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煤储层物性是影响煤层气解吸、扩散、渗流的关键因素,其好坏直接决定煤层气井的产气效果.本文以高阶煤为例,基于压汞、低温液氮吸附、等温吸附、煤粒甲烷放散初速度测试以及煤层气井现场自然解吸数据,系统探讨了构造破坏作用下高阶煤的孔隙性、吸附性、扩散性、渗透性等物性的响应规律,建立了不同煤体结构高阶煤储层几何模型、扩散模式图及气体产出综合模式图.研究认为,高阶煤经历构造作用后孔隙性得到改造,不同孔径段孔隙数量均有所增加,中、大孔增加最为明显,孔隙连通性发生差异性变化,这种孔隙性的变化是造成不同煤体结构煤的吸附/解吸性、扩散性等储层物性出现差异的根本所在.原生结构和碎裂结构煤基质孔隙以微孔为主,相对缺少大孔以及大孔连通性较差的孔隙特征,制约着初期气体的解吸和扩散,而较小孔径段孔隙连通性相对较好利于后期气体的解吸和扩散,更由于气体解吸衰减速度慢,易形成长期的产能;碎粒结构和糜棱结构煤吸附、解吸能力增强,自然条件下气体扩散能力强,但储层条件下渗透率的强应力敏感性,导致该类储层渗透性最差,渗流能力弱制约了扩散和解吸的发生;气体综合产出过程中,不同煤体结构的煤储层随着储层压力的变化基质孔隙气体扩散模式发生动态演化,过渡型扩散不断增强,Fick扩散不断弱化,气体的扩散能力不断降低,其中微孔和过渡孔是限制气体扩散的主要孔径因素;提出的储层条件下气体产出的综合模式图可以显示制约不同煤体结构煤储层气体产出的关键因素所在,有助于对储层进行针对性改造.
Coal reservoir physical properties are the key factors affecting the desorption, diffusion and seepage of coalbed methane, which directly determines the gas production effect of coalbed methane wells.In this paper, high-rank coal, for example, based on mercury intrusion, low temperature liquid nitrogen adsorption, isothermal adsorption, coal The initial rate of grain methane release and the natural desorption data of coalbed methane wells, the response rules of physical properties such as porosity, adsorption, diffusivity and permeability of high-rank coal under structural failure were discussed systematically. Coal reservoir geometry model, diffusion mode diagram and gas output comprehensive model diagram.The study shows that high-grade coal experienced structural changes after the porosity has been modified, the number of pores in different pore diameters have increased, the largest increase in the large hole, The connectivity of pores is different, which is the fundamental reason for differences in the physical properties of the coal such as adsorption / desorption and diffusivity of coal with different coal structures.The pores of the primary structure and the fractured structure of coal matrix are characterized by micro Pore-dominated, relatively lacking of macropores and poor connectivity of macropores, restricting the desorption and diffusion of initial gases, whereas the pore connectivity of smaller pore sizes is relatively Good for post-desorption and diffusion of gas, but also due to slow desorption gas desorption, easy to form long-term capacity; fine structure and mylonitial coal adsorption, desorption enhanced ability to natural gas diffusion ability, but under reservoir conditions The strong stress sensitivity of permeability leads to the worst permeability of this kind of reservoirs and the weak seepage ability restricts the occurrence of diffusion and desorption. During the process of gas comprehensive output, the coal reservoirs with different coal structures will change with reservoir pressure The gas diffusion matrix of the matrix changed dynamically, the transitional diffusion increased continuously, the diffusion of Fick continued to weaken, and the diffusion ability of gas decreased continuously. Micropores and transitional pores were the main pore diameter to restrict gas diffusion. The output of the integrated model map can show the key factors restricting the gas output of coal-bed methane reservoirs with different coal structures, which can be helpful for the targeted transformation of the reservoir.