The production of crude oil can include up to three different stages and they are primary, secondary and tertiary. The tertiary method is also known as the Enhanced oil recovery (EOR). Different methods of enhanced oil recovery (EOR) are designed to recover oil left in the reservoir after both primary and secondary recovery methods have been implemented as per their economic limits.
It is also defined as the process where some external energy, sources were introduced to enhance the production of oil from the oil field which is left out after the exploitation of the primary and secondary methods economically. These external sources can be gases, chemicals or even steam through injection systems and the processes involved are gas injection, chemical injection, thermal injection and microbial injection.
The purpose of Enhanced oil recovery (EOR) is to increase oil production, primarily through an increase in temperature, pressure, or an enhancement of the oil's ability to flow through the reservoir. The challenge of EOR is that the remaining oil is located in regions of the reservoir that are difficult to access, and the oil is held in the pores by capillary pressure. During primary recovery, the natural pressure of the reservoir drives oil into the wellbore, and artificial lift techniques (such as pumps) bring the oil to the surface. Only about 10 percent of a reservoir's original oil in place (OOIP) is typically produced during primary recovery. Secondary recovery methods applied to the field's productive life generally by injecting water or gas to displace oil and drive it to a production wellbore, resulting in the recovery of 20 to 40 percent of the original oil in place. Once the reservoir is half empty it is very expensive to extract and not profitable for the companies to produce oil. At this point of time the companies may abandon the reservoir which is half full.
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In the past twenty years, many research organizations and oil companies have conducted extensive theoretical and laboratory EOR (enhanced oil recovery) researches to include validating pilot and field trials relevant to much needed domestic commercial application, while western countries had terminated such endeavors almost completely due to low oil prices. In recent years, oil demand has increased and now these operations have become more desirable.
On an average, two-thirds of the original oil discovered in the U.S remains in the ground after conventional recovery operations. This oil represents about 200 billion barrels. Due to these factors most of the major oil companies are interested in techniques to extract this oil. And that's where enhanced oil recovery comes in.
2. CURRENT TECHNOLOGIES
2.1 Gas injection:
This is the most common and effective method to improve the oil production from the field, which is noted as the most effective one for production of oil for different oil fields. This was first tried in Texas in the 1970's.
This technique has been aimed to improve the pressure of reservoir, maintaining low operating costs with the increase in production of oil. The initial expenses for the basic equipment and components of gas are very high, due to which this technique has not seen widespread application. On the other hand the operating costs for this system are very low, these upfront investment costs were the barriers for the smaller independent oil companies to implement this gas injection EOR; however the investment return made possible for even independent smaller companies with the record oil prices.
This method associates with nitrogen, natural gas and mainly carbon dioxide with the injection process into the field. The gas (carbon dioxide) spreads and pushes the extra oil to the place it can be extracted out easily. Gradually carbon dioxide dissolves in the oil which helps to improve the oil flow rate by reducing the viscosity of the oil. In these applications, more than half and up to two thirds of the injected carbon dioxide returns with the oil produced and is usually re-injected into the reservoir to minimize the operating costs and the remaining gas is trapped in the oil reservoir in various means. The utilization of the carbon dioxide for the gas injection EOR resulted in the prevention of plenty harmful gases from entering the natural air.
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2.2 Thermal recovery:
Steam injection technique has been commercially used since 1960's in California fields. As heat is required to enhance the oil flow rate, steam is sent into the reservoir through the injection system to reduce its viscosity or thin the heavy viscous oil, and improve its ability to flow through the reservoir which can be produced at the producing bore well. Dolberry oil assessed that steam associate for 52percent of present techniques used for Enhanced oil recovery, when compared to the carbon dioxide at 31percent and nitrogen 17percent.
The technology called "Steam Slugging" contains a mixture of steam and carbon dioxide that appeared to double the production of oil within a less period of time which produced good results, making extra ten barrels per day with added advantages like water disposal and cleaning of the bore well. In this process each well is injected for about to 12 hours and then the well is left soaked for 12 to 15 hours in which the gas (carbon dioxide) compounds with the oil while and at the same time nitrogen gas helps in pulling the oil to the place where pressure is low. The extra heat produced by the extra pressure helps to loosen the oil in the "pay zone". Eventually the oil produced in this process is extracted in the pay zone surroundings.
2.3 Chemical recovery:
There are two types of chemicals that can be sent to the field to enhance the oil production, they are polymers and surfactants. The long chain molecules called polymers which thickens the water used to sweep oil through the reservoir into producing wells. Surfactants are detergent like chemicals that helps to obstruct droplets of oil from moving in the reservoir by lowering the interfacial tension. Implementation of this technique is generally obstructed by the cost factor in chemicals. In this process, the chemicals are sent into the different wells through injection system which helps in extracting the oil from the wells which are nearby.
2.4 Microbial enhanced oil recovery:
This method is not used very often because of the high prices and the developments in this technique are very recent. This method refers to the use of micro organisms to recover extra oil from live oil fields, improving the oil production in the reserve. In this method micro organisms are introduced into the reserve to produce harmless by-products, such as gases or slippery natural substances which help to push oil out of the well.
The use of micro organisms and their metabolic products to improve the oil production involves the injection of the selected microorganisms into the oil field and the subsequent stimulation and transportation of their in-situ growth products in order that their presence will help in further reduction of residual oil left in the oil field after secondary recovery is exhausted.
3. GLOBAL TRENDS
Most of the oil companies aimed to decrease the exploration costs of the existing oil fields and increase their production and recoverable reserves. Many integration methods and co-operations have been established among the companies especially in the Enhanced oil recovery (EOR) area, aiming not only to increase their reserves, but also to extend the useful reservoir lifetime.
In a study USA case is analyzed from 1986 to the beginning of 1998, since this is the country that has applied most of these techniques. Recently formed strategic associations in this period are also analyzed. A bibliometric analysis has been performed which shows R&D tendencies of EOR method in universities, oil companies and institutions. The study shows that the EOR methods applied worldwide enhanced the production of oil and gas reserves, supported on technologies such as multilateral and horizontal wells, 3D-4D seismic techniques, simulators, nuclear magnetic resonance, materials (polymers, foams, nutrients etc) and equipment (coiled tubing) etc have been proved to be very effective.
Current trends in United States enhanced oil recovery (EOR) projects are analyzed for the period from 1980-1987. The analysis is based on the U.S. Department of Energy (DOE) EOR project data base which contains information on more than 1200 projects. The National Institute for Petroleum and Energy Research (NIPER) keeps this data base up to date and analyze trends in the data under the provisions of a cooperative agreement with the DOE. The noticeable trend is the steady decline in the number of projects starting per year since 1981, which corresponds the steady decline in the oil prices during that period. On the other hand, polymer and immiscible carbon dioxide projects which peaked in number of starts in 1983. The trend seems to be clearly moving towards the lower risk projects within the screening criteria. True field experimentation with assumptions of higher risks has been decreasing.
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This trend has seen a change in 1986 as the planned projects appeared to have reversed the decline in project starts, however during this time sharp drop in oil prices led companies to abandon some projects and postpone others. Only the large capital investments already made has seen new starts. Despite the temporary setback, long-term EOR prospects remain good, largely because EOR remains one of the cheapest sources of new oil reserves and could play a key role in maintaining steady oil production for the future.
The global market for EOR, estimated at nearly $62.5 billion (for barrels of crude oil) for 2009, has shown exciting growth since 2005 totaling $3.1 billion. Hazy regulations, technological challenges and costly implementation, kept oil companies from using EOR. However, EOR is becoming more attractive and feasible due to the government interest and investment, new technologies and availability of resources (such as CO2). It is expected that the EOR takes a good place in the world market.
A number of factors fueled government's interest in EOR, the first one being the increase in oil production besides increase in the oil revenue. Countries that are able to increase their oil production are often lowering their increase in demand for oil import. It is estimated that 13 billion tons of carbon dioxide worldwide could be captured through the use of CO2-EOR, which helps to reduce industrial emissions and in turn reduce green house gases. In Texas, where EOR now accounts for 20% of its oil production, it is estimated the benefits of EOR production will result in additional revenue of $200 billion and will create 1.5 million jobs.
This is the only technology that combines the benefits of two traditional enhanced oil recovery methods to retrieve more oil which would have been waste remaining in the ground of no use. This method increased revenue and profits for the oil drillers who are able to extract 10percent more of the previously unrecoverable oil from an oil field.
The U.S Department of energy estimates that there are approximately 240 billion barrels of oil that can be recovered with next generation enhanced oil recovery methods. Oil drillers are not the only group who would benefit from more effective oil recovery methods. It is expected that the governments and local treasuries would make $280 billion in profit in the form of taxes and royalties from the produced oil.
In the process of gas injection most of the carbon dioxide is injected into ground which is produced by human activities such as oil refining or fertilizer manufacturing not only enhances the oil production, but also helps in the reduction of the green house gases which affects the atmosphere.
Although the advantages of the Enhanced oil recovery (EOR) process has not been recognized until the recent years, the process has seen a rapid growth in the recent years which helped many companies, governments in enhancing their oil production.
This process not only helps in producing more oil but also stood as an environmental friendly system which helps in eradicating the green house gases. These statements strongly support the Enhanced oil recovery (EOR) to be the future technique to recover more oil with low operating costs and environment friendly method.