煤岩力学非均质性对孔渗性质的影响规律

Influence of Mechanical Heterogeneity of Coal Rock on Porosity and Permeability

煤岩是由有机质和无机矿物组成的复杂不均匀多孔介质,非均质性较强,目前研究鲜有考虑煤岩力学非均质性对煤岩渗透率与孔隙度时空演化规律的影响。基于Weibull概率密度分布函数表征煤岩弹性模量的非均质性,建立了考虑煤岩内甲烷解吸引起的气压变化、线性热膨胀效应和煤岩骨架收缩变形的热流固耦合三维有限元模型,通过煤岩渗透率与孔隙度与温度场、应力场和压力场间的交叉耦合关联式,分析了非均质度下煤岩表征单元体内渗透率与孔隙度参数的变化规律。结果表明:煤岩力学非均质性是影响煤岩渗透率与孔隙度分布的重要因素之一,非均质煤层的渗透率与孔隙度分布呈现出明显的波动震荡特征,在不同位置处的孔渗参数大小不等;随着井眼距离增加,渗透率和孔隙度可能呈现与均质煤岩情况恰好相反的变化趋势。因此,煤岩的孔隙度与渗透率演化是一个复杂的热流固耦合过程。研究结果对指导煤层气高效开采具有重要的理论意义。

Coal rock is a complex and inhomogeneous porous medium composed of organic matter and inorganic minerals,with strong heterogeneity.At present,few studies have considered the influence of coal rock mechanical heterogeneity on the spatiotemporal evolution of coal rock permeability and porosity.A three-dimensional finite element model of thermo-fluid-solid coupling considering the pressure change,linear thermal expansion effect and shrinkage and deformation of coal rock skeleton due to methane desorption in coal was established,which based on the Weibull probability density distribution function to represent the heterogeneity of the elastic modulus of coal rock.The permeability and porosity in coal rocks were cross-coupling correlations between temperature field,stress field and pressure field,and the variation law of permeability and porosity parameters under heterogeneity was analyzed.The results show that coal and rock mechanics heterogeneity is one of the important factors that affect the permeability and porosity distribution of coal rock.The permeability and porosity distribution of heterogeneous coal seams show obvious fluctuation and shock characteristics at different locations.Pore permeability parameters vary in size;as the distance of the borehole increases,the permeability and porosity may show the opposite trend of the homogeneous coal rock.Therefore,the evolution of porosity and permeability of coal rock is a complex process of thermal fluid-solid coupling.The research results of have important theoretical significance for guiding the efficient exploitation of coalbed methane.