贵州下寒武统牛蹄塘组页岩气成藏条件与有利区分析

Reservoir forming condition and favorable zones of shale gas in lower cambrian Niutitang formation in Guizhou

以贵州下寒武统牛蹄塘组为例,通过X射线衍射矿物分析、扫描电镜观察、孔渗测量、液氮吸附法和等温吸附模拟实验等多种方法,对研究区页岩气成藏条件进行了研究。分析得出,牛蹄塘组页岩厚度大,有机质丰度高,TOC分布在0.22%-22.15%,平均值为4.73%,热演化程度处于高成熟-过成熟阶段,RO值为1.6%-4.0%,主要发育I型干酪根。黑色页岩脆性矿物含量较高,石英含量平均达到58.25%。页岩主要发育有机质生烃形成的孔隙、次生溶蚀孔隙、黏土矿物伊利石化体积缩小形成的微孔隙等三种类型。页岩孔隙度平均为4.64%,渗透率平均为0.010 6×10-3μm2,有利于页岩气的富集。页岩比表面积在5.32-16.56 m2/g,平均为10.87 m2/g,孔体积为0.007-0.015 m L/g,平均为0.012 m L/g。等温吸附实验测得吸附量为1.41-2.48 m3/t,平均为2.09 m3/t,吸附能力较强。综合对比结果表明：岑巩-铜仁、印江-思南、湄潭-凤冈三个地区是页岩气勘探开发有利目标区,其中,印江-思南目标区是页岩气勘探开发的最有利区域,岑巩-铜仁和湄潭-凤冈地区页岩气勘探潜力较大。

Lower cambrian Niutitang formation is the main strata for exploration in the upper Yangtze platform.Based on X-ray diffraction mineral analysis,scanning electron microscopy（ SEM） observation,the measurement of porosity and permeability,liquid nitrogen adsorption methods,and isothermal adsorption methods,the accumulation conditions of shale gas from the lower cambrian Niutitang formation in Guizhou was investigated.It was found that the study region features is great organic rich shale thickness,high organic abundance. The TOC value ranges from 0. 22% to 22. 15%,with an average of 4. 73%. The vitrinite reflectance ranges from1. 60% to 4. 15% with an average of 2. 8%,and thermal evolution degree has reached high over thermal evolution level and consists mainly of kerogen of I type. The black shale is rich in brittle minerals,and quartz content is relatively high with an average of 58. 25%. Three types of pores are present in the shale,such as the pores in the formation of the hydrocarbon generation,the secondary dissolution pores and the micropores produced by volume reduction of illitization of clay mineral. The porosity of shale averages at 4. 64% and permeability 0. 010 6 × 10-3μm2,which are beneficial to the generation and enrichment of shale gas. Specific surface area of shale is between 5. 32 to 16. 56 m2/ g,with an average of 10. 87 m2/ g. Pore volume is in the range of 0. 007 - 0. 015 m L / g,with the mean of 0. 012 m L / g. The adsorption isotherm experiments suggest that adsorbed gas in black shale is from 1. 41 m3/ t to 2. 48 m3/ t,with an average of 2. 09 m3/ t,which indicate a strong adsorption capacity and there is a positive correlation between the adsorption ability and TOC.The results of comprehensive comparison show that three areas of Cengong-Tongren,Yinjiang-Sinan and Meitan-Fenggang are favorable targets for shale gas exploration and development. Yinjiang-Sinan is the most favorable region for shale gas exploration and development. The regions of Cengong-Tongren and Meitan-Fenggang have considerable exploration potential of shale gas.