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.

地球上皮中的岩石通常是多孔的，毛孔和裂缝充满了水，油或气体等液体。作用在这些岩石上的力是由上覆岩石的重量和板块构造产生的，将谷物，毛孔和裂缝变形，改变它们的形状和体积。这种变形发生在任何破裂或断层之前，并用称为毛弹性的理论描述。该理论指出，裂缝和孔位的裂缝和孔的方向对岩石对压力的反应产生了重大控制。充满流体的平行裂纹发生在主要地震易于断层周围的模式中，并且这些裂纹比裂缝或孔的随机方向产生的响应要强得多。因此，岩石的毛弹性对于我们对大断层进行预测地震的能力很重要，并引起了人类活动的地震性，例如​​钻孔中的液体注入二氧化碳或液压破裂（或“压裂”）。岩石的毛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处于非常特殊的应力状态，而地球可能不存在。常规三轴应力（CTS）在圆柱岩样品上施加垂直应力，然后在侧面持续压力。我们知道，地球上的应力在各个方向都有所不同，这种疾病称为真实三轴应力（TTS）。但是，在这种应力状态下，我们没有测量的孔隙弹性数据。 UCL的新委托设备是专门设计的，可以在真实三轴应力下变形流体饱和的岩石样品，从而为解决核心科学问题提供了独特而及时的机会：没有公开的孔隙弹性系数测量在TTS下测量的孔隙弹性系数，并且我们肯定需要更好的数据来确定更好的SeismisismaciCanciCaharciCanciCakard的模型。研究人员的最新工作表明，与CTS下的类似负载路径相比，TTS产生的裂纹模式和密度显着不同：TTS产生主要比对的平行裂纹，而CTS倾向于产生径向裂纹。我们必须系统地收集这些数据在地壳中最有可能的原位应力条件下 - 真正的三轴应力 - 我们可以使用这些新数据来使经过测试，更健壮的地震危险模型。最近的工作表明，裂纹织物对于易于地震的断层的流体加压和潜在弱化的裂纹织物是多么重要。断裂阵列围绕地震活性断层的平行裂纹可能会导致沿断层等于正常应力的短期流体压力变化，从而使断层在地震中滑动。这可能会带来巨大的后果，以评估主要断层的地震风险。已婚，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，对地热能或液压压裂的偏斜钻孔），这增加了我们的基本原理的紧迫性。我们将从我们的研究中生产开源软件，并免费提供给其他科学家，工程师和更广泛的公众。目前正在测试的第一个工具将量化孔和裂纹的三维（3D）模式，包括其方向，尺寸和形状。这些特征的统计分布将被量化并用于使用已发表的理论来帮助预测毛弹性。第二个工具将使用我们新测得的毛弹性数据来修改已发表的地震触发模型。在当前模型中包含毛弹性变形与摩擦行为混合在一起，但它们是非常不同的物理现象。我们的新代码将结合我们以前关于断层区域弹性特性空间变化的工作，以及新的实验室测量，以对触发地震危害的更强大的预测进行更强的预测。

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