Natural Resource

The grater Sylhet region is the most enriched area of Bangladesh in mineral resources. A large quantity of the total proven gas reserve and the only oil field of the country are located here. The area has also vast deposit of limestone, peat, glass-sand hard- rock grave. But the economic value of hydrocarbon reserves are overwhelmingly dominant. The region is geologically known as the Surma Basin and covers the north-eastern parts of the foredeep and Folded-Belt division of the Bengal Basin which happens to be one of the most prominent tectonically-active sedimentary basins of the world. Parts of the Sylhet region which are apparently flat having are within the foredeep division while the hilly areas are called folded Belt. Thickness of the sedimentary pile with the foredeep area is in excess of 15 kilometers; the Folded Belt representing the uplifted parts of this sedimentary pile. This huge sedimentary body is dominantly composed of sand and mud with subordinated limestone which started depositing in a deep-basement (bottom of the basin being composed of igneous-metamorphic complex) basin about 5o million years ago with the gradual rise of the Himalayas due to collision between Indian and Burmese Plates and subsequent erosion. The sand-mud composition of the sedimentary body, along with technically-developed favorable structural set up (exposed and covered folds and faults mainly) have made the Sylhet region highly potential for occurrence of natural resources. Muds act as sources, sands as reservoirs, while folds (anticlines) act as traps for hydrocarbons (gas and oil). Age of the sediments, local geothermal gradient, pressure of the overburden etc. have been sufficient for the source materials to be"cooked" to from hydrocarbon.

Natural Gas:

There are eight gas fields located in Sylhet region. Also the first 3 gas fields of the country were discovered in this region between mid 1950s and early 60s – Sylhet gas field in 1955, Chatak in 1959 and Rashidpur in 1960. These predate the discovery of Titas gas field which is at present the largest natural gas supplier of the country. Other gas fields of the region according to their year of discovery are Koilastila 1962, Hobigonj 1963, Beanibazar 1981, Fenchugonj 1988 and Jalalabad 1989. All these reserves have been discovered in structural traps formed by mild folds (anticlines) that occur in the subsurface and have no direct surface expressions. The intensity of these folds increase west to east in the direction of the Folded Belt region; which relates to the development of grater thrust in that direction due to tectonic activity. However, the discovery gas fields are mostly located in the nearly-plan lands of along the western fringe zones of the intensively folded areas. Gas is discovered within sandstone layers of Bhuban and Bokabil formations in the subsurface, which is about 35 million years old. Sandstone act as good reservoirs because of their high porosity; however, the gas is generated in some neighboring clayey layers with high organic contents and lager migrates to the sandy units, which are sealed by impervious sedimentary layers. Impervious layers prevent further migration of the gas. Total reserve of the gas fields of the Sylhet region is about 14 trillion cubic feet with a recoverable reserve of about 8.5 tcf.

Table 1: Gas in Place And Reserve Of Different Gas Fields As Declared By Petrobangla

S. No	Fields	Year of Discovery	Reserve Estimated by Company... Year		GIIP (proven + probable)	Recoverable proven + probable)	Cumulative Production (Dec. 2000)	Net Recoverable
A. Producing
1	Bakhrabad	1969	IKM	1992	1432	867	586.568	280.432
2	Habiganj	1963	IKM	1992	3669	1895	818.315	1076.685
3	Kailashtilia	1962	KM	1992	3657	2529	231.820	2297.180
4	Rashidpur	1960	IKM	1992	2242	1309	194.920	1114.080
5	Sylhet	1955	HHS	1986	444	266	166.084	99.916
6	Titas	1962	IKM	1992	4138	2100	1783.400	316.600
7	Narsingdi	1990	IKM	1992	194	126	29.205	96.795
8	Meghna	1990	IKM	1992	159	104	23.278	80.722
9	Sangu	1996	Cairn/Shell	1997	1031	848	91.026	756.974
10	Saidanadi	1996	Bapex	1996	200	140	14.816	125.184
11	Jalalabad	1989	Unocal/PB	2000	1195	815	52.298	762.702
12	Beanibazar	1981	IKM	1992	243	167	4.681	162.319
	Total A				18604	11166	3996.411	7169.589
B. Non Producing
13	Begumganj	1977	Welldrill	1991	25	15	0	15
14	Fenchuganj	1988	Bapex	1988	350	10	0	210
15	Kutubdia	1977	Welldrill	1991	780	468	0	468
16	Shahbazpur	1995	Bapex	1995	514	333	0	333
17	Semutang	1969	HHS	1991	164	98	0	98
18	Bibiyana	1998	Unocal	2000	3150	2401	0	2401
19	M’bazar	1999	Unocal	2000	500	400	0	400
	Sub total B				5483	3925	0	3925
	Sub total A+B)				240087	15091	3996.4	11094.59
	C. Production Suspended
20	Chattak	1959	Niko/Bapex	1998	447	268	27	241.5
21	Kamta	1981	Niko/Bapex	1998	33	23	21.1	1.9
22	Feni	1981	Niko/Bapex	1998	178	125	40	85.49
	Grand Total (A +B+ C) in BCF				24745	15507	4083.52	11423.48
	Grand Total (A +B+ C) in Tcf				24.745	15.507	4.08	11.42

Source:Marketing and Production Division, Petrobangla (Revived on 15/02/2001)

Crude oil:

The only oil field of the country is located in Haripur of the Sylhet district, which, was discovered in 1986. Although a relatively large quantity of gas has been discovered in the county, the amount of oil discovery is very small. This is in a sharp contrast to many hydrocarbon provinces of the world where large volumes of both gas and oil co-exist. Geologists of our country are somewhat confused by this reality and most opine that exploration into even deeper sedimentary layers then those producing gas may help discover oil. The Horipur oil is discovered in sandstone layers within a subsurface fold called Sylhet Anticline which is about 13 kilometers long and 3 kilometers wide; producing horizons are around 2000 meters depths and two closely spaced oil-horizons have been detected. Maximum oil reserve is estimated to be around 21 million barrels. Oil production under natural pressure was 400 barrels per day in 1987 which dropped to about 100 barrels in 1994 and since then it has remained suspended due to necessity of further development of the field. Between 1987 and 1994, a total of 0.56 million of crude oil have been produced. The quality of the Haripur oil is similar to that discovered in Assam.

Limestone: Limestone of Eocene time are exposed on or close to the surface in the Takergaht-Lalghat areas of the north-western part of the Sylhet region along its border with the Indian state of Meghalaya. Reserve is about 30 million tons and it is the second largest discovered limestone in the country after the Jaipurhat. Preliminary reserve estimation was done in the sixties and seventies while the Geological Survey of Bangladesh in 1982 ascertained the reserve by putting 5 depths of about 30 to 100 meters below the surface, the deposit has a thickness of 152 meters and the reserve is estimated to be 17 million tons. In Lalghat and Takerghat areas limestone deposits occur at much shallow depths and their reserve are estimated to be about 10 and 2 million tons respectively. In these areas, limestone deposits are also sporadically exposed. The limestone body has brought to the surface by upliftment due to techtonic activity; most of its parts fall within the Indian Territory and Bangladesh sharply disappear under the alluvium cover in the south with a very high angle of dip. The Takerghat limestone deposit is being extracted since the Independence of Bangladesh and it’s reserve is fast diminishing.

Coal:

Peat, Glass-sand, hard rock Gravel: about 2.5 million tons of peat reserve was discovered in the Maulvibazar area in the early fifties. The deposit occurs 1.5 meter from surface, 1.6 meter thick and extends over an area of about 10 square kilometers. Peat deposits also exist in the Pagla and Chorka areas of the Sunamgonj district, has an estimated reserve of about 3 million tons and at comparable thickness and deposits occur as modern sediments within valleys and floodplains.

Silica/Glass Sand:

Shahzibazar of the Hobigonj district has Glass-sand reserve of about 1.41 million tons which discovered in the early fifties is dominantly composed of silica (over 95%) and occur in centimeter scale lenses that appear within 1-2 meter from the surfacee.

Hard Rock:

Hard-rock gravels of up to 1 meter in diameter are found on the stream beds that drain the hilly areas of Meghalaya and fall on the flat land within Bangladesh territory along the northern parts of the Sylhet region. This is particularly prominent in Jafflong-tamabil areas where total estimated reserve is about 45.6 million cubic meters. Gravels occur both on the present streambeds and up to several meters depth.