川南地区五峰组—龙马溪组页岩储层纳米孔隙发育特征及其控制因素——以四川盆地南部长宁双河剖面为例

上奥陶统五峰组—下志留统龙马溪组页岩是四川盆地南部页岩气勘探开发的主要目的层之一。以川南长宁双河剖面为例，对该剖面41个露头样品进行了有机碳、矿物组成、二氧化碳和氮气吸附以及扫描电镜观测等分析测试，系统研究了奥陶系宝塔组灰岩和五峰组页岩以及下志留统龙马溪组页岩纳米孔隙发育特征，探讨了影响纳米孔隙发育的主要因素。五峰组—龙马溪组页岩富含有机质，矿物组成以生物成因石英和碳酸盐矿物为主，黏土矿物次之，含少量长石。五峰组—龙马溪组页岩纳米孔隙以狭缝型为主，孔径主要分布在0.3~0.9 nm、40~50 nm和100~200 nm之间，以有机孔为主，其次为矿物基质孔。纳米孔隙发育主要受有机碳、石英和碳酸盐矿物含量控制，主要表现为总孔体积与TOC和石英含量显著正相关，与碳酸盐矿物含量显著负相关，与黏土矿物和长石含量相关性不大，这表明五峰组—龙马溪组页岩内有机孔占据主导地位；奥陶系宝塔组碳酸盐矿物含量高，纳米孔隙极不发育，是上覆五峰组—龙马溪组页岩储层的良好封闭层。

Characteristics and controlling factors of nano pores in shale reservoirs of Wufeng-Longmaxi formations in southern Sichuan Basin: insights from Shuanghe outcrop in Changning area

Shale reservoirs within the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation(Wufeng-Longmaxi shales) have been one of the main targets for shale gas exploration and exploitation in the south of Sichuan Basin. This study focuses on the Wufeng-Longmaxi shales of the Shuanghe outcrop in Changning area, southern Sichuan Basin. Measurements including TOC, mineral composition, carbon dioxide and nitrogen adsorptions and FE-SEM were conducted on 41 samples to depict the nano porosity within the Ordovician Baota limestones and Wufeng-Longmaxi shale reservoirs and hence to clarify the regulating factors of the occurrence of nano pores. The Wufeng-Longmaxi shales are rich in organic matter. The mineral composition is dominated by biogenic quartz and carbonate minerals, followed by clay minerals and a small amount of feldspar. The nano pores in Wufeng-Longmaxi shales are dominated by silts, with pore diameters mainly distributed between 0.3-0.9, 40-50 and 100-200 nm, mainly organic pores, followed by mineral matrix pores. The occurrence of nano pores is controlled by the contents of organic matter, quartz and carbonates. Total pore volumes of selected samples are strongly correlated with TOC and quartz contents positively and carbonate contents negatively, and have no correlation with clays or feldspar. This indicates that nano pores within these samples are dominated by organic matter pores. The Ordovician Baota limestones are depleted in various nano pores, hence resulting in a good underlying sealing layer of Wufeng-Longmaxi shale reservoirs.