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考虑基质吸附变形特性的煤岩渗透率演化研究

Study on coal permeability evolution considering adsorptive deformation characteristics of matrix

  • 摘要: 渗透率是煤层气勘探与温室气体存储中必不可少的参数,准确认识煤层内气体流动不仅能够合理预测煤层气产量,还能提高CO2地质封存的效率。一般的煤岩渗透率预测模型都是从有效应力以及气体吸附的角度出发进行模型的相关理论推导,但在实际情况中,煤岩的基质内部构造复杂不定,与吸附相关的矿物成分分布存在不均匀的现象,这就往往会忽略基质区域非均匀吸附变形这一因素的影响。因此,通过将煤岩的基质区域划分为2个吸附能力不同的区域,重新推导了煤岩渗透率模型,利用现场数据以及实验室数据对提出的模型进行比较验证,并通过有限元软件分析了基质区域的非均匀吸附对渗透率演化的影响,结果表明:① 提出的模型与现场及实验室实验数据具有较高的匹配度,不同边界条件下的渗透率预测数据具有较高的可靠性。② 基质的非吸附膨胀区域的渗透率会在吸附膨胀区域的挤压效应下降低,并且越靠近吸附膨胀变形区域处,受到的挤压效果越强,非吸附膨胀区域渗透率降低程度越明显。③ 随着基质吸附区域面积的增加会使相邻基质区域受到的应力扰动越早,并使得受挤压的基质区域平衡时气体渗透率越低。改进的渗透率模型可以更加深入地了解煤岩内部基质区域相互作用对渗透率产生的影响,对煤层气开采具有一定的理论指导意义。

     

    Abstract: Permeability is an essential parameter in CBM exploration and greenhouse gas storage. Accurate understanding of gas flow in coal seam can not only reasonably predict CBM production, but also improve the efficiency of CO2 geological storage. The general coal rock permeability prediction model is from the effective stress and gas adsorption point of view for the theoretical derivation of the model, but in practice, the complexity and uncertainty of the internal structure of the matrix of the coal rock, and adsorption related to the distribution of the mineral constituents of the phenomenon of inhomogeneous, which tends to ignore the matrix region of non-uniform adsorption deformation of the influence of this factor. Therefore, in this paper, the matrix region of coal and rock is divided into two regions with different adsorption capacity, and the permeability model of coal and rock is re-derived. The field data and laboratory data are used to compare and verify the proposed model, and the influence of non-uniform adsorption of matrix region on permeability evolution is analyzed by finite element software. The results show that: ① The proposed model has a high matching degree with field and laboratory experimental data, and the permeability prediction data under different boundary conditions have high reliability. ② The permeability of the non-adsorption expansion area of the matrix will be reduced by the squeezing effect of the adsorption expansion area, and the closer to the adsorption expansion deformation area, the stronger the squeezing effect, and the more obvious the reduction in permeability of the non-adsorption expansion area. ③ With the increase of the adsorption area of the matrix, the stress disturbance of the adjacent matrix region will be earlier, and the gas permeability will be lower when the compressed matrix region is in equilibrium. The improved permeability model can better understand the influence of regional matrix interaction in coal and rock on permeability, and has certain theoretical guiding significance for coalbed methane exploitation.

     

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