CO2驱替煤层CH4试验研究

 通过对大煤样试件(100 mm×100 mm×200 mm)进行注CO2驱替煤层CH4试验，较真实地模拟在煤层中储存CO2以及驱替开采煤层气的过程。研究发现：CH4在煤体中渗透率与体积应力呈负指数相关规律；煤体对CO2的渗透率高于对CH4气体的渗透率2个数量级以上；随体积应力及驱替压力的不同，单位体积煤体可储存17.47～28.00体积CO2，CO2/CH4置换体积比可达7.03～13.91；在恒定体积应力及驱替压力条件下，CO2注入、CH4置换、产出均能够平稳进行；2种不同煤层CH4含量条件与驱替置换方式下，产出气体中初期CH4含量高达20%～50%，随时间延续产出气体中CH4含量有所下降，但仍能持续保持在10%～16%；驱替压力、驱替速度、注入倍数、煤层CH4含量、储层结构及其渗透性等因素共同决定着CO2/CH4驱替置换效果；在CO2注入煤体进行置换吸附期间，受气体吸附解吸、煤基质自身变形等因素影响，煤体会发生膨胀现象。该研究成果对CO2煤层处置及驱替置换开采煤层气实践具有重要理论意义与指导价值。

EXPERIMENTAL STUDY OF COALBEDS METHANE REPLACEMENT BY CARBON DIOXIDE

Carbon dioxide is one of the main greenhouse gases. Geological disposal of carbon dioxide in coalbeds is regarded as an economical approach because of the mutual benefit of greenhouse gas sequestration and recovery of coalbed methane by replacement. In the past,most of works were focused on either theoretical analyses and numerical simulations,or experiments of adsorption and desorption of different gases on coal grains in size of millimeters or the less. In this paper,the experimental study results of carbon dioxide storage and methane replacement in coal specimens of large size(100 mm×100 mm×200 mm) are presented,which realistically simulates the process of the greenhouse gas sequestration and methane replacement in coalbed. In the experiment,the permeability of coal specimen is measured firstly with methane and carbon dioxide respectively;and it is found that the permeability of coal is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the testing condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen. Under the simulated stress condition in the experiment,17.47 to 28.00 units of carbon dioxide can be stored in per unit of coal;and the replacement ratio of carbon dioxide to methane is as large as 7.03 to 13.91. The processes of injection,adsorption and desorption,replacement,and output of gases can proceed smoothly under the given pressures;the percentage of methane in the production gas can be amounted to 20% to 50% at the early stage and still can be maintained at the level of 10% to 16% even at the last stage during the experiment process. It is concluded that the effects of carbon dioxide storage and methane replacement are determined by several factors including injection replacement pressure,injection amount and velocity,methane content in the coalbed,and the development of pores and fissures in the coalbed,etc.. During the process of carbon dioxide injection and gas replacement,coal body swelling can be found with comprehensive effects of gas adsorption and desorption,and the deformation of coal framework. The research is expected to provide certain illuminations for practice of carbon dioxide disposal in coalbed or methane replacement recovery by carbon dioxide in the future.