cauvery Basin based on basin modeling techniques. Petromod 1D software (v. 12.2)
was used to simulate the burial and thermal history of the Pesalai-1, Palk Bay-1, Delft1 and Pedro-1 wells using data from unpublished well reports held at Petroleum
Resources Development Secretariat in Sri Lanka. In addition, data available in the
public domain were also used to derive some input data and boundary conditions.
Results of the study show that southern part of the Cauvery Basin in Sri Lanka has
experienced higher heat flows. The present-day geothermal gradient in Pesalai-1 and
Palk Bay-1, Delft-1 and Pedro-1 wells are 25.5o
C/km, 25.0o
C/km, 21.3o
C/km and
18.5o
C/km, respectively. The present-day geothermal gradient of the basin increases
from the north to the south. The highest bottom hole temperature (~90o
C), was
recorded in the Pesalai-1 well. The Pesalai area has experienced higher heat flows than
the Palk Bay area. Current heat flows in Pesalai and Palk Bay areas are around 52
mW/m2 and 48 mW/m2
, respectively. The pre-rift heat flow in the Sri Lankan sector of
the Cauvery Basin varied between 46 -40 mW/m2
. Area where the Delft-1 and Pedro-1
well are located have undergone upliftment during the Albian to the end of the Eocene
(around 100-34 Ma). The Sri Lankan Cauvery Basin has had a relatively a higher
sediment influx after the Eocene. The sediment thickness decreases towards the north
of the basin. Sediments penetrated by the Palk Bay-1, Delft-1 and Pedro-1 wells are
thermally immature. However, Albian sediment penetrated by the Pesalai-1 well is
marginally matured and has just entered the oil window
