Harrow and Hillingdon Geological Society

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Kebabs, carbonates and baggy trousers: adventures of a geologist in Kurdistan

Paul Logan

Paul Logan has spent 36 years in the oil and gas industry, having worked for British Gas Exploration, Getty Oil, Hamilton Petroleum, BHP and Heritage Oil and is now Exploration Manager for Taipan Resources Inc and working in Kenya. This presentation was based on his experiences with Heritage Oil, for whom he spent 5 or 6 years exploring in Kurdistan.

Kurdistan

Kurdistan is the northern part of Iraq and has a population of 5 million and an area of 80,000km2, about the same size as Switzerland. It is one of 3 ethnic areas in greater Iraq, with Shias in the south near Basra, Sunnis in most of Iraq and Kurds in the north. The Kurds are Muslim but not Arabs. The Kurdish language is distinct and is based on Iranian languages, such as Persian and Pashto, with two main dialects, Sorani and Kurmanji. It is geographically diverse, from hot and dry plains to cooler mountainous areas with natural springs and snowfall in the winter. The capital city of Erbil claims to be the oldest continuously inhabited city in the world.

The Kurds rebelled against Sadam Hussein for years and were in danger of extermination until saved by the 1st Gulf War, and particularly by the no-fly zone established over Kurdistan (along with that over Basra). There is also a rebel Kurdish movement in Turkey. Since the 2nd Gulf War, Iraq is divided into 3 zones and Kurdistan is now an autonomous region of Iraq. A liberal foreign investment law was ratified in June 2006, providing incentives for foreign investors.

Geology

Kurdistan lies in the Low Folded Zone of the Zagros fold-belt. It is underexplored and highly prospective – estimated by the USGS in 2000 to hold c.40 billion barrels of oil and 60 trillion cubic feet of gas. Approximately 40 international oil companies are in the region and interest continues to grow. Refineries are being built. According to Kurdistan Minister of Natural Resources, Kurdistan is hoping to produce 1 billion barrels per day by mid 2014 and the Iraqi National budget for 2011 included 100,000 barrels per day exported from Kurdistan.

General view of Miran valley

Northerly movement of the Arabian Plate resulted in collision with the Anatolian Plates - this first produced a series of E-W trending anticlines. This was followed by the stress introduced against the Iranian Plates in a NE-SW direction resulting in the NW trending anticlines of NE Iraq; some are overprinted over the Anatolian trend in N Iraq. Jurassic, Cretaceous and Tertiary rocks are folded with many low-angle faults which sole down (flatten out) in thick anhydrite layers.

Miran lies near the Southwest boundary of the High Folded Zone. It consists of two anticlines, Miran West and the overriding Miran East. The area is characterised by two ridges built by Lower Eocene limestones, both merging into one ridge towards the northwest. The eastern Tasluja ridge exposes Palaeocene shale of the Kolosh Formation on both sides. Two major anticlines were mapped. Miran West, with an estimated areal extent of 200km2 and Miran East with an estimated areal extent of 130km2. Miran west is terminated by transverse faults from both NW and SE directions. Faults mapped correspond well with the seismic interpretation and are related either to the detachment thrusts or the back thrusts. There are 2 structures in the subsurface, separated by a major NW-SE trending thrust fault, which forms a distinct very sharp ridge down the centre of the valley.

Miran West & Miran East Seismic cross-section west to east

Tertiary deposits comprise a thick sequence of thin limestones overlying mudstones with thin limestone layers.

Sinjar Formation

Balambo Formation

In the Cretaceous, Maastrichtian deposition was strongly influenced by two things:
• obduction of the Southern Neo-Tethys from which derived large amounts of flysch into the Mesopotamian basin; and
• the development of a carbonate ramp to the northwest of the Anah-Qalat Dizeh Fault.
Areas outside the ramp were dominated by turbidites at the margin of the obduction zone (Tanjero Formation) or basinal mudstones and marls (Shiranish Formation). The ramp was dominated by reef limestone (Aqra and Bekhme formations).

The Aptian-Albian sequence of north-eastern Iraq is represented by two basic facies, the carbonate ramp of the Qamchuqa, occupying the regions to the northwest of the Anah - Qalat Dizeh Fault, and the basinal mudstones of the Balambo Formation. To the west, an inner shelf lagoon was dominated by the deposition of clay and evaporites assigned to the Upper Sarmord and Jawan Formations. The facies changes are clearly expressed in the topography as viewed on Google Earth (a primary tool for exploration these days). The limestones are quite heavily dolomitised in the east and produce quite rugged topography but, moving west, they become more and more muddy and the topography is much smoother.

The Liassic of north-eastern Iraq was dominated by a shallow marine evaporite shelf, represented by the Butmah, Adaiyah, Mus and Alan formations. Further to the east, the Liassic sequence is represented by ramp limestones and dolomites represented by the Sarki and Sehkaniayn formations respectively. The boundary between the two facies lies slightly to the east of Miran.

Hydrocarbon systems and seals

Hydrocarbon exploration and production requires 3 essentials:
• Source rock – and organic rich sediment, which, when cooked, generates oil and gas. Analysis of the thermal history of the Kurdistan sediments indicates that Shiranish is Oil Mature in synclinal areas, Middle and Upper Jurassic are in Oil Mature to Late Mature and the Top of the Upper Triassic is in Oil Late Mature. Oil seeps through fractures at the surface demonstrate the presence of the source rock. Indeed, much of the oil generated has escaped from the source rock through fractures in the overlying rocks.
• Reservoir rock – a permeable formation which can hold the oil and gas in the pore spaces or in fractures. The theoretical maximum permeability of a rock comprising perfect spheres is 42%. In this case it is fractured carbonates with the oil under pressure on top of water. In Kurdistan there are 3 reservoir layers with oil at the top and 2 gas units.
• Seal and structure – an impermeable claystone or mudstone containing a domed structure in the reservoir rock. Processing of seismic data can include flattening the seismic lines, which reveals a prograded wedge in the sequence stratigraphy.

The speaker digressed slightly to explain that the currently controversial shale-oil and shale-gas involve drilling into the source rock directly and extraction needs closely spaced wells and fracking. This involves pumping water down the boreholes at slightly higher pressure than the formation pressure to induce microfractures, which only spread a metre or so from the hole. This is a technique that has been used in the oil industry for many years without any apparent problems. The technique does not involve explosives, though the Russians experimented in the 1960s with nuclear fracking.

Reservoir geology

A significant percentage of oil and gas reserves are trapped in fractured carbonate reservoirs – more than 60% of the world’s proven oil reserves and 40% of the world’s gas reserves. Such reservoirs contain hydrocarbons in either:
• Primary (inter-granular) porosity
• Fractures and joints -form as a result of mechanical stress (folding and/or faulting)
o Damage zones –associated with major faults
o Fracture corridors – propagated sub-vertically as a result of stress
o Micro-fracturing – with the reservoir fabric
Most carbonate reservoirs are naturally fractured and contain fractures that can range from isolated microscopic fissures to kilometre-long fracture corridors, creating paths for hydrocarbons. Fracture corridors will be concentrated in areas where deformation is greatest, often on the flanks of structures. Well results have demonstrated that, where open fractures are encountered in wells, the reservoir will support potential production rates of approximately 8,000 - 10,000 barrels per day.

Oil seep through fracture at surface Fractures in Balambo Formation Upper Cretaceous Fracture concentration

In Kurdistan, the reservoir rock is fractured deep-water carbonates, which are not very good reservoirs. Porosity is very low, except where dolomite layers have been dedolomitised. Regional fracture studies have produced fracture density maps. Fractured carbonate reservoirs are usually more fractured and jointed on the flanks and the more intense fracture development tends to be associated with faults. This is evidenced by field work observations. A high-angle well drilled on the flanks will typically connect with many more fractures/joint systems. A vertical (or near-vertical) well drilled on the crest may not connect with many fractures, which tend to be sub-vertical and more widely spaced. The 1st well drilled was on the crest of the structure, which is the least fractured zone.

While there is some primary porosity (up to 21% but more typically less than 10%), it is the fractures that give the rocks their permeability and exploration has concentrated on identifying a mechanical stratigraphy, rather than the conventional lithostratigraphy or chronostratigraphy, based on the mechanical strength of the rocks. Well logging using tools such as resistivity, neutron logging and natural gamma radiation gives a complete picture of the borehole.

Miran Cretaceous reservoir formations are of Campanian-Maastrichtian (Shiranish), Turonian (Kometan) and Albian ages (Balambo/Qamchuqa).

Exploration – practicalities

Having used Google Earth as a primary exploration tool, along with other information, the geologist goes into the field to look at the rocks. Acquiring seismic data would normally use explosives but there was some reluctance to allow several tons of explosives to be imported into northern Iraq so a vibroseis truck was used. Initially, 2-D seismic data was acquired on a grid pattern with lines 7-10km apart but that does not reveal what is between the lines. 3-D seismic data is now used with grids as small as 100 by 100m.

Drilling involves what is essentially a large crane to hold the drill string, with a rotating table that rotates the bit down the hole. The drill string is held in tension, with just sufficient pressure on the bit for it to press down on the bottom of the hole. Wells cost c$30M per hole and the success rate worldwide is 1 in 14. Some of the offshore deeper wells can cost over $100M per hole. However, one local inhabitant did it much cheaper in that he drilled a well for water down to 10m and there he struck oil.

Culture – kebabs and baggy trousers

There are 2 main cities in Kurdistan, the capital – Erbil – and Suleimaniah and the capital has 6,000 years of continuous human habitation. It is dominated by the Citadel, a World Heritage site that had people living in it until a few years ago. It is now being restored. One interesting feature is the internal columns in the central open courtyard are of “chicken-wire” anhydrite.

A basic item of sustenance for the people is the kebab and naan bread and the national Kurdish costume includes baggy trousers.

The speaker’s final anecdote related the story of the bust of a donkey wearing a tie, which represents the Donkey Party. It took Kurdish sculptor Zerak Mira seven months to create and cost £2,500. It is located on Nali Street, Sulaimaniyah, which is named for a famous Kurdish poet who wrote a well-known poem about donkeys. The statue was unveiled at a ceremony attended by a number of Kurdish artists and intellectuals and the Donkeys' Party Secretary General, Omar Kalol, said he hopes the statue will encourage people in Kurdistan to treat animals better, especially donkeys.

"The statue of the donkey has more than one meaning," said Mr Kalol. "The donkey played a very distinguished role in the Kurdish armed liberation movement ... and it was the only friend of the Kurdish fighters in the mountains of Kurdistan during the struggle for Kurdish rights," he said, referring to decades-long guerrilla war in northern Iraq and Iran.

The Donkeys' Party was founded and officially authorised in 2005. Its administrative structure is based around the life of a donkey, with its headquarters and branches named after various structures that house donkeys, and its party ranks range from "little donkey" to "donkey." The party has demanded that Kurdistan regional government provide it with financial support to open a radio station, which is to be named "Zarin," the Kurdish word for the sound a donkey makes.

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