The science of seismic

Seismic technology continues to improve, helping operators to unearth more of Africa’s oil and gas riches.

IT IS AT the centre of the oil industry, and responsible for unearthing huge discoveries around the world, yet few outside of the business know quite how it works.

The science behind seismic technology – almost always a precursor to drilling – is incredibly complicated with new techniques constantly pushing the boundaries of what is possible.

Oil companies now routinely incorporate 2D and 3D seismic studies into their pre-drill work in order to better understand prospects before hiring a rig to test structures at a cost of many millions of dollars.

Given the cost and complexity of modern day exploration – and the remoteness in some cases, way off the African shoreline – anything that can help mitigate risk is hugely valuable for the oil companies.

Time and again, seismic technology – in all its forms – has proved itself in the field.

It is a means of glimpsing the oil potential under the surface. Better, maybe, to think of it more like a hospital ultrasound scan, imaging the inside of a human body, perhaps to view a baby before it is born.

Angola is born

In a sense, this is precisely what happened to Angola, now one of Africa’s biggest oil producers.

For years, the country remained a fairly marginal producer, long overshadowed by Nigeria. Now, after many successful years of drilling and seismic work, Angola is probably the continent’s leading oil producer, pumping around 2 million barrels per day (bpd).

More than a decade ago, one BP executive told a small briefing at the company’s former Finsbury Circus headquarters in London why it was so excited about Angola, showing various seismic charts and telling those present: "You can practically see the oil under the water."

That vindication is now evidenced in Angola’s success as an oil producer, and supports BP’s decision to invest billions of dollars in a country it now identifies as one of its core world growth spots.

According to seismic specialists, Schlumberger, the traditional reflective method of seismic simply images rock structures from the Earth’s surface to calculate rock types and the possibility that these might form underground hydrocarbon reservoirs.

It is based on measuring the time taken for sound waves to travel from a seismic source – such as a man-made explosion – through the earth to a rock layer that reflects the sound back to a recording device.

But clarity and interpretation are key factors. Usually, reading seismic is not that straightforward.

For BP in Angola, the rest is history. Last October, it announced its nineteenth discovery, Tebe, in its prolific ultra deepwater Block 31, where it took over as operator back in 1999. The latest discovery site is located about 350 km northwest of Luanda.

BP also holds a stake in other prolific Angolan blocks, including the Total-operated Block 17, dubbed the Golden Block, because of its similar oil strike rate.

Most recently, in April, Eni unveiled another pair of discoveries from Angola’s Block 15/06, Nzanza-1 and Cinguvu-1, again roughly 350 km northwest of the capital.

Unearthing Africa’s potential

Just as seismic analysis helped BP and others like Eni and Total open up Angola’s rich potential, this technology is continuing to prise open new frontiers, such as Ghana.

Again, living in the shadow of Nigeria for decades, there were many that scoffed at the prospect of finding large amounts of oil in the country, until new exploration technology – from seismic to deepwater drilling rigs – put it to the test.

Now, with a 1 billion barrels oil field under development, Ghana is enjoying something of a renaissance, with the Jubilee find triggering a wave of new upstream investment from international oil companies.

The same thing has happened in landlocked Uganda, another country once seen as barren of oil, but now a hotspot for exploration and production investment.

More oil companies have flocked in as a result, triggering more spending on seismic work, and ultimately leading to more drilling.

It shows how in places once deemed high risk, accurate seismic data can help steer oil companies and – if the drill bit ultimately delivers – de-risk new territories.

It is no longer unthinkable to attract investment dollars into previously risky territories such as Ghana and Uganda, at least from an exploration perspective.

It may be a similar story in a few years with other emerging locations such as Madagascar, Tanzania, or even inland, in the Democratic Republic of Congo.

Technology advances

Schlumberger’s seismic unit WesternGeco, which has helped oil companies locate reserves all over the world, continues to seek ways to improve on what is possible.

This includes new wide-azimuth and multi-azimuth seismic which improves imaging, resulting in reduced drilling risk.

These innovations address the challenge of the lack of variation in the azimuths of the recorded seismic ray-paths. The company has deployed the technology for BP in the Nile Delta, among other many projects.

As the search for hydrocarbons continues to intensify, oil and gas companies are looking at increasingly complex geological environments, where imaging technologies and velocity modelling play a key role in reducing exploration risk.

In March, WesternGeco acquired another seismic specialist Nexus Geosciences of the US, which has developed proprietary technologies for faster imaging, modelling and interpretation.

Maurice Nessim, vice president of WesternGeco GeoSolutions, says it will help oil companies to build their models of oil fields and structures more rapidly, to reduce uncertainties wherever they may operate.

"Our customers are exploring in areas of increasing geological complexity while under considerable time pressures," said Nessim. "The combination of Nexus proven imaging and modelling expertise with WesternGeco advanced imaging solutions and global reach will allow us to help our customers meet these challenges more effectively." 

Into the fourth dimension

Another advance is the deployment of 4D technology, or time lapse seismic, which involves acquisition, processing, and interpretation of repeated surveys over a producing field.

Operators such as BP have used this kind of technology as part of a ‘life of field’ initiative that recognises that maximising value from a producing asset is just as valuable as locating a new one through exploration.

The objective of using 4D technology is to determine any changes occurring in the reservoir as a result of production or injection of water or gas into the reservoir by comparing the repeated datasets.

Indeed, the application of such technology is critical to BP’s notion of the ‘Field of the Future’, a key corporate project to extract more value from existing assets, although the use of seismic is just one part of the jigsaw.

The plan is to deploy any existing and new technologies and integrate them with real-time data management systems for continuous field monitoring and operation. Data will flow from the reservoirs, wells and process plant, onshore and offshore, to the desks of BP’s experts anywhere in the world to ensure greater control and visibility.

The company reckons that this approach could effectively add many millions of barrels of oil to its reserves from fields all over the world.

Environment

It can be a tough job too with seismic contractors asked to work in the most extreme conditions, even onshore. In Nigeria, this could mean dealing with swampland terrain, or avoiding gunmen, or even unfriendly wildlife such as crocodiles.

There are other challenges too facing both the oil companies and seismic contractors.

Just as the oil and gas and marine industries are facing pressures on the environmental front, so too is this being felt among the seismic community.

Dubai-based Polarcus Limited is a relative newcomer, a pure play marine geophysical business specialising in high-end towed streamer 3D data acquisition.

It has taken on three state-of-the-art vessels which it says set new standards for reduced environmental footprint for the seismic industry.

Its first vessel, the Polarcus Naila, commenced the group’s very first data acquisitioon project in April off the coast of Cameroon, one of Africa’s traditional oil producers, on behalf of operator Noble Energy of the US.

The survey is being acquired with a 10 streamer seismic array, each streamer being 6,000 meters long and with 100 meters separation between streamers.

The second vessel in the fleet, Polarcus Nadia, is to shoot seismic off the coast of Liberia later in the year, after the signing of a contract in January with another seismic group, TGS. More contracts have been lined up for the North Sea and offshore Norway.

Seismic work remains at the heart of Africa’s exploration drive. If upstream investment goes up, then this equates to more business for the seismic community.

And while there are no guarantees when it comes to finding oil, seismic data is taking out more and more of the guesswork.

 

Alain Charles Publishing, University House, 11-13 Lower Grosvenor Place, London, SW1W 0EX, UK
T: +44 20 7834 7676, F: +44 20 7973 0076, W: www.alaincharles.com

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