A new experimental multi-physics method for quantifying cation exchange capacity of shaly-sand formations

Abstract

In this paper, a new method is proposed to quantify cation exchange capacity (CEC) in rocks with complex mineralogy and in the presence of multiple types of clay minerals by integrating nitrogen adsorption-desorption, nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) measurements (including quantitative XRD). In the new method, a successive controlled nitrogen adsorption-desorption measurements as well as NMR measurements were performed on multiple samples from the same rock type. Then, an inversion algorithm was introduced to estimate surface area and volume of hydration water of each mineral, which were used as inputs to our recently-developed novel physics-based CEC estimation workflow. The CEC estimates obtained from the new method were compared against those from the ammonium acetate method and inductively coupled plasma mass spectrometry (ICP-MS) measurements in synthetic and actual powdered shaly sand rock samples. The results showed that the CEC estimates from the two methods were in good agreement, with less than 4 meq/100 g difference (i.e., average relative error of less than 23%). The experimental results demonstrated reliability of the proposed method for CEC quantification in clay-rich formations with complex lithology in the presence of multiple types of clay minerals.