Abstract: The way of oilfield development decides the rate of oil and gas recovery. This study intends to introduce the application of new type polymer in tertiary oil recovery technology, through applying new type polymer in order to increase substantially the salt resistance properties of tertiary oil recovery, the recovery rate of the third and fourth EOR is about to increase substantially. Whereas the predominant oilfields in China have very high moisture ratio, and the dependence on foreign oil is climbing high along the international cooperation pace, stable and enhanced oil output is prerequisite as according to the specific role of petroleum to the national safety strategies. Adopting polymer in tertiary oil recovery is one of the main measures to decrease oilfield water content and continuously increase crude oil recovery rate. The polymer polyacrylamide, due to its properties as of poor salt resistance, instability and environmental pollution, has become the important technical barrier yet to resolve. Therefore, R+D on new type polymer are crucial to making technology progress on oilfield development.

1. New type polymer tertiary oil recovery technology

In petroleum industry, primary oil recovery means the use of the energy of an oil reservoir; secondary oil recovery means to input energy flow to the reservoir by injecting water and gas, and tertiary oil recovery means to improve the performance among oil, gas, water and rock by applying chemicals. Among the three measures, tertiary oil recovery is the most wildly applied and also with highest recovery rate, in China it is also the main measure to decrease oilfield water content and to enhance Oil Recovery (EOR). The important role of promoting new technologies of tertiary oil recovery becomes increasingly outstanding to China petroleum industry. Under the guiding idea of improving polymer molecular salt resistance properties via comb polymer molecular structure, R+D on new type salt-resistant polymer got good application results in oilfields as of Daqing, Shengli, Dagang, Karamay, Northeast and Bohai. Comparing with normal polyacrylamide, new type salt-resistant polymer can increase more than 2% recovery rate under condition of well environment protection plus 10% cost reduction, thus recoverable reserves value of crude oil has been increased substantially.

2. Development and scale of tertiary oil recovery technology

2.1 Development of tertiary oil recovery technology

Tertiary oil recovery technology has gone through three big progresses. The first one was in 1950s and 1960s, when steam flooding was applied in heavy oil exploitation worldwide. The second one was in 1980s, when chemical flooding developed a lot yet steam flooding still dominated, for the reason that chemical flooding was restricted by high cost of chemicals together with other uncertain rates. The third progress was in 1990s, when miscible gas injection flooding technology was applied widely, thanks to its wide application scope, low cost, less green house effect and better environment friendliness.

So far there are many pilot test areas of tertiary oil recovery technology application in some oilfield in China, and the test results show that it can increase substantially fat oil recovery. Based upon the polymer recovery technology, it has formed a corresponding processing technology and industrial scale. Spacing test results show, microbial enhanced oil recovery technology, as one of polymer oil recovery technologies, has the potential to increase oil recovery rate furthermore.

2.2 Application of Polymer Flooding in Major Domestic Oil Field

Tertiary oil recovery technology has been wildly used in USA, Canada, Venezuela, Indonesia, etc, particularly in USA, government pay high attention to tertiary oil recovery technology, through various polices and incentive measures, by clearing off investment barriers for enterprises, encouraging its application and less carbon emission, mitigate risks in heavy oil production related technology transfer. 

Tertiary oil recovery technology tests have been wildly conducted in oilfield Daqing, Shengli and Dagang of China, among them in six blocks of Daqing Oilfield the experimental area of polymer EOR technology reaches 50 square kilometers, with geological reserves more than 1.2xlOston and tertiary oil recovery annual output close to 500x104 ton, 8% of the oilfield total output, at average it increases 120 ton oil output per ton of polymer application, a very good result. In 8 blocks of Shengli Oilfield, total application area of tertiary oil recovery technology projects reaches 30.7 square kilometers, with geological reserves more than 8149x104ton and anticipated increase of recoverable reserves 712.5x104 ton, more than 8% increase of EOR rate. In Dagang Oilfield, so far 11.8 square kilometers application area, with geological reserves 3362x104 ton, anticipated increase of EOR rate around 8% and recoverable reserves 269x104 ton.

3. Methods of tertiary oil recovery technology

3.1 Conduct advanced research

In worldwide scope polymer oil recovery technology has been developed very fast, USA ranks no.1 in tertiary oil recovery application and output, while in Daqing Oilfield of China, with advanced petroleum technology and management, based on tertiary oil recovery technology support as from development of water recovery technology, polymer recovery technology or compound recovery technology, foaming compound recovery technology and so on, it has been turned out a stable output for more than 20 years. Aiming at international advanced technical research subjects, following the mode combining of indoor research, pilot test, industrial test, and application, in order to construct a solid foundation for the future development of the petroleum industry, thereafter more advanced researches are going to be conducted, especially on Alkaline-water oil recovery, alkaline-polymer oil recovery, compound oil recovery, microbial oil recovery, CO oil recovery, etc.

3.2 Main research directions

3.2.1 Research on three elements compounds oil recovery

So far this direction focus on research of low cost, good efficient surfactant agent, and on research of formulation based upon surfactant agent compound in order to decrease the active ingredient cost of three elements compounds. The research of chromatographic separation effect of three elements compounds has induced high attention of CNPC and Sinopec, and their corresponding oilfields have developed effective ways to decrease chromatographic separation, so this research will provide bases for further choices among big well formulas.

3.2.2 Research on foaming compound oil recovery

It is an alternative advanced EOR technology, through foaming compound penetrating into narrow channels, which three elements compound are not capable to reach, recovering column alike residual oil. This technology combines the advantages of foaming EOR and heat EOR technologies, as well as CO₂ and N₂ EOR technologies, and it can substantially elevate the oil recovery effect. Plenty of experiment results show that foaming compound oil recovery injection method obtain good EOR effect and higher crude oil recovery rate. After injection, the oil recovery rate increase along with that of temperature, and under higher temperature condition, the oil recovery rate enhanced by foaming compound technology reaches 16%.

3.2.3 Research on microbial oil recovery

It has been developed rapidly in recent decade, and all main oilfields of china have carried on related indoor research and production application, especially, scale application of measures to maintain and increase production has been adopted in many oilfields with microbial anti-wax and single well swallowing technologies. So far there are more than 20 site test blocks in China, with some technique problems yet to resolve, principally on following research topics ①Screening ofmicrobial species in the natural environment; ②At reservoirtemperature, prompting microbial growth and reproduction ③Microbial oil recovery, reducing pressure on oil wells.

3.2.4 Research on Gel formation system deep fluid steering technology

Weak gel formation system deep fluid steering technology is a new technology started from 90’ of 20^th century in aim for improving water oil recovery effects and improving crude oil recovery rate. After injection of gel system, gel formatted and blocked big water channels, thus steered injected water towards low permeability layer and increased the contacting surface of injected water, in the end improved the water oil recovery effect and oil recovery rate. At present this technology has been applied in main blocks of Daqing Oilfield, turning out with very obvious recovery effect result.

4. Conclusion

Tertiary oil recovery technology is a new advanced technology for enhancing crude oil recovery rate by utilizing physical, chemical and microbial techniques, the related output with application of this technology is keep increasing its percentages against the petroleum total output, and a series of related technologies have been formed, among them polymer oil recovery has induced scaled industrial application, including in predominant oilfields of China, and in there the prior tests results will provide reliable technical support measures for further stable oil production. Next proposed step is research on three elements compound oil recovery, especially CO mixed phase oil recovery, foaming and microbial oil recovery, to provide technical support for recovery of difficult recoverable reserves such as heavy and super heavy oil. 

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