Shale Plays of the Middle East
The shale revolution in the USA has been phenomenal. Thanks to horizontal drilling and hydraulic fracturing technologies, shale has doubled US oil production from nearly 5 MMbopd in 2008 to 11 MMbopd in 2018. In the same decade, US annual natural gas production increased from 21.1 Tcf to 32.7 Tcf. The shale revolution has been limited so far to a few basins and plays in the US: the Permian, Barnet and Eagle Ford in Texas, the Bakken in North Dakota, and the Marcellus in the Appalachian east. However, all conventional petroleum basins around the world also contain large volumes of organic-rich shale formations. Since the Middle East has the largest concentration of giant oil and gas fields, its prolific source rock formations should offer enormous opportunities for stimulation and production. The Palaeozoic to Cenozoic sediments constitute a 12 km-thick volume of sediments on the Arabian platform and Zagros foreland basin, and almost every stratigraphic period contains at least one shale formation over a hundred metres thick, either distributed regionally or concentrated in specific countries. These shale plays remain unexploited.
The term ‘shale’ in geology specifically refers to a laminated (fissile), indurated, fine-grained sedimentary rock in which clay-sized minerals predominate. Shale is essentially mudstone but with a fissile texture. However, in the current petroleum industry ‘shale’ has been used in a too broad sense, including any fine-grained, low-permeability sedimentary rock – mudstone, shale, siltstone, marl and chalk – that requires hydraulic fracturing to produce oil and gas. Here I reluctantly adopt this current industry use but exclude the purely limestone and dolomite formations which occur so abundantly in the Middle East stratigraphy. What follows is a general outline of the Middle East shale horizons; local variations in depositional environment, unconformity, thermal maturity, and organic richness are plentiful. Overall, the formations become deeper from the western Arabian platform toward the Zagros foreland basin.
Geologic Framework of the Middle East
The Middle East has prolific oil fields because it has inherited a unique set of geological conditions that favour the generation and accumulation of large oil reserves on the Afro-Arabian platform of Gondwana (see GEO ExPro, Vol. 7, No. 1: Why So Much Oil in the Middle East). During Palaeozoic-Mesozoic times, for nearly 500 million years, the Middle East was a vast, stable continental shelf facing the east-west running Tethys Ocean. The continental shelf was 2,000–3,000 km wide and at least 6,000 km long. During Cenozoic times, foreland basins formed by the collision of the Arabian-Asian plates and uplift of the Zagros-Taurus mountains and filled with 3,000m thick sediments, were superimposed onto the shelf sediments. In this manner, the shelf sediments, including organic-rich shales, were deeply buried and preserved.
Regionally distributed shale formations in the Middle East cluster in three stratigraphic groups: Ordovician–Silurian, Jurassic–Cretaceous, and Paleocene–Eocene. Early Palaeozoic periods were characterised by rapid radiation of life forms as well as a global rise in sea levels. During warm Jurassic–Cretaceous times, the Tethys Ocean was at its highest level and located in plankton-rich equatorial latitudes, which favoured deposition of organicrich, anoxic deepwater shale sediments. A third group of shale formations belonging to the Paleocene–Eocene periods were deposited in foreland basins atop the shelf sediments.
Infra-Cambrian and Deep Palaeozoic Shales in the Middle East
The Huqf Group of Oman contains the best known Infra-Cambrian source rocks to have generated oil, stored not only in Permo-Carboniferous reservoirs but also within the Huqf Group itself (‘Q’ reservoir as encountered in Runib Field in southern Oman). The group consists of alternating carbonates, siliciclastics, and evaporates deposited in a deep, restricted and anoxic basin. The calcareous mudstone of the Shuram Formation (up to 600m thick) and the dolomite and shale sediments of the Ara Formation (up to 1,700m) are the major organic-rich source rocks. In many fields, the Ara Shale (with kerogen type II possibly of cyanobacterial origin) is still within the oil and gas windows; it is capped by Ara Salt, equivalent of the regional Hormuz Salt (beneath the Cambrian sediments) in the Persian Gulf.
Lower Palaeozoic formations in the Middle East greatly vary in thermal maturity depending on their burial depth; in the Zagros foreland basin, for example, they have been often metamorphosed to micaceous quartzite level. Upper Palaeozoic source rock formations are not continuous across the Middle East due to sea-level fall and tectonic disturbance toward the end of the Palaeozoic.
Notable Cambrian shale formations deposited in fluvial to marginal marine environments in the Middle East include the Pre-Saq Formation (Lower Cambrian) in Saudi Arabia, Lower Haima (Miqrat) in southern Oman which has charged oil and gas in the Upper Haima clastic sediments, and the 1,000m-thick Middle Cambrian Sosnik Shale in southeastern Turkey.
Ordovician shale formations were deposited in continental to marginal marine environments and have different stratigraphic names: Hiswa (Jordan), Bedinan (Turkey), Sawab (Syria), Hanadir (Saudi Arabia), and Safiq Shale in Oman (which extends into the Lower Silurian).
The Silurian is marked by a major petroleum source rock that was widely deposited in an open marine environment in the Middle East and North Africa. This marine ‘hot shale’ (as characterised by high gamma logs) is also named differently in various countries: Tanezzuft (Libya), Kohla (Egypt), Qusaiba (Saudi Arabia), Mudawwara (Jordan), Tanf (Syria), Akkas (western Iraq desert), and so forth. The Silurian shale has been well studied as it has generated gas as well as light crude, stored in Mid-Upper Palaeozoic reservoirs. The Qusaiba hot shale in Saudi Arabia ranges in thickness from 250m in outcrop to over 1,000m in the basin and has an average TOC of 4–5% (Cole et al., 1994).
A few organic-rich Devonian shales exist locally, such as Koprulu in southeast Turkey, Jauf in Saudi Arabia, and Misfar in Oman. The Permian-age Khuf Formation (and its equivalents), consisting of limestone, dolomite, shale and anhydrite, was widely deposited under tidal and shallow marine conditions in the Middle East. The formation often acts both as a reservoir and source rock.
Mesozoic Shales: Jurassic and Cretaceous Source Rocks of the Middle East
Triassic source-rock formations, notably Kurra Chine in Syria and Iraq and Jilh in Saudi Arabia and UAE, consist of dolomite, shale and anhydrite, and were deposited in a shallow marine environment.
The richest and thickest petroleum source rocks in the Middle East belong to the Jurassic and Cretaceous periods. In some fields, multiple Jurassic and Cretaceous deepwater shale horizons, highly organic with kerogen type II, are present. These Mesozoic formations may be the most feasible shale plays to develop, although they are predominantly marlstone and bituminous limestone, and their calcareous nature may respond differently to fracking than siliceous shales such as Barnet. The Jurassic sediments are capped by evaporate rocks.
Chemical studies of the Jurassic Sargelu Formation in northern Iraq by Roger Abdula (2010) show that Sargelu has a rather uniform lithology with variable thickness from 25 to 485m and that its richest horizon has TOC values of 11%. The same formation in Iran has given TOC values of 3–4% (Bordenave and Bruwood, 1990). Above the uppermost Jurassic evaporate deposits, several source rock formations of Cretaceous age are regionally present and are known by different stratigraphic names. These source rocks, mainly black shale and argillaceous limestone, have generated light crude stored in multiple Cretaceous carbonate reservoirs. The stratigraphic thickness and organic richness of these Cretaceous sources are remarkable: the Kazhdumi black shale in the Zagros Basin of Iran, for instance, reaches up to 450m and has TOC values of 3–12%.
Paleogene Foreland Shale
With the subduction of the Tethys Ocean beneath the Asian continent, the tectonic regime on the Arabian platform changed to the continental collision, uplift and foreland sedimentation that has characterised Middle East geology for the past 50 million years. The shallow marine shale formations of Paleocene age in the foreland basins have proved to be effective petroleum source rocks. These are known by different stratigraphic names: Taqiya (Jordan), Aaliji (Syria and norther Iraq), Pabdeh (Iran), and Um Er Radhuma (southern Iraq, UAE and Qatar). The Sinan Formation of Maastrichtian-Paleocene age in southeast Turkey consists of dark-grey limestone and marl and has proved to be a source/reservoir rock in both the Selmo and Selmo West fields.
Some Eocene shale horizons are also potential source rocks, such as the Jaddala Formation in Syria and northern Iraq, Andhur in Oman, and Jeza in Yemen. In many parts of the Middle East the Paleocene–Eocene rocks are capped by evaporates, thus preserving these petroleum systems.
Shale Gas in the Middle East
For Iran and Qatar, respectively the second and third largest repositories of natural gas in the world (Russia being number one), shale gas may not be of a high priority. However, for some Middle Eastern countries, especially Saudi Arabia and UAE, which are in dire need of natural gas for electric power and residential use, the prospect of shale gas produced from their own fields is enormously attractive. Ahmad Kenawi, Halliburton’s vice-president for the Middle East and North Africa, recently reported that the national oil companies of Saudi Arabia, Oman, Bahrain and Kuwait are seriously looking into how they can develop their shale gas resources. Saudi Arabia started its first commercial production of shale gas from the North Arabia field in May 2018 and supplied 55 Mcfgpd to a power plant in Wa’adi Al Shamal in the north of the country.
Shale gas reserves in Saudi Arabia are estimated to be more than 600 Tcf – twice the amount of conventional natural gas in the country. Saudi Aramco has focused on three specific areas for development of shale gas. These are the Ghawar field, which is the world’s largest oil field; the Jafurah Basin, located close to Ghawar and expected to be the Eagle Ford of Saudi Arabia; and the vast Rub al-Kahli Basin in the south of the country.
Challenges to Development of Unconventional Resources in the Middle East
Despite the widespread occurrence of shale formations in the Middle East, there are several important obstacles to the development of these plays. Currently, production from conventional carbonate reservoirs is more economic for Middle Eastern petroleum companies. Decades of drilling and production have provided ample information about these reservoirs, while production from the shale formations will require new data on reservoirs and oil quality in addition to deep drilling and the necessary infrastructure and strategies, all of which will require major financial investment. As long as oil prices remain at the current level, the Middle Eastern companies will have little commercial incentive to develop their shale plays; indeed, production from these new plays may even reduce oil prices further.
Moreover, developing shale plays requires huge amounts of fresh water for hydraulic fracturing (several millions gallons of water per horizontal well as in the US), but there is an acute shortage of fresh water in the Middle East, with low precipitation and a largely arid climate. This climatic constraint will persist on a long-term basis. Dry (gas) fracking, when developed fully, can provide a workable solution. Fluid-induced seismicity associated with shale stimulation is another major obstacle in those parts of the Middle East criss-crossed by active faults of various sizes.
While the shale geology is highly promising in the Middle East, the region faces economic and technological challenges to develop these resources. As in the US, the shale revolution in the Middle East will perhaps be triggered by shale gas in certain fields.
- Cole et al., Saudi Arabia Journal of Technology, 1994.
- Roger Abdula (MS thesis, Colorado School of Mines, 2010).
- (Bordenave and Bruwood, Advances in Organic Geochemistry, 1990).
- (Carla Sertin, Arabian Business, 15 February 2019).
Further Reading on Oil and Gas Exploration in the Middle East
Developments in Middle East Oil and Gas Exploration
Peter Elliott; NVentures
It was a successful 2018 in Middle East oil and gas exploration for the small Gulf states and UAE.
This article appeared in Vol. 15, No. 6 - 2019
The Best Geological Site in the Middle East
Join us as we take a look at just one of Oman's many geological wonders: Wadi Nakhr, in the Al Hajar Mountains.
This article appeared in Vol. 15, No. 1 - 2018
How Much Oil in the Middle East?
Rasoul Sorkhabi, Ph.D.
“No such galaxy of fields of the first magnitude over such a wide area has been developed in the history of the oil industry.” - Everette Lee DeGolyer, Oil in the Near East, 10 May 1940, Texas.
This article appeared in Vol. 11, No. 1 - 2014
Why So Much Oil in the Middle East?
Rasoul Sorkhabi, Ph.D.
In terms of oil reserves, the Middle East is second to none. This “oil miracle” of the world has been shaped by a set of favorable factors, some global and others local, inscribed in the geologic history of the region.
This article appeared in Vol. 7, No. 1 - 2010