Laboratory measurements of elastic properties of carbonate rocks during injection of reactive CO2‐saturated water
Laboratory measurements of elastic properties of carbonate rocks during injection of reactive CO2‐saturated water
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DOI：
10.1029/2010gl045606
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发表时间：
2011-01
影响因子：
5.2
通讯作者：
S. Vialle;T. Vanorio
中科院分区：
文献类型：
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作者：
S. Vialle;T. Vanorio
为了研究富CO2水注入碳酸盐岩样品的物理和化学耦合效应，我们监测了6种碳酸盐岩的弹性和运移性质，以及恒定围压下孔隙流体的钙含量和pH。碳酸盐样品的范围从含有白云石的方解石灰岩到纯方解石泥岩，这使我们能够研究矿物组成和微结构如何影响观察到的变化的幅度。饱和岩石和干燥岩石(即岩石骨架)的弹性性质在注入时都表现出逐渐的强度损失，这从干P波和S波速度(以及替代体积和剪切模量值)的不断减小中得到了证明。观测到的弹性性质变化幅度各不相同，P波和S波速度的最大相对变化分别为24.7%(871m/S)和21.2%(443m/S)。渗透率(高达495%)和孔隙度(高达19%)的相对增加也伴随着渗透率的下降。观察到的变化可能源于微观结构的变化，这是通过扫描电子显微镜随着时间的推移进行监测的。孔隙度的变化是两个相互竞争和相互依赖的过程的结果：方解石的化学溶解和由此产生的在压力下的机械压实。研究结果表明，当注入与围岩化学不平衡的流体时，弹性性质的变化不能用现有的岩石物理模型来描述。
To investigate the coupled physical and chemical effects of injecting CO2‐rich water into carbonate rock samples, we monitor the elastic and transport properties of six carbonate rocks, along with the calcium content and pH of the pore fluid under constant confining pressure. Carbonate samples range from calcite limestones containing dolomite to pure calcite mudstones, which allow us to study how mineral composition and microstructure affect the magnitude of the observed changes. The elastic properties of both the saturated and dry rock (i.e., rock frame) show a gradual loss of sstrength upon injection, as testified by the continuous decrease in the dry P‐ and S‐wave velocity (and by proxy the bulk and shear moduli). The magnitude of the observed changes in the elastic properties varies among the samples, with a maximum relative change of 24.7% (871 m/s) and 21.2% (443 m/s) in P‐ and S‐ wave velocities, respectively. The decrease is also accompanied by a relative increase in permeability (up to 495%) and porosity (up to 19%). The observed changes likely derive from a change in microstructure, which is monitored over time via scanning electron microscopy. The variation in porosity results from two competing and interdependent processes: the chemical dissolution of calcite and the resulting mechanical compaction under pressure. The results of this study show that, upon injection of fluids that are in chemical disequilibrium with the hosting rock, the variation of the elastic properties cannot be described by existing rock‐physics models.