EARLIER this month, it was reported that Senegal could be “the next Guyana” based on specific geological similarities between the offshore areas of both countries.

It may seem remarkable that two countries, Guyana and Senegal, on different continents and separated by the vast Atlantic Ocean could share similar geology. It’s worthwhile to examine and explain this.

Energy companies and foreign experts are apt to throw around geologic terms—from new “plays”, to terms like “cretaceous carbonate”—that don’t always mean much to the average person. But basic concepts of geology are a critically important factor in why Guyana has seen such an incredible series of oil finds in the Stabroek Block more than 200km offshore.
The geology of an oil-bearing formation impacts everything, from how much oil there is to how difficult it is to extract, although other factors like the distance from shore and the depth of the water also impact that calculation.

How and where these deposits form has been the subject of intensive study for more than a century by geologists and geophysicists.
Sedimentary basins like the one off the coast of Guyana are the remains of vast shallow seas that formed as ancient supercontinents split up millions of years ago. As organisms like algae and plankton died over millions of years, their remains built up at the bottom of the sea, and, over time, some of that organic matter was slowly compressed and heated into crude oil.

A certain portion of that oil can be “trapped” by specific types of geologic features and layers of non-porous rock to form a reservoir that can be drilled into.
When companies and officials talk about a type of “play”, they are indicating the geologic era in which that organic matter was deposited, like the Cretaceous Period, which began 145 million years ago. In many cases, these “plays” can rest on top of one another as basins of trapped oil separated by millions of years of rock.

For most of the wells drilled by the Exxon-led consortium in the Stabroek Block, oil was found more than 5,000 meters under the ocean floor, in 2-kilometer-deep water, making drilling an expensive and technically complex feat. The Liza and Ranger discoveries were made in different types of carbonate and sandstone, but both were from the Cretaceous Era.

However, more recent discoveries, like the Hammerhead-1 find, are particularly interesting because they occurred at a shallower depth in different rocks, in this case sandstone from the more recent Miocene Era. Finds like this are special, because they prove that multiple geologic eras left behind oil in different layers of rock offshore Guyana.
According to the Guyana Oil and Gas Association, the Guyana Basin once formed one side of a shallow sea that emerged in the Cretaceous Era as South America split from Africa due to continental drift. The West African side of this drift has already been a prolific oil producer in the past years, led by countries like Nigeria and Ghana.

That’s a key reason why oil companies were interested in Guyana in the first place, and why places like Senegal, that also bordered this ancient sea, could find similar wealth.
But despite Guyana’s geologic potential, reports from Wood Mackenzie and Rystad Energy note that it took years of searching, and the largest underwater seismic mapping project ever conducted to actually find drillable prospects.

That points to the difficulty and sophistication of offshore drilling, and the inherent uncertainties that come with predicting and pinpointing geologic formations created millions of years ago.

It also makes Guyana’s production timeline all the more remarkable. If all goes according to plan, Guyana will move from its first discovery in 2015 to active production just five years later.

As the energy industry gathers more data about Guyana’s geology with each well drilled, we will all learn more about how our offshore energy basins compare to other key oil-and-gas-producing regions of the world.