Influence of Rock Mineralogy on Reactive Fracture Evolution in Carbonate-Rich Caprocks,Environmental Science & Technology

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Influence of Rock Mineralogy on Reactive Fracture Evolution in Carbonate-Rich Caprocks
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2018-08-21 , DOI: 10.1021/acs.est.8b01021
Kasparas Spokas ₁ , Catherine A. Peters ₁ , Laura Pyrak-Nolte _{2,

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Affiliation

Fractures present environmental risks for subsurface engineering activities, such as geologic storage of greenhouse gases, because of the possibility of unwanted upward fluid migration. The risks of fluid leakage may be exacerbated if fractures are subjected to physical and chemical perturbations that alter their geometry. This study investigated this by constructing a 2D fracture model to numerically simulate fluid flow, acid-driven reactions, and mechanical deformation. Three rock mineralogies were simulated: a limestone with 100% calcite, a limestone with 68% calcite, and a banded shale with 34% calcite. One might expect transmissivity to increase fastest for rocks with more calcite due to its high solubility and fast reaction rate. Yet, results show that initially transmissivity increases fastest for rocks with less calcite because of their ability to deliver unbuffered-acid downstream faster. Moreover, less reactive minerals become persistent asperities that sustain mechanical support within the fracture. However, later in the simulations, the spatial pattern of less reactive mineral, not abundance, controls transmissivity evolution. Results show that a banded mineral pattern creates persistent bottlenecks, prevents channelization, and stabilizes transmissivity. For sites for geologic storage of CO₂ that have carbonate caprocks, banded mineral variation may limit reactive evolution of fracture transmissivity and increase storage reliability.

中文翻译：

岩石矿物学对富含碳酸盐岩盖层反应性裂缝演化的影响

由于可能会有不希望的向上的流体运移，因此，裂缝对于地下工程活动（例如温室气体的地质存储）具有环境风险。如果裂缝受到物理和化学扰动，改变其几何形状，则流体泄漏的风险可能会加剧。这项研究通过构建一个二维断裂模型以数值模拟流体流动，酸驱动反应和机械变形的方法对此进行了研究。模拟了三种岩石矿物学：方解石为100％的石灰石，方解石为68％的石灰石和方解石为34％的带状页岩。人们可能会希望方解石具有较高的溶解度和快速的反应速率，因此对于具有更多方解石的岩石，其透射率会最快地增加。然而，结果表明，方解石较少的岩石最初的透射率增加最快，因为它们能够更快地向下游输送无缓冲酸。此外，反应性较低的矿物会变成持久的凹凸不平，从而在裂缝内维持机械支撑。但是，在稍后的模拟中，反应性较低的矿物（而不是丰度）的空间模式控制着透射率的演变。结果表明，带状矿物图案会造成持久的瓶颈，防止通道化，并稳定透射率。对于用于CO地质存储的场所控制透射率的演变。结果表明，带状矿物图案会造成持久的瓶颈，防止通道化，并稳定透射率。对于用于CO地质存储的场所控制透射率的演变。结果表明，带状矿物图案会造成持久的瓶颈，防止通道化，并稳定透射率。对于用于CO地质存储的场所₂具有碳酸盐岩盖层，带状矿物变化可能会限制裂缝透射率的反应演化，并增加储存可靠性。

更新日期：2018-08-22

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