二连盆地巴彦宝力格煤田伊敏组低煤阶煤层气成藏条件及有利区预测

Accumulation conditions and favorable areas prediction of low⁃rank CBM in Yimin Formation of Bayanbaolige coalfield in Erlian Basin

为了明确二连盆地巴彦宝力格煤田伊敏组煤层气资源潜力,在伊敏组煤层发育及含气性分析基础上,对沉积环境、煤层厚度、构造特征、储层物性、盖层封闭能力及水文地质条件等煤层气成藏条件进行了系统剖析。结果表明:巴彦宝力格煤田伊敏组煤层的煤岩组分以暗煤为主,最大镜质体反射率为0.38%~0.46%,属于褐煤-长焰煤;伊敏组主力煤层为2#、3#、4#、4-1#煤,煤层分布广泛,结构简单,平均厚度为21.33 m,具备丰富的生气物质基础;煤层含气量差异较大,平均含气量为0.79~1.57 m^(3)/t,其中4#煤层含气量最高,4-1#煤层含气性最差;煤层沉积环境以扇三角洲及滨浅湖湖沼相为主,有利于形成广覆式中厚煤层;盆地构造形态简单,煤层主要赋存于向斜,受断裂影响较小,并且顶底板多为分布稳定的厚层泥岩;煤系含水层处于承压水封闭环境,为煤层气赋存提供了良好的保存条件;伊敏组煤层气有利勘探区主要位于中部的巴彦宝力格向斜轴部地区及东北部的五间房向斜轴部地区。研究成果对伊敏组及类似条件的低煤阶煤层气勘探开发具有指导意义。

In order to clarify CBM resources potential in Yimin Formation of Bayanbaolige coalfield in Erlian Basin,based on analysis of coalbed development and gas content in Yimin Formation,CBM accumulation conditions of sedimentary environment,coalbed thickness,structural characteristics,reservoir property,sealing capacity and hydrogeological conditions are systematically analyzed.The results show that coal rock composition of the coalbeds in Yimin Formation in Bayanbaolige coalfield is mainly dull coal with maximum vitrinite reflectance of 0.38%~0.46%,belonging to lignite-long flame coal.Main coalbeds of Yimin Formation include 2#,3#,4#and 4-1#coal‑beds,widely distributed with simple structure,and with average thickness of 21.33 m,being rich material basis for gas generation.Gas contents of coalbeds have much difference,with average gas content of 0.79~1.57 m^(3)/t,being the maximum in 4#coalbed is the least in 4-1#coalbed.Sedimentary environment is dominated by fan delta and shallow lake shore lacustrine facies,which is conducive to the formation of widely-covered medium-thick coalbeds.Basin structural morphology is simple,with coalbeds mainly hosted in synclines,which is less affected by faults,and the roofs and floors are mostly thick mudstone with stable distribution.Coal measures aquifers are in confined-water sealed environment,which provide good preservation conditions for CBM occurrence.Favorable exploration areas of CBM in Yimin Formation are mainly located in Bayanbaolige syncline-axis area in the center and Wujian‑fang syncline-axis area in the northeast.The research provides guiding significance for exploration and development of low-rank CBM in Yimin Formation and that with similar conditions.