页岩油富集可动性地球化学评价参数探讨——以威利斯顿盆地Bakken组和渤海湾盆地济阳坳陷古近系沙河街组页岩为例

Geochemical parameters for evaluating shale oil enrichment and mobility:A case study of shales in the Bakken Formation,Williston Basin and the Shahejie Formation,Jiyang Depression

地球化学参数是页岩油富集可动性评价的重要指标。通过矿物/页岩抽提残渣混油/烷烃热解实验,以及产油页岩有机试剂抽提前、后热解参数对比正演模拟,剖析威利斯顿盆地Bakken组和渤海湾盆地济阳坳陷古近系沙河街组产油页岩的实例,分析页岩油富集特征与地球化学参数响应,研究评价页岩油富集可动性的含油饱和度指数(OSI)及烃产率指数(PI)下限值。研究表明:页岩中的油在常规热解过程中,除了热解游离烃量(S1)之外,也对热解裂解烃量(S2)有贡献,影响了S2曲线的峰型及热解烃峰值温度(T_(max))。页岩内由于原油富集,造成页岩热解参数呈现出异常高OSI和PI值、异常低T_(max)值,OSI值、PI值及T_(max)值之间具有协同变化的关系。富含油的贫有机质页岩的热解参数异常较为明显,富有机质页岩在总有机碳含量(TOC)达到特定值后OSI和PI值趋于稳定。这些页岩由于液-固相互作用影响了烃类可动性下限值。威利斯顿盆地Bakken组1口井和济阳坳陷沙河街组3口井系统解剖结果表明,这些井页岩油富集可动性的OSI下限值为50~75 mg/g,对应PI下限值为0.12~0.20,页岩油富集可动性的OSI下限与页岩岩性和原油性质密切相关,富碳酸盐页岩具有较低的OSI下限值。

Geochemical parameters serve as important indicators for shale oil enrichment and mobility evaluation.Using pyrolysis experiments of minerals/post-extraction shale residues mixed with oil/alkanes,as well as the comparison and forward modeling of pyrolysis parameters of oil-generating shales before and after shale extraction using organic reagents,we perform a case study of the oil-generating shales in the Bakken Formation of the Williston Basin and the Paleogene Shahejie Formation of the Jiyang Depression in the Bohai Bay Basin.Accordingly,the characteristics of shale oil enrichment and corresponding responses of geochemical parameters are analyzed to investigate the lower limits of the oil saturation index(OSI)and productivity index(PI)as indicators of shale oil enrichment and mobility.The results reveal that conventional Rock-Eval pyrolysis on oil in rock generates both free hydrocarbons(S1)and pyrolyzed hydrocarbons(S2),affecting the S2 curve’s peak style and peak temperature for hydrocarbon pyrolysis(T_(max)).Crude oil enrichment in shales,thereby,leads to anomalously high values of OSI and PI and anomalously low T_(max)values,with these three parameters in coordinated variation.Oil-rich shales with a low organic matter content exhibit more pronounced anomalies in pyrolysis parameters.In contrast,for organic-rich shales,their OSI and PI values tend to stabilize after the total organic carbon(TOC)content reaches a specific threshold.The liquid-solid interactions in shales affect the lower limits of indicators for hydrocarbon mobility.A systematic analysis of the Bakken Formation in one well in the Williston Basin and the Shahejie Formation in three wells in the Jiyang Depression indicates that the lower limits of OSI for the enriched shale oil and its mobility fall below 50~75 mg/g,corresponding to PI values of 0.12~0.20.The lower limit of OSI for the enriched shale oil and its mobility is closely associated with shale lithology and crude oil properties,with carbonate-rich shales exhibiting lower limits of OSI for shale oil mobility.