煤孔隙发育特征对原位注CO2置驱CH4的影响
Influence of coal pore development characteristics on in-situ injecting CO2 to replace and drive CH4
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摘要: 注CO2增产煤层气的机理有置换、载携和稀释扩散等，均与煤孔隙息息相关。为厘清煤孔隙对原位注CO2置驱CH4的影响，分析了3个原煤煤样的孔隙特征，采用自行研制的受载煤体注气置驱甲烷实验台，研究不同条件下原煤渗透性和吸附性，开展原位注CO2置驱CH4分步实验，深入探讨置驱的全过程。实验结果表明：YCW褐煤、SL肥煤和YMY无烟煤吸附孔占比依次为28.71%、88.24%和89.24%，渗流孔发育程度依次降低；随煤变质程度升高，煤吸附性变大、渗透性变小；置驱过程分为3个时期，早期阶段注入CO2主要起置换作用，中期阶段注入CO2起置换、载携和稀释作用，后期阶段注入CO2起载携、稀释作用；吸附孔和渗流孔均发育的YCW褐煤，提高注气压力或降低外部载荷能有效促进置换、载携、稀释作用，对整个置驱过程改善大，但对仅吸附孔发育的SL肥煤和YMY无烟煤的置驱过程改善小，如注气压力1 MPa、外部载荷6 MPa下，YCW褐煤、SL肥煤、YMY无烟煤的置驱效率依次为62.4%、48.4%和62.3%，当注气压力为2 MPa、外部载荷为4 MPa时，3个煤样的置驱效率依次为94.4%、72.2%和71.0%。Abstract: The mechanism of injecting CO2 to increase the production of CBM includes replacement, carrying, dilution and diffusion, etc, which are closely related to coal pores. In order to clarify the influence of coal pores on in-situ injecting CO2 to replace and drive CH4, the pore structure characteristics of three raw coal samples were analyzed, and then a self-made experiment platform was used to realize the injected gas replacement and driving CH4 in loaded coal. It is used to study the permeability and adsorption of raw coal under different conditions, and a step-by-step experiment of in-situ injecting CO2 to replace and drive CH4 is carried out, and the whole process of replacement and driving is deeply discussed. The experimental results show that the proportions of adsorption pores of YCW lignite, SL fat coal and YMY anthracite are 28.71%, 88.24%, and 89.24%, the development degree of seepage pores decreases sequentially. As the degree of coal metamorphism increases, the adsorption capacity of coal becomes larger and the permeability becomes smaller. The process of replacement and driving can be divided into three stages. In the early stage, injecting CO2 mainly plays the role of replacement. In the middle stage, injecting CO2 plays the role of replacement, carrying and dilution. In the later stage, injecting CO2 plays the role of carrying and dilution. For YCW lignite with adsorption pore and seepage pore, increasing gas injection pressure or reducing external load can effectively promote replacement, carrying and dilution, greatly improving the whole replacement and driving process, but little improving for SL fat coal and YMY anthracite with only adsorption pore. For example, when the gas injection pressure is 1 MPa and the external load is 6 MPa, the replacement and driving efficiency of YCW lignite, SL fat coal, and YMY anthracite is 62.4%, 48.4%, and 62.3%. When the gas injection pressure is 2 MPa and the external load is 4 MPa, the replacement and drive efficiency of three coal samples is 94.4%, 72.2%, and 71.0%, respectively.
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Keywords:
- in-situ state /
- coal pores /
- adsorption /
- permeability /
- replacement and driving CH4 /
- injecting CO2
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