郭涛，金晓波，武迪迪，等. 川东南南川区块龙潭组深部煤层气成藏特征及勘探前景[J]. 煤田地质与勘探，2024，52(4)：60−67. DOI: 10.12363/issn.1001-1986.23.10.0684
引用本文: 郭涛，金晓波，武迪迪，等. 川东南南川区块龙潭组深部煤层气成藏特征及勘探前景[J]. 煤田地质与勘探，2024，52(4)：60−67. DOI: 10.12363/issn.1001-1986.23.10.0684
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GUO Tao，JIN Xiaobo，WU Didi，et al. Accumulation characteristics and exploration prospects of deep coalbed methane in the Longtan Formation of the Nanchuan block on the southeastern margin of the Sichuan Basin[J]. Coal Geology & Exploration，2024，52(4)：60−67. DOI: 10.12363/issn.1001-1986.23.10.0684
Citation: GUO Tao，JIN Xiaobo，WU Didi，et al. Accumulation characteristics and exploration prospects of deep coalbed methane in the Longtan Formation of the Nanchuan block on the southeastern margin of the Sichuan Basin[J]. Coal Geology & Exploration，2024，52(4)：60−67. DOI: 10.12363/issn.1001-1986.23.10.0684
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川东南南川区块龙潭组深部煤层气成藏特征及勘探前景

Accumulation characteristics and exploration prospects of deep coalbed methane in the Longtan Formation of the Nanchuan block on the southeastern margin of the Sichuan Basin

    摘要
  • 摘要: 四川盆地东南缘南川区块Y2井直井自喷日产气1.3×104 m3，获四川盆地东南缘深部煤层气勘探战略突破。为了系统揭示南川区块深部煤层气富集高产规律，通过区域地质、测试、化验及生产资料，从煤岩煤质、孔裂隙发育特征、含气性、可压性入手，开展深部煤层气成藏特征及勘探潜力评价。结果表明：研究区深部煤储层全区稳定分布，厚度在1.5~4.2 m，镜质体随机反射率Rran在1.6%~2.2%，为高镜质组含量、低灰分煤层，为煤层气成藏提供了物质基础；煤储层为“微孔−微裂隙”型储层，微孔占比达78.4%，其比表面积贡献达95%，利于煤层气吸附与保存，微裂隙发育，利于压裂改造及气体渗流；煤层具有“高含气量、富含游离气”的特征，总含气量12~37 m3/t，深部煤层气游离气占比一般在24%~36%，吸附临界转换深度在1500 m左右；深部煤层水平应力差异系数小，煤体结构好，顶板为良好的应力隔档，天然裂缝与最大主应力夹角小，具有良好的可压性；丁山、林滩场等盆缘宽缓背斜及盆内高陡背斜是川东南深部煤层气勘探的有利区带。研究成果对川东南深部煤层气勘探具有重要的指导作用，也可为全国类似盆地深部煤层气勘探提供借鉴。

     

    Abstract: Vertical well Y2 in the Nanchuan bloc on the southeastern margin of the Sichuan Basin has yielded daily production of natural flowing gas of 13000 m3, signifying a strategic breakthrough in deep coalbed methane (CBM) exploration on the margin. This study aims to systematically reveal the enrichment and high-yield patterns of CBM in the Nanchuan block. Using data on the regional geology, tests, assays, and production, this study investigated the accumulation characteristic and conducted exploration potential evaluation for deep CBM in the Nanchuan block from the perspective of the quality, pore and fissure characteristics, gas content, and fracability of coals. The results are as follows: (1) The deep coal reservoirs in the study area exhibit stable distribution, with thicknesses ranging from 1.5 m to 4.2 m and vitrinite reflectance (Rran) from 1.6% to 2.2%, establishing them coal seams with high Rran values and low ash content. These coal seams provide a material basis for CBM accumulation. (2) The coal reservoirs are of micro pore-micro and -fissure type, with micro-pores accounting for 78.4% and contributing 95% to the total specific surface area. These are conducive to CBM adsorption and preservation. Furthermore, these reservoirs exhibit well-developed micro-fractures, which are beneficial for fracturing and gas seepage. (3) The coal seams feature high gas content and rich free gas, with a total gas content ranging between 12 m3/t and 37 m3/t and free gas generally accounting for 24% to 36% of the deep CBM. The critical conversion depth of absorption is about 1500 m. (4) The deep coals exhibit small horizontal stress difference coefficients, favorable coal structures, strong stress barriers as roof, and small angles between natural cracks and the maximum principal stress, which contribute to high fracability. (5) Wide and gentle anticlines in the Dingshan and Lintanchang areas on basin margins emerge as favorable zones for deep CBM exploration. The results of this study will serve as a guide for deep CBM exploration on the southeastern margin of the Sichuan Basin and provide a reference for deep CBM exploration in similar basins.

     

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