The Impact of Acid Strength and Mineral Composition on Spontaneous Imbibition with Reactive Fluids

Capillary rise experiments are conducted in a set of calcareous and siliceous rocks with varying mineralogy and petrophysical properties to understand the coupled impact of reactivity and spontaneous imbibition. A capillary rise experiment is performed in each sample: first with deionized water, then with a dilute acidic solution, and finally again with deionized water, and the capillary rise profile for each is recorded. Pre- and post-acid petrophysical properties such as porosity, permeability, pore size distribution, and contact angle are measured for each sample. The mineral makeup of the rocks significantly influences how the acidic fluids penetrate the samples. The primary reactions are the dissolution of Ca- and Mg-rich minerals which alter the pore network. The higher acid strength results in higher capillary rise in calcareous rocks and results in an increase in the average pore size. The same pH acid results in lower capillary rise in the siliceous rocks, and a general decrease in the average pore size is observed. Changes in contact angle indicate increased water affinity in carbonate and reduced affinity in sandstone. The link between capillary interactions and fluid reactivity is often overlooked in fluid flow studies, and this research sheds light on the importance of reactivity during spontaneous imbibition, offering insights into dissolution and precipitation processes during capillary flow.