Introduction
Ghana has four sedimentary basins. These are the Cote d'Ivoire-Tano Basin (including Cape Three Points Sub-basin), the Saltpond Basin, the Accra/Keta Basin and the Inland Voltaian Basin.
The offshore basins cover about 60,000 km² (0-3500m water depth) extending from the Cote d'Ivoire-Ghana maritime border in the west to the Ghana-Togo maritime border in the east. The onshore/coastal expressions of the Tano and Keta basins respectively and located at the southwestern and southeastern corner of Ghana, have a total size of about 4,000 sq. km. The Inland Voltaian basin is the largest sedimentary basin in Ghana. It occupies the central-eastern-northern part of Ghana. It is about 103,600 sq. km in size.
The Sedimentary basins are divided into quadrants of size one degree by one degree, equivalent to about 12, 420 sq. km. Each quadrant is further divided into eighteen (18) blocks with each block size equal to about 690 sq. km.
History
Hydrocarbon exploration in Ghana's sedimentary basins started precisely in 1896 onshore Tano basin in today's administrative Western Region. This was due to the presence of onshore oil and gas seepages found by early explorers in that area. Between 1896 and 1957, twenty-one (21) shallow exploration wildcats were drilled. Most of these shallow wells encountered hydrocarbon in shallow horizons. It is important to note that exploration activities within this period was purely wildcatting/chasing seepages.
Ghana was not left behind when global activities moved offshore. The first offshore well was drilled in the Saltpond Basin in 1970. The success of that well led to increased interest offshore Ghana. Subsequently, more acreages were awarded and exploration activities intensified in the 1970s mainly in the Tano-Cape Three Points and Saltpond basins. The Tano basin also recorded its first offshore exploratory success in 1970 with the Volta Tano well and subsequently the North Tano field.
The first and only exploratory well in the Voltaian basin was drilled in 1974 by Shell, following the acquisition of a 206-line kilometer 2D seismic data at the southern part of the Voltaian basin. Oil and gas production in the Saltpond Field started in 1978 and peaked at 4,500 bopd. The first deepwater well, the South Dixcove -1X was drilled in 900m of water in 1978 by Phillips Petroleum offshore Cape Three Points.
In the early 1980s, the government established a new statutory and legal framework for petroleum exploration as well as institutional capacity in order to accelerate the country's Exploration and Production (E & P) efforts. Ghana National Petroleum Corporation Law, 1983 P.N.D.C. Law 64 and Petroleum (Exploration and Production) Law, 1984, PNDC Law 84 were enacted.
PNDCL 64 established the Ghana National Petroleum Corporation (GNPC) as a statutory corporation with commercial functions to handle the country's E & P activities. GNPC started operations in 1985, the same year the Saltpond Field was shut-in.
Prior to the establishment of GNPC in 1983, the well count onshore and offshore Ghana was 54, while 2D seismic coverage remained considerably sparse. GNPC funded the acquisition of several vintages of 2D seismic over blocks onshore and offshore Tano, offshore Saltpond basin, onshore and offshore Keta basin, which led to a densely gridded 2D seismic coverage offshore and attracted more oil and gas companies into Ghana.
In the late 1990s and early 2000, significant milestones were achieved in our exploration efforts. They include an extensive 2D seismic acquisition offshore Saltpond Field, the WCTP-2X oil discovery in deepwater by Hunt Oil, and Dana Petroleum Plc.'s heavy oil discovery with the WT-1X well.
Prior to the Mahogany significant discovery in June 2007, GNPC spent years and scarce resources recovering, reorganising, reprocessing and interpreting petroleum data available to improve the exploration database and packaging it for promotion to the international industry. These promotional efforts succeeded in attracting credible oil and gas companies such as Anadarko, Tullow Oil, Kosmos Energy, Eni etc. into Ghana.
The discovery of significant oil and gas accumulations in 2007 and the commencement of production of the Jubilee field in November 2010 were the most significant events in Ghana's O&G sector in the last 2000s.
With Jubilee, the floodgates appear to have opened to further investments/exploration activities. Ghana's O&G sector is rapidly transforming on every front – investment (both core and ancillary), scale of operations, discoveries and reserves, policy, legislation and new institutions.
Seismic Data coverage has increased: 2D seismic data totalled about 70,000 line kilometres in 2011, while 3D seismic coverage is over 24,000 sq. km. Over 160 wells have so far been drilled in Ghana's sedimentary basins.
Source: http://www.gnpcghana.com/SitePages/ContentPage.aspx?ItemID=26