鄂尔多斯盆地延长组7段页岩全组分定量生烃模拟及原油可动性评价

Quantitative full-component hydrocarbon-generating simulation and crude oil mobility evaluation of shale in 7th Member of Yanchang Formation,Ordos Basin

页岩油和致密油是中国目前油气勘探的热点,页岩生烃模拟实验可为此类油气资源勘探提供重要数据。以鄂尔多斯盆地延长组7段(长7段)页岩为例,利用金管-高压釜模拟生烃装置,系统研究了II型有机质在与'生油窗'对应的成熟度范围(Easy Ro0.7%~1.6%)内生烃产物中的气体烃(C1-5)、轻烃(C6-14)、重烃(C14+)、各族组分,以及生烃残渣的地球化学特征。发现长7段页岩在生油期可同时生成2.35~103.91 mL/g的气体烃和10.83~88.24 mg/g的轻烃。重烃的生成高峰对应的Easy Ro约为1.0%,与其中的饱和烃、芳烃和非烃的高峰产率对应的成熟度非常接近。重烃中沥青质的产率在Easy Ro约1.35%后开始下降,说明沥青质在此后才开始大量裂解与固化。而对原油物性影响很大的轻重比[(气体烃+轻烃)/重烃]及气油比[气体烃/(轻烃+重烃)]随成熟度增加而不断增大,其增速分别在Easy Ro为1.05%~1.15%之后明显变快。在生油过程中,长7段页岩残渣HI值和H元素的大量减少、干酪根固体碳同位素的变重均发生在Easy Ro约1.00%之前。干酪根碳同位素的变化相对较小,在鄂尔多斯盆地可以作为母源指标。通过对生烃产物中6种常见生物标志物成熟度参数的对比,证实多环芳烃成熟度参数中的甲基菲指数(MPI)和甲基菲比值(F1)在整个生油窗内都与成熟度有很好的线性相关性,可用于鄂尔多斯盆地母源为长7段页岩的原油成熟度判识。生烃产物的各地球化学特征变化节点、以及成熟度指标可用于鄂尔多斯盆地长7段页岩油或相关致密油资源的可采性评价。

Shale oil and tight oil are current hot spots of oil and gas exploration,and the shale hydrocarbon-generating simulation experiment can provide important information for the exploration of these oil and gas resources.Taking the shale in 7 th Member of Yanchang Formation(Chang-7 Member),Ordos Basin,the gold tube-autoclave hydrocarbon-generating simulator is used to systematically study the Type-II organic matter,the gaseous hydrocarbon(C1-5),light hydrocarbon(C6-14),heavy hydrocarbon(C14+),other components of hydrocarbon-generating products in the maturity range(Easy Ro0.7%-1.6%)corresponding to"oil-generation window",and the geochemical characteristics of hydrocarbon generation residues.It is found that in the shale of Chang-7 Member during oil-generation period,gaseous hydrocarbons of 2.35-103.91 mL/g and light hydrocarbons of 10.83-88.24 mg/g are produced simultaneously.The peak yield of heavy hydrocarbons corresponds to Easy Roof 1.00%,closely approaching to the maturities corresponding to the peak yield of saturated hydrocarbons,aromatics and non-hydrocarbons.Moreover,the asphaltene yield of heavy hydrocarbons starts to decline after reaching the Easy Ro of 1.35%,reflecting subsequent large scale of asphaltene cracking and solidification.However,the light/heavy ratio(gaseous hydrocarbon/light hydrocarbon)and gas/oil ratio(light hydrocarbon/heavy hydrocarbon)vital for physical property of crude oil are continuously increasing as thematurity getting higher,and the increasing rates are evidently accelerated after Easy Roof 1.05%-1.15%.During oil-generating process,the massive loss of HI and H element of shale residue and the kerogen solid carbon isotope becoming heavier occur prior to Easy Roof 1.00%;the kerogen solid carbon isotope changes less,and can be taken as an original source index in Ordos Basin.Through comparing six kinds of common biomarker maturity parameters in the hydrocarbon-generating products,it is validated that MPI and F1 among the PAH maturity are linearly correlated to maturity in the whole oil-generating window,and can be used to identify the crude oil maturity in the shale of Chang-7 Member in Ordos Basin.The change nodes of various geochemical characteristics of hydrocarbon-generating products and the maturity indexes can be applied to the exploitability assessment for shale oil or correlative tight oil in 7 th Member of Yanchang Formation,Ordos Basin.