Predicting fracture patterns in sandstones in fold-thrust belts

砂岩是碳氢化合物的重要储集层，很可能提供地下碳储存的大部分机会。许多油气藏赋存于挤压构造形成的褶皱中。然而，地下砂岩油藏的成功开采需要了解由于挤压而形成的裂缝模式--它们可以极大地改变储层的动态。存在很大的不确定性--大规模的结构模型能否预测通过该结构的裂缝损伤的分布、集中和方向？这是一个问题，这个案例学生的设计是为了回答这个问题，使用的是露头的一个例子研究。该项目是阿伯丁大学与米德兰山谷勘探有限公司(MVE)的合作伙伴，后者是向地下地学行业提供构造地质软件的世界领先者。这一合作关系将为学生提供与商业相关的构造地质学方面的出色培训。这一结果将立即使MVE及其广泛的客户群受益。MVE将满足津贴补充和实习的标准情况要求，以及实地工作的全部费用，并将免费为其Move软件提供技术支持。该项目涉及几个部分：实地结构绘图；三维模型建立；结构恢复；正演模拟；应力、应变和裂缝模式的计算；多种模型输出的组合；对照天然裂缝模式测试模型预测。因此，学生将接触到工业结构地质学家遵循的整个工作流程。所有这些活动都在MVE的MOVE软件中得到支持。现场案例研究位于苏格兰西北部的莫因冲断带南部，在托里多尼亚砂岩中发育的暴露良好且可接近的褶皱冲断构造为地下结构提供了极好的类似物(规模和岩石类型)。学生将使用MVE的MOVE软件在野外以数字方式绘制这些地图。将利用与英国地质勘探局合作提供的地质和地形数据，为测绘工作提供便利。该映射为为所选折叠的结构创建3D模型(在移动中)提供了基础。然后，这些模型将被恢复到它们未变形(展开)的状态，然后在移动中进行正向建模，以形成进化历史。然后，折叠的历史将被用Move的质量弹簧解算器来模拟组成层的应力演变。当填充了理论岩石特性、不同的加载条件和断裂标准时，将创建一组裂缝模式的模型预测，这些模型预测可以组合在一起形成断裂概率图。这些预测将与现场进行的裂缝模式的直接测量结果进行对比检验。现有的通过大型褶皱构造预测裂缝的方法使用的是现场实例，通过地下井和钻孔的点测量进行放大，并插入到围岩中。然而，扩大规模充满了不确定性--这些预测通常不会得到随后的钻探活动的支持。通过使用露头测试，学生将解决基本问题，如断裂模式是否与宿主大型褶皱(例如曲率)的最终(观察到)几何形状相关，或反映结构的总应变历史。该方法还将描述结构的哪些部分对模型输入参数(流变学、强制断裂标准、加载条件)特别敏感，从而有可能预测断裂模式。将在实地和通过建模在阿伯丁和格拉斯哥的MVE办事处提供关于构造地质学所有相关方面的培训。学生将完成他们的博士学位，为从事工业或继续研究事业做好准备。

Sandstones are important reservoirs for hydrocarbons and are likely to provide most of the opportunities for underground carbon storage. Many reservoirs are hosted in folds formed by compressional tectonics. However, the successful exploitation of subsurface sandstone reservoirs demands understanding of the fractures patterns that form as a consequence of the compression - they can greatly alter the reservoir performance. Significant uncertainty exists - can models of the structure on a large scale predict the distribution, concentration and orientation of fracture damage through this structure? It is this question that this CASE studentship is designed to answer, using an example study from outcrop. This project partners the University of Aberdeen with Midland Valley Exploration Ltd (MVE), world leaders in the provision of structural geology software to the subsurface geoscience industries. The partnership will provide the student with excellent training in commercially-relevant structural geology. The results will immediately benefit MVE and their extensive client base. MVE will meet the standard CASE requirements of a stipend supplement and internship, together with the entire cost of fieldwork and will provide their Move software with technical support without charge. The project involves several components: field structural mapping; 3D model-building; structural restoration; forward modelling; computation of stress, strain and fracture patterns; combination of multiple model outputs; and testing model predictions against natural fracture patterns. The student will therefore be exposed to the entire workflow followed by industrial structural geologists. All of these activities are supported within MVE's Move software. The field case study is located in the southern the Moine Thrust Belt, NW Scotland, where well-exposed and accessible fold-thrust structures, developed in Torridonian sandstones, provide excellent analogues (scale and rock type) for structures in the subsurface. The student will map these digitally in the field using by MVE's Move software. Mapping will be facilitated by using geological and terrain data available through collaboration with BGS. The mapping provides the foundation for creating a 3D model (in Move) for the structure of selected folds. The models in turn will be restored to their undeformed (unfolded) state and then forward-modelled in Move to form evolutionary histories. The history of folding will then be used to model the stress evolution of the constituent beds using Move's mass spring solver. When populated with theoretical rock properties, different loading conditions and fracture criteria, an array of model predictions for fracture patterns will be created that can be combined to form fracture probability maps. These predictions will be tested against direct measurements of fracture patterns made in the field. Existing predictions of fractures through large-scale fold structures use in situ examples with point measurements from subsurface wells and drill holes up-scaled and interpolated to surrounding rocks. Yet up-scaling is fraught with uncertainty - commonly the predictions are not supported by subsequent drilling campaigns. By using an outcrop-based test the student will resolve fundamental questions such as whether fracture patterns correlate with final (observed) geometry of the hosting large-scale fold (e.g. curvature) or reflect the total strain history of the structure. The approach will also delineate which parts of structures are particularly sensitive to model input parameters (rheology, imposed fracture criteria, loading conditions) thereby risking predictions of fracture patterns. Training will be provided in all relevant aspects of structural geology both in the field and through modelling, both in Aberdeen and within MVE offices in Glasgow. The student will complete their PhD well-placed to follow a career in industry or to continue in research.