Wetzel Maria, Kempka Thomas, Kühn Michael
Fluid Systems Modelling, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
Institute of Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany.
Materials (Basel). 2018 Apr 1;11(4):542. doi: 10.3390/ma11040542.
The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution.
由于化学反应导致的地质力学性质变化的量化对于地下地质利用至关重要，因为矿物溶解通常会降低岩石刚度。在本研究中，基于微CT图像数值确定了两种数字岩石样本（枫丹白露砂岩和本特海姆砂岩）的有效弹性模量。使用从数字岩石样本中提取的代表性子立方体，针对三种合成的方解石空间分布（涂层、部分填充和随机分布），量化了由于孔隙网络中10%体积的方解石胶结物溶解导致的岩石刚度降低。由于方解石含量降低，体积模量和剪切模量分别最大降低了34%和38%。总孔隙率显然是主导参数，而空间方解石分布的影响较小，除了孔隙网络内随机选择的胶结物分布。此外，对方解石胶结物应用降低47%的初始刚度只会导致稍微较弱的力学行为。与一般分析方法相比，使用本文介绍的定量方法显著提高了弹性岩石性质预测的准确性，并进一步能够量化与孔隙率和矿物分布的空间变化相关的不确定性。
