Fossil fuels such as coal, oil, and natural gas have been pivotal in shaping modern society, yet their use has resulted in significant emissions of greenhouse gases like carbon dioxide CO₂. In pursuit of sustainable development, China has adopted strategies aimed at achieving carbon peak and carbon neutrality, prioritizing carbon reduction and energy transformation. CO₂ storage is an effective strategy for mitigating the greenhouse effect, a practice that has gained global traction. The CO₂-water-rock reaction plays a crucial role in CO₂ geological sequestration, with the rock surface being a critical site for this reaction. Understanding the topography of rock surfaces is essential for assessing the degree of CO₂-water-rock reactions and ensuring the safety of CO₂ geological sequestration. Methods for characterizing rock surface topography are mainly classified into two categories. The first relies on scanning electron microscopy observations and energy-dispersive X-ray spectroscopy analysis, which, despite offering detailed surface topography, is limited by its inability to capture depth information adequately. The second category encompasses quantitative characterization methods based on surface roughness and fractal dimension derived from statistical principles. While these methods provide valuable quantitative parameters, their physical significance is not intuitively clear, nor do they directly correlate with rock erosion.

This paper introduces a new quantitative method for assessing the degree of CO₂-water-rock reactions through a method based on three-dimensional point cloud computing. This method aims to quantify the reaction degree on the rock surface more intuitively by measuring erosion volume. Utilizing three-dimensional laser scanning technology, point cloud data is acquired to construct a three-dimensional model of the rock surface. This model helps define the depression volume and determine the base level of the rock surface before and after CO₂-water treatment, using the root-mean-square roughness as a reference. In this paper, we propose two new methods for volume calculation, namely the concave method and the convex method. By applying these methods to calculate the volume of a regular model, their accuracy and applicability are compared. This comparison allows for the quantitative characterization of the erosion volume on the rock surface before and after CO₂-water treatment. Depending on the specific conditions, either calculation method can be selected to quantify the erosion volume of the rock surface before and after CO₂-water treatment. Finally, the paper uses coal samples from the Zhengtong Coal Mine, Changwu County, Xianyang City, Shaanxi Province, to validate the feasibility of the proposed erosion volume calculation method. [Results and Conclusions] These tests sought to simulate the CO₂-water-rock reactions and assess the effectiveness of the method in quantifying and characterizing the reaction degree. After CO₂-water treatment, a clear distinction in erosion across different areas on the rock surface was observed. Furthermore, the results revealed a significant proportional relationship between the erosion volume on the rock surface and the root-mean-square roughness.