Quantifying the Anisotropy of Poroelasticity in Stressed Rock

量化受力岩石中孔隙弹性的各向异性

• 批准号: NE/T007826/1
• 负责人: David Healy
• 金额: $ 36.07万
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FT007826%2F1
• 关键词: Quantifying; Anisotropy; Poroelasticity; Stressed; Rock

Rocks in the upper crust of the Earth are often porous, with the pores and cracks filled with fluids like water, oil or gas. Forces acting on these rocks, arising from the weight of the overlying rocks and from plate tectonics, deform the grains and pores and cracks, changing their shape and volume. This deformation occurs before any fracturing or faulting, and is described by a theory called poroelasticity. This theory states that the orientations of the cracks and pores, where the pore fluid resides, exerts a major control on the response of the rock to stress. Fluid-filled parallel cracks occur in patterns around major earthquake prone faults, and these produce a much stronger response than random orientations of cracks or pores. Therefore, the poroelastic properties of rocks are important for our ability to forecast earthquakes on big faults and induced seismicity from human activities such as fluid injection in boreholes for CO2 sequestration or hydraulic fracturing (or 'fracking'). The poroelastic properties of rocks have been measured in the laboratory but all the data measured to date has been under a very special stress condition that probably does not exist in the Earth. Conventional triaxial stress (CTS) applies a vertical stress on a cylindrical rock sample, and then a constant pressure around the sides. We know that the stresses in the Earth vary in all directions, a condition known as true triaxial stress (TTS). And yet we have no poroelastic data from measurements under this stress state. A newly commissioned apparatus at UCL has been specifically designed to deform fluid saturated rock samples under true triaxial stresses and thus provide a unique and timely opportunity to address the core scientific issues: there are no published measurements of poroelastic coefficients measured under TTS and we urgently need better data to constrain better models of seismic hazard. Recent work by the investigators has shown that TTS produces significantly different patterns and densities of cracks in comparison to similar loading paths under CTS: TTS produces predominantly aligned parallel cracks, whereas CTS tends to produce radial cracks. We must systematically collect these data under the most likely in situ stress conditions within the crust - true triaxial stress - and we can use these new data to make tested, more robust, models of seismic hazard. Recent work has shown how important crack fabrics are for the fluid pressurisation, and potential weakening, of earthquake-prone faults. Arrays of fault parallel cracks around seismically active faults could produce a short-term fluid pressure change along the fault equal to the fault normal stress, allowing the fault to slip in an earthquake. This has potentially massive consequences assessing earthquake risk on major faults. Married with the increasing demand for accurate predictions of directional variations in stress and strain in the subsurface (e.g. deviated drilling for geothermal energy or hydraulic fracturing), this adds urgency to our rationale. We will produce open source software from our research, freely available to other scientists, engineers and the wider public. The first tool, currently being tested, will quantify the three-dimensional (3D) patterns of pores and cracks, including their orientations, sizes and shapes. The statistical distributions of these features will be quantified and used to help predict the poroelastic properties using the published theory. The second tool will use our newly measured poroelastic data to revise published models of earthquake triggering. The inclusion of poroelastic deformation in the current models is mixed with the frictional behaviour, but these are very different physical phenomena. Our new code will combine our previous work on the spatial variations of elastic properties around fault zones with the new laboratory measurements to make more robust forecasts of triggered earthquake hazard.

地球上地壳的岩石通常是多孔的，孔隙和裂缝中充满了水、石油或天然气等流体。作用在这些岩石上的力（由上覆岩石的重量和板块构造产生）使颗粒、孔隙和裂缝变形，改变其形状和体积。这种变形发生在任何压裂或断层之前，并由称为孔隙弹性的理论描述。该理论指出，孔隙流体所在的裂缝和孔隙的方向对岩石对应力的响应具有主要控制作用。充满流体的平行裂缝出现在主要地震易发断层周围的模式中，这些裂缝产生的响应比裂缝或孔隙的随机方向强得多。因此，岩石的孔隙弹性特性对于我们预测大断层地震和人类活动诱发地震的能力非常重要，例如在钻孔中注入流体以封存二氧化碳或水力压裂（或“水力压裂”）。岩石的孔隙弹性特性已在实验室中测量，但迄今为止测量的所有数据都是在地球上可能不存在的非常特殊的应力条件下进行的。传统的三轴应力 (CTS) 在圆柱形岩石样品上施加垂直应力，然后在侧面施加恒定压力。我们知道地球上的应力在各个方向上都有所变化，这种情况称为真三轴应力 (TTS)。然而，我们没有在这种应力状态下测量的多孔弹性数据。伦敦大学学院新近投入使用的设备经过专门设计，可在真正的三轴应力下使流体饱和岩石样品变形，从而为解决核心科学问题提供了独特而及时的机会：目前还没有公开的 TTS 下孔隙弹性系数测量结果，我们迫切需要更好的数据来约束更好的地震灾害模型。研究人员最近的工作表明，与 CTS 下的类似加载路径相比，TTS 产生的裂纹模式和密度显着不同：TTS 主要产生对齐的平行裂纹，而 CTS 倾向于产生径向裂纹。我们必须在地壳内最可能的原位应力条件（真三轴应力）下系统地收集这些数据，并且我们可以使用这些新数据来建立经过测试的、更稳健的地震灾害模型。最近的研究表明，裂缝结构对于地震多发断层的流体加压和潜在弱化有多么重要。地震活动断层周围的断层平行裂缝阵列可以沿断层产生与断层正应力相等的短期流体压力变化，从而使断层在地震中滑动。这对于评估主要断层的地震风险可能会产生巨大的影响。随着对地下应力和应变方向变化的准确预测的需求不断增加（例如地热能或水力压裂的斜钻探），这增加了我们的理由的紧迫性。我们将根据我们的研究成果制作开源软件，免费提供给其他科学家、工程师和广大公众。目前正在测试的第一个工具将量化孔隙和裂缝的三维 (3D) 模式，包括它们的方向、大小和形状。这些特征的统计分布将被量化并用于帮助使用已发表的理论预测多孔弹性特性。第二个工具将使用我们新测量的孔隙弹性数据来修改已发布的地震触发模型。当前模型中包含多孔弹性变形与摩擦行为，但这些是非常不同的物理现象。我们的新代码将把我们之前关于断层带周围弹性特性空间变化的工作与新的实验室测量相结合，以便对引发的地震灾害做出更可靠的预测。

项目成果

Stress-Induced Anisotropic Poroelasticity in Westerly Granite

西风花岗岩中应力引起的各向异性孔隙弹性

• DOI: 10.1029/2023jb026909
• 发表时间: 2023
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Elsigood B

De-risking the energy transition by quantifying the uncertainties in fault stability

通过量化故障稳定性的不确定性来降低能源转型的风险

• DOI: 10.5194/se-13-15-2022
• 发表时间: 2022
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Healy D

Physical properties of 3D printed materials and their applicability as proxies for heterogeneous geomaterials

3D 打印材料的物理特性及其作为非均质岩土材料代理的适用性

• 发表时间: 2023
• 作者: Adamus F

Listening to Manchester: Using citizen science Raspberry Shake seismometers to quantify road traffic

聆听曼彻斯特：使用公民科学 Raspberry Shake 地震仪来量化道路交通

• DOI: 10.31223/x57d47
• 发表时间: 2023
• 作者: Healy D

Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

压力下硬石膏的快速水化和弱化：对地壳和地幔自然水化的影响

• DOI: 10.5194/se-14-985-2023
• 发表时间: 2023
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Heeb J