UNDERSTANDING OIL BLOCKS, BASINS, RESERVOIRS AND WELLS.

The petroleum industry, with its labyrinth of technical terms and complex processes, often seems daunting. However, understanding its basic building blocks can unravel the mystery. This article delves into four fundamental terms: oil blocks, oil basins, oil reservoirs, and oil wells—cornerstones of hydrocarbon exploration and production.

Maps of oil fields in Ghana.
(Source: Petroleum Commission)

OIL BLOCK

An oil block, also called a concession or lease area, refers to a specific geographic area designated by a government for hydrocarbon exploration and production. These blocks are defined using latitude and longitude coordinates and can range from small onshore plots to vast offshore regions.

 Key Features of an Oil Block:

• Licensing: Governments or regulatory agencies grant rights to companies through licensing rounds or negotiations. The contract defines terms like royalties, exploration obligations, and profit-sharing.
• Exploration Activities: Seismic surveys, geological studies, and exploratory drilling are conducted to assess the presence of hydrocarbons.
• Risk and Reward: Not every oil block contains commercially viable hydrocarbons, making exploration a high-stakes venture.

In Ghana, oil blocks like Jubilee and TEN (Tweneboa-Enyenra-Ntomme) have been pivotal. These blocks, located offshore, are leased by international firms such as Tullow Oil and Kosmos Energy, alongside local stakeholders like the Ghana National Petroleum Corporation (GNPC).

OIL BASIN

An oil basin is a geographical depression where sedimentary rocks favorable for oil and gas accumulation are found. Basins are critical for understanding regional hydrocarbon potential.

Characteristics of an Oil Basin:

• Geological Formation: Basins are created by tectonic activities, such as subsidence or rifting. Over time, layers of sediments compact and undergo chemical changes, forming hydrocarbons.
• Reservoir Potential: Basins house multiple oil reservoirs, which may vary in depth, size, and quality of hydrocarbons.

Tano Basin in Ghana is a prolific area in Ghana that hosts major fields like Jubilee and TEN (Tweneboa, Enyenra, and Ntomme). Recent discoveries and increased interest in the nearby Volta and Keta Basins indicate Ghana’s commitment to maximizing its energy potential.

Ghana's Cape Three Points Basin, for instance, has been the focus of numerous exploration activities. This basin hosted the Afina discovery by Springfield Exploration and Production, a Ghanaian company, which unlocked reserves estimated to produce up to 12,000 barrels per day (bpd).

Permian Basin in the United States is one of the world's most productive oil regions, contributing significantly to America's shale revolution with production exceeding 5 million barrels per day.

OIL RESERVOIR

An oil reservoir is a porous rock formation saturated with hydrocarbons—oil, gas, or both. It is the target of extraction operations once exploration confirms its presence.

 Components of an Oil Reservoir:

• Reservoir Rock: Sandstone or limestone formations with high porosity and permeability to store hydrocarbons.
• Cap Rock: An impermeable layer, such as shale, that traps hydrocarbons beneath, preventing their escape.
• Hydrocarbon Types: Reservoirs can contain light crude, heavy oil, natural gas, or a combination.

Oil reservoirs can vary in complexity. For instance, conventional reservoirs allow easier extraction, while unconventional ones (like shale or tight reservoirs) require advanced techniques such as hydraulic fracturing.

In Ghana, the Jubilee Field reservoir, discovered in 2007, was a game-changer, holding an estimated 600 million barrels of recoverable oil. Jubilee's development has solidified Ghana's position as an oil producer in Sub-Saharan Africa.

OIL WELL

An oil well is a physical structure drilled into the earth to extract hydrocarbons from a reservoir. Wells can be onshore or offshore, and technologies like horizontal drilling and hydraulic fracturing have revolutionized their productivity.

Types of Wells:

• Exploratory Wells: To confirm the presence of oil.
• Production Wells: To extract oil commercially.
• Injection Wells: To pump water or gas into the reservoir to maintain pressure.

The FPSO Kwame Nkrumah connects to multiple production wells in the Jubilee Field, with the capacity to produce 120,000 barrels of oil per day.

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