Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions

Abstract

Abstract:Recently, both core-and pore-scale imbibition experiments have shown nonequilibrium dissolution of supercritical CO 2 (scCO 2 ) and a prolonged depletion of residual scCO 2 . In this study, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2 ). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time.Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2 -water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes -scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10-100 µm), observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints, are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.

Scaling the impacts of pore-scale characteristics on unstable supercritical CO2-water drainage using a complete capillary number

“…Under the experimental conditions (40 °C, 9 MPa), the solubility of scCO 2 dissolved in water is 1.225 mol/L (Spycher and Pruess, 2005). Meanwhile, in previous studies (Chang et al, 2016(Chang et al, , 2017(Chang et al, , 2019, we have showed the dissolution and mass transfer of scCO 2 in water in the sandstone-analogue Micromodel #1 is non-equilibrium, considerably limited by small area-to-volume ratios that represent the pore-throat configurations and characteristics of phase interfaces. Table 2 lists the imposed volumetric injection rates for the four micromodels.…”

“…This sequence was repeated for a wide range of flow rates. Detailed descriptions of the experimental procedures can be found in Chang et al (2017). Because scCO 2 was continuously injected into the micromodel, the dissolution of scCO 2 in residual water during drainage may have negligible effects on CO 2 saturation and distribution in the pore network.…”

“…Carbon capture and storage (CCS) has been considered as an effective technology to reduce greenhouse gas emissions into the atmosphere (IPCC, 2005). A number of laboratory experiments have been conducted under reservoir conditions with natural rock samples to (1) investigate the fundamentals of displacement between supercritical CO 2 (scCO 2 ) and brine and (2) provide parameter measurements for aquifer-scale storage capacity/efficiency estimation (Bennion and Bachu, 2008;Zhang et al, 2011a;Krevor et al, 2012;Pini et al, 2012;Berg and Ott, 2012;Akbarabadi et al, 2013;Chang et al, 2013Chang et al, , 2014Chang et al, , 2016Chang et al, , 2017Chang et al, , 2019Tsuji et al, 2016). At the laboratory scale (pore and core scales), the storage efficiency is represented by CO 2 saturation (the volumetric fraction of pore space filled by CO 2 ) in the pore (Bachu, 2015).…”

Wettability impact on supercritical CO2 capillary trapping: Pore‐scale visualization and quantification

“…Their work also indicated that even though the two‐pore network model (pore doublet model) [ Chatzis and Dullien , ] can well describe snap‐off mechanism, it fails in describing the bypass trapping when considering the fluid distribution. Later, the effects of Ca [ Chatzis et al ., ; Soroush et al ., ; Kimbrel et al ., ] and pore structure [ Tanino and Blunt , ; Chaudhary et al ., ; Geistlinger et al ., ] on immiscible flow and capillary trapping were extensively investigated using advanced visualization technology, including X‐ray computed tomography core‐flooding experiments [ Krevor et al ., ; Pentland et al ., ; El‐Maghraby and Blunt , ; Iglauer et al ., ; Andrew et al ., ; Geistlinger et al ., ; Xu et al ., ; Zuo and Benson , ; Li et al ., ; Niu et al ., ; Khishvand et al ., ; Rahman et al ., ; Herring et al ., , ], and micromodel experiments [ Zhang et al ., , ; Wang et al ., ; Kazemifar et al ., ; Cao et al ., ; Chang et al ., , ; Zhao et al ., ]. These studies indicated that (1) at Ca on the order of 10 −7 or even smaller, the snap‐off trapping mechanism by the precursor‐thin film dominates, and it is enhanced by the roughness of pore surface and the throat‐body aspect ratio of pores; (2) at Ca > 10 −7 , the main trapping mechanism involves propagation of invading fluid fingers that lead to islands of defending fluid being bypassed.…”

“…Another advantage of our micromodels is that they can withstand up to 10 MPa pressure drop. The widely used overburden pressure cell [ Zhang et al ., , ; Wang et al ., ; Chang et al ., , ; Jimenez‐Martínez et al ., ] is not needed in our experiment system, allowing us to directly record immiscible displacement behavior at the pore scale without using dyes to enhance the difference of fluorescent signal intensity between scCO 2 and brine phases. Our micromodels exhibited no significant changes in contact angles before and after experiments and retained relatively uniform spatially distributed wettability (see Figure and supporting information Figures S1–S5).…”