化学变化对康沃尔深层花岗岩地热系统摩擦特性的影响:近原位条件下的直接剪切实验

IF 3.9 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
N. Harpers, N. Forbes Inskip, M. J. Allen, J. Buckman, D. R. Faulkner, H. Claes, R. Shail, S. den Hartog, A. Busch
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引用次数: 0

摘要

主岩的地球化学改变可能会影响地热系统的生产力和诱发地震的可能性。除了自然蚀变之外,在生产和取热之后,在较低温度和不同压力下重新注入的流体可能会与岩石发生化学不平衡,从而影响矿物溶解度和溶解/沉淀过程。在本研究中,我们利用具有不同程度蚀变的样品进行直接剪切实验,研究地球化学蚀变对花岗岩摩擦行为的影响及其致震潜力。这些样品来自英格兰西南部康沃尔郡的卡门内利斯花岗岩,代表了联合唐斯深层地热发电项目中用于提取热量的岩层。实验在室温和 180°C 的温度下对花岗岩粉末(称为刨花)进行,模拟的原地约束压力和孔隙压力分别为 130 兆帕和 50 兆帕(深度为 5 千米)。随着蚀变程度的增加,沟槽的摩擦强度降低,而摩擦稳定性增加。在高温条件下,所有样品的摩擦稳定性都有所降低,但与蚀变阶段的趋势保持一致。对剪切刨花的微观结构研究表明,蚀变通过减小晶粒尺寸和增加粘土组分来分散剪切力,从而促进了普遍剪切织物的形成。我们的研究表明,在测试压力范围内,花岗岩的蚀变越多,断层的剪切就越稳定。这种改变行为在高温下会持续,但整体摩擦稳定性会降低,从而增加了高温下诱发地震的可能性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Effects of Chemical Alteration on Frictional Properties in a Deep, Granitic, Geothermal System in Cornwall: Direct Shear Experiments at Near In Situ Conditions

Effects of Chemical Alteration on Frictional Properties in a Deep, Granitic, Geothermal System in Cornwall: Direct Shear Experiments at Near In Situ Conditions

The geochemical alteration of host rocks might affect the productivity and the potential for induced seismicity of geothermal systems. In addition to natural alteration, following production and heat extraction, re-injected fluids at lower temperatures and different pressures may be in chemical disequilibrium with the rock, impacting mineral solubility and dissolution/precipitation processes. In this study, we investigate the effect of geochemical alteration on the frictional behavior of granites, and their seismogenic potential, by conducting direct shear experiments using samples with varying degrees of alteration. The samples originate from the Carnmenellis granite in Cornwall, SW England, and represent the formation used in the United Downs Deep Geothermal Power Project for heat extraction. Experiments were conducted on granite powders (referred to as gouges) at room temperature and 180°C, at simulated in situ confining and pore pressures of 130 and 50 MPa, respectively (∼5 km depth). With increasing degree of alteration, the frictional strength of the gouges decreases while frictional stability increases. At high temperature, frictional stability is reduced for all samples while maintaining the trend with alteration stage. Microstructural investigation of the sheared gouges shows alteration delocalizes shear by reducing grain size and increasing clay fraction, which promotes the formation of pervasive shear fabrics. Our work suggests that, within the range of tested pressures, more alteration of granite initially causes more stable shearing in a fault. This behavior with alteration is sustained at high temperatures, but the overall frictional stability is reduced which increases the potential for induced seismicity at higher temperatures.

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来源期刊
Journal of Geophysical Research: Solid Earth
Journal of Geophysical Research: Solid Earth Earth and Planetary Sciences-Geophysics
CiteScore
7.50
自引率
15.40%
发文量
559
期刊介绍: The Journal of Geophysical Research: Solid Earth serves as the premier publication for the breadth of solid Earth geophysics including (in alphabetical order): electromagnetic methods; exploration geophysics; geodesy and gravity; geodynamics, rheology, and plate kinematics; geomagnetism and paleomagnetism; hydrogeophysics; Instruments, techniques, and models; solid Earth interactions with the cryosphere, atmosphere, oceans, and climate; marine geology and geophysics; natural and anthropogenic hazards; near surface geophysics; petrology, geochemistry, and mineralogy; planet Earth physics and chemistry; rock mechanics and deformation; seismology; tectonophysics; and volcanology. JGR: Solid Earth has long distinguished itself as the venue for publication of Research Articles backed solidly by data and as well as presenting theoretical and numerical developments with broad applications. Research Articles published in JGR: Solid Earth have had long-term impacts in their fields. JGR: Solid Earth provides a venue for special issues and special themes based on conferences, workshops, and community initiatives. JGR: Solid Earth also publishes Commentaries on research and emerging trends in the field; these are commissioned by the editors, and suggestion are welcome.
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