Multi-Physics Models for Proppant Placement in Energy Georeservoirs

地下能源技术在当代地质力学中具有至关重要的意义，其中包括增强型地热系统（EGS）。EGS利用地热能从地下深处的热渗透增强岩层中发电。该项目解决了在地热能源开采过程中对更有效的支撑剂（保持裂缝张开的颗粒材料）使用的需求。具体来说，解决支撑剂放置问题将有助于地质油藏的优化、增长和进一步开发，并将加速EGS技术从目前的早期开发阶段向商业应用的转变。这将有利于全球可再生能源市场和全球可持续能源输送。这项研究也有可能有助于定量理解几个额外的地质力学问题，如泥浆流和泥浆流，水坝的内部侵蚀和建筑物周围土壤的冲刷。该研究项目提高了致密悬浮液流动的基本物理知识，并开发了新的理论，可以改进工程设计，将支撑剂投放到具有不规则、粗糙表面的分支水力裂缝中。这一活动产生的模型将首次通过考虑颗粒-颗粒相互作用与流体动力力之间的相互作用以及流体、颗粒和断裂特性的作用来捕获颗粒聚集。我们的多学科团队由一名岩土工程师和一名数学建模师组成，他们将与其他项目合作，通过研究、工程和教育活动，扩大妇女和其他代表性不足的群体在科学领域的参与。该项目旨在更好地了解和缓解支撑剂注入水力裂缝过程中导致支撑剂测井的情况。该项目产品将在提高渗透率的过程中有效地放置支撑剂，从而潜在地减少对环境的影响。该项目的首要目标是获得对这一现象的定量理解，并要求发展新的数学理论。目前预测支撑剂流动和输运的实践依赖于从实验室测试中得出的经验关系，这些测试涉及大宽度、光滑、直槽，适用于简化的单裂缝模型。然而，大多数水力裂缝都是粗糙且分支的，这为流体和支撑剂的输送创造了复杂的路径。致密浆体流动和输运的物理特性包括颗粒-颗粒和流体-颗粒的相互作用。特别是对于用于支撑剂投放的流体，这种物理特性还没有得到很好的理解，因此在当前的模型中没有得到充分的解释。建立了实际裂缝网络中支撑剂流动的数学模型，并通过实验室规模的实验进行验证。实验组件包括在3d打印裂缝中使用压裂测试中扫描的岩石表面进行下一代槽流实验。裂缝将用透明材料打印，从而可以使用颗粒图像测速（PIV）来跟踪支撑剂颗粒的运动。该项目的理论部分包括两个相互关联的部分，一个是建立一个考虑颗粒-颗粒和颗粒-流体相互作用的连续尺度本构律，另一个是开发一个计算效率高的算法，用于模拟粗糙壁和（随机）不同孔径裂缝中的支撑剂流动。连续尺度模型将参数化，参数反映裂缝表面的粗糙度、平均裂缝宽度以及流体和支撑剂颗粒的物理力学性质。这些和其他有效的模型参数将从离散数值模拟和槽流实验中确定。该模型将为油藏工程师提供实用的工具，以确保在水力裂缝中正确放置支撑剂，并预测和规划可靠的提高储层渗透率的措施。

Underground energy technologies are of crucial importance in contemporary geomechanics, including Enhanced Geothermal Systems (EGS). EGS use geothermal energy to produce electricity from hot deep underground permeability-enhanced rock formations. This project addresses the need for more effective proppant (granular material that keeps the fractures open) usage during geothermal energy recovery. Specifically, resolving proppant placement issues will aid optimization, growth and further development of georeservoirs, and will speed up transformation of the EGS technology from its current early development stage to commercial use. This will benefit global renewable energy market and global sustainable energy delivery. This research has also a potential for contributing to quantitative understanding of several additional geomechanical issues, such as mud flows and slurry flows, internal erosion of dams and scouring of soil around structures. This research project advances the knowledge of fundamental physics of flow of dense suspensions, and develops new theories that would improve engineering design for proppant placement into branching hydraulic fractures with irregular, rough surfaces. The models resulting from this activity will, for the first time, capture particle agglomeration by accounting for the interplay between particle-particle interactions and fluid hydrodynamic forces and the role of fluid, particle and fracture properties. Our multidisciplinary team, consisting of a geotechnical engineer and a mathematical modeler, will collaborate with other programs to broaden participation of women and other underrepresented groups in science through research, engineering and educational engagements.This project seeks to better understand and mitigate the conditions resulting in proppant logging during proppant-fluid injection into hydraulic fractures. The project products will lead to efficient proppant placement during permeability enhancement, potentially reducing its environmental impact. The overarching goal of this project is to gain quantitative understanding of this phenomenon and requires development of new mathematical theories. Current practice for predicting proppant flow and transport relies on empirical relationships developed from laboratory tests involving large width, smooth, straight slots, appropriate for use in simplified single-fracture models. However, most hydraulic fractures are rough and branching, which creates a complex path for the fluid and proppant transport. The physics of dense slurry flow and transport includes particle-particle and fluid-particle interactions. Especially for fluids used in proppant placement, this physics is not properly understood and, hence, not adequately accounted for in current models. A mathematical model of proppant flow in realistic fracture networks will be developed, and validated with laboratory-scale experiments. The experimental component comprises next-generation slot-flow experiments in 3-D printed fractures using scanned rock surfaces from fracturing tests. The fractures will be printed with transparent materials, enabling the use of Particle Image Velocimetry (PIV) to track the movement of proppant particles. The project's theoretical part consists of two interrelated components, development of a continuum-scale constitutive law that accounts for particle-particle and particle-fluid interactions, and development of a computationally efficient algorithm for modeling proppant flow in fractures with rough walls and (randomly) varying apertures. The continuum-scale models will be parameterized with parameters reflecting properties of fracture surface's roughness, average fracture width, and physical and mechanical properties of fluid and proppant particles. These and other effective model parameters will be determined from both discrete numerical simulations and slot-flow experiments. The model will serve as a practical tool for reservoir engineers to ensure the proper proppant placement in hydraulic fractures and to predict and plan the reliable permeability enhancement of georeservoirs.