Key Technologies of Carbon Dioxide Flooding and Storage in China

The oilfields which have been developed gradually entered the stage of high water cut and recovery degree in China. The newly discovered oilfields are mainly composed of ultra-low permeability reservoirs and tight reservoirs, which are difficult to be recovered. As a consequence, China faces the severe challenge of increasing or even maintaining oil production. There is an urgent need for a new method to enhance the oil recovery of old oilfields and producing rate of new reservoirs. Meanwhile, China's environmental problems have become increasingly serious. From 2008, China has exceeded the United States and become the country that emits the most greenhouse gases in the world. Therefore, the Chinese government encountered the huge pressures of society and politics. However, the practice has showed that carbon dioxide flooding cannot only improve oil recovery, but also achieve the goal of reducing the emission of carbon dioxide. This technique is the best way to decrease the emission of carbon dioxide under the current conditions of economy and technology. As a result, many giant companies, organizations, or governments have paid much attention to this technique. In China, as early as the mid-1960s, some laboratory experiments regarding carbon dioxide flooding were carried out in Shengli Oilfield and Daqing Oilfield. Furthermore, in the mid-1990s, some pilot tests were conducted in Daqing Oilfield, Jiangsu Oilfield, Zhongyuan Oilfield, and Shengli Oilfield. But because of shortage of natural resources of carbon dioxide and serious contradiction of gas channeling, this technique developed slowly. During the period of "the eleventh five-year plan", PetroChina discovered a natural gas reservoir that contains a large amount of carbon dioxide in Songliao Basin. Carbon dioxide gas was required to be separated and re-injected to the layers during the development of natural gas. For this reason, the government specially set up some projects including national level, corporation level, and oilfield level. Aiming at the characteristics of continental reservoir in China, these projects reemphasized the technique of carbon dioxide flooding. After nearly ten years of research, we have deepened two basic theories, which are suitable for Chinese continental sedimentary reservoir of CO2 miscible flooding theory and the storage mechanism of CO2 storage in the reservoir and saline layer. We also formed and developed six key technologies: the reservoir engineering technology of CO2 flooding and storage, CO2 flooding technology with high efficiency of injection and production, CO2 long distance pipeline and supercritical injection technology, treatment and cyclic gas injection technology of the produced fluid by CO2 flooding, monitoring and dynamic analysis and evaluation technology of CO2, and CO2 flooding and storage potential evaluation and strategic planning. Relevant research results supported the Black 59, Black 79, Black 46, and Yi 59 Blocks in Jilin Oilfield to build five kinds of demonstration area of CO2 storage and flooding, covering the geological reserves of 12 million 880 thousand tons, 69 gas injection wells groups. The cumulative gas injection was 970 thousand tons, which has increased 102 thousand tons oil. The annual oil production capacity reached 121 thousand tons. So it showed significant economic benefits. The annual CO2 storage capacity was 350 thousand tons, indicating a crucial social significance of greenhouse gas emissions. At present, the technology has been extended to the oilfields in Western China. Ordos Basin and Junggar Basin pilot tests are being carried out. The prospect of carbon dioxide flooding and storage technology in China is broad.