滇东黔西典型区块煤系气共生组合规律及其地质成因

Symbiotic combination of coal measure gas and its geological origin in typical blocks of Eastern Yunnan and Western Guizhou

  • 摘要: 煤系气是重要的天然气资源,为了明确煤系气共生组合类型及地质成因,以滇东黔西13口煤层气勘探开发井气测录井资料为依托,分析了研究区二叠纪煤系砂岩、泥页岩气测显示特征,结果显示:研究区内煤层成群分布,煤层总厚度较大,煤阶主要为中-高阶,变质程度较高,含气性良好;煤系砂岩、泥页岩气测显示异常频繁,异常层位总厚度较大,平面及垂向分布差异显著;煤层气、砂岩气、泥页岩气共生组合方式多样化,煤系垂向叠置多套不同类型的煤系气藏,且区域间同样存在较大的差异。划分出独立砂岩气藏、独立泥页岩气藏、泥页岩-砂岩互层气藏、单煤层煤-泥页岩-砂岩互层气藏、多煤层煤-泥页岩-砂岩互层气藏等5种类型。龙潭组煤层、砂岩、泥页岩薄互层式叠置,造成不同气藏交替成藏。其中单煤层气藏在黔西龙潭组全层段均有分布且主要发育于煤系上段,而滇东龙潭组单煤层互层气藏主要存在于煤系中段;多煤层互层型气藏存在于龙潭组全层段,且主要存在于黔西龙潭组中段、滇东龙潭组下段。对煤系气藏地质成因进行了研究,发现煤系气藏受沉积环境、构造作用、热演化作用和水文条件耦合影响,相对稳定的沉积环境(如三角洲)、良好的保存条件、相对封闭的水文特征、较高的热演化程度是煤系三气富集的有利条件。

     

    Abstract: Coal-measure gas is an important natural gas resource.In order to understand the type and geological origin of the coal-measure gas symbiosis combination, based on the logging data of 13 coal-bed methane exploration and development wells in eastern Yunnan and western Guizhou, the Permian coal measures in the study area are analyzed.The characteristics of sandstone and shale gas surveys show that the coal seams in the study area are distributed in groups, the total thickness of the coal seams is relatively large, the coal ranks are mainly middle-high rank, the metamorphism is high, and the gas content is good.The gas survey in coal measure sandstone and mud shale shows that the abnormality is frequent, the total thickness of the abnormal horizon is large, and the plane and vertical distribution are significantly different.The co-existence combination of coalbed methane, sandstone gas, and shale gas is diversified, and the coal measures are vertically stacked with multiple sets of different types of coal measure gas reservoirs, and there are also large differences between regions.Five types of gas reservoirs are classified including separate independent sandstone gas reservoirs, independent shale gas reservoirs, shale-sandstone interbedded gas reservoirs, single-coal-shale-sandstone interbedded gas reservoirs, and multi-coal coal-shale-shale-sandstone interbedded gas reservoirs.Longtan Formation coal seams, sandstone, and shale are thinly interbedded, causing different gas reservoirs to form alternately.Among them, single coalbed methane reservoirs are distributed throughout the entire interval of Longtan Formation in western Guizhou and mainly developed in the upper coal measures, while single-coal interbedded gas reservoirs of Longtan Formation in eastern Yunnan mainly exist in the middle section of coal measures.Multi-coal interbedded gas reservoirs exist in the whole section of Longtan Formation, and mainly exist in the middle section of Longtan Formation in western Guizhou and the lower section of Longtan Formation in eastern Yunnan.The geological genesis of coal-measure gas reservoirs is studied, and it is found that coal-measure gas reservoirs are affected by the coupling of depositional environment, tectonic effect, thermal evolution and hydrological conditions.The relative stable depositional environment(such as delta),good preservation conditions, and relative closed hydrological characteristics and a high degree of thermal evolution are favorable conditions for the enrichment of three gases in coal measures.

     

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