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沁水盆地煤系气含气层段发育特征及其地质控制效应

Distribution and geological controls on gas-bearing section of coal measure gases in Qinshui Basin

  • 摘要: 为揭示煤系气共生成藏特征及其地质控制效应,以沁水盆地石炭-二叠纪太原组-山西组煤系为研究对象,通过资料收集、现场和室内试验测试、理论分析等综合研究手段,厘定了煤系气储层空间叠置特征,定量表征了煤系气储层多尺度储集空间,判识了煤系气共生含气层段空间发育规律,明确了煤系气共生成藏类型及其地质控制效应。结果表明,海陆交互相沉积的岩性多样、旋回性叠置煤系,具备了煤系气共生成藏基础及合探共采条件,目标煤系从“无机储层”至“混合储层”到“有机储层”,有机质丰度逐渐增高,形成一个不存在自然界限的连续岩性序列。煤系气共生含气层段垂向上呈间隔式分布,共生气藏组合类型包括煤系页岩气主导型共生气藏、煤层气主导型共生气藏和多元型煤系气共生气藏。煤系气共生含气层段地质控制效应显著,煤层发育程度决定了共生含气层段的形成基础;埋藏条件造就了优势气藏类型的差异性,煤层固气能力更强,更易形成独立煤层气藏,而煤系页岩气和煤系气砂岩气成藏条件相对更为苛刻,对地质基础与时空配置条件要求极高;储层物性特征限制了煤系页岩气和煤系砂岩气的成藏潜力。研究成果有助于今后进一步深入开展煤系气共生成藏机理研究,系统完善煤系气共探合采评价体系。

     

    Abstract: To study the characteristics of coupled accumulation and determine the geological control effects on coal measures gases (CMGs), coal measures of the Carboniferous-Permian Taiyuan and Shanxi formations at Qinshui Basin were selected as the target formations. Various methods including field data collection, field/lab measurements, and theoretical analyses were applied to described the spatial superposition of CMG reservoirs, quantitatively determine the multi-scale pore system, identify the spatial development pattern of CMGs gas-bearing section, and clarify the types of CMGs coupled accumulation and geological controls. Results show that coal measures deposited at the unique marine-terrigenous depositional environment was characterized by lithological diversity and cyclic superposition which was served as the potential basics for coupled accumulation and co-exploration/development of CMGs. The abundance of the organic matter gradually increased from the “inorganic reservoir” to “organic reservoir”, forming a continuous rock sequence without a natural boundary in target coal measures. Gas-bearing sections was characterized by a vertically intermittent distribution and the dominant coupled accumulation assemblages can be subdivided into: shale gas dominated coupled accumulation type, CBM dominated coupled accumulation type, and multiple CMGs coupled accumulation type. Obviously, the effective gas-bearing sections need the appropriate combination of source, reservoir and cap. Coal reservoirs directly controlled the distribution of effective gas-bearing section. Reservoir burial conditions restricted the possibility of an effective gas-bearing section. Moreover, coals were believed to be more favorable for independent coalbed methane accumulation, whereas shale gas and sandstone gas required extremely strict geological, spatial and temporal conditions. Additionally, both organic-inorganic fabric and physical characteristics limited the potential of effective gas-bearing sections. Inspired by the findings of this study, further studies on the coupled accumulation mechanism and the co-exploration evaluation system of CMGs should be continuously conducted.

     

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