Determining reservoir intervals in the Bowland Shale using petrophysics and rock physics models
Determining reservoir intervals in the Bowland Shale using petrophysics and rock physics models
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DOI：
10.1093/gji/ggab334
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发表时间：
2021-08
影响因子：
2.8
通讯作者：
I. Anderson;Jingsheng Ma;Xiaoyang Wu;D. Stow
中科院分区：
文献类型：
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作者：
I. Anderson;Jingsheng Ma;Xiaoyang Wu;D. Stow
利用英国第一口页岩气勘探井的电缆测井数据，对Bowland页岩的未来页岩气储层进行了评估。准确识别这些层段对于确定水平生产井的理想着陆点至关重要，但由于泥岩的非均质性，这项任务具有挑战性。这种非均质性导致了储层质量和力学性质的地层变化，并导致了复杂的地球物理行为，包括地震各向异性。我们生成岩石物理测井，如矿物学、孔隙度和有机含量，并将这些数据与岩心研究结果进行校准。如果通过与这些参数相关的综合截止值来定义“储层质量”，我们发现井中存在超过100米的储层质量页岩，主要位于上部。为了研究地球物理特征与岩石性质之间的联系，研究人员利用有效介质理论建立了一个各向同性岩石物理模型，以重建页岩的弹性特性，并为后续的地震反演研究提供前瞻性模板。我们发现，页岩的矿物学非均质性对模拟的弹性性质有深远的影响，掩盖了孔隙度、有机质含量和含水饱和度引起的更离散的变化，页岩的最佳储层质量区间在岩石物理交叉图上具有独特的响应。最后，通过建立各向异性岩石物理模型，考虑页岩中天然裂缝的密度，以反映微成像测井观察到的高角度裂缝。我们利用剪切波分裂测井数据反演裂缝密度，发现裂缝密度高达4%，这与微成像观测结果有很好的相关性。我们的工作进一步支持了之前作者基于岩心的研究结论，即Bowland页岩具有良好的储层特征，并且我们提出，如果这些层段的力学性质合适，并且之间有足够的应力屏障来限制垂直水力裂缝的生长，那么页岩中可以有多个层段可以进行堆叠水平井。最后，我们的岩石物理模板可以为解释Bowland页岩远景区域的叠前地震数据集和选择最佳钻井位置提供有用的工具。
An evaluation of prospective shale gas reservoir intervals in the Bowland Shale is presented using a wireline log data set from the UK's first shale gas exploration well. Accurate identification of such intervals is crucial in determining ideal landing zones for drilling horizontal production wells, but the task is challenging due to the heterogeneous nature of mudrocks. This heterogeneity leads to stratigraphic variations in reservoir quality and mechanical properties, and leads to complex geophysical behaviour, including seismic anisotropy. We generate petrophysical logs such as mineralogy, porosity, and organic content and calibrate these to the results of core studies. If ‘reservoir quality’ is defined by combined cut-offs relating to these parameters, we find that over 100 m of reservoir quality shale is present in the well, located primarily within the upper section. To examine the link between geophysical signature and rock properties, an isotropic rock physics model is developed, using effective medium theories, to recreate the elastic properties of the shale and produce forward-looking templates for subsequent seismic inversion studies. We find that the mineralogical heterogeneity in the shale has a profound impact on modelled elastic properties, obscuring more discrete changes due to porosity, organic content and water saturation and that the best reservoir quality intervals of the shale bear a distinctive response on rock physics cross-plots. Finally, we consider the density of natural fractures in the shale by developing an anisotropic rock physics model to reflect high-angle fractures observed on micro-imagery logs. We invert crack density using shear wave splitting well log data and find a crack density of up to 4 per cent which correlates well with micro-imagery observations. Our work further supports previous authors’ core-based studies in concluding that the Bowland Shale holds good reservoir characteristics, and we propose that there are multiple intervals within the shale that could be targeted with stacked horizontal wells, should those intervals’ mechanical properties also be suitable and there be adequate stress barriers between to restrict vertical hydraulic fracture growth. Finally, our rock physics templates may provide useful tools in interpreting pre-stack seismic data sets in prospective areas of the Bowland Shale and picking the best locations for drilling wells.