宁武盆地南部深部煤层气临界深度与成藏特征

Critical depth and accumulation characteristics of deep coalbed methane in the southern Ningwu Basin

近年来,随着深部煤层气勘探开发技术的不断突破,深部煤层气已逐渐成为中国油气资源重要的勘探开发新领域。但是,关于煤层气深度界线的科学内涵、深部煤层气藏的地质特征、煤层气富集模式等基础科学问题仍处于初期探索阶段。为此,以宁武盆地宁武南区块上石炭统太原组9号煤层为研究对象,基于区块20余口煤层气井的钻井、测井及试井资料等,联合等温吸附、气体同位素等实验测试手段,探讨了宁武南区块深部煤层气临界深度与成藏特征。研究结果表明:①研究区深部煤层气临界深度为1200 m,临界深度以深,深部煤层气藏具有煤层厚度大、热演化程度高、含气量及含气饱和度高、煤体结构好和孔隙度低的地质特征。②地温梯度和热演化程度是影响研究区深部煤层气临界深度及煤层气成藏条件的重要因素。结论认为,该盆地的宁武南区块深部煤层气地质特征与鄂尔多斯盆地大宁—吉县、临兴、延川南等深部煤层气区块具有可比性,展现出宁武盆地深部煤层气良好的勘探开发前景。

In recent years,deep coalbed methane(CBM)has gradually become an important exploration and development field for oil and gas resources in China with continuous breakthroughs in deep CBM exploration and development technologies,but the basic scientific issues such as the scientific connotation of CBM depth limit,the geological characteristics of deep CBM reservoirs and the CBM enrichment patterns are still in the early exploration stage.Taking the No.9 coal seam of Taiyuan Formation in the Ningwunan Block of southern Ningwu Basin as the research object,this paper discusses the critical depth and accumulation characteristics of deep CBM in the Ningwunan Block based on drilling,logging and testing data of more than 20 CBM wells in this block,combined with isothermal adsorption and gas isotope experimental results.And the following research results are obtained.First,the critical depth of the deep CBM in the study area is 1200 m,and the deep CBM reservoir below the critical depth is geologically characterized by great coal seam thickness,high degree of thermal evolution,high gas content,high gas saturation,good coal structure and low porosity.Second,geothermal gradient and thermal evolution degree are important factors influencing the critical depth and accumulation conditions of deep CBM in the study area.In conclusion,the geological characteristics of deep CBM in the Ningwunan Block of southern Ningwu Basin are comparable to those of deep CBM blocks in the Ordos Basin such as Daning-Jixian,Linxing,and Yanchuannan,indicating promising exploration and development prospects of deep CBM in the Ningwu Basin.