Macroscopic permeability progression of Nanan granite under confining pressures and its microscopic evolution after cooling at atmospheric pressure: A comparative study

IF 3.5 2区工程技术 Q3 ENERGY & FUELS

Geothermics Pub Date : 2024-10-14 DOI:10.1016/j.geothermics.2024.103180

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引用次数: 0

Abstract

Permeability is one of the key factors for influencing the mass transfer behavior in rocks and plays a key role in heat extraction of enhanced geothermal systems (EGSs), so the practice of EGSs needs cooling water to be injected to enhance the permeability within geothermal reservoirs. Macroscopic and microscopic experimental investigation on how cool water affects permeability evolution is still limited. To solve this, we experimentally explored the permeability evolution of Nanan granite after air and water cooling under different confining pressures combined with optical microscopy and X-ray micro computed tomography (CT) observation. Lots of microdefects were observed in Nanan granite after two cooling paths, which dominantly drives the evolution of permeability from a microscopic scale. The permeabilities of granite under water-cooling conditions are always larger than those under air-cooling conditions, because the comparison shows that water-cooling treatment enhances the permeability of specimens. The permeabilities of granite specimens after two cooling paths decrease with the confining stress. More microcracks and better connectivity among microcracks produce a larger permeability within the specimen after water cooling. The observed microcracks are regarded as the seepage channels and direct microscale evidence of the permeability evolution of granite after two cooling paths. Our results provide support that cooled water injection is an efficient way for permeability enhancement due to thermal microcracks propagation in thermal simulation.

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南安花岗岩在约束压力下的宏观渗透率变化及其在常压下冷却后的微观演变：对比研究

渗透性是影响岩石传质行为的关键因素之一，在强化地热系统（EGSs）的热量提取中起着关键作用，因此，EGSs 的实践需要注入冷却水以提高地热储层内的渗透性。关于冷却水如何影响渗透率演化的宏观和微观实验研究仍然有限。为了解决这个问题，我们结合光学显微镜和 X 射线显微计算机断层扫描（CT）观测，实验探索了南安花岗岩在不同约束压力下空冷和水冷后的渗透率演化。结果表明，南安花岗岩在两种冷却方式下均存在大量微缺陷，从微观尺度上主导了渗透率的演化。水冷条件下花岗岩的渗透率总是大于空冷条件下的渗透率，因为比较表明水冷处理提高了试样的渗透率。经过两种冷却路径后，花岗岩试样的渗透率随着约束应力的增加而降低。水冷却后，更多的微裂缝和微裂缝之间更好的连通性在试样内部产生了更大的渗透性。观察到的微裂缝被视为渗流通道，是花岗岩经过两种冷却路径后渗透性演变的直接微观证据。我们的研究结果证明，在热模拟中，冷却水注入是通过热微裂纹传播提高渗透率的有效方法。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Geothermics 工程技术-地球科学综合

CiteScore

7.70

自引率

15.40%

发文量

237

审稿时长

4.5 months

期刊介绍： Geothermics is an international journal devoted to the research and development of geothermal energy. The International Board of Editors of Geothermics, which comprises specialists in the various aspects of geothermal resources, exploration and development, guarantees the balanced, comprehensive view of scientific and technological developments in this promising energy field. It promulgates the state of the art and science of geothermal energy, its exploration and exploitation through a regular exchange of information from all parts of the world. The journal publishes articles dealing with the theory, exploration techniques and all aspects of the utilization of geothermal resources. Geothermics serves as the scientific house, or exchange medium, through which the growing community of geothermal specialists can provide and receive information.