Ever since oil was first discovered in the Gulf in 1931, production has been increased with relative ease. The region’s first well, Jebel Dukhan in Bahrain, saw its output rise from an initial 400 barrels a day (b/d) to a peak of 70,000 b/d. Last year, the GCC produced a total of 15.1 million barrels a day and further increases are being targeted to meet the global demand for oil.

Industry experience has shown that 5-15 per cent incremental reserves are common in EOR projects

Sultan al-Shidhani, Petroleum Development Oman

To maintain such production rates, the depleting oil reservoirs need to be pressurised. Newly tapped oilfields usually have sufficient natural pressure, but as they empty and pressure drops, pumps are used to draw the oil from the ground.

There are three stages in the life-cycle of a reservoir, requiring successively more extensive efforts to maintain the pressure needed to pump the oil to the surface. So-called primary recovery methods are sufficient to extract about 20 per cent of oil from a reservoir.

Once this option has been exhausted, secondary oil recovery will need to be deployed. Techniques include water flooding and immiscible gas injection. Water performs the double function of sweeping the oil towards the wells and maintaining pressure. Immiscible gas, which does not dissolve into the oil, maintains the pressure by pushing into the empty space.

Advanced oil recovery methods

Once production by secondary recovery techniques is no longer viable, more advanced methods are needed. These tertiary recovery techniques are grouped under the heading enhanced oil recovery (EOR).

Today, EOR accounts for 4 per cent of global oil production, according to UK/Dutch oil giant Shell. With many of the region’s oil fields reaching advanced stages of maturity, the use of EOR techniques is becoming more widespread in the Middle East.

Designer water will become more prominent over the coming years … and can be implemented relatively cheaply

Christiaan van der Harst, Shell

This third push delivers a final increase in production, with the amount of additional oil extracted varying according to field and technology. “Industry experience has shown that 5-15 per cent incremental reserves are common in EOR projects,” says Sultan al-Shidhani, study centre manager at Petroleum Development Oman (PDO), a Shell subsidiary. Oman is at the forefront of developing EOR capacities in the GCC, as its oil fields are significantly depleted.

“The EOR development projects are expected to contribute about 20 per cent of PDO’s total production by the turn of the decade,” says Al-Shidhani.

For all its benefits, enhanced oil recovery is a complex and costly undertaking. It can take 5-10 years before the increased production offsets the additional cost. Careful selection of the correct method is important. There are four main EOR categories: thermal; chemical: gas injection; and designer water injection.

Miscible gas will gain as more … sour fields are developed and feedstock, such as CO2 an H2S, becomes available

Mohammed Mughairy, WorleyParsons Oman

Thermal EOR is applied to oil reservoirs where the viscosity of the oil is very high, meaning the oil is heavy and does not flow easily. In the process, steam is injected into the reservoir, reducing the viscosity and allowing the oil to flow into the production wells.

Thermal EOR itself can be subdivided into categories. The first, in-situ combustion, works by setting alight part of the oil in a reservoir, so creating hot steam and gas. This is the most challenging thermal EOR method and is used only in reservoirs with high permeability.

Steam driven oil recovery

The steamflood, or steam drive, EOR method involves continuous injection of steam into the reservoir and works best when the reservoir has good permeability and the reservoir rock is not fractured. Fractures would allow the steam to pass through to the production wells instead of working its way through the reservoir rock.

Once injected, the steam forms a bank in the reservoir, which spreads away from the injector and condensates into hot water. The condensation process releases latent heat that makes the oil flow more easily. The oil is pushed ahead of the hot-water front and towards the wells.

The primary advantage of steam injection is that it does not necessitate separate injection wells. Instead, operators inject steam into the reservoir via the production wells to heat the immediate vicinity of the well shaft and reduce the viscosity of the oil. After injecting the steam, the well is temporarily sealed off, and the steam condenses, giving off additional heat.

When the well is opened again after a few days, the oil and water mix can be pumped up until the oil content becomes too low. Once a flow connection between the wells has been established, it is possible to convert a cyclic steam injection into a steamflood project.

An added advantage of steam injection is that light hydrocarbons are vaporised by the heat and move ahead of the steam bank, mixing with the heavier oil to make it flow more easily, in essence adding miscible-gas EOR properties to the process.

Oman is the pioneer of thermally assisted gas-oil gravity drainage with the launch of the first such project in 2010 at the Qarn Alam field. A complex technique, it is ideal for highly fractured reservoirs. Unlike steamflooding, steam is injected directly into the fractures, heating the reservoir rock and lowering the oil’s viscosity.

The steam does not push the oil to the producing well. Instead, the less viscorous oil sinks through the fractures to producing wells situated towards the bottom of the reservoir.

Despite the process generating huge amounts of wastewater, the Qarn Alam project was deemed a success. Engineering company Mott MacDonald, which worked on the project, estimates the output can be boosted by a factor of 25 over a period of 30 years.

The heat needed for thermal EOR is most commonly generated by burning gas, or by utilising geothermal energy from water layers located under the reservoir. One drawback with thermal EOR is that natural gas is itself a hydrocarbon, which makes the recovery method less efficient.

Solar power oil recovery method

One technology that lends itself to generating steam is concentrated solar power. Curved mirrors concentrate sun rays on tubes filled with water, converting it to steam. The first commercial solar EOR project was launched in the US in February. Industry experts expect this method to catch on in the years ahead. 

“Solar energy could be a good option in the Middle East,” says Christiaan van der Harst, Shell regional resource volume manager for Middle East and North Africa.

Chemical oil production techniques

Recently, EOR operators have focused on chemicals techniques for heavy oil recovery. During thermal EOR, heat leaks into geological layers that do not contain oil. This reduces the efficiency of the process.

Chemicals used in EOR enhance the flow of the oil, either by changing the properties of the water used to push the oil to the wells, or by altering the surface tension between oil and water molecules.

Polymer EOR relies on increasing the viscosity of the water, so improving the sweep efficiency of waterfloods.

Surfactants and alkalis can be added to reduce the surface tension between oil and water molecules, leading to lower residual oil saturations in the reservoir. 

The problems with polymer flooding relate to the cost of the chemicals, and the cost and complexity of separating the produced fluids – a mixture of oil, gas, water and chemicals. In addition, mixing large quantities of chemicals into the injection water can pose difficulties, especially on offshore platforms.

In terms of gas injection, methods range from hydrocarbon gases to carbon dioxide or nitrogen. CO2 has been injected into fields in Texas since the early 1970s, helped by the fact there was a natural source of CO2 nearby. The first regional EOR projects using CO2 are now being developed in Abu Dhabi and Saudi Arabia.

There are two major methods for using gas in EOR: miscible and immiscible gas injection. Miscible gas injection works by injecting gas at or above the minimum miscibility pressure (MMP), causing the oil to be dissolved in the gas, improving the flow. In immiscible gas EOR, gas is pumped into the field below MMP, causing the gas to not mix into the oil, taking up the empty space created by oil extraction and maintaining pressure in the reservoir.

There are difficulties associated with miscible gas EOR. A gas will dissolve in oil only under certain temperature and pressure conditions – and only if it has the right chemical composition. To ensure the economic viability of this method, injection and production wells must be precisely placed for maximum recovery, so that the oil displaced with the miscible gas can reach a well that will bring it to the surface.

When gases, some of which are toxic, are being injected at about 500 times atmospheric pressure, surface facilities have to be robust. Miscible gas requires more expensive tubings, flowlines and processing plants, or the continuous injection of special corrosion inhibitors. The method necessitates large, expensive compressors, which are expensive to operate and can have a low uptime.

Nevertheless, the method will remain an attractive option in the region.

“Miscible gas will gain as more marginal sour fields are developed and feedstock such as CO2 an H2S becomes available,” says Mohammed Mughairy, select manager at WorleyParsons in Oman.

Saline solution

Designer water is the latest EOR method to be developed and it is showing promise. “I believe that designer water will become a lot more prominent over the coming years. It is a relatively straightforward and cost-effective technique, which can be implemented in waterflooded fields without major modifications to the infrastructure,” says Van der Harst.

The method works by modifying the salinity of the injected water, which changes the ‘wettability’ of the reservoir rock, thus reducing the amount of oil left behind by conventional waterfloods. Designer water can increase recovery by more than 10 per cent, according to Shell.

EOR techniques are set to play an increasingly important role in the Middle East in the years ahead as national oil companies look to arrest production declines in mature oil fields.

The choice of technology will mostly be determined by the nature of the oil field, but cost will come into consideration. High oil prices will be needed to make some schemes viable and the price of some technologies needs to come down to make their applications feasible.

While the oil prices are currently back above $100 a barrel due to political uncertainty in the Middle East, this may not always be the case.