塔里木盆地志留系沥青砂的二次生烃及地质意义

Secondary hydrocarbon generation of the Silurian asphalt sandstone in the Tarim Basin and its geological implication

通过有机岩石学观察、地球化学分析及黄金管热模拟实验对塔里木盆地志留系沥青砂的二次生烃潜力进行了探讨。对代表井沥青砂岩样品的有机岩石学观察发现,沥青砂中的有机质类型除了固体沥青外,还存在一定量液态油。有机碳分析表明,志留系沥青砂岩中有机碳含量比较高,其分布范围为0.56%～3.46%,这些事实表明该地区志留系沥青砂很可能具有一定的生烃能力。进一步热模拟实验的结果证实,该地区志留系沥青砂在足够的热应力作用下能生成一定量的烃类且产物以气态烃为主,其中塔中117井与跃南1井原始沥青砂样品的最大生气量分别可达46.80mL/g和41.11mL/g;同时,通过对比热解实验,可以发现沥青砂中的液态油是产气的主要贡献者。最后,基于哈得11井原油裂解的动力学参数进行地质推演表明,在目前埋藏条件下,塔里木盆地志留系沥青砂在其分布的部分区域可发生二次裂解生气,且该裂解气可能成为该地区天然气的一个重要气源。

This paper investigated the secondary hydrocarbon generation potential of the Silurian asphalt sandstone in Tarim through organic petrologic observation,geochemical analysis and simulated experiment of goldtube pyrolysis.Observation on the organic petrologic features of asphalt sandstone samples from selected wells indicates that liquid oils also exist as another main type of organic matters in addition to solid asphalt.Analysis of total organic carbon（TOC）reveals that the Silurian asphalt sandstone with relative high value of TOC,which ranges from 0.56%to 3.46%.These studies suggest that the Silurian asphalt sandstone in Tarim Basin may have some potential of secondary hydrocarbon generation.Gold-tube pyrolysis experiments further confirm that the Silurian asphalt sandstone in Tarim can generate certain amount of hydrocarbons,mostly gaseous hydrocarbons,under intense thermal stress.The maximum gas yields of samples from Tazhong-11 well and Yuenan-1 well reach 46.80 mL/g and 41.11 mL/g respectively.Furthermore,comparative pyrolysis experiments on the original and chloroform-extracted samples reveal that the gas are mostly generated from cracking of the liquid oil in asphalt sandstone.Finally,geologic deduction is performed by using the kinetic parameters of HD-11 oil cracking.The results show that gas generation from secondary cracking is possible for the Silurian asphalt sandstone in certain zones in Tarim Basin under current burial depth.And those cracking gas may be an important sources for the gas reservoirs in the study area.