According to the “Ghana Geological Survey Bulletin No. 40” exploration for oil and gas in Ghana started in 1896 in onshore Tano basin (Western Region). This was due to the presence of onshore oil and gas seepages found by early explorers in that area. During that period early wells were drilled without geological understanding and the benefit of seismic data.
The wells were drilled by West Africa Oil and Fuel Company between 1896 and 1903 (WAOFCO-1, 2, 3, 4 & 5). WAOFCO – 2, the second well on the Takinta concession with a total depth of 35 metres, was the first documented discovery well in the country, producing 5 bopd between 1896 & 1897.
The early part of the twentieth century, (1909 to 1925) also saw the influx of international oil companies on the shores of Ghana. Notable among them was a French oil company, Societe Francaise de Petrole (SFP) which drilled a total of six onshore wells between 1909 and 1913 (SFP-1, 2, 3, 4, 5, & 6). SFP-1 struck oil at 10-17 metres depth and produced 7 bopd. SFP-3, 4, 5 & 6 all had very good oil indications and/or flowed at relatively shallow horizons, according to available records. Another company, African and Eastern Trade Corporation (AETC) also drilled two wells (AETC-1&2) in onshore Tano between 1923 and 1925, progressively encountering heavy oil, light oil and gas at various depths.
After 1925 and for almost 30 years of inactivity in exploration, Gulf Oil Company acquired the onshore Tano license and drilled four (4) wells at Bonyere, Epunsa, and Kobnaswaso from 1956 to 1957, as indicated below (Table 1). Apart from well logs, there is very little information on these wells as the wells were drilled without the help of seismic data. From 1896 to 1957 a period of 61 years, 17 onshore wells had been drilled in the Onshore Tano basin
1957 – 1966
Onshore exploration activities continued during the First Republic (1957-1966). Acting under the auspices of a Ghana-Soviet Union friendship pact, Soviet and Romanian Geoscientists explored for oil and gas in the Accra/Keta and Voltaian basins.
During this period, the Soviet team drilling for water in the onshore Voltaian basin encountered traces of oil and gas in some of the boreholes in some areas in the Northern and Upper East Regions. Also, calcic waters associated with hydrocarbons were encountered in some of these boreholes. Furthermore, the book “Rocks and Mineral Resources of Ghana”, authored by G. O. Kesse, reports that salt used to be mined at Daboya along the White Volta northwest of Tamale in the Northern Region. The association of salt deposits with hydrocarbons in sedimentary basins worldwide is well documented and these are all indicative pointers to the possibility of commercial accumulation of hydrocarbons in the Voltaian Basin.
1966 - 1972
In the latter part of 1966, the Industrial Export Company of Romania drilled a stratigraphic well near Atiavi in the Keta Basin. The well penetrated Quaternary, Tertiary, Cretaceous and Devonian age sediments until the crystalline basement was reached at 1,539 m. There was no indication of hydrocarbons. After the departure of the Soviet and Romanian teams in 1966, following the overthrow of President Kwame Nkrumah's government, there was a shift from onshore to offshore exploration in 1967.
Private oil companies were invited to undertake oil exploration in Ghana with most of these oil companies showing interest in the continental shelf. This marked the beginning of offshore exploration. The entire shelf was divided into 22 blocks and totally licenced by 1968. The licence empowered the companies to undertake oil exploration over a period of three (3) years beginning 1st January, 1969. They were required to drill one or more wells to a total depth of 3,657.5 m (12,000 ft.) within 18 months of the signing of Petroleum Agreement.
During 1970, a milestone discovery was made by Signal/Amoco Group with Seago 10-1 well. This well lead to the discovery of the Saltpond Oil Field (Devonian Section). The Takoradi 11-1 well had encouraging gas shows with subsequent re-mapping suggesting strongly that the well was drilled off structure and could possibly have been a gas discovery if it had been located on the structure.
1973 - 1979
In the era of 1972-1979, exploration for commercial oil, both onshore and offshore, continued and intensified. Seventeen (17) wells were drilled, with two of the wells being onshore, one in the Accra/Keta basin and the other in the Voltaian basin. The Premuase-1 well in the Voltaian basin, incidentally, is the only exploratory well in this vast frontier region to date.
The Saltpond Field came on stream and started producing oil in 1978 with Agri-Petco as the operator. Later in the same year, the first deepwater well, the South Dixcove -1X (SD -1X) was drilled by Phillips Petroleum in the offshore Cape Three Points in 2,927 ft of water.
1979 – 2001
In 1979, Phillips Petroleum appraised the South Tano discovery and made gas and condensate find on the satellite 1S-3AX structure down dip of the main field. They went ahead to further appraise the South Tano find by drilling IS-4X in 1981 and later declared the South Tano discovery sub-commercial and finally relinquished the block. Geophysical Services Incorporated (GSI) in 1982 entered into a Petroleum Agreement with the then Ministry of Fuel and Power to acquire a Non-Exclusive 2D seismic survey to accelerate the exploration and production of hydrocarbons offshore Ghana. The data was acquired in late 1982 to 1983 and covered the area from the Eastern border of Ghana to Cape Three Points.
With the establishment of the GNPC (1983), the passage of Petroleum Exploration and Production Law (1984) and promulgation of Petroleum Income Tax Law (1987), several Petroleum Agreements with international oil companies such as Atlantic Richfield Corporation (ARCO), Amoco, and Diamond Shamrock (Onshore Keta) were executed. The Canadian government, acting through Petro Canada International Assistance Corporation (P.C.I.A.C), expended considerable funds to support GNPC in acquiring extensive 2D seismic data in the offshore Tano/Cape Three Points Basin in 1984 (PCIAC – 84 -97, 98 & 99 vintages). These datasets are still some of the best in the basin. In addition, P.C.I.A.C funded the drilling of two appraisal wells (ST-5) and ST-6) over the Tano field. They also funded the drilling of shallow wells in the Onshore Tano Basin.
Similarly, the Government of Japan in a bilateral cooperation also assisted the Government of Ghana by acquiring offshore 2D seismic data for GNPC in 1987. This data covered the area from the Eastern border of Ghana to Cape Three Points and it was an infill to the 1982/83 GSI Speculative Survey. In 1989, GNPC funded the acquisition, processing and interpretation of first 3D seismic over the South Tano Field. Following interpretation of the 3D seismic data and subsequent commissioned studies to determine the viability of the Integrated Tano Fields Development Project to use the gas for power generation, GNPC drilled three wells over the South Tano Field in 1994 using its acquired drillship (Discoverer 511) and three other rigs in addition to other infrastructure to help facilitate rapid development of the Tano Fields.
As part of the integrated Tano Fields development project, GNPC ordered a power barge to utilise the anticipated gas from the Tano Fields. The infrastructure for the power generation barge was built at Effasu-Mangyea and power transmission lines to link the national grid in the Jomoro district in the Western Region to Essiama and Elubo with funds that GNPC had secured. The Saltpond Field, which had been in production since 1978, was later shut-in the mid 1980’s by Primary Fuels Incorporated (PFI) who had acquired AgriPetco’s interest in the Saltpond Field. PFI drilled three wells; one gas well and two dry wells and finally pulled out due to uneconomic production rates.
2001 – 2007
Within this period, exploration for commercial hydrocarbons intensified with some independent Oil Companies such as Kosmos Energy, Hess Corporation and Tullow Oil, acquiring exploration and production rights over areas in deep water. There was a shift of focus from shallow water to deepwater areas which was occasioned by other deepwater discoveries made in the region and by the results of four deepwater wells drilled in Ghana between 1999 and 2003. These wells proved the existence of an active petroleum system in the deepwater, a fact which hitherto was unknown. Hunt Oil’s WCTP-2X well encountered 14ft of light oil column. This effectively reduced the risk of petroleum generation in the deepwater areas of Ghana.
Kosmos Energy (block operator), Anadarko (technical operator), Tullow Oil and E. O. Group struck a significant (about 312ft net) column of high grade oil in the Mahogany prospect with the Mahogany-1 well in the West Cape Three Points Licence. This is the most significant discovery crowning years of concerted effort by all. From August 2007 to 2013, 23 discoveries (Odum, Ebony, Tweneboa, Sankofa, Dzata, Owo, Teak-1, Paradise-1, Banda-1, Gye Nyame, etc) have been made. Except Ebony, all recent discoveries were made in deepwater (water depths ranging from 800 to 1600m). The Mahogany and Hyedua discoveries have been appraised and put into production as Jubilee Field.
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