EGEL
Energy GeoEngineering Laboratory

Water-CO2-mineral systems: Interfacial tension, contact angle, and diffusion--Implications to CO2 geological storage

Water-CO2-mineral systems: Interfacial tension, contact angle, and diffusion-Implications to CO2 geological storage

​Espinoza, D. and Santamarina, J. C. (2010a). "Water-CO2-mineral systems: Interfacial tension, contact angle, and diffusion-Implications to CO2 geological storage." Water Resources Research, Vol. 46.
D. Nicolas Espinoza and J. Carlos Santamarina
xx
2010
The interfacial interaction between mineral surfaces and immiscible fluids determines the efficiency of enhanced oil or gas recovery operations as well as our ability to inject and store CO2 in geological formations. Previous studies have shown that the interfacial tension and contact angle in CO2watermineral systems change noticeably with fluid pressure. We compile previous results and extend the scope of available data to include saline water, different substrates (quartz, calcite, oilwet quartz, and polytetrafluoroethylene (PTFE)), and a wide pressure range (up to 20 MPa at 298K). Data analysis provides interfacial tension and contact angle as a function of fluid pressure; in addition, we recover the diffusion coefficient of water in liquid CO2 from longterm observations. Results show that CO2water interfacial tension decreases significantly as pressure increases in agreement with previous studies. Contact angle varies with CO2 pressure in all experiments in response to changes in CO2water interfacial tension: it increases on nonwetting surfaces such as PTFE and oilwet quartz and slightly decreases in waterwet quartz and calcite surfaces. Water solubility and its high diffusivity (D = 2 × 108 to 2 × 107 m2/s) in liquid CO2 govern the evolution of interparticle pendular water. CO2derived ionic species interaction with the substrate leads to surface modification if reactions are favorable, e.g., calcite dissolution by carbonic acid and precipitation as water diffuses and migrates into the bulk CO2. Pressuredependent interfacial tension and contact angle affect injection patterns and breakthrough mechanisms, in other words, the performance of geological formations that act as either reservoirs or seals.