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    Home > Enhanced oil recovery and the role of surfactants

    Enhanced oil recovery and the role of surfactants

    Chemical Weekly 2019-11-06

    oil-refining


    Enhanced Oil Recovery (EOR) technique in which the phase behaviour inside the reservoir is manipulated by injection of surfactants and co-surfactants, creating advantageous conditions to mobilize trapped oil. But it must be remembered that surfactants are but one way in which EOR can be done.


    Drivers for EOR

    The drivers for EOR are obvious. Though oil demand is growing globally at a slower pace than in the recent past and the prognosis is for further deceleration as other energy sources play a greater role, oil demand will continue to grow in emerging economies. It is a geographical accident that many of these growth centres are poorly endowed with hydrocarbons, and need to exploit existing reserves to the fullest extent practically possible. This is the case in India where domestic oil production has stayed unchanged for several years now (at about 250-million barrels), and imports have been rising to meet growing demand. Self-sufficiency in oil is now at a dismal 15% (though the country is a net exporter of refined products).


    This is a matter of deep concern for the government, as it poses a severe drain on foreign exchange reserves, and impacts the value of Indian Rupee against major currencies. It is the stated aim of the government to reduce imports by 10% by 2022 – an ambitious task that will require a multi-pronged approach, including ramping up production using EOR techniques. Although there are a few EOR projects in operation today, much more will need to be done.


    Oil recovery stages

    Oil production typically goes through three stages. Primary recovery relies on natural flow, while secondary recovery relies on water or gas injection to coax more oil out. Tertiary treatments – also termed as EOR – are a host of technologies that rely on chemical, thermal, gas or solvents to extract oil that cannot otherwise be gotten out. All involve the injection of fluids into a reservoir to generate fluid properties or interfacial conditions that are more favourable for oil displacement. The injection of steam, for example, heats the oil and makes it more fluid, while gas injection (generally natural gas, nitrogen, or carbon dioxide) pushes additional oil to a production well. Chemical EOR generally involves flooding a reservoir with an alkali-surfactant-polymer combination, a surfactant-polymer mix, or a polymer-only injection.


    Choice of surfactants

    Surfactant flooding boosts oil production by lowering interfacial tension (IFT), so increasing oil mobility and allowing better displacement of the oil by injected water. Anionic surfactants are the most widely used surfactant class and include petroleum sulphonates, alkyl/aryl sulphates and alkyl/aryl sulphonates, amongst others. Each comes with its own advantages and disadvantages. While petroleum sulphonates give ultralow IFT and are stable at high temperatures, they are not stable at high salinity. The alkyl/aryl sulphates lack stability to high temperatures and are not tolerant to high salinity, whereas the expensive alkyl/aryl sulphonates are stable at high temperatures, but not to high salinity/hardness.


    To overcome the limitations, researchers have developed alternatives such as internal olefin sulphonates that have excellent compatibility to difficult crude oils and good high temperature stability; and alcohol alkoxy carboxylates that are stable at high temperature (unlike sulphates), have high tolerance to salinity/hardness, and are less expensive than sulphonates. More exotic surfactants have also been developed, for specific crude oil types, but their usage is limited due to the specificity and/or costs.


    Before surfactants can be deployed in the field they need to undergo extensive trials – in laboratories for proof-of-concept; and in pilot wells. Their development requires detailed reservoir data, and is best done in partnership with the oil company or the oilfield service provider who have access to this information and can validate claims in field studies.


    The decision about which surfactant to use depends on factors such as reservoir temperature, pressure, depth, salinity, and permeability. The advent of high-throughput experimentation has allowed researchers to custom-make surfactants of high purity and specificity at relatively low cost. If a surfactant is properly selected according to the environmental variables such as pressure, temperature, salinity, it can lead to more efficient enhanced recovery from an oil reservoir. On the other hand, poor selection can result in a low recovery and even be detrimental to the reservoir.


    Most surfactant EOR trials have so far taken place in the US and in China. In India, studies have been done on the Mangala field in Rajasthan, operated by Cairn India, since 2014, and the results have been encouraging.


    Significant market potential

    The potential for surfactant use in EOR seems significant at first glance. While a small field can use about 700-tonnes annually, and a mid-size field about 7,000-tonnes, large fields can take up anywhere in the range of 14,000-tonnes each year. It is therefore no surprise that some of the leading surfactant producers in the world are eyeing the opportunity and have set up dedicated business units to serve this end-use.


    But the business has several challenges – the most important of which is cost. Surfactant costs are anywhere in the range of $15-20 per incremental barrel of oil produced, and in a low oil price scenario (around $60) this is a significant cost that oil companies are hesitant to bear. There are also environmental and sustainability challenges with respect to surfactant usage and these are being addressed through the development of bio-surfactants and bio-based surfactants, amongst other approaches.


    Recent developments in surfactant EOR have greatly reduced the surfactant concentration required for effective oil recovery. While initial development in the 1970’s and 80’s used anywhere between 2-12% surfactant concentration, recent advances have lowered concentrations to 0.1-0.5%, dramatically lowering the amount required and costs. Surfactant manufacturers are also now delivering safer products than ever before, including ones derived from plant resources.


    Role for EOR

    According to the International Energy Agency, a think tank, there are currently around 375 EOR projects operating globally, producing just over 2-mbpd of oil, around 2% of global oil production. The low share stems from the fact that while the lifecycle cost of EOR can be competitive with other production opportunities, it frequently entails high up-front capital requirements and long payback periods. As a result, EOR production has historically relied on some form of support or strategic choice. Today, over 80% of global EOR production benefits from some sort of government incentive or is prioritised by national oil companies as part of their efforts to maximise the return from national resources. While costs for EOR have come down since 2014, the costs of other projects – including shale and offshore developments – have come down more quickly.


    The IEA believes that while shale has taken much of the limelight in recent years, it is much too soon to write EOR technologies out of the future of global energy. EOR using carbon dioxide injection, in particular, is expected to see faster growth, given the additional benefit it offers of being a carbon sequestering opportunity. But chemical EOR will continue to represent a niche, which will afford opportunities for surfactant producers.

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