黔西北寒武系牛蹄塘组与志留系龙马溪组页岩生烃和储集能力差异分析

Difference analysis of hydrocarbon generation and reservoir capacity between the Cambrian Niutitang Formation and the Silurian Longmaxi Formation in Northwest Guizhou

以黔西北牛蹄塘组和龙马溪组页岩为研究对象,在对钻井岩心样品进行有机地球化学和储层分析实验的基础 上,对牛蹄塘组和龙马溪组页岩气成藏条件进行了对比。牛蹄塘组和龙马溪组原始T OC分 别为8.68%~10.50%和 0.60%~9.45%,原 始生烃潜量分别为62.77~75.20mg/g和4.44~69.70mg/g,演 化至成熟时平均产气量分别为93.35cm3/g 和58.58cm3/g,证 明了牛蹄塘组页岩原始生烃能力远好于龙马溪组页岩。牛蹄塘组和龙马溪组页岩最大吸附气含量分 别为1.81~9.07m3/t和2.24~2.49m3/t,孔隙大小主 要分布在3.48~3.65nm范围内,牛蹄塘组页岩总孔体积和比表面积总体 上小于龙马溪组页岩。综合研究认为:牛蹄塘组页岩与龙马溪组页岩相比,更有利于富集吸附态天然气,但牛蹄塘组页 岩天然气生成时期早、演化时间长,导致大部分天然气散失,加之页岩孔隙度降低也导致游离气富集能力下降,最终使 得牛蹄塘组页岩气成藏能力弱于龙马溪组。

Based on the organic geochemistry and reservoir analysis experiments of drilling core samples, the shale gas accumulation conditions of the Cambrian Niutitang Formation and the Silurian Longmaxi Formation in Northwest Guizhou are compared. The original TOC of shale of Niutitang Formation and Longmaxi Formation is 8.68%~10.50% and 0.60%~9.45% respectively, the original hydrocarbon generation potential is 62.77~75.20 mg/g and 4.44~69.70 mg/g respectively, and the average gas production is 93.35 cm3/g and 58.58 cm3/g respectively, which proves that the original hydrocarbon generation capacity of Niutitang Formation is much better than that of Longmaxi Formation. The maximum adsorbed gas content of shale of Niutitang Formation and Longmaxi Formation is 1.81~9.07 m3/t and 2.24~2.49 m3/t respectively. The pore size is mainly distributed in the range of 3.48~3.65 nm. The total pore volume and specific surface area of Niutitang shale are generally smaller than those of Longmaxi shale. Comprehensive study shows that Niutitang shale is more conducive to enriching adsorbed natural gas than Longmaxi Formation shale. However, shale gas of Niutitang Formation is formed much early and evolved for a very long time, which leads to the loss of most natural gas, the decrease of shale porosity, and the decrease of free gas enrichment capacity. Thus, the gas accumulation capacity of Niutitang shale is weaker than Longmaxi shale.