海陆过渡相地层有机质纳米孔成因及地质意义 ——以鄂尔多斯盆地东部山西组为例

海陆过渡相煤系地层已经发现丰富的非常规天然气资源。本文以鄂尔多斯盆地东部山西组煤系地层为例，通过开展微观特征分析及物理模拟实验，查明山西组主要孔隙类型为有机质孔隙、残余原生孔隙、不稳定矿物溶蚀孔、黏土矿物层间孔，认为黏土矿物层间孔和有机质纳米孔隙是页岩储集空间与常规砂岩储层的显著区别；山西组煤系地层广泛发育的有机质纳米孔，经过模拟实验认为形成于早期液态烃裂解气，随着原油沥青化，气泡被固化在沥青条带中形成纳米孔隙；集中发生在晚侏罗世至早白垩世末的异常热事件控制了裂解气生成的强度和范围，在此过程中沥青化产生的有机质纳米孔大幅度提高煤系地层非常规气储集空间和资源丰度。这一认识对于深入了解山西组煤系地层孔隙结构特征及非常规油气地质评价选区具有重要意义。

Genesis and geological significance of organic matter nanopores in transitional facie strata: taking Shanxi Formation in eastern Ordos basin as an example

Abundant unconventional natural gas resources have been found in coal measures deposited transitionalfacies in Carboniferous-Permian strata. In this paper, the author had carried out microscopic characteristics and physical simulation experiments on Shanxi Formation in Ordos basin, and found out that the main pore types of Shanxi formation includes organic matter pore, residual primary pore, unstable mineral dissolution pore and clay mineral interlayer pore. Interlayer pores of clay minerals and nano pores of organic matter are significant differences between shale and conventional sandstone reservoirs. Nano pores of organic matter are widely developed in coal measure strata of Shanxi formation. Through simulation experiments, it is believed that the forming processof nanopores is seriously related to the cracking gas of early formed liquid hydrocarbon in strata. With the asphaltation of crude oil, bubbles solidified in asphalt strips and converted nano pores. From Late Jurassic to the end of Early Cretaceous, abnormal thermal eventswhich controlled the generation intensity and scope of pyrolysis gas occurred widely in Ordos basin. Duringthe process of asphalting, lots of organic matter nanopores formed, which greatly improved the resource abundance of unconventional gas in coal measures. Thisknowledge from the experimentscouldtakea better understanding of the pore structure characteristics in coal measuresand be helpful for the selection of unconventional oil and gas prospecting area in Shanxi Formation.