柴达木盆地英雄岭页岩油地质特征、评价标准及发现意义

Geological characteristics,evaluation criteria and discovery significance of Paleogene Yingxiongling shale oil in Qaidam Basin,NW China

柴达木盆地英雄岭地区古近系下干柴沟组上段页岩油获勘探重大突破,但咸湖相烃源岩低有机碳含量与页岩油成因机理、页岩油评价标准、资源潜力不清等问题,制约了英雄岭页岩油评价和勘探。把英雄岭地区以富有机质纹层状页岩与灰质白云岩高频间互为特征的页岩型和混积型页岩油类型作为攻关重点,通过大量岩心、钻井、地震及化验资料分析和综合研究,认为英雄岭下干柴沟组上段页岩油具有富氢烃源岩“二段式生烃”且滞留烃量大、多类储集空间发育且储集性能好、源储一体甜点厚度大且含油级别高、盐间与盐下压力系数高且地层能量充足、原油轻质组分多气油比高且品质佳、脆性矿物含量高且可压性好等6个特征。初步建立了以有机碳含量、有机质热演化程度、有效孔隙度、含油饱和度、脆性矿物含量、压力系数、页理密度、埋藏深度等8项参数为主的页岩油评价标准。结合下干柴沟组上段烃源岩厚度、烃源岩面积、油层纵向分布和游离烃含量等参数,初步估算英雄岭地区页岩油资源量达到21×10^(8) t;指出构造稳定区为当前最有利勘探区,落实英雄岭页岩油有利勘探面积800 km^(2)。

Major breakthroughs of shale oil exploration have been made recently in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area,Qaidam Basin.However,the low total organic carbon content of saline-lacustrine source rock,and unclear genetic mechanism,evaluation criteria and resources potential of the shale oil have restricted the exploration and evaluation of Yingxiongling shale oil.Through analysis of large amounts of core,well drilling,seismic,laboratory test data and integrated study,focusing on the shale and mixed types of shale oil reservoirs characterized by high-frequency interbedded organic-rich laminated shale and limy dolomite,it is concluded that the shale oil in the upper member of Lower Ganchaigou Formation in the Yingxiongling area have six geological characteristics:(1)two-stage hydrocarbon generation of hydrogen-rich source rock and large amount of retained oil;(2)multiple types of reservoir space and good reservoir properties;(3)source-reservoir integration,thick“sweet spot”and high oil-bearing grade;(4)high pressure coefficient between and under salt layers,and sufficient formation energy;(5)high content of light components,high gas-oil ratio,and good quality of the crude oil;(6)high content of brittle minerals and good fracability.The evaluation criterion of shale oil is preliminarily established based on the eight parameters:total organic carbon content,maturity,effective porosity,oil saturation,brittle mineral content,pressure coefficient,lamellation density,and burial depth.Combined with parameters of E32 source rock thickness,area,vertical distribution of oil layers,and free hydrocarbon content,the shale oil resources have been preliminarily estimated as 21×10^(8) t.The structurally stable area is the predominant objective of shale oil exploration and the favorable exploration area for Yingxiongling shale oil is nearly 800 km^(2).