Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone: Insights from the Otway Basin, SE Australia
Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone: Insights from the Otway Basin, SE Australia
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DOI：
10.1111/bre.12345
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发表时间：
2019-03
期刊：
影响因子：
3.2
通讯作者：
N. Debenham;N. Farrell;S. Holford;R. King;D. Healy
中科院分区：
文献类型：
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作者：
N. Debenham;N. Farrell;S. Holford;R. King;D. Healy
对含断层储集岩渗透率结构的了解是制定强有力的油气勘探和流体监测战略的基础。研究往往描述经历了简单构造史的低孔容积岩的渗透率结构，而对于具有多条滑移史的断层对多孔碎屑岩渗透性结构的影响的研究却很有限。我们介绍了对位于澳大利亚东南部奥特韦盆地东北-西南方向30公里的Castle Cove断层上盘内的Eumeralla组(一种致密的火山成因砂岩)进行的岩石物理、显微结构和矿物学综合调查的结果。这个晚侏罗世-新生代盆地经历了多期伸展和挤压。岩心塞和相对于断裂面定向的薄片是从距离Castle Cove断层面225米的上盘取样的。当接近断层面时，连通孔隙度增加约10%(225m时增加17%，0.5m时增加24%)，渗透率增加两个数量级(从225m时的0.04md增加到0.5m时的1.26md)。背散射扫描电子显微镜分析表明，断裂作用引起的微构造变化增强了Eumeralla组的微米级渗透率结构。这些微结构的变化归因于断层变形导致的微裂缝的形成和原始孔衬绿泥石形态的破坏。与正断层和随后的逆断层有关的复杂变形，即宏观裂缝、可变方向微裂缝和上盘背斜的形成，显著影响了原岩的断层外流体流动性质。然而，尽管主岩渗透性结构得到了增强，Castle Cove的Eumeralla组仍被认为是致密砂岩。研究表明，寄主岩石的高分辨率综合分析对于描述经历了复杂变形的高孔隙度、低渗透率和丰富粘土的储集岩的微米级渗透率结构至关重要。
Knowledge of the permeability structure of fault‐bearing reservoir rocks is fundamental for developing robust hydrocarbon exploration and fluid monitoring strategies. Studies often describe the permeability structure of low porosity host rocks that have experienced simple tectonic histories, while investigations of the influence of faults with multiple‐slip histories on the permeability structure of porous clastic rocks are limited. We present results from an integrated petrophysical, microstructural, and mineralogical investigation of the Eumeralla Formation (a tight volcanogenic sandstone) within the hanging wall of the Castle Cove Fault which strikes 30 km NE–SW in the Otway Basin, southeast Australia. This late Jurassic to Cenozoic‐age basin has experienced multiple phases of extension and compression. Core plugs and thin sections oriented relative to the fault plane were sampled from the hanging wall at distances of up to 225 m from the Castle Cove Fault plane. As the fault plane is approached, connected porosities increase by ca. 10% (17% at 225 m to 24% at 0.5 m) and permeabilities increase by two orders of magnitude (from 0.04 mD at 225 m to 1.26 mD at 0.5 m). Backscattered Scanning Electron Microscope analysis shows that microstructural changes due to faulting have enhanced the micrometre‐scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore‐lining chlorite morphology as a result of fault deformation. Complex deformation, that is, formation of macrofractures, variably oriented microfractures, and a hanging wall anticline, associated with normal faulting and subsequent reverse faulting, has significantly influenced the off‐fault fluid flow properties of the protolith. However, despite enhancement of the host rock permeability structure, the Eumeralla Formation at Castle Cove is still considered a tight sandstone. Our study shows that high‐resolution integrated analyses of the host rock are critical for describing the micrometre‐scale permeability structure of reservoir rocks with high porosities, low permeabilities, and abundant clays that have experienced complex deformation.