西昌盆地下古生界筇竹寺组与龙马溪组烃源岩特征

文中基于露头和钻井资料,通过岩石学、地球化学等手段,对西昌盆地下古生界下寒武统筇竹寺组和下志留统龙马溪组的烃源岩进行了评价。研究结果表明:1)筇竹寺组主要岩性有5种,为一套潮坪-浅水陆棚相沉积,厚度自东向西变薄并逐渐尖灭;龙马溪组主要岩性有4种,为一套浅水陆棚-深水陆棚相沉积,厚度自东向西变薄并逐渐尖灭。2)筇竹寺组总有机碳质量分数(TOC)在0.042%~0.800%,平均值小于0.5%,烃源岩不发育,生烃潜量(S1+S2)介于0.08~0.65 mg/g,镜质组反射率(Ro)在2.00%~3.00%,岩石热解最高峰温(Tmaх)在422~453℃,处于过热成熟演化阶段;龙马溪组TOC在0.043%~5.100%,平均值小于1.445%,烃源岩在下部较发育,S1+S2介于0.01~2.01 mg/g,Ro在2.10%~2.46%,有机质成熟度高,处于过成熟演化阶段。3)龙马溪组烃源岩的生烃量为3.59×10^8 m^3,与四川盆地南缘龙马溪组生烃强度相差较大,故西昌盆地下古生界油气勘探前景相对较差。

Characteristics of source rocks of Qiongzhusi Formation and Longmaxi Formation of Lower Paleozoic in Xichang Basin

Based on outcrop and drilling data,the source rocks of Lower Cambrian Qiongzhusi Formation and Lower Silurian Longmaxi Formation of Lower Paleozoic in Xichang Basin are evaluated by means of petrology and geochemistry.The results show that:(1)the Qiongzhusi Formation has five main lithologies,which is a set of tidal flat-shallow shelf facies,and it becomes thinner from east to west and gradually pinches out;Longmaxi Formation has four main lithology,which is a set of shallow water shelf-deep shelf facies deposit,and it becomes thinner from east to west and gradually pinches out.(2)The TOC content of Qiongzhusi Formation ranges from 0.042%to 0.800%,with an average of less than 0.5%,the source rock is undeveloped.The hydrocarbon generation potential value(S1+S2)is between 0.08 mg/g and 0.65 mg/g,the vitrinite reflectance(Ro)is between 2.0%and 3.0%,the maximum pyrolysis temperature(Tmax)is between 422℃and 453℃,and it is in the stage of over mature evolution.The TOC content of Longmaxi Formation is between 0.043%and 5.100%,with an average of less than 1.445%.The source rock is relatively developed in the lower part,S1+S2 is between 0.01 mg/g and 2.01 mg/g,Ro is between 2.10%and 2.46%,the organic matter maturity is high,and it is in the stage of over mature evolution.(3)The hydrocarbon generation intensity of Longmaxi Formation is 3.59×10^8 m^3,which is quite different from that of Longmaxi Formation in the southern margin of Sichuan Basin,so the exploration prospect of Lower Paleozoic in Xichang Basin is relatively poor.