鲁西南地区煤成气盖层类型及分布

Coal Gas Caprock Types and Distribution in Southwestern Shandong

运用石油地质学与煤成气地质学等研究方法,分析了鲁西南地区煤成气盖层类型及其分布特征。研究表明,鲁西南地区除发育较好的煤成气烃源岩、储集层外,盖层保存也较完整,具备了该地区良好的煤成气成藏条件。在各凹陷区内,石炭—二叠系保存完整,其煤层上覆的泥质岩分布广泛,且多含有机质,厚度100～400m,其中包括一套对煤成气封闭能力最佳的杂色铝土质泥岩层(俗称"B层铝土"),厚10～30m;古近系也发育了多套以泥质岩为主的沉积,泥质岩总厚度达1000m以上,这些泥质岩大多为暗色,富集有机质。这些形成于不同时期的煤系地层上覆泥岩层共同构成了本区较好的区域性盖层。尤其在成武凹陷、鱼台凹陷和大汶口凹陷发育的古近系化学蒸发岩类——石膏、岩盐,是该地区煤成气最重要的区域盖层。

Applying research methods of petroleum geology and coal gas geology on the study, analyzed the coal gas caprock types and distribution features in the Shandong Province. The results demonstrated that except well developed hydrocarbon source rocks and reservoir beds, caprocks are also perfectly preserved, thus a good coal gas reservoir-forming condition. In each depression, Permo- Carboniferous strata are integrally preserved, coal seam overlying argillaceous rocks are vastly distributed and contain much organic matters, 100-400m thick. In which, a set of variegated bauxitic mudstone （commonly called ＂B allite＂） 10-30m thick, is provided with excellent confining ability over coal gas. Multiple sets of mainly argillaceous deposits developed during Paleogene with total thickness exceed 1000m, mostly dark colored and organic matter enriched. All coal measures strata overlying mudstone layers formed during different periods were jointly composed better regional caprocks in the area. Especially, Paleogene chemical evaporitesgypsum, rock salt etc. developed in Chengwu, Yutai and Dawenkou depressions are most important regional coal gas caproeks in the area.