No abstract

Summary Polymer flooding is one of the most promising chemical enhanced-oil-recovery (EOR) techniques. It offers a high incremental-oil-recovery factor (IORF), low cost, and wide reservoir applicability. The first large commercial polymer-flooding application began in Daqing Oil Field and remains the largest polymer application in the world. However, encouraged by the success of previous field applications and new findings regarding the viscoelasticity of polymers in the reduction of residual oil saturation (ROS), high-concentration high-molecular-weight (MW) polymer-flooding (HCHMW) field tests have been conducted in many oil fields in China. Although some of these field tests in Daqing are well-documented, subsequent progress has seldom been reported. Moreover, recent references about the latest polymer-flooding applications in China reveal that HCHMW has only a limited application in Daqing. This is not in agreement with previous reports and expectations, especially given that viscoelasticity has been drawing increased attention. This paper explains why HCHMW is not currently widely used. New types of amphiphilic polymers are also field tested in China. Lessons learned from polymer-flooding practices in offshore reservoirs, heavy-oil reservoirs, and conglomerate reservoirs are given to help reduce risks and costs of polymer flooding in the low-oil-price era. EOR techniques in post-polymer-flooding reservoir field tests are also compared. In addition to providing useful information for engineers, this paper helps clarify some misconceptions—such as injecting the most viscous polymer possible—in polymer-flooding implementations, according to polymer-flooding practice in China. Annual oil production using polymer flooding as well as polymer utility factors (UFs) are given. Various technical parameters, such as polymer slug, viscosity, IORF, oil-increase factor (OIF), and water-cut decrease, are provided to better understand polymer-flooding evaluation as well economics.

This paper provides field scale EOR survey in China which is in line with biennial worldwide EOR survey published by Oil& Gas Journal (OGJ). The EOR progress in China is not available due to language difference and other reasons in OGJ EOR survey. From 2018, EOR survey in China will be published biennially. The first part of this survey mainly focuses on basic information. Chemical flooding, unconventional heavy oil, green recovery and natural gas recovery progress in China will be surveyed and discussed in detail in the other four parts elsewhere. The EOR projects including field tests and field applications in China are summarized in the same pattern as OGJ to the largest extent for better readership outside China. Most data is collected from published journal papers and reports. Different from other countries, there are only four major oil companies in China: CNPC, SINOPEC, CNOOC and Yanchang Oil. The 28 branch companies of these four companies are both operator and owners. Oil and gas production from CNOOC is all offshore. CNPC is the largest oil company in China and its oil production in 2016 accounts for 54% oil production in China. EOR survey in China includes chemical flooding (polymer, SP and ASP flooding, gas flooding (CO2, nitrogen and air), thermal production, MEOR, and foam flooding. EOR production in China in 2016 accounts for 18% total oil production, while chemical EOR accounts for 10 %. Up to present, there has been more than 34 ASP flooding projects in China, most in Daqing. The total ASP oil production in 2016 is 407 million tons. More than 30 SP flooding projects have been carried out, with incremental oil recovery factor of 7%-18% OOIP. More than 170 polymer flooding projects have been carried out. Polymer flooding has been used widely in Daqing, Shengli, Xinjiang, Liaohe, He'nan and Bohai. The incremental oil recovery from polymer flooding and ASP flooding is 7%-15% and 18%-30% OOIP respectively. Gas flooding in China is not as successful as chemical EOR. Polymer flooding production in the largest offshore oilfield in CNOOC accounts for 25% total oil production in 2016. While EOR production in China accounts for 15%-18% in recent years, however, the world EOR oil production only accounts for about 3.3% total oil production. EOR is greatly affected by oil price, as indicated from 26 years EOR content change in America. It is the first time that detailed EOR survey in China in line with worldwide EOR survey in OGJ is given. The EOR survey in China provides valuable and helpful information for engineers and researchers in oil and gas industry.

Based on a large number of empirical statistics of tertiary oil recovery technology in China, including polymer flooding, chemical flooding, gas flooding, in situ combustion, steam flooding, ect., 22 key reservoir parameters were filterized. Five levels of quantitative screening criteria were developed for different tertiary oil recovery methods. The mean algorithm for the downward approximation and the grey correlation theory were used in this paper to quickly select the appropriate tertiary oil recovery method for the target blocks, which provides a preferred development method for subsequent potential evaluation. In the rapid analogy evaluation method of tertiary oil recovery potential, the total similarity ratio between the target block and the example block is determined. The target block is matched with the appropriate instance block according to the total similarity ratio value, using 80% as the boundary. The ratio of the geological reserves is used to predict the oil recovery interval, the actual annual injection data, and the economic profit, thus quickly predicting the economic potential of the tertiary oil recovery technology in the target block. Currently, our research team has integrated these two methods into the tertiary oil production potential evaluation software EORSYS3.0. The empirical analysis shows that this method is reasonable and the conclusion is reliable. In addition, the actual enhanced recovery value is within the effective range predicted by the method. The method and results of this paper will provide an important decision-making reference for the application and sustainable development of China Petroleum’s main tertiary oil recovery technology in the next 5–10 years.