韩城北部煤层气储层物性特征及其主控因素研究

    Study on physical property characteristics and main controlling factors of coalbed methane reservoir in northern Hancheng Mine Area

    • 摘要: 在全面收集研究区煤层及煤层气地质勘查资料及实验测试成果的基础上,采用定量化分析方法,系统分析煤层吸附能力、含气性、地应力、孔渗性等的变化规律,重点探讨影响该区煤层气赋存的主控因素及开发地质条件。研究表明:该区煤层含气量总体受埋深控制,西高东低;纵向上,随埋深增大,煤的变质程度增高;埋深小于1 000 m,压力的正效应起主导作用,含气量、含气饱和度、渗透率随埋深的增大而增高,孔隙度随埋深的增大而降低;埋深超过1 000 m,温度的负效应起主导作用,含气量、含气饱和度随埋深的增大而降低,孔隙度逐渐反弹,渗透率逐渐降低;二者过渡埋深范围为750~1 000 m;埋深小于750 m,以水平应力为主,为压缩型地应力场;埋深介于750~1 000 m之间,部分转换为以垂直应力为主,表现出拉张型地应力场,有利于裂隙发育,渗透性变好,渗透率随埋深增大而增高;埋深大于1 000 m,重新转换为压缩型地应力场,渗透率随埋深增加而大幅降低。

       

      Abstract: Based on the comprehensive collection of geological exploration data and experimental test results of coal seam and coalbed methane in the study area, we adopt quantitative analysis method to systematically analyze the change law of adsorption capacity, gas content, in-situ stress, porosity and permeability of coal seam, and emphatically discuss the main controlling factors and development geological conditions affecting the occurrence of coalbed methane in the area. The study shows that the gas content of coal seam in this area is generally controlled by the burial depth, which is high in the west and low in the east. Longitudinally, the metamorphic degree of coal increases with the increase of buried depth. When the burial depth is less than 1 000 m, the positive effect of pressure plays a dominant role. The gas content, gas saturation and permeability increase with the burial depth increasing, while the porosity decreases with the burial depth increasing. When the burial depth is more than 1 000 m, the negative effect of temperature plays a dominant role. The gas content and gas saturation decrease with the increase of the burial depth, the porosity gradually rebounds, and the permeability gradually decreases. The transitional burial depth of both is from 750 m to 1 000 m. The buried depth is less than 750 m, the horizontal stress is the main stress field, and it is a compressive in-situ stress field. The buried depth is between 750 and 1 000 m, and the vertical stress is predominant in part, showing tensile in-situ stress field, which is conducive to the development of fracture, and the permeability is better, and the permeability increases with the increase of the buried depth. When the buried depth is greater than 1 000 m, it is transformed into compressive in-situ stress field again, and the permeability decreases greatly with the increase of buried depth.

       

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