Pore matrix dissolution in carbonates: An in-situ experimental investigation of carbonated water injection

Carbonate rocks in underground formations are major targets for oil extraction and carbon storage. The solid part of these porous rocks contains certain minerals, such as calcite and dolomite, that can interact with aqueous solutions. Interactions could be reactive, which leads to the dissolution of these minerals. In this study, we investigated the evolution of carbonate rock dissolution during the flow of carbonated water in pores that initially contain both oil and brine. Carbonated water is an aqueous solution enriched with carbon dioxide (CO₂); hence, it is acidic. In our experiments, we observed that the reactive flow and transport of carbonated water is characterized by two distinct periods. The first is a pre-dissolution period where the CO₂ molecules diffused from the flowing carbonated water into the oil causing it to swell. As separate oil globules swelled, they reconnected and moved in the direction of the flowing water toward the outlet of the rock sample. In the second stage, significant mineral dissolution occurred creating wormholes that had either a conical or a dominant pattern. The pattern and extent of dissolution was dependent on the flow rate of the carbonated water and its CO₂ concentration.地下岩层中的碳酸盐岩（carbonate rocks）是石油开采与碳封存的核心目标储层。这类多孔岩石（porous rocks）的固相组分包含方解石（calcite）、白云石（dolomite）等可与水溶液（aqueous solution）发生反应性相互作用的矿物，该类反应过程会引发矿物溶蚀（dissolution）。本研究针对初始同时含油与地层盐水的孔隙中，碳酸水（carbonated water）流经时碳酸盐岩溶蚀的演化过程展开系统探究。碳酸水是富含二氧化碳（CO₂）的水溶液，因此呈酸性。实验中我们观察到，碳酸水的反应性流动与输运过程可分为两个截然不同的阶段：第一阶段为预溶蚀期，二氧化碳分子从流动的碳酸水中扩散至油相，引发油相膨胀；独立油滴在膨胀后发生聚并，并随水流方向向岩样（rock sample）出口运移。第二阶段则发生显著的矿物溶蚀，形成兼具锥状与优势发育形态的蠕虫状溶蚀孔道（wormholes）；溶蚀的形态与规模取决于碳酸水的流速及其二氧化碳浓度。