海陆过渡相页岩气形成热模拟实验研究

Pyrolytic study on the gas-generating process of transitional shale

晚古生代海陆过渡相泥页岩在中国南北方广泛分布,页岩气资源潜力巨大。应用生烃热模拟实验,对采集于鄂尔多斯盆地上古生界山西组山2段未成熟海陆过渡相富有机质页岩的页岩气形成过程进行研究。实验结果表明,山2段海陆过渡相页岩在实验最低温度(T=337.2℃,Ro=0.74%)时就生成液态烃和气态烃,在385.3℃(Ro=1.08%)时液态烃达到生成高峰,此后甲烷(CH_4)产率迅速增大,干燥系数开始变大;重烃气(C_(2-5))达到生成高峰(T=456.2℃,Ro=2.09%)时甲烷产率曲线出现拐点;甲烷主要由液态烃裂解形成,部分由重烃气裂解形成;在实验最高温度(T=599.7℃,Ro=4.45%)时甲烷产率达956.93mL/g_(TOC),干燥系数达99.75%,但仍有少量重烃气和液态烃可以继续裂解生成甲烷。山2段页岩气形成具有3个阶段,即337.2℃≤T≤385.3℃(0.74%≤Ro≤1.08%)为生油阶段,伴有少量页岩气形成;385.3℃<T≤456.2℃(1.08%<Ro≤2.09%)为油气共生阶段,页岩气以湿气为主;456.2℃<T≤599.7℃(2.09%<Ro≤4.45%)为生气阶段,页岩气以干气为主。海陆过渡相山2段页岩具有与海相Barnett页岩相似的气态烃形成过程,但是页岩气产率高。研究认为海陆过渡相山2段富有机质页岩具有页岩气勘探所需要的良好物质基础和生烃潜力。

Late Paleozoic mudstone and shale deposited in the marine-terrestrial transitional environments are widely developed in southern and northern China,showing great potential of shale gas,In order to study the process of gas generation,pyrolysis experiment was conducted on immature organic-rich shale samples collected from the section 2 of Shanxi Formation （Shan 2）in Ordos Basin,north China,Pyrolysis results indicate that liquid and gaseous hydrocarbon have been generated at the lowest experimental temperature （T=337.2℃,RO=0.74%）,The peak of liquid hydrocarbon generation arrived at 385.3℃（RO=1.08%）,where methane’s yield accelerates and dry coefficient increases,As the generation of heavy hydrocarbon reaches peak stage （456.2℃,RO=2.09%）,inflection point occurs in the methane-yield curve,Methane is mainly generated from thermal pyrolysis of liquid hydrocarbon,with part formed from thermal pyrolysis of heavy gaseous hydrocarbon,The yield of methane reaches 956.93mL/gTOC at the highest temperature（T=599.7℃,RO=4.45%）with a dry coefficient of 99.75%,leaving small amount of liquid and heavy gaseous hydrocarbon cracking to methane,The process of gas generation could be divided into three stages：（1）Stage of primary oil production at 337.2-385.3℃（0.74%≤RO≤1.08%）with small amount of shale gas;（2）Stage of oil and gas co-existent with wet gas at 385.3-456.2℃（1.08%≤RO≤2.09%）;（3）Stage of dry gas formation at 456.2-599.7℃ （2.09%≤RO≤4.45%）,Compared with marine Barnett shale,transitional Shan 2 shale in Ordos Basin has the same process of gas generation but higher gas yield,The results of this study indicate that Shan 2 shale has bright gas generation potential.