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

TLDR

Interfacial interactions between mineral surfaces and immiscible fluids control the efficiency of enhanced oil or gas recovery and the injection and storage of CO₂, with interfacial tension and contact angle in CO₂–water–mineral systems varying noticeably with fluid pressure. The study compiles and expands previous data to include saline water, multiple substrates (quartz, calcite, oil‑wet quartz, PTFE), and a pressure range up to 20 MPa at 298 K. Data analysis yields interfacial tension and contact angle as functions of fluid pressure and recovers the diffusion coefficient of water in liquid CO₂ from long‑term observations. Results show that interfacial tension decreases with pressure, contact angles shift according to surface wettability, water diffuses rapidly in liquid CO₂ influencing pendular water evolution, CO₂‑derived ions modify mineral surfaces (e.g., calcite dissolution), and these pressure‑dependent interfacial properties alter injection patterns and breakthrough behavior, thereby affecting reservoir and seal performance.

Abstract

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 CO 2 in geological formations. Previous studies have shown that the interfacial tension and contact angle in CO 2 ‐water‐mineral 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, oil‐wet 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 CO 2 from long‐term observations. Results show that CO 2 ‐water interfacial tension decreases significantly as pressure increases in agreement with previous studies. Contact angle varies with CO 2 pressure in all experiments in response to changes in CO 2 ‐water interfacial tension: it increases on nonwetting surfaces such as PTFE and oil‐wet quartz and slightly decreases in water‐wet quartz and calcite surfaces. Water solubility and its high diffusivity ( D = 2 × 10 −8 to 2 × 10 −7 m 2 /s) in liquid CO 2 govern the evolution of interparticle pendular water. CO 2 ‐derived 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 CO 2 . Pressure‐dependent 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.