The Upper Assam Basin is a poly history basin from where hydrocarbons are being produced for more than a century. Geologic setting of Assam-Arakan basin. Assam –Arakan Basin Geological Setting: It includes Assam, Nagaland, Arunachal Pradesh, Manipur, Mizoram and Tripura. The eastern limit is. Unconsolidated Sand Stone Reservoir to Eliminate Sand Breakthrough Problem Having Active Aquifer Drive: A Detailed Case Study in Assam-Arakan Basin.

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During this time, sedimentation in the Surma basin including Sylhet trough and the Aeakan synclinorium took place in intermontane basins, depositing the arenaceous Lower Dupitila sediments over a post—Girujan unconformity and the argillaceous Upper Dupitilas over a post-Lower Dupitila unconformity. The shelf-to-basinal slope, i. The southeastern slope of the Upper Assam Shelf, southeast atakan the Brahmaputra arch, having local structural highs and lows, upto the Naga thrust, and extending 8 to 10 km beneath the Naga schuppen belt.

During shallowing of the sea in the basinal area, the succeeding sediments of the Barail Group were deposited under environments ranging from moderately deep marine to deltaic. These clastics, making the lower part of the Kopili Formation, were deposited in open marine conditions during Late Eocene, when marine transgression was waning out. In the Digboi and Kharsang oil fields, oil occurs in Tipam Sandstone and Girujan Clay formations, respectively, overlying the Naga thrust.

However, the area to the north of the Brahmaputra river up to the Eastern Himalayan foothills has remained poorly explored. Major tectonic elements of the basin are: Other significant milestones in oil exploration in Upper Assam were the discoveries of the Nahorkatiya, Moran and Rudrasagar oil fields inandrespectively.

In the North Bank of the Brahmaputra river, however, environmental conditions were deltaic with the deposition of sandstones with minor shales and siltstones. A Comprehensive Petroleum System events of Assam basin.

In the Khoraghat and Nambar fields situated in southeastern part of the Dhansiri Valley, oil occurs in the Bokabil Formation Middle Miocene which is not developed towards north in the Brahmaputra valley. In the Borholla field of the Dhansiri valley and Champang field of the neighbouring schuppen belt, oil reserves occur in structurally controlled subtle trap in fractured basement rocks.


The Assam — Arakan Fold Belt This fold belt may be divided into two zones bounded by prominent thrusts, viz, i the Naga fold zone, lying in between the Disang and Tapu thrusts and having exposures of Disang shales and Barail sediments, and ii the central flysch zone, lying between the Tapu thrust and Changrang — Zunki thrust and having exposures of mainly Disang shales.

In the Naga Schuppen belt, oil accumulations in the Lakshmijan and the Champang oil fields occur in that zone of the shelf which is overridden by the Naga thrust. The Assam-Arakan sedimentary Basin is a shelf—slope—basinal system.

The oilfields, discovered so far, are situated mainly in the areas south and southeast of the Brahmaputra river and a few in the thrust belts, associated with Naga-Patkai hills. All the oil araoan gas fields, discovered till date in the Upper Assam shelf, are situated mostly on the southeastern slope of the Brahmaputra arch, and almost all the major oil fields like Nahorkatiya, Lakwa, Lakhmani, Geleki, Dikom Kathaloni etc.

The Assam-Arakan Basin is situated in the northeastern part of India categorized as category-I basin. During Paleocene, there was a marine transgression on the southern edge of the Shillong Plateau, depositing sediments of the Therria Formation consisting of limestone, sandstone and shale. Oil within the Kopili Formation composed predominantly of shales with subordinate sandstone occurs in strati-structural combination traps, as in the Geleki field. Bassin Indo-Burmese trench system that developed during the oblique subduction of the Indian plate below the Burmese plate became the locus of aswam of Upper Disang shales under deep marine conditions.

Following completion of collision and subduction of the oceanic part of the Indian plate during Late Oligocene to Early Miocene? East of the hinge zone, i.

Assam Arakan Basin

Towards the close of Middle Eocene, limestone deposition ceased because of an increase in the influx of finer clastics in the shelf. It developed as a composite shelf-slope-basinal system under a passive margin setup during the period from Early Cretaceous to the close of Oligocene. In the subthrust, the source sequences occur at greater depths and, therefore, should be in a higher state of thermal maturity.

During the growth of these structures, the Girujan Clay Formation was deposited in the synclinal lows structural basins in Cachar area as indicated by seismic and well data from the Katakhal syncline of Cachar area where the Girujan Clay Formation is named as the Govindpur Formation.


The limestones with negligible impurities were, perhaps, deposited on sea mounds.

Assam Arakan Basin | NDR – National Data Repository India

The basin covers an area of Sq. These lateral tectonic movements were accompanied by upliftment and total withdrawal of the sea, heralding the onset of continental sedimentation the Tipam Sandstone Formation on the Assam Shelf as well as on the earlier basinal area. The Andaman trenchwhich has been receiving mostly argillaceous sediments since, possibly, Upper Cretaceous-Paleocene, is the southward extension of the Indo — Burmese trench system.

This foredeep was the site of deposition of the Surma Group of sediments under shallow marine lower part to brackish water upper part environments. In this shelf—slope—basinal architecture, the hinge zone, at and across which the Upper Cretaceous-Eocene shelf facies changes over to basinal facies, is envisaged to lie below the Naga schuppen belt. The basinal geosynclinal part is occupied by the Cachar, Tripura, Mizoram and Manipur fold belts. Organic matter is mainly humic and sapropelic.

Assam Arakan Basin Basin Introduction:. In the North Cachar area, exploration by deep drilling is yet to be initiated. Some of the prominent faults, particularly those near the Naga thrust, are reverse faults, e. It is expected that the source sequences within the Kopili and Barail formations in the subthrust would be at the peak oil generating state.

Oil reserves in Kopili sandstones Upper Eocene are found mainly in the Geleki field. The development of aseam frontal foredeep in front of the rising Himalaya, during Mio-Pliocene and later times, due to tectonic loading by thrust slices was filled with coarser sediments.

The Lakadang Formation Early Eocene comprising limestone and coal bearing sandstones was deposited in shallow marine to qssam conditions, while the overlying Tura Sandstone Formation Early Eocene was deposited under fluvio-deltaic environment. Organic matter richness of shales increases towards the Naga thrust.

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