High temperature and high pressure resistant annular sealing technology is recognized as a world - class problem that restricts heavy oil production. However, thanks to the efforts of Chinese researchers, a breakthrough has been made.

Binnan oil production plant test site

The reporter learned that from November 2017 to a few days ago, the core component independently developed by Tianding Lianchuang Sealing Technology (Beijing) Co., Ltd. (hereinafter referred to as Tianding Lianchuang) -- the world's first packer sealing cylinder made of TD350, a sealing material resistant to 350℃ and 20MPa, Forty days of test and assessment have been successfully carried out in two on-site production Wells in Binnan Oil Production Plant of Shengli Oilfield, SINOPEC.

What tests have been performed on the packer casing during the 40 days? From room temperature to high temperature, after 15 days of continuous high temperature steam injection (steam injection temperature 330-355℃, steam injection pressure 12-19.7MPa, steam dryness above 70%), natural cooling in the steaming well, and then reverse pressure seal inspection, the test results show that the high temperature packer seal cylinder has maintained excellent sealing performance. It greatly exceeds the performance of packers used in the oil field.

Industry experts believe that this marks the first major breakthrough in China's ultra-high temperature downhole sealing and control technology in the world, and will provide a strong technical support for enhanced oil recovery in heavy oil reservoirs. Weng Duan, professor of Materials Science and Engineering Department of Tsinghua University, director and deputy secretary general of China Materials Research Society, said: "It is expected to fill the gap of high temperature and high pressure sealing materials and products in the process of heavy oil exploitation at home and abroad, which is of great significance to reduce the cost of oil recovery and improve the efficiency and benefit of heavy oil exploitation."

Huge development potential

Heavy oil is the crude oil whose relative density is greater than 0.92 and oil viscosity is greater than 50 centipoises at 20℃, also known as heavy oil. At 50℃, the viscosity of more than 100 thousand centipoises of heavy oil is super heavy oil, this crude oil is basically solid in the ground conditions, the foot step deformation.

According to public reports, the world's recoverable heavy oil reserves are about 400 billion tons, 2.7 times that of conventional crude oil (150 billion tons). Of the world's estimated 10 trillion barrels of remaining oil resources, more than 70 percent 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. Heavy oil is mainly distributed in Bohai Sea area, and 62% of the proven oil reserves in this area are heavy oil.

But heavy oil reservoirs are low grade petroleum resources, because of their high viscosity, difficult to flow, difficult to exploit, the global annual production is only about 100 million tons. Since the end of last century, the annual production of heavy oil in China has been stable at more than 10 million tons. At present, the average recovery rate of heavy oil in the oil fields being exploited in China is less than 20%, and the development potential is huge.

The chairman of Tianding joint venture and the leaders of Shengli Oilfield Petroleum Engineering Technology Research Institute

Steam leakage restricts thermal recovery efficiency

According to Song Wei, chairman of Tiandin, the prominent feature of heavy oil is that it is very sensitive to temperature. Every 8-10℃ increase in temperature will reduce the viscosity by 1 times. Therefore, the high pressure saturated steam is injected into the reservoir for thermal recovery, and the production increase effect is very significant. "When high temperature and high pressure steam of 250-350℃ is injected into the formation, the oil layer and crude oil in the near wellbore zone are heated, the viscosity of crude oil can be significantly reduced to a few centipoises, the flow resistance of crude oil is greatly reduced, and the oil well production is bound to increase significantly."

For many years, steam thermal flooding has become the mainstream direction of heavy oil production in the world. In China, steam thermal recovery technology has been the main technology for heavy oil recovery since 1980s. However, the development of ultra-heavy oil requires high steam injection pressure and high temperature, so the general heavy oil exploitation method is not feasible, and there is almost no reference experience at home and abroad.

Industry experts point out that the key to thermal recovery of heavy oil is the quality of steam injection. According to the research of American Society of Mechanical Engineers (ASME), when the steam injection temperature reaches 350℃ and the dry gas saturation (steam dryness) reaches 100%, it is the best solution for heavy oil viscosity reduction.

"In recent years, with the successful development of critical/supercritical boilers and other equipment, the quality of steam injection at the wellhead can be fully guaranteed in the production of heavy oil. However, the problem of annular sealing has not been well solved, which has greatly affected the quality of steam in the wellbore below the thermal recovery packer in the well, and leakage often occurs during steam injection for heavy oil production in the oilfield, which has become the key bottleneck restricting the thermal recovery of heavy oil in the oilfield." Song Wei told reporters.

The reporter learned that over the years, many companies at home and abroad have participated in the research of large annulus sealing technology in the field of heavy oil thermal recovery. The core is to solve the material problem, that is, to find a kind of sealing material with high temperature and pressure resistance and long-term high elasticity, but the effect is not satisfactory. Among them, the perfluoroether material developed by DuPont in the United States has become the leader in this field because of its high temperature resistance of 315℃, but it still cannot meet the requirements of the actual working conditions of high temperature and high pressure required by heavy oil exploitation. Baker Hughes' removable packer, designed for ultra-HP/HT Wells, was introduced in early 2016 and can withstand temperatures of 204 ° C.

The world's first sealing technology has been successfully tested

In order to solve this problem, since 2015, the R&D team of Tiading joint venture company has cooperated with the School of Mechanical Engineering of Tsinghua University, Petroleum Engineering Research Institute of Shengli Oilfield and other units. With the help of Yunhui Capital, after three years of scientific research, the company has successfully developed the world's first project. TD350, a high elastic composite material that can withstand 350℃ and 20 MPa supersaturated water vapor pressure, has been authorized by 7 invention patents and 25 utility model patents.

It is introduced that TD350 is a kind of composite polymer material with high temperature resistance, high pressure resistance, oil resistance, water resistance, especially under high temperature conditions can still maintain similar to the elasticity of rubber, at 350℃, 20MPa pressure can continue to seal the oil sleeve annulus for a long time, the highest temperature can be up to 361℃, the highest pressure can be up to 25MPa.

Day ding lianchuang company cooperate with shengli oilfield petroleum engineering institute of technology, using its home-grown TD350 sealed chamber has carried out in shengli oilfield petroleum engineering the three-year ground 11 test examination, has realized the thermal recovery of heavy oil analog device of big annular seal, for the exploitation of underground traffic control of heavy oil field provides a solid foundation.

"From November 2017, Binnan Oil Production Plant of Shengli Oilfield took the lead in making a bold attempt. Two on-site production Wells were selected, and dozens of professional technicians were assigned to three teams to carry out experiments day and night with experts from the Petroleum Engineering Institute to verify the sealing performance of the new material under different actual working conditions. Song Hui said.

Field test, according to a report of a complete set of experimental temperature from room temperature to high temperature, and then to soak, after high temperature steam injection quality improved significantly, packer sealing tube always 30 consecutive days without leakage, due to the annulus pressure to zero, can not wash well operation, without pressure operation well, saving a large amount of water at the same time, also greatly improve the safety of construction.

"For the first time, the TD350 high temperature sealing cylinder can simultaneously seal under the conditions of ultra-high temperature and normal temperature alternating working conditions, which breaks through the bottleneck that the thermal recovery process of heavy oil cannot be further effectively implemented due to the sealing problem for a long time, and lays a foundation for improving the thermal recovery process of high temperature heavy oil and realizing efficient oil recovery in the next step." "Said Wang Lushan, vice president of the Institute of Petroleum Engineering Technology of Victory Oilfield.

It is understood that there are more than 5000 heavy oil thermal recovery Wells in Shengli Oilfield. Due to the loose sealing at the bottom of the heavy oil well, the steam loss is large, the unit steam oil production is low and the oil production cost is high. That, coupled with low oil prices, has left more than half of the Wells suspended. If the technology can be scaled up, a large number of suspended Wells could potentially restore economic value.