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Saudi Arabia is pumping crude at record levels in 2015 as it looks to cling onto market share in the face of the North American shale oil revolution. Output is currently estimated at about 10.5 million barrels a day (b/d) and at the heart of the kingdom’s operations is the workhorse Ghawar oil field.

Ghawar is by far the largest known conventional oil field in the world and accounts for almost half of Saudi Arabia’s crude production capacity. Discovered in 1948, the field is located in the far northeast of the kingdom, close to the majority of its oil reserves on the Gulf coast.

The supergiant field, which is 280 kilometres long and 26km wide, has an estimated production capacity of 5 million b/d.

Sheer scale

Based on this capacity, if the Ghawar field was a country, it would be the fourth-biggest oil producer in the world. It is estimated that as much as 65 per cent of all Saudi oil production between 1948 and 2000 came from Ghawar.

The field has all the characteristics to be a major oil producer: high porosity of reservoir rock; high permeability; and high recovery potential.

Ghawar is a single field divided into six areas. From north to south these are: Fazran; Ain Dar; Shedgum; Uthmaniyah; Haradh; and Hawiyah. Although there are several reservoirs in field, the Arab-D reservoir accounts for the vast majority of reserves and production.

In the official history of the Ghawar field, published by state oil major Saudi Aramco, its discovery is described as an “educated hunch”. In 1940, young geologist Ernie Berg was spending his second field season mapping areas adjacent to the Abqaiq field, which was already being drilled.

Berg mapped a dry river bed known as Wadi Sahaba in the Haradh area, and noticed it took a sharp south turn. After further mapping a large enough area to see a trend, it became apparent the wadi was diverted by a broad, low-relief dome, the surface expression of a much larger subsurface dome.

Wildcat drilling was then suspended due to World War 2, but a shallow drilling campaign to confirm the geological structure continued. This confirmed a continuous anticline stretching northward from Haradh.

After the war, drilling resumed and Aramco focused on Ain Dar due to its proximity to the producing Abqaiq field. Ain Dar-1 was completed in 1948 and started production in 1951 at a rate of 15,600 b/d of dry oil.

Further drilling between 1949 and 1953 brought about the discoveries of other areas to the south, and the continuous reservoir was named the Ghawar field in 1952, after a Bedouin name for the area of pasturage. Production from the Ghawar field peaked at 5.7 million b/d in 1981 – the highest sustained oil production rate for any one field in the history of the industry. Output then receded during the 1980s due to oversupply in the global crude market. Production at the Ghawar field was surpassed for some years by the Samotlor field in Russia, as Saudi Arabia lowered output across its oil sector.

Highest production

However, in the mid-1990s, Aramco developed the southern Hawiyah and Haradh areas of the field, which had until then not been fully utilised. This pushed production back above 5 million b/d and it is thought to remain close to this level today. In 2010, an Aramco official said that more than 65 billion barrels had been produced from the field since 1951, and that the total reserves of the field had originally exceeded 100 billion barrels.

The Paris-based International Energy Agency (IEA) estimated in a 2008 report that the cumulative oil production from Ghawar had reached 66 billion barrels by 2007 and the remaining reserves totalled 74 billion barrels.

Estimates on Ghawar’s remaining production vary widely, but it is thought that as of the end of 2014, the field had produced more than 50 per cent of its original estimated reserves.

Depletion of the kingdom’s biggest fields – Ghawar and also Safaniya – has been a growing concern for Aramco and the global oil industry, as the fields have long been a source of consistent and reliable supply. Ghawar itself provides up to 6 per cent of the world’s total oil production.

One of the biggest focuses for Aramco will be to maintain the production from these fields and it will inevitably mean the development of enhanced oil recovery (EOR) projects.

EOR techniques are already being employed in the oil and gas industry in neighbouring Oman, where the maturity of its major fields makes tertiary recovery essential to maintain field production. Although Saudi Arabia’s major fields are still some years away from the need for EOR techniques such as steam flooding and chemicals injection, it is an eventuality for which Aramco is preparing.

Field maintenance

Several international oil field services companies assist Aramco’s maintenance department at a number of its onshore fields. The oil major has long-term arrangements with US-based Baker Hughes and Halliburton, involving activities such as 3D mapping of onshore fields as well as identifying areas where EOR could best be deployed.

Aramco is already undertaking a pilot EOR scheme at Ghawar, and is building a $100m carbon dioxide (CO2) injection plant at Uthmaniyah, the largest operational segment of the Ghawar field.

The project calls for the construction of surface facilities that will enable Aramco to inject about 40 million cubic feet a day (cf/d) of CO2 into an area of the field flooded by water. The CO2 will increase the pressure in the reservoir, pushing crude oil to the surface.

It is estimated that Saudi Arabia will not need to deploy widespread EOR techniques for at least another 20 years.

Aramco said recently that $40bn needs to be spent over the next decade to maintain the kingdom’s crude capacity at 12 million b/d and double gas output. Despite research and investment in EOR, Aramco believes that careful reservoir management, new drilling technology and state-of-the-art information gathering can significantly extend the conventional production life of many of its fields.

Along with EOR, another major initiative in Saudi Arabia’s oil and gas industry is the development of unconventional gas assets, and Ghawar could be at the centre of this.

Aramco has been looking at developing tight gas and shale gas formations at South Ghawar as well as the Empty Quarter and Jalamid in the northern desert region.

In July 2014, the oil major awarded a long-term contract to US-based Foster Wheeler to carry out front-end engineering and design work for its unconventional gas fields across the country.

The award came after Aramco said it planned to put its shale gas aspirations on the backburner and concentrate instead on tight gas formations, where the productions costs could be as little as $2-3 a million BTUs of gas.

Over the past decade, technology used to extract oil and gas from tight and shale formations has revolutionised the global hydrocarbons industry, pushing the US back to the top of the global oil producer list.

But large low-cost oil fields in the Gulf, including the largest of them all, will continue to play a vital role in meeting the world’s energy needs for many years to come.

Key fact

If the Ghawar field was a country, it would be the fourth-biggest oil producer in the world

Source: MEED