煤系气叠置含气系统与天然气成藏特征——以沁水盆地榆社—武乡示范区为例

Superimposed gas-bearing system of coal measure gas and its natural gas accumulation characteristics:A case study of Yushe-Wuxiang demonstration area in the Qinshui Basin

中国煤系气资源丰富,其中沁水盆地是中国煤系气分布的主要盆地之一,明确煤系气叠置含气系统分布特征,有助于实现煤系气的共探合采。为此,以沁水盆地榆社—武乡示范区石炭系—二叠系含煤地层为研究对象,在分析煤系气地质特征的基础上,划分了煤系气叠置含气系统,研究了煤系气的源岩—储层共生组合特征、储层分布特征、共生成藏特征,并详细分析了示范井的压裂合采效果,预测了示范井产量。研究结果表明:①研究区目标煤系空间上发育3个独立叠置含气系统,其中含气系统Ⅰ是以15号煤和富有机质泥岩为主要烃源岩的“泥岩—煤—泥岩”组合;含气系统Ⅱ是以11号、12号煤和富有机质泥岩为主要烃源岩的“泥岩—砂岩—煤—泥岩”组合和以8号煤与富有机质泥岩为主要烃源岩的“泥岩—煤—砂岩—泥岩”组合;含气系统Ⅲ是以3号煤和富有机质泥岩为主要烃源岩的“泥岩—煤—砂岩”组合;②煤系气储层具有单层厚度薄、累计厚度大的空间展布特征,各含气系统中气藏组合类型以煤层气为主,页岩气和致密砂岩气发育较差;③示范井煤系气合采甜点含气层段发育于含气系统Ⅱ和Ⅲ,具备压裂合采基础,运用电缆桥塞与射孔联作投球分层压裂工艺配套技术实现了深部煤系气的有效开采。结论认为:①叠置含气系统兼容性是控制煤系气开采的关键因素,未来仍需不断优化排采制度以提高煤系气的合采产能;②研究成果对深化煤系气共生成藏机理、优选合采甜点层段、释放深部煤层气资源和实现煤系气高效合采均具有理论和实践意义。

There are abundant coal measure gas resources in China,and the Qinshui Basin is one of the main distribution basins of coal measure gas in China.It is helpful to realize the co-prospecting and co-production of coal measure gas by clarifying the hydrocarbon accumulation characteristics of the coal measure gas superimposed gas-bearing system.Taking the Carboniferous-Permian coal-bearing strata in the Yushe-Wuxiang Block of the Qinshui Basin as the research object,this paper classifies the superimposed gas-bearing system of coal measure gas by analyzing the geological characteristics of coal measure gas.Then,the source rock-reservoir symbiotic assemblage characteristics,reservoir distribution characteristics and symbiotic accumulation characteristics of coal measure gas are studied.Finally,the fracturing co-production effects of the demonstration wells are analyzed in detail,and the production rates of the demonstration wells are predicted.And the following research results are obtained.First,three independent gas-bearing systems are developed in the target coal measure of the study area,among which gas-bearing system I is a"mudstone-coal-mudstone"assemblage with 15^(#)coal and organicrich mudstone as the main source rocks,gas-bearing system II is a"mudstone-sandstone-coal-mudstone"assemblage with 11^(#)and 12^(#)coal and organic-rich mudstone as the main source rocks and a"mudstone-coal-sandstone-mudstone"assemblage with 8^(#)coal and organic-rich mudstone as the main source rocks,and gas-bearing system III is a"mudstone-coal-sandstone"assemblage with 3^(#)coal and organic-rich mudstone as the main source rocks.Second,the reservoirs of coal measure gas have the spatial distribution characteristics of small singlelayer thickness and large cumulative thickness,and the gas reservoir combination type in each gas-bearing system is mainly coalbed methane with poorly developed shale gas and tight sandstone gas.Third,the gas-bearing sections of the co-production sweet spots of coal measure gas in the demonstration wells are developed in gas-bearing systems II and III,which have the foundation of fracturing coproduction.The cable bridge plug and perforation combined with ball separate-fracturing process makes the greatest contribution to coproduction capacity,which makes the efficient exploitation of deep coal measure gas feasible.In conclusion,the compatibility of the superimposed gas-bearing system is a key factor controlling the exploitation of coal measure gas,and in the future,it is still necessary to continuously optimize the production system to increase the co-production capacity of coal measure gas.What's more,the research results are of theoretical and practical significance to further understand the symbiotic accumulation mechanism of coal measure gas,select the co-production sweet spot interval,liberate deep coalbed methane resources and realize the efficient co-production of coal measure gas.