The present study aimed to quantify the thermally induced deformation and the associated evolution of permeability in Blaubeuren limestone, an outcrop analogue of the Upper Jurassic (Malm) carbonate formation, providing references for hydro-thermo-mechanical responses of the reservoir rock to temperature changes within future enhanced geothermal systems as located in the Southern German Molasse Basin. Experiments deriving the changes in the primary (water-accessible) pore volume and the bulk volume of three water-saturated rock samples were conducted via loading the samples to defined stress states (σ3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\sigma}_{3}$$\end{document} of 15 MPa; σ1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\sigma}_{1}$$\end{document} of up to 75 MPa ), respectively, and then cycling sample temperature between 30 °C and defined levels up to 120 °C at a sustained pore pressure of 0.5 MPa. Permeability was measured under isothermal conditions at each attained temperature. The primary voids dilated upon heating and partly contracted via cooling in each applied temperature cycle yielding thereby residual dilation. However, the concomitant bulk sample deformation manifested residual compaction. The permeability increased with increasing temperature and showed residual decreases by the end of the temperature cycling tests. Flow of pore fluid from the primary voids into the secondary voids at increased temperatures due to the decreased fluid viscosity mimicked irreversible dilation in the primary voids. The interplay between pressure solution-driven compaction and thermal expansion in rock solids was considered to account for the sample deformation and the development of permeability. It is presumable that the pressure solution-driven compaction and the contraction in rock solids would influence the long-term hydro-thermo-mechanical behavior of the Upper Jurassic carbonate reservoir rocks in the cooling process related to fluid injection at the geothermal systems located therein.

中文翻译：

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上侏罗统（马尔姆）石灰岩对温度变化的响应：岩石变形和渗透率的实验结果

然后在 0.5 MPa 的持续孔隙压力下，在 30 °C 和高达 120 °C 的定义水平之间循环样品温度。在等温条件下在每个达到的温度下测量渗透率。主要空隙在加热时膨胀，并在每个施加的温度循环中通过冷却部分收缩，从而产生残余膨胀。然而，伴随的大块样品变形表现出残余压实。渗透率随着温度的升高而增加，并在温度循环测试结束时显示出残余量减少。由于流体粘度降低，孔隙流体在升高的温度下从主要空隙流入次要空隙，模拟主要空隙中的不可逆膨胀。压力溶液驱动的压实与岩石固体中的热膨胀之间的相互作用被认为是样品变形和渗透率发展的原因。据推测，压力溶液驱动的压实和岩石固体的收缩会影响上侏罗统碳酸盐岩储集岩在与位于其中的地热系统中的流体注入相关的冷却过程中的长期水热力学行为。