Reaction Rates in Chemically Heterogeneous Rock: Coupled Impact of Structure and Flow Properties Studied by X-ray Microtomography
Reaction Rates in Chemically Heterogeneous Rock: Coupled Impact of Structure and Flow Properties Studied by X-ray Microtomography
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DOI：
10.1021/acs.est.6b06224
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发表时间：
2017-04-04
影响因子：
11.4
通讯作者：
Bijeljic, Branko
中科院分区：
文献类型：
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作者：
Al-Khulaifi, Yousef;Lin, Qingyang;Bijeljic, Branko
我们研究溶解在一个化学非均匀介质中，由两种矿物与对比的初始结构和运输性能。我们进行了一个反应传输实验，使用CO2饱和的盐水在油藏条件下，在毫米级的复合核心组成的志留系白云岩和Ketton石灰岩（方解石）串联排列。我们反复使用X射线显微断层扫描（XMT）的复合核心的图像和收集流出物，以评估个别矿物溶解。从图像分析的矿物溶解是可比的，使用电感耦合等离子体质谱法（ICP-MS）从流出物分析测量。我们发现，方解石的白云石的有效反应速率的比率随时间的推移而降低，表明动态传输效应的影响源自孔结构的变化，再加上内在的反应速率的差异。此外，在最初的非均质白云岩不断发展的流动和运输的不均匀性是一个关键的决定因素，在方解石中产生两个阶段的溶解。第一阶段的特征在于孔隙空间的均匀溶解，而第二阶段遵循单通道生长机制。这意味着具有非均匀流动特征的介质（白云石）中的空间记忆效应可以改变具有均匀流动特征的介质（方解石）中的溶解模式。
We study dissolution in a chemically heterogeneous medium consisting of two minerals with contrasting initial structure and transport properties. We perform a reactive transport experiment using CO2-saturated brine at reservoir conditions in a millimeter-scale composite core composed of Silurian dolomite and Ketton limestone (calcite) arranged in series. We repeatedly image the composite core using X-ray microtomography (XMT) and collect effluent to assess the individual mineral dissolution. The mineral dissolution from image analysis was comparable to that measured from effluent analysis using inductively coupled plasma mass spectrometry (ICP-MS). We find that the ratio of the effective reaction rate of calcite to that of dolomite decreases with time, indicating the influence of dynamic transport effects originating from changes in pore structure coupled with differences in intrinsic reaction rates. Moreover, evolving flow and transport heterogeneity in the initially heterogeneous dolomite is a key determinant in producing a two-stage dissolution in the calcite. The first stage is characterized by a uniform dissolution of the pore space, while the second stage follows a single-channel growth regime. This implies that spatial memory effects in the medium with a heterogeneous flow characteristic (dolomite) can change the dissolution patterns in the medium with a homogeneous flow characteristic (calcite).