Second types of in situ replacement of methane hydrate by liquid carbon dioxide replacement were proposed and verified by experiments. Through visible hydrate reaction device and image equipment to intuitively record injecting CO2 and gas hydrate decomposition in situ hydrate, and maintain the bulk of hydrate stable structure, proved the feasibility of hydrate decomposition and generation in second types of in situ replacement process at the same time. By controlling the pressure properly, the CH4 replacement process in the four phase zone (Hydrate?Water?Liquid?Vapor) of the CO2?CH4 mixed hydrate was realized, and the rich CH4 gas production was obtained. The CH4 gas production characteristics and the replacement rate of CO2 to CH4 hydrate were analyzed by gas chromatography and gas production measurement. The results showed that lower pressure was favorable for obtaining better replacement effect, compared with 5 MPa, the gas production increased by 14.6% and the methane hydrate replacement rate increased by 13.7% at 4.5 MPa.
[1] Chong Z R, Yang S H B, Babu P, et al. Review of natural gas hydrates as an energy resource: Prospects and challenges[J]. Applied Energy,2016, 162: 1633-1652.
[2] Anderson B J, Boswell R, Collett T S, et al. Review of the findings of the Ignik Sikumi CO2-CH4 gas hydrate exchange field trial[Z]. Beijing, China: China Geological Survey, 2014.
[3] Makogon Y F, Omelchenko R Y. Commercial gas production from Messoyakha deposit in hydrate conditions[J]. Journal of Natural Gas Science and Engineering,2013, 11（3）: 1-6.
[4] Collett T, Bahk J, Frye M, et al. Historical methane hydrate project review[R]. Washington D.C.: Department of Energy, USA, 2013.
[5] Yamamoto K. Overview and introduction: Pressure core-sampling and analyses in the 2012–2013 MH21 offshore test of gas production from methane hydrates in the eastern Nankai Trough[J]. Marine and Petroleum Geology, 2015, 66（2）: 296-309.
[6] 祝有海，赵省民，卢振权. 中国冻土区天然气水合物的找矿选区及其资源潜力[J]. 天然气工业,2011，31(1): 13-19.
Zhu Y H,Zhao S M,Lu Z Q. Prospecting of Natural Gas Hydrate in Permafrost Regions of China and Resource Potential[J]. Natural Gas Industry,2011，31(1):13-19.
[7] 王南，裴玲，雷丹凤，等. 中国非常规天然气资源分布及开发现状[J]. 油气地质与采收率,2015，22(1): 26-31.
Wang N,Pei L,Lei D F,et al. Distribution and Development of Unconventional Natural Gas Resources in China[J]. Petroleum Geology and Recovery Efficiency,2015，22(1):26-31.
[8] 广州海洋地质调查局. 中国地调局广州海洋局“十二五” 重点成果回顾（一）在南海天然气水合物资源勘查研究取得重大突破[Z]. 2016.
Guangzhou Marine Geological Survey. China Meteorological Administration Guangzhou Oceanic Administration “12th Five-Year”key results review(1) Significant breakthroughs have been made in the exploration of natural gas hydrate resources in the South China Sea [Z].2016.
[9] Chen Z, Feng J, Li X, et al. Preparation of Warm Brine in Situ Seafloor Based on the Hydrate Process for Marine Gas Hydrate Thermal Stimulation[J]. Industrial & Engineering Chemistry Research.,2014, 53(36): 14142-14157.
[10] Fan S, Zhang Y, Tian G, et al. Natural Gas Hydrate Dissociation by Presence of Ethylene Glycol[J]. Energy & Fuels,2006, 20(1): 324-326.
[11] 张旭辉，鲁晓兵，刘乐乐. 天然气水合物开采方法研究进展[J]. 地球物理学进展, 2014，29(2): 858-869.
Zhang X H,Lu X B,Liu L L. Research Progress of Natural Gas Hydrate Mining Method[J]. Progress in Geophysics,2014，29(2):858-869.
[12] Ebinuma T. Method for dumping and disposing of carbon dioxide gas and apparatus therefor：US 07/846,290 [P]. 1993-11-16.
[13] Ohgaki K, Takano K, Sangawa H, et al. Methane Exploitation by Carbon Dioxide from Gas Hydrates-Phase Equilibria for CO2-CH4 Mixed Hydrate System[J]. Journal of Chemical Engineering of Japan, 1996, 29(3): 478-483.
[14] Goel N. In situ methane hydrate dissociation with carbon dioxide sequestration: Current knowledge and issues[J]. Journal of Petroleum Science and Engineering,2006, 51（3-4）: 169–184.
[15] Ota M, Saito T, Aida T, et al. Macro and microscopic CH4-CO2 replacement in CH4 hydrate under pressurized CO2[J]. AICHE JOURNAL,2007, 53(10): 2715-2721.
[16] Ota M, Abe Y, Watanabe M, et al. Methane recovery from methane hydrate using pressurized CO2[J]. Fluid Phase Equilibria,2005, 228-229（3）: 553-559.
[17] Bi Y, Yang T, Guo K. Determination of the upper-quadruple-phase equilibrium region for carbon dioxide and methane mixed gas hydrates[J]. Journal of Petroleum Science and Engineering, 2013, 101（2）: 62-67.
[18] Ersland G, Huseb? J, Graue A, et al. Measuring gas hydrate formation and exchange with CO2 in Bentheim sandstone using MRI tomography[J]. Chemical Engineering Journal, 2010, 158(1): 25-31.
[19] Jung J W, Espinoza D N, Santamarina J C. Properties and phenomena relevant to CH4-CO2 replacement in hydrate-bearing sediments[J]. Journal of Geophysical Research, 2010, 115(B10)：155-162.
[20] Jung J W, Santamarina J C. CH4-CO2 replacement in hydrate-bearing sediments: A pore-scale study[J]. Geochemistry, Geophysics, Geosystems, 2010, 11(12)：68-82.
[21] Yoon J, Kawamura T, Yamamoto Y, et al. Transformation of Methane Hydrate to Carbon Dioxide Hydrate: In Situ Raman Spectroscopic Observations[J]. The Journal of Physical Chemistry A, 2004, 108(23): 5057-5059.
[22] Ota M, Morohashi K, Abe Y, et al. Replacement of CH4 in the hydrate by use of liquid CO2[J]. Energy Conversion and Management, 2005, 46(11): 1680-1691.
[23] Anderson B J, Boswell R, Collett T S, et al. Review of the findings of the Ignik Sikumi CO2-CH4 gas hydrate exchange field trial[C]. Beijing, China: China Geological Survey, 2014.
[24] Brewer P G, Peltzer E T, Walz P M, et al. Deep-Sea Field Test of the CH4 Hydrate to CO2 Hydrate Spontaneous Conversion Hypothesis[J]. Energy & Fuels, 2014, 28(11): 7061-7069.
[25] 郑新，孙志高，樊栓狮，等. 天然气水合物储气实验研究[J]. 天然气工业, 2003,23(1): 95-97.
Zheng X,Sun Z G,Fan S S,et al. Experimental Study on Natural Gas Hydrate storage gas[J]. Natural Gas Industry,2003,23(1):95-97.
[26] Ganji H, Aalaie J, Boroojerdi S H, et al. Effect of polymer nanocomposites on methane hydrate stability and storage capacity[J]. Journal of Petroleum Science and Engineering, 2013, 112（3）: 32-35.
[27] Najibi H, Mirzaee Shayegan M, Heidary H. Experimental investigation of methane hydrate formation in the presence of copper oxide nanoparticles and SDS[J]. Journal of Natural Gas Science and Engineering, 2015,23:315-323.
