Ghana National Petroleum Corp. (GNPC) plans a two well offshore drilling program it hopes will lead to a resumption of hydrocarbon production in the West African state.
The wells will be drilled in South Tano field in the extreme western sector of Ghana's offshore area, near the boundary with Ivory Coast.
If the program is successful, the state company will develop a novel floating production system to handle and export oil. Gas will provide fuel for an electrical power generating unit integrated into a floating production system. Power will move ashore through a submarine cable.
North and South Tano fields were discovered by Phillips Petroleum Corp., which relinquished the acreage in 1982. The South Tano discovery well flowed 1,614 b/d of oil and 8.2 MMcfd of gas.
Studies by a unit of ARCO, when it was a partner in a group that later acquired the Tano block, pegged North Tano hydrocarbons in place at 53.6 million bbl of oil and 102 bcf of gas. Braspetro, under contract with GNPC, estimated South Tano hydrocarbons in place at 82 million bbl of oil and 100 bcf of gas.
GNPC is evaluating the possibility of rehabilitating Saltpond oil field about 150 miles east-northeast of North and South Tano. Saltpond has been shut in since 1985.
WHAT'S PLANNED
First drilling in South Tano will be a horizontal well near the 1X South Tano drilled by Phillips in 1978. GNPC plans to place the well on extended test for 6-12 months to provide details about the reservoir in preparation for full scale oil and gas development.
The second well in South Tano will initially be a vertical well. Depending on results, it could be sidetracked into a horizontal section.
GNPC will use the Production Pioneer jack up, formerly designated DF-80, acquired last June by the state company from Norwegian owners and refurbished at Mobile, Ala., by Oceandril, Houston. The rig was towed to Ghana last March.
The extended well tests will use National subsea trees acquired from Hamilton Bros. Oil & Gas Ltd. after its abandonment of Crawford field in the North Sea.
Trees will be connected to a Vetco Gray mudline suspension system.
Modec Inc., Houston, is providing project management for the tests.
The tests will be conducted through Sonat's Discoverer 511 drillship, which is under long term lease to GNPC. Process equipment is being fitted to the vessel. It will be tandem moored to a crude storage tanker.
GNPC said anticipated full development after the extended well tests will involve producing oil and associated gas from three subsea wells in the central South Tano field and producing North Tano field and the associated 3-AX structure mainly for gas.
This will be done through a tanker based floating production, storage, and offloading system with onboard power generation from combined cycle gas turbines. The system is being engineered by Single Buoy Moorings, Monaco.
GNPC said the project should be able to sustain production of about 90,000 kw of power, which will be fed into the national transmission grid through which power is exported from hydroelectric sources to Cote d'lvoire, Togo, and Benin.
It also will make power available in the southwest coastal area of Ghana, not currently connected to the national distribution system.
GNPC, in anticipation of production from North Tano, is refurbishing subsea trees used by Phillips in the abandoned Espoir field off Cote d'lvoire. This is being undertaken under a contract with Vetco Gray and Oceaneering, also of Houston.
Six wells have been drilled in South Tano field. Only one was dry.
The 1X and 4X produced 27 gravity crude. The 5X and 6X drilled by Petro-Canada International Assistance Corp., flowed gas and condensate.
The 3AX flowed nonassociated gas from a separate fault block south of the main structure.
GNPC said South Tano is an anticline bounded on the north and south by faults.
North Tano field is in an elongated anticline penetrated by three wells: 1N-1x, 1N-2x and 1 Volta Tano. All yielded oil and gas.
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