Heather Saucier examines the geology of the Mediterranean and North African region, and assesses where more discoveries could be made.
The location of four assessment units in the Nile Delta Basin Province in the Eastern Mediterranean. (Map not definitive for political boundaries.) Map from USGS.
Eni’s recent discovery of the supergiant, deepwater Zohr gas field (See Egypt's Breadbasket) roughly 100mi off the coast of Egypt – believed to contain up to 30 Tcf of natural gas in place – marks what could be the largest gas find in the Mediterranean Sea and one of the largest in the world in recent years.
In fact, after its full development, Eni CEO Claudio Descalzi said the field will be able to satisfy Egypt’s natural gas demand for decades.
While the discovery has caused some political stirrings regarding overlapping maritime borders and energy export deals, it also serves as an important reminder of the vast number of opportunities that still exist in one of the Earth’s most prosperous geological gas havens.
When assessments of mean undiscovered resources by the US Geological Survey (USGS) in the Nile Delta Basin and the Levant Basin are combined, the Eastern Mediterranean becomes the No. 2 spot in the world – just behind Western Siberia – for gas resources. Together, the basins have an estimated mean of 345 Tcf, says Christopher Schenk, a Denver-based geologist who has overseen the USGS’ oil and gas assessments for nearly 20 years.
Part of the ancient Roman aqueduct at Caesarea Maritima about half way between Haifa and Tel Aviv on the Mediterranean coast. Photo by Chris Schenk. Courtesy of the USGS.
The secret lies in the salt. Named after the salt marches in the Italian town of Messina, the Messinian salt that remained after the Mediterranean Sea dried up during the Miocene Period, measured as thick as hundreds, even thousands of feet, Schenk says.
“It’s one of the most amazing geological phenomena ever,” he says of the Messinian salt event. “If you look at the 2D seismic data for this area, you can just see these beautiful, large structures. It’s a very nice system. You can imagine oil and gas coming up from below and being trapped in structures. The salt seal has been quite effective for the Levant and for the Nile.”
Noble Energy was the first to piece together the geology of the Eastern Mediterranean – drilling 11 successful wells and discovering 40 Tcf of recoverable natural gas resources in the Levant Basin, since entering the region in 1998. The company’s finds include the Leviathan field, which has been appraised to hold 22 Tcf of recoverable resources and was the largest discovery in the world in 2010.
Yet, other operators including Eni, BG Group, Shell and BP, have begun making their own discoveries – bringing sighs of relief to countries in need of natural gas.
As large as the Zohr field discovery may be, an abundance of resources await to be discovered in areas where drilling is currently taking place, and in substantially underexplored areas ripe with potential.
Schematic geologic cross section of the Nile Delta Basin Province illustrating the geologic definition of three of the four assessment units (AU) in this study (dotted red lines): Nile Margin Reservoir AU, Nile Cone AU, and Eratosthenes Seamount AU. The forth AU, Mediterranean Ridge, is out of the plane of the cross section. Key: 1 – Miocene (post-Messinian and Pliocene-Quaternary; 2 – Messinian Salt; 3 – Miocene (pre-Messinian); 4 – Paleogene-Cretaceous; 5 – hypothesized pre-Cretaceous; 6 – Eratosthenes Seamount. Source: USGS.
Nile Delta and Levant basins
By their very geological components, deltas are ideal places to explore, as they contain source rocks, reservoir rocks and traps. In the Nile Delta Basin, an area that has been explored for quite some time, channel sandstones, sheet sands and basin floor fan sands make up the meat of that particular play, Schenk says.
Chalk cliffs near Rosh Hanikra western Galilee region coastal Israel. Photo by Chris Schenk. Courtesy of the USGS.
With an estimated mean of 223 Tcf of natural gas, the world’s largest delta remains plentiful despite discoveries that total roughly 75 Tcf of natural gas to date, Schenk says. The basin’s most prospective area is the Nile Cone, with an estimated mean of 217 Tcf. The basin also has an estimated mean of 1.8 billion bbl of oil.
“A petroleum charge is confirmed by more than 100 producing fields, numerous oil seeps, mud volcanoes and gas chimneys imaged on seismic profiles,” reports the USGS.
Although a far cry from the enormous Zohr prospect, a discovery of 5 Tcf in the Nile Delta Basin was also made last year by BP Egypt from its Atoll-1 deepwater exploration well. “Success in Atoll further increases our confidence in the quality of the Nile Delta as a world class gas basin,” said Bob Dudley, BP Group chief executive, in a statement to the press.
Just east of the Nile Delta Basin, the Levant Basin has an estimated mean of 122 Tcf of natural gas, with its most promising plays located in its subsalt areas, which have an estimated mean of 81 Tcf, Schenk says. Its oil prospects have an estimated mean of 1.7 billion bbl.
Geologic features including nearshore marine sandstones and deepwater slope and fan sandstones help make the Levant Basin a prospective play. Noble Energy relied on seismic data, spot-on interpretations and proficient project execution to achieve production in the Mari-B field in 2004, and the Tamar field, which boasts 10 Tcf of recoverable resources, in 2013. Today, Tamar supplies more than 50% of the energy resources Israel uses to generate electricity.
Location of the three assessment units (AU) in the Levant Basin Province in the Eastern Mediterranean. The boundaries of the Levant Sub-Salt AU and Plio-Pleistocene Reservoirs AU are coincident. Map from USGS.
“Interpretation of seismic was key. We saw hints that suggested the possibility of a really porous sandstone reservoir in a reasonably simple structure with a salt seal,” says Susan Cunningham, executive vice president of Exploration, New Ventures, Geoscience, EHSR and Business Innovation at Noble Energy. “We also saw the possibility of a flat spot on the seismic – an indicator of hydrocarbons.”
When determining which blocks to lease in the Levant Basin, Noble Energy obtained available 2D seismic and underwent a basin-wide study to determine where structures similar to Tamar could be found. “We could see the running room in the basin and applied for the perspective acreage offshore Israel and Cyprus,” Cunningham says.
The company discovered the Aphrodite gas field with an estimated 4 Tcf in Cyprus’ maritime Exclusive Economic Zone in 2011. It has been reported that the resources in offshore Cyprus are more than the country could consume in a century.
Subsequent discoveries by other operators in the Levant Basin and the recent Zohr discovery will help countries such as Israel, Egypt, Jordan and Cyprus meet their needs for power, but could also enable them to become exporters to Europe and other parts of the world. In fact, reports of competition have already begun hitting mainstream media outlets.
Geologic cross section southern part of the Levant Basin Province illustrating the definition of the three assessment units (AU) in this study. The areas of the Levant Sub-Salt Reservoirs AU and the Plio-Pleistocene Reservoirs AU are coincident, and neither AU overlaps with the Levant Margin Reservoirs AU. Dashed line separates Cenozoic (above) from pre-Cenozoic rocks. Messinian-age salt (between the M and N seismic horizons) is shown in green. Key: A – Permian to Aalenian age; B – Bajocian to Turonian age; C – Senonian to Early Oligocene age; D – Oligocene to Late Miocene Age; E – Late Miocene (Messinian) age; F – Plio-Pleistocene age rocks. Source: USGS.
While many operators are exploring in the Nile Delta and Levant basins, a long list of prospects exist in areas that remain more obscure on the oil and gas map.
Perhaps most notable is the Essaouira Basin off the west coast of Morocco with an estimated mean of 45 Tcf of natural gas and 7 billion bbl of oil, according to the USGS. Unlike the Nile Delta and Levant basins, the salt present in the Essaouira originated during the initial rifting of the Atlantic Ocean, Schenk says.
“I think this is a very exciting place in the offshore basin,” he says. “Although not many wells have been drilled here, the area has potential for source rocks, reservoirs, traps and seals. It has all the elements of a system that could really work.”
While some of the potential play is located in deep water, shallow prospects also exist, Schenk says.
Offshore Greece also holds potential, according to a 2012 study taken by Athens-based Flow Energy. The study estimates that south of Crete, an impressive 123 Tcf of natural gas and 1.5 billion bbl of oil are awaiting discovery.
Another underexplored gas prospect, the Provence Basin, is located just south of France. While no wells have been drilled in this area, the known presence of Messinian salt removes a bit of risk from this play, Schenk said. In fact, in terms of undiscovered resources, the USGS estimates a mean of 13 Tcf of natural gas and 500 MMbbl of oil in this basin.
As new technology and more 2D and 3D seismic data become available, discoveries in the Mediterranean will become less risky. Using 2D and 3D seismic is “absolutely routine” now, Schenk says. “That forms the basis for all of these new discoveries in the Levant Basin for sure,” he adds.
Such technology will likely pave the way for others as well in this resource-rich pocket of the world.