THE past few months have seen announcement after announcement of new oil reserves offshore. The remarkable run of 10 discoveries in the Stabroek Block since 2015 is the product of ExxonMobil’s largest ever seismic survey campaign. The results have been enough proof of Guyana’s potential that the company is continuing to gather data and explore new prospects.

Exploration for oil and gas all starts with seismic surveys. Marine seismic surveys, like those conducted offshore Guyana, are some of the most technically complex practices in the petroleum industry. They rely on a fleet of specialized vessels and highly trained geophysicists, technicians and engineers to create 2- and 3-dimensional maps of the layers of rock under the sea floor.

The process of conducting a seismic survey is similar to how certain whales and bats emit sound and receive back vibrations to help them navigate their surroundings. In this case, special devices emit a sound underwater in short pulses, and by measuring when that sound bounces back and how the sound waves change shape, scientists can get a picture of what layers of rock look like underneath the sea floor.

According to the International Association of Geophysical Contractors, the process starts with a fleet of research ships that tow an array of underwater chambers behind them that are filled with either water or air under pressure. These chambers release bursts of high-pressure energy into the water to create acoustic pulses that pass through water and rock.
An array of hypersensitive underwater microphones, called hydrophones, are towed further behind these vessels and record the sound when it bounces back off the underlying bedrock. The sensors are towed behind the exploration ship like a huge floating net, and they measure the characteristics of that sound and how long it takes to bounce back in the same way that an ultrasound maps a human body.

Scientists can then analyze that data using advanced computers and software and create a map of what exists thousands of metres below the ocean floor. Finally, geophysicists analyze these maps and rock formations to determine where organic material that is thousands of years old might be trapped between two layers of rock. When they find such a formation, they analyze it further to determine if it might contain oil or gas.

Although it is an expensive process, seismic surveying cuts down on overall costs by improving the accuracy of drilling site selection and minimizing the number of exploration wells that need to be drilled to find energy resources. This not only saves money but also minimizes the impact of exploration on the marine environment.

Exxon contracted a fleet of vessels to conduct a massive seismic campaign after the Liza 1 discovery, the largest 3-D campaign in the company’s history. That effort covered more than 20,000 square km and included two research vessels to gather data, two support ships, and two supply ships.

This kind of exploration, which can also be conducted on land using a convoy of specialized trucks, is a vital part of exploring for oil and gas. Thanks to seismic data, oil and gas drilling is a much more precise and targeted effort today than it was a few decades ago.
That precision comes at a cost, though. Large seismic studies, like that conducted by Exxon, routinely cost hundreds of millions of dollars. But that search led to the discovery of billions of barrels of oil equivalent, mostly in the southern and eastern portion of the Stabroek block.

The success rate of prior seismic campaigns has certainly fueled an appetite for further surveying activity, and ExxonMobil and its partners seem optimistic that there is much more to discover. Future seismic campaigns, by Exxon and other companies, are the first step in learning how large our energy bounty will grow in the future.