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(Abstract) Despite the strong development momentum of renewable energy, oil and gas resources will still be an important part of global energy consumption for a long time. Improving oil and gas energy efficiency is essential to meet the growing global energy demand, and it is also the key to achieving energy security, economic development and environmental protection.

Despite the strong development momentum of renewable energy, oil and gas resources will still be an important part of global energy consumption for a long time. Improving oil and gas energy efficiency is essential to meet the growing global energy demand, and it is also the key to achieving energy security, economic development and environmental protection. Efficient production and utilization of oil and gas energy can also reduce energy import dependence and enhance energy security, which is of great strategic significance to China's green and sustainable development.

Challenges and Countermeasures of Conventional Oil and Gas Exploitation in China

At present, China's conventional oil and gas exploitation is facing challenges-old oil fields have entered a high water cut period, new oil fields have low grade, development costs have increased year by year, and the challenges of benefit development have intensified. In terms of the development of old oilfields, the water cut and recovery degree are more than 70% respectively. Most oilfields have entered the "double high" stage of high water cut and high recovery degree. The newly discovered oilfields basically have the "three low" low-grade characteristics of low abundance, low permeability and low production. Whether it is the high water cut old oilfields to improve oil recovery or the "three low" new oilfields, the cost is increasing year by year, the cost of tons of oil increases and the benefits become worse. From the point of view of oil and gas recovery rate, the global average recovery rate of crude oil is 36%, except for 46% in Daqing oil field, the recovery rate of crude oil in other oil fields is 22% to 29%, which makes it more difficult to further improve the recovery rate of crude oil. Easy to exploit resources are relatively gradually reduced, low-grade difficult to use crude oil reserves increased year by year, improve the efficiency of extraction has become an important goal of the oil and gas industry, can use conventional oil and gas to improve oil and gas recovery technology and energy efficiency of technical countermeasures.

First, improving water drive technology is still the main technology to improve recovery rate in China. Both high water cut and low permeability reservoirs in China's onshore oilfields adopt subdivision and development layer system, perfect injection and production system, continuously deepen formation understanding, high-efficiency reservoir deep regulation and flooding, strengthen old well condition management, screen horizontal well technology, fracturing and acidizing technology, develop new underground and surface water treatment systems, improve the utilization rate of injection water and return water, dynamically optimize and control injection and production parameters, and realize long-term oil stability and water control in old oilfields, enhanced oil recovery of 8% to 10%. China's Daqing, Shengli and other high water-cut oil fields and extra-high water-cut oil fields still need to carry out development tests to improve water flooding, and find out the technical combination suitable for the development of this oil field. At the same time, we should pay attention to the transformation of oil field development mode, and obtain the maximum energy efficiency with the minimum water consumption.

Second, chemical flooding technology is still the preferred technology to improve oil recovery in China's high water-bearing old oil fields. By using different technology combinations of "surfactant + polymer + alkali", the oil-water interface properties are improved mainly through polymer flooding, ternary composite flooding, binary composite flooding and other technologies, so that more crude oil is displaced from the rock pores. This technology can improve the oil recovery rate by 8% to 15%. Daqing, Shengli and other high water cut oilfields using this technology, oil recovery greatly improved, but most oilfields have not found suitable for the oil field chemical flooding technology, the next step should be to establish suitable for the oil field chemical flooding test area and test base, to achieve low cost, low pollution, high efficiency and green chemical flooding technology, improve the efficiency of chemical flooding.

Third, gas drive is the necessary technology to improve the recovery rate of China's ultra-high water-cut oil fields and low permeability/tight oil and gas fields. By injecting gas (such as carbon dioxide, natural gas or nitrogen) into the reservoir to increase the pressure of the reservoir and improve the mobility of oil and gas, if the injection of carbon dioxide, not only improve the oil recovery, but also reduce greenhouse gas emissions, to achieve carbon capture, storage and utilization (CCUS). This method has expanded its application scale in Jilin, Daqing and Shengli oilfields in China, increasing crude oil recovery by 10% to 20%, and achieving a win-win situation of improving the economic and environmental benefits of oilfields.

Fourth, thermal recovery technology is the main technology of heavy oil, super-heavy oil and oil sand mining in China. By injecting heat into the reservoir to reduce the viscosity of the oil, improve its fluidity, the poor or non-flowing crude oil is extracted to the surface. According to the characteristics of different heavy oil reservoirs in Liaohe, Xinjiang and Shengli oilfields in China, the heating reservoir technologies such as gas injection huff and puff, steam flooding, steam-assisted gravity oil drainage and burning oil layers have been successfully applied to improve the recovery rate of heavy oil by 20% to 50%. At present, China's heavy oil recovery rate is relatively high, but the gasoline ratio is too low, resulting in low heat utilization rate and high cost. How to develop a low-cost, efficient, green and environmentally friendly heavy oil thermal recovery process is a new challenge.

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