The coupled effect of salt precipitation and fines mobilization on CO₂ injectivity in sandstone

Abstract

Appreciable CO2 injectivity is required to inject large volumes of CO2 through a minimum number of wells. In situ geochemical CO2‐brine‐rock reactions may dissolve sandstone rock minerals, and consequently release fine particles into the pore fluid. If the fine particles (‘fines’) are mobilized during CO2 injection, well injectivity could be severely impaired. The transport of fines under CO2 injection conditions involves the complex multiphase flow of dry supercritical CO2, saline formation brine, and fine particles. While transported fines could plug narrow pore channels, the saline pore water could be vaporized by supercritical CO2 to precipitate solid salt into the pores. To understand the impact of mineral dissolution on CO2 injectivity, it is important to consider the coupled effect of fine particle mobilization and salt precipitation. We conducted core‐flood experiments and theoretical modelling to investigate the coupled effect of the fines mobilization and salt precipitation on CO2 injectivity. We found that salt precipitation could increase CO2 injectivity impairment induced by the fines mobilization. The deposited salt reduces the flow area, making the pores more susceptible to particle entrapment. Injectivity impairment increased with decreasing initial rock permeability and increasing saturating brine salinity. Irreducible brine saturation and pore size distribution were identified as parameters that strongly determine the contribution of salt precipitation during the transport of fines. Injectivity impairment was also slightly higher when the rock was first exposed to salt precipitation, before the entrapment of fines. The current findings highlight the complexity and uniqueness of fines transportation under CO2 injection conditions and the impact of mineral dissolution on CO2 injectivity. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Well Injectivity during CO2 Geosequestration: A Review of Hydro-Physical, Chemical, and Geomechanical Effects

“…120 Salt precipitation is another cause of fines-induced injectivity impairments through making the pores susceptible to fines entrapment by size exclusion capture in thin pore throats. 82,121,122 Mineral dissolution is also likely to increase the portion of dislodged fines in saline aquifers; however, there are some arguments on how it affects the wellbore injectivity. For instance, Pearce et al 113 showed that at lower pH condition of CO 2 -rich brines, the impacts of fines migration can be either negative or positive.…”

“…Despite the seemingly simple process of salt formation, there exist conflicting results regarding the influences of drying-out on CO 2 injectivity. , While most research has revealed the drastic injectivity impairments caused by a porosity reduction of 2–15% and a permeability decline of 13–83%, ,,,− some other research has shown that the increased relative permeability of CO 2 , due to water vaporization, compensates for the negative impacts of pore plugging. ,,, Bacci et al claimed that such disagreements mainly arise from the role of brine mobility, and a significant porosity change only occurs under sufficiently high brine mobility when the continuous recharge of the precipitation front increases the salt concentration.…”

“…Salt precipitation is another cause of fines-induced injectivity impairments through making the pores susceptible to fines entrapment by size exclusion capture in thin pore throats. ,, …”

Theoretical modeling of the effect of temperature on CO2 injectivity in deep saline formations

“…For a cylindrical core, radius and length L reconstructed into a bundle of parallel, noninteracting capillary tubes with varying radii (), it can be shown that, the total number of capillary tubes in the core is given by (Fig. ): …”

“…. r N ), it can be shown that, the total number of capillary tubes in the core is given by 44 (Fig. 6):…”