走滑断裂内部结构差异特征及其多尺度交互识别模式—以准噶尔盆地车排子凸起石炭系火山岩为例

Differential characteristics of internal structures of strike-slip faults and their multiscale interactive identification mode: a case study of Carboniferous volcanic rocks in Chepaizi Uplift, Junggar Basin

  • 摘要: 准噶尔盆地车排子凸起石炭系发育多期压扭性走滑断裂,其顶部风化严重,非均质性强,成层性差,标志层不明显,导致断裂识别难度大。为揭示断裂带内部结构单元特征并建立其识别方法,基于野外地质调查,对走滑断裂内部结构进行精细解析,结合岩心、测井、地震资料及分析测试,明确不同级别压扭性走滑断裂内部结构单元差异特征,在此基础上创新建立了多尺度交互标定识别模式。结果显示:走滑断裂内部包括断层核、滑动破碎带、诱导裂缝带3个结构单元,4级及以上断裂发育完整的3个单元5个带,5级断裂不发育断层核;断层核发育断层泥,胶结严重、致密、几乎不具渗透性,滑动破碎带和诱导裂缝带发育多组裂缝,并伴生溶蚀孔洞,ACCAL值较高,DEN值较低,前者物性更好;对于同一断裂,主动盘的裂缝发育程度与规模均优于被动盘;从原岩到断裂带再到原岩,岩心破碎程度先增高后降低,ACCAL值先增大后减小,DEN值先减小后增大,成像测井图像先变暗后变亮。该识别模式不仅实现了断裂内部结构的定量化表征,同时,也为缺少地质资料区域的断裂预测提供了新方法,对明确走滑断裂控藏规律具有重要实践价值。

     

    Abstract: Multi-phase transpressive strike-slip faults are well developed in the Carboniferous strata of the Chepaizi Uplift, Junggar Basin. These faults are characterized by severe weathering at the top, strong heterogeneity, poor stratification, and indistinct marker beds, resulting in great difficulty in fault identification. To better understand the unit characteristics within the fault zone and establish a method for their identification, a detailed analysis was carried out based on field geological investigations. By integrating core data, well logging, seismic data, and analytical testing, the differential characteristics of internal structural units of transpressive strike-slip faults at different levels were clarified. On this basis, an innovative multiscale interactive calibration identification mode was established. The results showed that the strike-slip faults consist of three structural units: fault core, slip-fracture zone, and induced fracture zone. Faults of level 4 and above exhibit complete development of all three units and five zones, while level 5 faults do not develop fault core. Fault cores develop fault gouge with severe cementation, high compaction, and almost no permeability. In contrast, both the slip-fracture zones and induced fracture zones develop multiple sets of fractures, accompanied by dissolution pores. These zones have higher acoustic time (AC) and caliper (CAL) log values, and lower bulk density (DEN), among which the slip-fracture zones have better physical properties. For the same fault, the active side exhibits more extensive and larger-scale fracture development than the passive side. Across a fault zone, from protolith to fault zone and then back to protolith, the degree of core fragmentation increases first and then decreases; AC and CAL values also increase first and then decrease; DEN values decrease first and then increase; imaging logging images change from dark to bright. The proposed identification mode enables quantitative characterization of internal fault structures and provides a method for fracture prediction in areas lacking geological data. This approach holds important practical value for clarifying the controlling roles of strike-slip faults in hydrocarbon accumulation.

     

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