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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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 arakab.
The shelf part of the basin spreads over the Brahmaputra valley and the Dhansiri atakan, the latter lying between the Mikir hills and the Naga foothills. The generalized stratigraphic succession. However, the area to the north of the Brahmaputra river up to the Eastern Himalayan foothills has remained poorly explored.
The Assam-Arakan basin witnessed two major phases of tectonic development. From the Digboi, the baisn runs westward to the southern slope of the Shillong plateau. Disang shales, occurring in association with ophiolites, are somewhat metamorphosed here. This element contains most of the oil fields of the Upper Assam Shelf.
Major tectonic elements of the basin are:. 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 araakn named as the Govindpur Formation.
During shallowing of the sea in arakkan basinal area, the succeeding sediments of the Barail Group were deposited under environments ranging from moderately deep marine to deltaic. During this period, the Assam Shelf was being evolved in a passive margin tectonic setting and under shallow marine to brackish water sedimentation conditions.
Oil accumulations within the Bokabil Formation Middle Miocene in the Bawin and Nambar fields of the Dhansiri valley, occur in structural combination traps. This site is best viewed using current versions of Firefox v. 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.
Assam Arakan Basin
The Assam-Arakan Basin is situated in the northeastern part of India categorized as category-I basin. The limestones with negligible impurities were, perhaps, deposited on sea mounds. This foredeep was the site of deposition of the Surma Group of sediments under shallow marine lower part to brackish water upper part environments.
Following completion of collision and subduction of the oceanic part of the Indian plate during Late Oligocene to Early Miocene? Home Assam Arakan Basin.
The Andaman trenchwhich has been receiving mostly argillaceous sediments since, possibly, Upper Cretaceous-Paleocene, is the southward extension of the Indo — Burmese trench system. The Naga Metamorphic Complex, east of the Eastern thrust. 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.
During the post- Oligocene time, however, different parts of the mega basin witnessed different evolutionary trends, mostly under compressive tectonic forces.
In the Naga Schuppen zone, apart from the Digboi oil field, two more major oil fields, namely, the Kharsang field, having oil accumulations in Upper Miocene to Pliocene reservoirs and the Champang field, having oil accumulations in fractured granitic basement rock of Precambrian age, have been discovered.
Most of these hydrocarbon traps, particularly those developed in post- Barail sediments, orient parallel to the Naga thrust. The area within the Upper Assam shelf, having high petroleum potential, measures approximately sq km and contains about m thick sediments of mostly Tertiary period, and the area in the basinal part with moderate to high hydrocarbon potential measures about 60, sq km and contains more than 10,m thick sediments of mostly Tertiary period.
During Middle to Late Cretaceous, when baxin Indian plate was moving northward, a number of horst and graben features developed on the granitic crust in the southern slope of the Shillong Plateau and Dhansiri valley. The metamorphic complex occurs mostly to the east of the Indo-Myanmar international border. In the Dhansiri valley also, oil fields like the Borholla and Khoraghat and Nambar lie in the same belt. Presence of pelagic fauna indicates that these sediments were deposited in shallow shelf to open marine conditions during Maestrichtian to Early Paleocene time.
Assam Arakan Basin | NDR – National Data Repository India
During the last decade, oil and gas accumulations have been discovered within the Langpar arakaan Lakadong formations of Paleocene to Lower Eocene age in several structures like Dikom, Kathaloni, Tengakhat, Tamulikhat, Shalmari, Baghjan, Panidihing, etc. All the oil and 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 Kharsang, Digboi and Champang oil fields are located in this element. These lateral tectonic movements were accompanied by upliftment and total withdrawal of the sea, arakwn the onset of continental sedimentation the Tipam Sandstone Formation on the Assam Shelf as well as on the earlier basinal area. During this time, the basinal area to the east and southeast witnessed deposition of Lower Disang shales, radiolarian cherts and subordinate limestones in the distal deeper part of a marginal downwarp, i.
It may be mentioned that oil, generated in the Kopili and Barail source beds, accumulated in post-Barail sediments by vertical migration through such prominent faults.
Oil within the Kopili Formation composed predominantly of shales with subordinate sandstone occurs in strati-structural combination traps, as in the Geleki field. Oil reserves in Kopili sandstones Upper Eocene are found mainly in the Geleki field.
The southeastern slope of the Upper Assam Shelf, southeast assqm the Brahmaputra arch, having local structural highs and lows, upto the Naga thrust, and extending 8 to 10 km beneath the Naga schuppen belt. In the Digboi and Kharsang oil fields, oil occurs in Tipam Sandstone and Girujan Clay formations, respectively, overlying the Naga thrust.
Barail Coal-Shale Unit in the Schuppen belt also form important source rock sequence. The Dhekiajuli Formation, consisting of mostly soft sandstones, was deposited at the mountain fronts in the Upper Assam Shelf and in areas now overridden by younger Naga thrust. The basin covers an area of Sq. During Paleocene, there was a marine transgression on the southern edge of the Shillong Plateau, depositing sediments of the Therria Formation consisting of limestone, basln and shale.
The development of the 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. Oil within the Girujan Clay Formation as in the Kumchai and Kharsang fields also occurs in combination traps, but here the control of lithology on accumulation is more than that of structure.
The sequences can be divided into shelf facies and basinal geosynclinal facies.