The valley of the lower Indus has gradually supplanted and succeeded this original Tertiary gulf.
This commenced from Digboi- and proceeded along the southern side on the Brahmaputra valley, to Sylhet, and along the western flank of Arakan, through eastern Bengal to Akyab Gulf. The part southwest of Sylhet is now buried under alluvium of the Meghna and the delta of the Ganga.
The surface indications of oil and gas occur at intervals from the Arakan coast northeastwards through the Chittagong region to the Surma valley and thence along the north-western side of the Naga hills, almost to the extreme north-east of the Upper Assam valley.
Through vigorous prospecting, four oil-fields have so far been discovered, Digboi, Naharkatiya, Hugrijan and Moran in Upper Assam. In these areas deep test wells put down by the Oil and Natural Gas Commission have shown promise of oil and gas deposits capable of years of sustained production. Crude oil from Assam contains a large proportion of gasoline, paraffin and naphthalene. It is free from sulphur.
The Digboi Field:
The oil pools occur along the crest of a sharply folded anticline to the south of the Naga thrust. The productive oil-sands in the Digboi field belong to over 20 separate horizons showing much lateral variation. The Digboi oil has an average specific gravity of 0.85 and generally has a high wax content.lt contains 9% gasoline, 38% kerosene, 49% lubricating oils and 3% fuel oil.
The Naharkatiya Field:
A deep well drilled on a structural summit pointed out by a sesmic survey in the Brahmaputra alluvium, about 32 kms from Digboi, has brought to light the existence of the new promising oil-fields of Naharkatiya. Subsequent detailed seismic surveys have shown that the structure of the field is much more complex than was thought at first, the tertiary strata being cut through by many faults of small and large throws.
This new field may have a potential production of 2.5 million tonnes annually. The oil in this area is of mixed paraffin and asphalt base with an average specific gravity of 0.850, yielding excellent paraffin, wax, lubricating oil some bitumen, and various other by-products.
The Moran-Hugrijan Field:
Drilling has proved an oil-bearing Barail horizon at a depth of 3,355 m on a faulted dome near Moran, some 40 km southwest of Naharkatiya. Exploratory drilling is in progress in Moran and adjacent areas in Upper Assam.
Moran’s potential may be estimated at one million tonnes per annum. While drilling continues in Upper Assam, extensive geophysical prospecting is being carried out to locate oil-bearing strata elsewhere in the same area under the Brahmaputra alluvium.
The reserve of petroleum (crude) at Bombay High has been estimated at 330.35 million tonnes. The greatest success achieved by the ONGC with respect to offshore surveys for oil was that of Mumbai High in 1974. It is located on the continental shelf off the coast of Maharashtra about 176 km northwest of Mumbai. Oil is taken from the depth of over 1,400 metre with the help of a specially designed platform known as Sagar Samrat.
Geophysical investigations during the last 13 years have proved the existence, underneath the alluvium of north Gujarat and the Rann of Kachchh, of a wide basin of post-Nummulitic sediments capable of enclosing productive petroliferous horizons, resting upon the faulted surface of the Traps. It stretches from Surat district, across the Gulf of Cambay, to beyond Bhavnagar in Saurashtra.
Drilling tests, including offshore drilling, to establish the commercial possibilities of oil-fields within the Cambay basin are being carried out. The north boundary of the Cambay basin probably extends beyond Ahmednagar and the Rann of Kachchh, a considerable distance towards southern Rajasthan, while its southern extent buried under the shallow water of the Gulf of Cam-bay, may be much beyond Piram Island.
Gravity and seismic methods of exploring the structure of the floor rocks under the Rann of Kachchh and some alluvial tracts of northern Gujarat are being employed for further survey of the basin. The Oil and Natural Gas Commission since 1958 has drilled test wells near Ahmedabad at Khambhat Lunej and confirmed the occurrence of a commercially exploitable oil-field.
In 1960 oil was struck in the first well at Ankleshwar, nearly 160 kms south of Cambay town; it has indicated the existence of a new oil-field, capacity 2.8 million tonnes per annum. Pt. Jawaharlal Nehru called it the foundation of prosperity. Gujarat can, therefore, be reasonably expected to be an oil-producing area in the future. The main oil belt extends from Surat to Amreti Kachchh, Vadodara, Bharuch, Surat, Ahmedabad, Kheda, Mehsana are the main oil producing districts.
Jammu and Kashmir:
There are possibilities of occurrence of gas and oil in the Jammu region, particularly along the Ravi-Jwalamukhi section, Nurpur, Dharamsala and Bilaspur in Himachal Pradesh.
A small gas occurrence reported in the Tertiary sediments, buried under alluvium in Tanjore district, lends support to the possibilities of occurrence of petroleum in the Cauvery delta. Test wells are being drilled. In addition to this, many private and joint sector refinary projects are there, mainly Reliance Petroleum (Jamnagar), International Petro (Parmar) Ashoka Leyland, Hindiya (Orissa) and Essar Petro (Vadinar).
Oilfields in North East India
Digboi north east of Tipam hill sin Dibrugarh distirct, is the oldest oilfield.
Naharkatiya fields started in 1953
Moranhugugan started in 1956, 40 km, from soutwest of Naharkatiya
Rudrasagar, Sibasagar, Lakura, Gaieki, Badapur, Barhola and Anguri are newly discovered oilfields.
In Arunachal Pradesh oilfields are in Manabhum, Kharsang, Charali
In Tripura, oilfields are in Mamunbhang, Baramura, Dantamura, Subhang, Manu Ampibagar Amarpurdambura
In Western India (Gujarat):
Ankleshwar 80 km of Vadodara, JL Nehru called Ankleshwar of fountain of prosperity
Khambat or Lunej (near ahmadabad) field started in 1958
Ahmadabad and Kalol
Offshore Oilfields of India:
Mumbai high, Sagar Samrat is its platform
Aliabet near Bhavnagar (Production is largest in Mumbai high 62%, Gujarat 20%, Assam 16.5% then in Tamil Nadu 1%)
Oil Refineries in Private Sector:
Reliance Petroleum in Jamnagar
International Petrol Parmar in Surat
Ashok Leylands in Daitori in Orissa
Essar Petro in Vadimar, Gujarat
Black Gold in Vyag
Petrodyne in Karaikal, Pondichery
Jindl ferro Alloy in Vizag
Portmardi TIDCO in Tuticorin, Tamil Nadu
Abon LLyod Chales in Tuticorin
Moplac Udyog in Haldia