Natural fractures in a United Kingdom shale reservoir analog, Cleveland Basin, northeast England
Natural fractures in a United Kingdom shale reservoir analog, Cleveland Basin, northeast England
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DOI：
10.1306/07141413144
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发表时间：
2014-11
期刊：
影响因子：
3.5
通讯作者：
J. Imber;H. Armstrong;S. Clancy;S. Daniels;Liam Herringshaw;K. McCaffrey;Joel Rodrigues;J. Trabucho-Alexandre;C. Warren
中科院分区：
文献类型：
--
作者：
J. Imber;H. Armstrong;S. Clancy;S. Daniels;Liam Herringshaw;K. McCaffrey;Joel Rodrigues;J. Trabucho-Alexandre;C. Warren
暴露良好的下侏罗统克利夫兰铁岩和惠特比泥岩地层中的断层和裂缝可能为了解英格兰北部有天然气远景的密西西比页岩的构造史提供线索。克利夫兰盆地普遍存在近垂向开口型裂缝。层-平行裂缝，其中一些含有块状方解石填充，优先发生在Jet Wyke和Port MulGrave的克利夫兰铁岩和惠特比泥岩地层的层理良好、富含粘土的泥岩中。近垂直裂缝与下伏和上覆平行裂缝表现为邻接或弯曲平行关系。总而言之，这些观察表明，床层平行的裂缝有时起到了自由面的作用。部分顺层裂缝向方解石充填断层滑动面弯曲并分支，表明顺层破裂与正断层作用是同步的，发生在垂直最大主应力的区域应力场中。这一明显的悖论可以用正常压实作用来解释，随后孔压和最小水平应力之间的胶结和耦合是由孔弹性变形或沿临界应力正断层的初始滑动所驱动的，导致富粘土单元内水平应力的升高超过垂直应力。与正断层相邻的扩张应变促进了平行裂缝的扩展。在惠特比东悬崖的惠特比泥岩建造顶部的更丰富的单元中，或者在萨尔特威克NAB的层状良好、富含粘土的页岩中，没有观察到层状平行裂缝。这一观察结果与Saltwick NAB缺乏正常断层是一致的，而且惠特比泥岩地层在这两个地方都是通过构造和/或地层与中侏罗世渗透性砂岩并置而排出的。
Faults and fractures within the well-exposed Lower Jurassic Cleveland Ironstone and Whitby Mudstone Formations may provide insights into the tectonic history of gas-prospective, Mississippian shale in northern England. Subvertical opening mode fractures occur throughout the Cleveland Basin. Bed-parallel fractures, some of which contain blocky calcite fills, occur preferentially within well-bedded, clay-rich mudstones of the Cleveland Ironstone and Whitby Mudstone Formations at Jet Wyke and Port Mulgrave. Subvertical fractures display abutting or curving-parallel relationships with under- and overlying bed-parallel fractures. Together, these observations suggest that bed-parallel fractures, at times, acted as free surfaces. Some bed-parallel fractures curve toward and branch from calcite-filled fault slip surfaces, indicating that bed-parallel fracturing and normal faulting were synchronous, occurring within a regional stress field with vertical maximum principal stress. This apparent paradox can be explained by normal compaction, followed by cementation and coupling between pore pressure and minimum horizontal stress driven by poroelastic deformation or incipient slip along critically stressed normal faults, causing elevation of horizontal stress in excess of the vertical stress within clay-rich units. Propagation of bed-parallel fractures was enhanced by dilatational strains adjacent to normal fault planes. Bed-parallel fractures have not been observed within more -rich units at the top of the Whitby Mudstone Formation at Whitby East Cliff, or within well-bedded, clay-rich shale at Saltwick Nab. This observation is consistent with the lack of normal faulting at Saltwick Nab, and the Whitby Mudstone Formation having been drained by structural and/or stratigraphical juxtaposition against permeable Middle Jurassic sandstones at both these localities.