川南—黔中地区下寒武统页岩气富集条件探讨

Shale gas accumulation conditions of the Lower Cambrian in southern Sichuan-central Guizhou,China

根据川南—黔中地区下寒武统黑色页岩的露头观测与钻井岩心描述、氩离子抛光—扫描电镜、等温吸附等方法所获地球化学和物性资料,探讨了页岩气富集条件。研究区富有机质页岩沉积相为深水陆棚相、中陆棚相等;有机碳含量普遍在2%以上;成熟度介于1.32%~4.78%之间,均值为2.85%;主要发育Ⅰ型干酪根;储集类型主要以微米-纳米孔隙发育为主,裂缝比较发育,孔隙度介于0.24%~11.9%之间,渗透率介于(0.000 087~0.535)×10^(-3)μm^2之间,等温吸附实验测试平均吸附气量为2.74m^3/t。黄页1井现场解析含气量介于0.16~0.99m^3/t之间,平均含气量为0.52m^3/t;金石1井现场解析含气量介于1.51~2.41m^3/t之间,均值为1.8m^3/t。研究表明:四川盆地内下寒武统页岩经历了有利于页岩气成藏的长期浅埋—长期隆升—快速深埋—快速抬升的埋藏史及热演化史且构造相对稳定,导致其具有较好页岩气保存条件;而盆外地区由于经历了多期次的生排烃,同时也遭受了多次构造运动的改造,致使页岩气藏的保存条件遭到不同程度的破坏。因此,优越的物质基础、保存条件等是页岩气富集成藏的主控因素。勘探选区上应往四川盆地内走,选区上要寻找有利于页岩气成藏的埋藏史及热演化史的同时采取"高中找低、强中找弱、好中找厚"的原则。

According to the Lower Cambrian black shale outcrop observation and drilling core description in southern Sichuan-central Guizhou,based on the method of argon ion polishing-scanning electron microscopy,geochemical isothermal adsorption method and geophysical data,this paper discussed the conditions of shale gas enrichment.In the study area the sedimentary facies of the organic-rich shale is deep water shelf facies and middle shelf facies; the organic carbon content is above 2% in general,and the maturity is 1.32%-4.78%,averaging at 2.85%.Type I kerogen is the dominant organic materials,and the reservoir types are mainly micron-nano porosity,with developed fractures.The shale property statistics show that porosity ranges between 0.24%-11.9% and permeability ranges between （0.000 087-0.535）×10-3μm2,and the average content of gas capacity from isothermal adsorption test is 2.74m^3/t.The content of gas of Huangye-1 well from field analysis is between 0.16m^3/t to 0.99m^3/t with an average of 0.52m^3/t.The content of gas of Jinshi-1 well from field analysis is between 1.51-2.41m^3/t,with an average of 1.8m^3/t.The research shows that shale in the Lower Cambrian in Sichuan Basin has good experience for shale gas accumulation of long shallow burial-long uplift-rapid deep subsidence-rapid uplift of the burial history and thermal evolution history and the structure is relatively stable,so it results in good shale gas preservation conditions,but outside the area of the basin,the hydrocarbon generation and expulsion,which experienced many times,also suffered from the transformation of tectonic movement,and the preservation conditions of shale gas reservoirs were destroyed in different degrees.Therefore,the superior material basis,preservation condition are the main controlling factors for shale gas enrichment.The exploration area should go to the Sichuan Basin,the constituency to find conducive to shale gas reservoirs of the burial history and thermal history,and at the same time we should take the principle which is “high to find low,strong to find weak,good to find thick”.