富有机质页岩解吸气地球化学特征及其指示意义

The geochemical characteristics and significance of the desorption gas in organic-enriched shale

利用页岩气现场解吸仪对龙马溪组页岩岩心进行二阶解吸(一阶45℃,二阶110℃),计量解吸气量和恢复损失气量的同时,连续采集不同解吸时段的解吸气样品并进行组分和同位素测定。结果表明:页岩解吸气以CH_4为主,含有少量的C_2H_6、CO_2和N_2,一阶解吸阶段页岩吸附能力弱的CH_4含量较高,表明这一阶段解吸气以游离气为主;二阶解吸阶段页岩吸附能力强的C_2H_6和CO_2含量较高,表明此阶段解吸气中吸附气所占比例逐渐增高;解吸气随解吸时间增加烷烃气碳同位素组成逐渐变重,主要受气体在扩散过程中的"质量分馏效应"和"吸附—脱附"作用影响;整个解吸过程中解吸气烷烃气碳同位素均发生倒转且倒转程度随解吸时间增加逐渐变大,主要受解吸过程中甲烷碳同位素组成逐渐变重影响。

Core samples of Longmaxi shale are desorped（45℃ and 110℃）using shale gas field instrument to measure the gas content,i.e.,measuring the adsorption gas content and loss gas contents,and sampling gas samples and determining component and isotope at the same time.Analytical results show that the desorption gas is dominated by CH_4,with a small amount of C2H6,CO2,N2.The high content of CH4 with weak adsorption capacity at the first stage shows desorption gas is mainly free gas,and the high content of C2H6 and CO2 with higher adsorption capacity at the second stage shows desorption gas is mainly adsorption gas.The carbon isotope becomes heavier with the increase of desorption time,mainly affected by the mass fractionation and adsorption-desorption.The carbon isotope is reversed and the inversion degree gradually increases with the desorption time,which is mainly affected by the carbon isotope of methane.