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Timor-Leste - A geological overview

“Imaging is everything if you want to understand petroleum systems.” - Jarrad Grahame, Senior Geoscientist for the Asia-Pacific region for CGG, the globally recognised geophysical services company. Timor-Leste’s geology shows the ideal conditions for significant deposits of oil-bearing rock.

The right geological ingredients for production

Timor Island is actually several distinct tectonic provinces that developed initially by rifting and drifting away from the Australian Plate, a massive tectonic structure which covers the whole Australian continent and stretches as far as southern India. The bulk of the island is a complicated mix of Tertiary, Cretaceous, Jurassic, Triassic, Permian, and volcanic rocks, all of which were formerly part of the ancient continent, Gondwana.

The southern coast of Timor-Leste which is surrounded by the Timor Sea is the first area which has been identified as a major hydrocarbon source via seismic data interpreted from well studies. So far, all known producing hydrocarbons reservoirs offshore are in late Triassic and Jurassic sands, but examples are abound from other regions of the world where Permian and Triassic stratigraphic layers have contained bountiful reserves of hydrocarbons, creating exciting future prospects for the country.

Timor-Leste geology, geological map, ANPM, 2nd Licensing Round, IN-VR
This is a snapshot of IPG's research, source:

In 2019, the Instituto do Petróleo e Geologia of Timor-Leste invested in understanding the hydrocarbons map of the country, and reconstructed a map of likely hydrocarbon deposits in and around the country, combining it with other studies from 2017 and 2018, the Institute .

Timor Leste is exhibiting all the conditions one would need for the presence of significant volumes of hydrocarbons. It has:

a) The source rock, as evidenced by the Bayu-Undan field, which Timor-Leste shares with Australia and which has been the mainstay of oil and gas production for over two decades. Geochemical studies have found similarities between this rock and those on the highly productive neighbouring Australian Northwest Shelf.

b) a seal made of impervious rock that retains the hydrocarbons within the reservoir rock. This is a middle Jurassic shale which would form a seal on the Late Triassic and Early-Middle Jurassic reservoir sandstones.

c) a mirror image in Indonesia.

Analogous Data in Seram

The island of Seram in Indonesia is about 500km northeast of Timor Leste and its geological conditions are remarkably similar. It is an island whose tectonic plates are much smaller than the continental plates which surround it and are being subducted underneath those plates. Yet the further underground one studies the geology, the less complex the stratigraphic layers become. The Oseil oilfield in Seram is analogously very positive for Timor Leste.

Prior to its discovery, oil production from the island was from small, shallow fields in shallow reservoirs. They were essentially oil seeps from deeper geological levels and there have been numerous oil and gas seeps documented onshore Timor Island.

The Oseil field, however, was a much larger oilfield (over 40 million barrels of reserves) located at a depth of about 1600m. Furthermore, it is located in an ‘inversion anticline’ which is considered a highly promising source of hydrocarbons for Timor-Leste by geologists. The Northwest Betano anticline in Timor-Leste is thought to contain about twice the volume of rock as the Oseil inversion anticline, so it could well be capable of holding a significantly sized hydrocarbon accumulation with further drilling and analysis.

Modern Technologies

In 2020, Norwegian marine seismic company, TGS, started a 2Dcubed seismic study offshore Timor-Leste across an area of 50,000 square kilometres. The 2D data will cover the entire offshore area south of Timor-Leste where the 11 offshore blocks in the country’s second licensing round, announced in October 2019, are located. 2Dcubed technology allows the company to generate ‘3D seismic migration volume from a set of 2D and 3D seismic lines,’ according to TGS.

Furthermore, speaking to IN-VR, CGG explained that in recent years it has undertaken numerous 2D seismic studies covering offshore Timor-Leste, the Banda Arc – a set of island arcs in eastern Indonesia – and up to Seram island. They have also been analysing and studying the data in their JumpStart project, which has contributed to big gains in the understanding of the geology of the region as there has been little data available historically. The CGG study encompassed 16,300 square kilometres. Mr Grahame explained to IN-VR that “one of the most important outcomes of these projects and studies is the key prospectivity insights that we can derive which have a significant amount of supporting evidence.

Both companies realise the importance of furthering the knowledge of the geological characteristics of Timor Leste. TGS’ studies will combine all open file and TGS multi-client data while CGG has said that it is happy to share some of the conclusions they have made from their studies and would be willing to provide datasets to interested parties.

Promising Prospects

Hydrocarbons cannot exist without a reservoir rock, a cap rock to fix them in place and immense geological pressure often helps too. All of those conditions are present and correct in Timor-Leste. The country has remained under-developed throughout much of its history, both socio-economically and in terms of its resources. The government is taking big steps to turn this around and is keen to move forward proactively and with full recognition that it needs outside help to do so.

Having a willing and able political system is nothing without the resources to back it up, though. Timor-Leste is a proven hydrocarbons producer and all the signs are there that there is much still waiting to be found. The bid round is ongoing and Timor-Leste has a rock solid foundation for future success.


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