Modelling and simulation of natural hydraulic fracturing applied to experiments on natural sandstone cores

IF 5.6 1区 工程技术 Q1 ENGINEERING, GEOLOGICAL
Junxiang Wang, Alixa Sonntag, Dongwon Lee, Giovanna Xotta, Valentina A. Salomoni, Holger Steeb, Arndt Wagner, Wolfgang Ehlers
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Abstract

Under in-situ conditions, natural hydraulic fractures (NHF) can occur in permeable rock structures as a result of a rapid decrease of pore water accompanied by a local pressure regression. Obviously, these phenomena are of great interest for the geo-engineering community, as for instance in the framework of mining technologies. Compared to induced hydraulic fractures, NHF do not evolve under an increasing pore pressure resulting from pressing a fracking fluid in the underground but occur and evolve under local pore-pressure reductions resulting in tensile stresses in the rock material. The present contribution concerns the question under what quantitative circumstances NHF emerge and evolve. By this means, the novelty of this article results from the combination of numerical investigations based on the Theory of Porous Media with a tailored experimental protocol applied to saturated porous sandstone cylinders. The numerical investigations include both pre-existing and evolving fractures described by use of an embedded phase-field fracture model. Based on this procedure, representative mechanical and hydraulic loading scenarios are simulated that are in line with experimental investigations on low-permeable sandstone cylinders accomplished in the Porous Media Lab of the University of Stuttgart. The values of two parameters, the hydraulic conductivity of the sandstone and the critical energy release rate of the fracture model, have turned out essential for the occurrence of tensile fractures in the sandstone cores, where the latter is quantitatively estimated by a comparison of experimental and numerical results. This parameter can be taken as reference for further studies of in-situ NHF phenomena and experimental results.

Abstract Image

应用于天然砂岩岩心实验的天然水力压裂建模和模拟
在原位条件下,渗透性岩石结构中会出现天然水力裂缝(NHF),这是孔隙水迅速减少并伴随局部压力下降的结果。显然,地质工程界对这些现象非常感兴趣,例如在采矿技术框架内。与诱导水力裂缝相比,NHF 并不是在压裂液压入地下导致孔隙压力增加的情况下形成的,而是在局部孔隙压力降低导致岩石材料产生拉伸应力的情况下出现和形成的。本论文涉及的问题是在何种定量条件下出现和演化 NHF。因此,本文的创新之处在于将基于多孔介质理论的数值研究与应用于饱和多孔砂岩圆柱体的定制实验方案相结合。数值研究包括利用嵌入式相场断裂模型描述的原有断裂和演化断裂。根据这一程序,模拟了具有代表性的机械和水力加载情况,这些情况与斯图加特大学多孔介质实验室完成的低渗透砂岩圆柱体实验研究相一致。砂岩的水力传导率和断裂模型的临界能量释放率这两个参数的值对砂岩岩芯拉伸断裂的发生至关重要。该参数可作为进一步研究原位 NHF 现象和实验结果的参考。
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来源期刊
Acta Geotechnica
Acta Geotechnica ENGINEERING, GEOLOGICAL-
CiteScore
9.90
自引率
17.50%
发文量
297
审稿时长
4 months
期刊介绍: Acta Geotechnica is an international journal devoted to the publication and dissemination of basic and applied research in geoengineering – an interdisciplinary field dealing with geomaterials such as soils and rocks. Coverage emphasizes the interplay between geomechanical models and their engineering applications. The journal presents original research papers on fundamental concepts in geomechanics and their novel applications in geoengineering based on experimental, analytical and/or numerical approaches. The main purpose of the journal is to foster understanding of the fundamental mechanisms behind the phenomena and processes in geomaterials, from kilometer-scale problems as they occur in geoscience, and down to the nano-scale, with their potential impact on geoengineering. The journal strives to report and archive progress in the field in a timely manner, presenting research papers, review articles, short notes and letters to the editors.
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