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    地质体可识别影响因素研究及应用以鄂尔多斯盆地陇东地区为例

    Factors affecting geobody identifiability and the application of its evaluation method: A case study of Longdong area, Ordos Basin

    • 摘要: 鄂尔多斯盆地长73亚段纹层型页岩油主要赋存于烃源岩底部多岩性复合地层中,该地层厚度为5 ~ 20 m,由页岩、凝灰岩、粉砂质泥岩及少量细砂岩呈纹层状叠置构成,储层以厘米级厚度的凝灰岩与粉砂质泥岩为主。因地层厚度未达λ/4(λ 为地震子波在目的层附近介质中的主波长)且储层与围岩地球物理性质差异微弱,其地震反射信号淹没于页岩强反射中,缺乏独立响应信号,故常规地震反演方法难以识别。针对上述问题,提出了地质体可识别理念,利用地震地质体识别度(SGI)进行表征,即地质体存在时对所在地震反射同相轴波形产生的可量化的改变程度,该值与地质体—围岩地球物理属性差、规模、结构及地震资料品质相关。以SGI为量化指标依据,构建“分级判别、分类施策”的非常规油藏地震预测技术体系:当SGI≥1时直接沿用常规反演、振幅属性分析等成熟技术实现快速预测;当SGI<1时依托地质体结构特征研发靶向识别预测技术;对于常规手段难以直接预测的总有机碳(TOC)含量、异常高压等地质参数,可以利用地质体的继承性与规律性间接进行预测。该体系跳出“地震分辨率”框架,以地质体特性为核心制定差异化技术策略,实现了长73亚段多类型页岩油藏从弹性参数到地质参数预测的拓展,为非常规油藏勘探提供了技术支撑与实践范例。

       

      Abstract: Laminated shale oil in the interval of Chang 73 of the Ordos Basin mainly occurs in the multi-lithology complex strata at the bottom of the source rock, with a formation thickness of 5–20 m. These strata are composed of shale, tuff, silty mudstone, and minor fine sandstone in a laminated stacking pattern, with reservoirs dominated by centimeter-scale tuff and silty mudstone. Due to the small thickness below the λ/4 resolution limit and the weak geophysical property contrasts between reservoirs and surrounding rocks, the seismic reflection signals of the reservoirs are overshadowed by the strong reflections from the shale, lacking independent responses. Thus it is challenging to accomplish reservoir prediction using conventional seismic inversion methods. To tackle this issue, we propose the concept of seismic geobody identifiability (SGI), defined as the quantifiable degree to which a geobody alters the waveform of its enclosing seismic reflection event. The SGI value depends on the geophysical property contrast between the geobody and surrounding rocks, geobody scale and structure, and seismic data quality. Using SGI as the quantitative criterion, we establish a seismic prediction technology system for unconventional reservoirs characterized by “hierarchical identification and classified implementation”. When SGI ≥ 1, mature techniques such as conventional inversion and amplitude attribute analysis are directly applied for rapid prediction. When SGI < 1, targeted identification and prediction techniques are developed based on geobody structural characteristics. For geological parameters that are difficult to predict directly using conventional methods, such as TOC and abnormal formation pressure, indirect prediction is performed by exploiting the inheritance and regularity of geobodies. This system surpasses the conventional framework of “seismic resolution” and formulates differentiated technical strategies centered on geobody properties. It extends reservoir prediction from elastic parameters to geological parameters for the multi-type shale oil accumulations in Chang 73, providing methodological support and a practical case for unconventional oil and gas exploration.

       

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