Discussion on SAGD technology

Thread Content

This post was last edited by 18 on 2009-5-22 at 12:35. SAGD is a cutting-edge technology for the international development of extra-heavy oil. Its theory is based on the principle of water injection for salt extraction: fresh water is injected to dissolve the solid salt in the salt layer. The salt solution with high concentration flows downward due to its high density, while the water solution with relatively lower density remains on top. By continuously injecting water into the upper part of the salt layer, high-concentration salt solutions from the lower parts of the layer can be extracted. Applying this principle to the steam injection thermal recovery process gives rise to the concept of gravity-driven oil drainage. SAGD is a steam flooding extraction method, which involves continuously injecting steam into the ground to heat the oil reservoir and drive the crude oil to the surrounding production wells for extraction. Currently, the use of SAGD technology to develop extra-heavy oil has become a mature technique for such oil development on an international scale. Thanks to this extraction method, Canada produced over 7 million tons of crude oil per year in 2004, with an ultimate recovery rate of more than 50%, reaching up to over 70% in some cases. In fact, CNPC is not unfamiliar with SAGD technology. As early as 1996, the Liaohe Oil Field applied this technology to drill China’s first pair of water wells – Well Du84-Ping1-1 and Well Ping1-2 in the Shu Area. Among the various pioneering technology projects of the group company, the Steam-Assisted Gravity Drainage (SAGD) technique for extracting ultra-heavy oil in the Liaohe Oil Field has become the project that receives the most attention from the group’s senior management. The ultra-heavy oil reservoirs in the Liaohe Oil Field are characterized by great burial depths, high viscosity of the crude oil, and high reservoir pressures. At 50 degrees Celsius, the viscosity of this ultra-heavy oil reaches as high as 200,000 millipascal-seconds, which is far higher than the values of 10,000 to 20,000 seen in other countries. Among the existing heavy oil extraction technologies in the world today, it is one of the 10 major development projects of China National Petroleum Corporation ； As a replacement technology to transform the development methods for heavy oil, can SAGD take on the task of developing ultra-heavy oil in the Liaohe Oil Field? China’s largest heavy oil production base—the Liaohe Oilfield—should bring a surprise to Chinese petroleum workers. From February 2005 to March 2006, the Guantao test area in Block Du84, Area 1 of the Liaohe Oil Field, was officially put into SAGD production. It operated for a total of 375 days, producing 51,253 tons of oil; the well cluster produced 220 tons per day. The production parameters met the standards set in the design plan, and the trial achieved initial success. Experts say that if a change in the development method for the super-heavy oil in the Liaohe Basin is implemented, it could increase the recoverable reserves of the Liaohe Oil Field by 100 million tons and extend the field’s development period by more than 8 years. SAGD is effective for exploiting heavy oil in China. China is another major producer of heavy oil in the world, alongside the United States, Venezuela, and Canada. The Liaohe Oil Field is China’s largest production base for heavy oil and ultra-heavy oil. Since 1997, the industrial exploitation of ultra-heavy oil in the Liaohe Basin has been carried out using steam flooding; by 2000, the production volume had exceeded 1 million tons, and it reached 2.67 million tons in 2005. As the production scale continues to expand, development contradictions gradually come to light. Firstly, when steam injection reaches an average of 7.7 cycles, it leads to issues such as low periodic production, low daily production levels, and a low oil-to-gas ratio; if this number reaches 10 cycles, the oil-to-gas ratio drops below 0.4. Some oil wells in the Liaohe Oil Field have undergone steam stimulation up to 10 cycles, resulting in a very weak foundation for stable production. Secondly, steam flooding results in a rapid decline in oil well production and low recovery rates; the annual overall decline is approximately 20%, with recovery rates not exceeding 23.6%. Thirdly, the undeveloped areas have poor reservoir conditions and complex oil-water relationships; 862 additional wells are planned, all of which are classified as Category II wells. The production volume of these oil wells is relatively low, resulting in high operational costs per unit. On the one hand, China’s heavy oil extraction industry urgently needs alternative technologies ； On the one hand, SAGD is a mature heavy oil development technology abroad. Therefore, Liaohe Oilfield Company organized experts to conduct a comprehensive analysis and study, and ultimately concluded unanimously that SAGD is feasible in the Liaohe area. To this end, the Liaohe Oilfield established a SAGD project leadership team and partnered with Canadian Oil Company at the end of 2003. By the end of last year, wells Guanping 11 and 12 in Block Du84, Area Shuyi of the Liaohe Oilfield, had been operating using SAGD technology for over 300 days. During this period, crude oil production remained stable at 120 tons per day, exceeding the design standards; compared to steam flooding, this approach resulted in an oil recovery rate increase of over 25%. This marks the initial success of the SAGD pilot test in the Liaohe Oilfield. “Based on preliminary assessments, there are over 100 million tons of reserves in the Liaohe Oil Field that are suitable for SAGD. Calculating based on a 20% increase in recovery rate, this would result in an additional 20 million tons of recoverable reserves, which is equivalent to adding another oil field with reserves of 100 million tons! ”Yin Wanquan, head of the Development Department at Liaohe Oilfield Company, said excitedly. SAGD has become the dominant alternative technology for the extraction of heavy oil in the Liaohe Basin. How to reduce costs and extract as much heavy oil and ultra-heavy oil as possible is a common challenge facing the global oil industry. To make SAGD technology the successor leading technology for the extraction of heavy oil in the Liaohe Basin, it must meet both the requirements of suitability and economic viability. This SAGD is not that SAGD. The ultra-heavy oil reservoirs in the Liaohe Oil Field differ from those abroad in that, first, they are located at great depths. The burial depth of the Guantao Formation is 650 meters, while that of the Xing VI Formation is 780 meters. Abroad, it is usually between 300 and 500 meters, whereas the limit of this technology is 1000 meters ； Secondly, the Liaohe Oil Field is of continental sedimentation; the significant variations in the orientation of the oil layers and their high heterogeneity result in short horizontal sections ； Third, the use of SAGD in the later stages of steam flooding extraction further increases the operational complexity ； Fourth, the crude oil has a high viscosity; at 50 degrees Celsius, the viscosity of the crude oil in the Guantao oil reservoir is 5 to 10 times that of similar oil reservoirs abroad. These issues determine that SAGD for the heavy oil in the Liaohe Basin must have its own characteristics. Abroad, SAGD technology is typically developed for paired water injection, whereas the Liaohe Oil Field uses vertical wells with steam injection and water injection for production. This approach to development has three advantages: First, it replaces the traditional vertical wells with steam injection wells, which means that one less well needs to be drilled for steam injection – making it economical and practical ； Second, the ultra-heavy oil reservoirs in the Liaohe Oil Field have complex interlayers, poor layer continuity, and weak vertical connectivity. The water depth abroad is usually 1,000 meters, whereas that in the Liaohe Oil Field is only a few hundred meters. By using direct well steam injection, the existing feature of many wells in the Liaohe Oil Field turns into an advantage; if one well doesn’t work, another can be used instead. Third, the monitoring system is another innovation in the application of SAGD technology at the Liaohe Oil Field, changing the practice abroad where monitoring is carried out using two wells. Since the start of the SAGD pilot tests, the scientific and technical personnel at the Liaohe Oil Field have made unremitting efforts to overcome numerous technical challenges, such as steam injection techniques, high-volume lifting technologies, and surface gathering and transportation systems; these solutions have all reached international advanced levels and meet the requirements of the SAGD process. The Liaohe Oilfield will reduce the operating costs of SAGD to a more economical level by achieving localization of surface lifting and monitoring technologies, as well as by utilizing the thermal energy of high-temperature produced fluids. The members of the project leadership team at the Liaohe Oilfield Company are very optimistic about the prospects of SAGD technology for the exploitation of heavy oil in the Liaohe region. They said that the recovery rate of SAGD technology abroad is as high as 70%. At present, the pilot test area in Area 1 is 29%, and it is expected that the recovery rate will reach 57% when gravity drainage is implemented in 8 years. SAGD is the most effective approach.