THE GEOLOGICAL SOCIETY
ExxonMobil recently announced that their recoverable oil and gas resources in Guyana had reached an unbelievable ten billion barrels of oil equivalent.
The first discovery was in 2015 and six years later Exxon and Guyana have achieved the unimaginable. Guyana accounts for 20 per cent of the world’s conventional oil found in the last five years. The cost of extraction is also considered the lowest in the world for deepwater (US$25 to US$35 per barrel).
Liza Phase 1 was the fastest deepwater field in history to move from discovery to production (under five years). And before 2030, with under 800,000 citizens, Guyana will produce more than one barrel per day for each of them.
Exxon, still the world’s largest multinational oil and gas company, operates three blocks in Guyana (Stabroek, Canje and Kaieteur), under production sharing contracts granted by the government.
Exxon, Hess and CNOOC (China National Offshore Oil Corporation) are partners in the Stabroek block (45 per cent, 30 per cent and 25 per cent respectively).
Other blocks have stakes from well-known companies like Total and Qatar Petroleum, and smaller independents like Frontera Energy, Ratio Oil and Eco Atlantic.
So far, over 20 oilfields have been discovered in the Stabroek block, which spans over 27,000 sq km. For comparison, Trinidad is just over 5,000 sq km. The fields are in water 1km to 2km deep. The discoveries are all of Upper Cretaceous age (66 to 100 million years ago) and are all sandstone reservoirs (except for one discovery, Ranger, which is limestone).
Ancient river and canyon systems flowed out from the continent, and the sands in these systems became encased in clays over millions of years. The sands later became charged by hydrocarbons migrating from underlying shales. Unlike Trinidad, there are few faults and folds in the rocks here, so the traps are all stratigraphic (caused by changes to the rock strata), and not created due to tectonic activity. It is worth noting that stratigraphic deepwater plays are quite rare and are considered very risky.
The first field found was Liza, already producing 120,000 barrels of oil per day (bopd).
Liza’s oil is light (32 API) and sweet (low sulphur, 0.5 per cent) and thus highly valuable. Again, Trinidad’s oil production is currently about 60,000 bopd. Last week, Exxon’s latest exploration well Cataback-1, was deemed a major discovery, taking the total recoverable resources to over 10 billion barrels of oil equivalent. The 20-plus fields in Stabroek have been named after fish such as Liza, Turbot, Tilapia, Redtail and Payara.
Let’s pause to elaborate on the concept of recoverable resources.
Typically, the amount of oil that is recoverable from a reservoir may be between ten and 40 per cent of the total oil in place. The actual amount that is recoverable depends on a multitude of factors including porosity and permeability of the reservoir rocks, thickness and lateral extent of the sands, density and viscosity of the oil, reservoir pressure and temperature
