Oil-gas mixing transportation technology

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Long-distance oil and gas mixed transportation technology remains a popular technique in the international oil industry today. The ultimate goal of developed countries in Europe and the United States in developing this technology is to achieve fully subsea development facilities for oil and gas fields in deep and ultra-deep waters, that is, to carry out extraction without surface platforms, thereby significantly reducing the development costs in harsh environmental conditions as well as in marginal oil and gas fields. Since the 1980s, research and application of it have accelerated internationally. At present, it has moved from the experimental stage to the phase of industrial application and improvement, with two key technologies already put into use: the first is long-distance pipeline mixed transportation technology. Norwegian company Statoil is turning the concept of underwater multiphase flow extraction systems into reality. In 2007, two parallel subsea transfer pipelines with a diameter of 750 mm and a length of 120 km were constructed in the Oman Ridge condensate field, located at a depth of 850 meters in Norwegian waters. These pipelines were used to transport the natural gas and condensate produced by 24 gas wells directly to onshore terminals. This system is the world’s first true underwater multiphase flow extraction system. It consists mainly of an underwater wellhead platform module, a self-pressurized mixed-flow submarine pipeline, a hydrate suppression system, an underwater power distribution system, and an underwater automation system. Its main feature is that all production facilities are located on the seabed, with no structures at the sea surface. The second item is subsea mixed-transfer pressurization technology. In 2007, BP in the UK installed and put into operation two subsea multiphase transfer pumps, each weighing 92 tons, at the King oil field in the Gulf of Mexico, USA. These pumps were used to transport oil well products at a depth of 1676 meters and at a distance of 24 km from the platform; they set world records both in terms of depth and distance for subsea pressure-driven transportation. Since the 1990s, our country has begun to catch up with international research advancements in this field. During the Ninth Five-Year Plan period, China National Petroleum Corporation initiated research on \"mixed-phase transportation of oil, gas, and water.\" By building on advanced foreign technologies, a series of research results were achieved. Since 2004, this technology has been gradually applied in onshore oil and gas field projects at home and abroad. Five long-distance oil and gas mixed transport pipelines with lengths ranging from 23 to 75 km and transmission pressures of 1.5 to 11 MPa have been designed and constructed independently in Kazakhstan, China’s Tarim Oil and Gas Field, and Daqing Oil Field. Among them, the maximum oil transport capacity of a single mixed transport pipeline reached 220×10000 tons per year, while the gas transport capacity reached 8×100000000 cubic meters per year. The combined indicators of transport capacity and length placed it among the top in the world, marking a new stage in the development of long-distance oil and gas mixed transport technology in China. However, at present, China’s technology for transporting oil and gas in a multiphase state still lags significantly behind the advanced levels abroad, as is evident in the following three aspects: first, multiphase flow simulation software. Countries such as the United States, the United Kingdom, France, Norway, and Canada all possess phase flow dynamics calculation software with independent intellectual property rights, whereas China still lacks such software that is independently developed and widely recognized in the industry, which is not in line with its status as a major oil country. At the same time, due to the complexity of multiphase flow, none of the existing multiphase flow dynamic calculation software abroad is universally applicable. If we rely on imported software for a long time and lack the ability for independent innovation, we will gradually lose our international competitiveness. The second is large-scale multiphase transfer pump technology. Internationally, the maximum power of a single oil-gas transfer pump used in practical engineering applications is 6000 kW, whereas the maximum power of domestic transfer pumps with proven manufacturing records is only 300 kW, showing a significant gap compared to international advanced levels. At the same time, the problem of a single pump type is also quite prominent. Third is the technology for large slug catchers. Countries such as the United States and Canada have specialized manufacturers of large slug catchers; the volume of a single slug catcher used in practical applications there has reached 5,600 m3. In China, however, there are no specialized manufacturers of slug catchers, and the largest slug catchers designed domestically have a volume of only 300 m3. In the coming period, if these 3 technical challenges can be overcome, it will not only lead to a significant improvement in China’s capabilities in multiphase flow simulation and the manufacturing of key equipment, but it will also yield economic benefits in the form of a reduction in the costs of software and equipment purchases by over 50%.