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Stress-mediated closing of fractures: Impact of matrix diffusion

机译:应力介导的裂缝闭合:基质扩散的影响

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Fracture apertures may decrease by several mechanisms when the fractures are subject to stress. This paper considers only stress-enhanced dissolution of the crystals on the stressed surfaces. First, it is argued that the stress-induced dissolution is active already at the smallest difference between effective stress on the stressed surfaces and the unstressed surface of a crystal when in contact with water. This is in contrast to the concept that there exists a critical stress below which, this does not happen, assumed in some earlier studies. Second, and in addition to, but independent of the first argument, it is shown that there is a very strong sink for the stress-enhanced dissolved crystal mass due to diffusion into the porous rock matrix. There, the solute reprecipitates on the crystal surfaces in the matrix, which are subject to lower stress than the crystals bearing the load in the fracture. Diffusion into the porous matrix of the rock has not previously been considered in this context. A simple model that includes this sink is developed, and it is shown that matrix diffusion can be the by far largest sink for the solute and can considerably increase the rate of closure of the fractures. It is further found that under some possibly not uncommon conditions, the dissolution rate of quartz crystals becomes essentially independent of the strength of the sinks for the dissolved silica.
机译:当裂缝受到应力作用时,裂缝的开孔可能会通过几种机制减小。本文仅考虑了应力表面上晶体的应力增强溶解。首先,认为与水接触时,应力诱导的溶解已经在晶体的受应力表面和未受应力表面上的有效应力之间的最小差处起作用。与之相反的是,存在一些关键压力的概念,在某些早期研究中假设该压力不会发生,但不会发生。其次,除了但不依赖于第一个论点,研究表明,由于扩散到多孔岩石基质中,应力增强的溶解晶体质量存在非常强的下陷。在那里,溶质在基体的晶体表面上再沉淀,该基体的应力比承受裂缝中载荷的晶体的应力低。在这种情况下,以前没有考虑扩散到岩石的多孔基质中。建立了一个包括该沉陷的简单模型,结果表明,基质扩散可能是溶质的最大沉陷,并且可以显着提高裂缝闭合的速率。进一步发现,在一些可能不常见的条件下,石英晶体的溶解速率基本上与溶解的二氧化硅的槽的强度无关。

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