The high-temperature and high-pressure annular sealing technology is widely recognized as a world-class challenge in the industry that restricts the exploitation of heavy oil in oil fields. However, with the efforts of Chinese researchers, this technology has recently made breakthrough progress.
Binnan Oil Production Plant Test Site
The reporter learned that from November 2017 until recently, the core component independently developed by Tianding Lianchuang Sealing Technology (Beijing) Co., Ltd. (hereinafter referred to as Tianding Lianchuang) - the world's first sealing material TD350 made of 350 ℃ and 20Mpa sealing material - has successfully conducted 40 days of testing and assessment on two on-site production wells at Sinopec Shengli Oilfield Binnan Oil Production Plant.
What tests have the packer sealing cylinder gone through in 40 days? From room temperature to high temperature, after 15 days of continuous steam injection (steam injection temperature of 330-355 ℃, steam injection pressure of 12-19.7 Mpa, and steam dryness of over 70%), soaking well for natural cooling, and then reverse pressure inspection, the test results have proven that the high-temperature packer sealing barrel has maintained excellent sealing performance, greatly exceeding the performance of the original packer sealing barrel in use in the oilfield.
Industry experts believe that this marks a significant breakthrough in China's ultra-high temperature downhole sealing technology globally, which will provide strong technical support for improving oil recovery in heavy oil reservoirs. Weng Duan, a professor at the Department of Materials Science and Engineering at Tsinghua University and a director and deputy secretary-general of the China Society for Materials Research, commented: "It is expected to fill the domestic and international gap in high-temperature and high-pressure sealing materials and products in the process of heavy oil extraction, which is of great significance in reducing oil recovery costs, improving the efficiency and benefits of heavy oil extraction
Huge development potential
Heavy oil refers to crude oil with a relative density greater than 0.92 and a reservoir viscosity greater than 50 centipoises at 20 ℃, also known as heavy oil. At 50 ℃, heavy oil with a viscosity of over 100000 centipoises is considered ultra heavy oil. After being extracted, this crude oil is basically solid under ground conditions and does not deform under foot pressure.
According to public reports, the global recoverable reserves of heavy oil are currently about 400 billion tons, which is 2.7 times the recoverable reserves of conventional crude oil (150 billion tons). Of the approximately 10 trillion barrels of remaining oil resources worldwide, over 70% are heavy oil resources. Heavy oil is expected to become an important strategic replacement resource.
Relevant data show that China is the fourth largest heavy oil resource country after the United States, Canada and Venezuela, with proven and controlled reserves of about 4 billion tons, mainly distributed in Liaohe Oilfield, Shengli Oilfield, Karamay Oilfield and Henan Oilfield. Offshore heavy oil is concentrated in the Bohai region, where 62% of the proven geological reserves of crude oil are heavy oil.
However, heavy oil reservoirs belong to low-grade petroleum resources, and due to their high viscosity, difficulty in flow, and difficulty in extraction, the global annual production is currently only nearly 100 million tons. Since the end of the last century, the annual production of heavy oil in China has been stable at over ten million tons. Currently, the average recovery rate of heavy oil in the oil fields being exploited in China is less than 20%, and the development potential is enormous.
Communication between Chairman of Tianding Lianchuang and Leaders of Shengli Oilfield Petroleum Engineering Technology Research Institute
Steam leakage restricts thermal recovery efficiency
According to Song Wei, Chairman of Tianding Lianchuang, the prominent feature of heavy oil is its sensitivity to temperature. Every time the temperature increases by 8-10 ℃, its viscosity decreases by twice. Therefore, injecting high-pressure saturated steam into the oil layer for thermal recovery has a significant increase in production. After injecting high-temperature and high-pressure steam at 250-350 ℃ into the formation, the oil layer and crude oil in the near wellbore zone are heated, and the viscosity of crude oil can be significantly reduced to a few centipoises. The flow resistance of crude oil is greatly reduced, and the production of oil wells will inevitably increase significantly
For many years, steam thermal drive has become the mainstream direction for heavy oil extraction in the world. Since the 1980s in China, steam thermal recovery technology has also been the main technology for heavy oil extraction. However, the development of super heavy oil requires high steam injection pressure and temperature, and the general method of heavy oil extraction is simply not feasible, and there is almost no experience to learn from at home and abroad.
Industry experts point out that the key to heavy oil thermal recovery is the quality of steam injection. According to research by the American Society of Mechanical Engineers (ASME), the best solution for reducing viscosity of heavy oil is when the steam injection temperature reaches 350 ℃ and the dry gas saturation (steam dryness) reaches 100%.
In recent years, with the successful development of critical/supercritical boilers and other equipment, oil fields have been able to fully ensure the quality of steam injection at the wellhead when extracting heavy oil. However, due to the lack of effective sealing of the annulus, the quality of steam in the wellbore below the thermal recovery packer has been greatly affected. Leakage often occurs during steam injection during heavy oil extraction, which has become a key bottleneck restricting the thermal recovery of heavy oil in oil fields Song Wei told reporters.
The reporter learned that for many years, many domestic and foreign companies have participated in the research of large annular sealing technology in the field of heavy oil thermal recovery. The core is to solve the material problem, that is, to find a sealing material that is resistant to high temperature, high pressure, and has high elasticity for a long time, but the results are not satisfactory. The perfluoroether material developed by DuPont in the United States has become a leader in this field due to its high temperature resistance of 315 ℃, but it still cannot meet the actual requirements of high temperature and high pressure conditions required for heavy oil extraction. The removable packer designed specifically for ultra-high temperature and high pressure wells, launched by Baker Hughes in the United States in early 2016, can withstand temperatures of only 204 ℃.
Successful initial trial of the world's first sealing technology
To overcome this challenge, since 2015, the R&D team of Tianding Lianchuang Company has collaborated with Tsinghua University School of Mechanical Engineering, Shengli Oilfield Petroleum Engineering Research Institute, and other units. With the assistance of Yunhui Capital, after three years of scientific research and research, we have successfully developed the world's first highly elastic composite material - TD350, which can withstand 350 ℃ and 20Mpa supersaturated water vapor pressure. We have also obtained 7 invention patent authorizations and 25 utility model patent authorizations.
It is reported that TD350 is a composite polymer material with high temperature, high pressure, oil, and water resistance characteristics. Especially under high temperature conditions, it can still maintain elasticity similar to rubber, and can seal the oil sleeve annulus for a long time under pressure of 350 ℃ and 20Mpa. The maximum withstand temperature can reach 361 ℃, and the maximum withstand pressure can reach 25Mpa.
Tianding Lianchuang Company collaborated with Shengli Oilfield Petroleum Engineering Technology Research Institute to conduct 11 ground tests and assessments using its self-developed TD350 sealing cylinder at Shengli Oilfield Petroleum Engineering Institute for three years, achieving large annular sealing of heavy oil thermal recovery simulation equipment, providing a solid foundation for the on-site promotion of underground sealing for heavy oil extraction.
Starting from November 2017, Binnan Oil Production Plant of Shengli Oilfield took the lead in making bold attempts, selecting two on-site production wells, equipped with dozens of professional technical personnel divided into three teams, and conducting experiments with experts from the Petroleum Engineering Institute day and night to verify the sealing performance of the new material under different actual working conditions.
The on-site test report shows that the entire experimental temperature ranges from room temperature to high temperature, and then to high temperature after soaking in the well. The steam injection quality has significantly improved, and the sealing cylinder of the packer has remained leak free for 30 consecutive days. Due to the zero annular pressure, the well can be lifted without flushing or pressure operation, saving a lot of water resources and greatly improving construction safety.
The TD350 high-temperature sealing cylinder has achieved sealing under both ultra-high temperature and room temperature alternating working conditions for the first time, breaking through the bottleneck of the oil field's long-term inability to effectively implement heavy oil thermal recovery technology due to sealing problems, laying the foundation for the next step of improving the high-temperature heavy oil thermal recovery process and achieving efficient oil recovery. "Wang Lushan, Vice President of Shengli Oilfield Petroleum Engineering Technology Research Institute, commented.
It is understood that there are currently over 5000 thermal recovery wells for heavy oil in Shengli Oilfield. Due to inadequate sealing at the bottom of the wells, steam loss is high, resulting in low unit steam oil production and high oil production costs. In addition, the current low oil price has resulted in over half of the wells being suspended. If this technology is promoted, a large number of suspended wells will have the potential to restore economic mining value.
