Systems and methods for enhancing carbon dioxide injectivity into a subterranean formation

A system, comprising:

• a freshwater circulation system configured to circulate freshwater into a wellbore formed from a terranean surface and to a subterranean formation that comprises a saline aquifer;
• a carbon dioxide (CO2) circulation system configured to circulate a CO2 fluid into the wellbore and to the subterranean formation;
• and
• a control system configured to perform operations comprising:
• determining a volume of freshwater sufficient to create a freshwater ring about the wellbore in the subterranean formation;
• causing the freshwater circulation system to circulate the determined volume of freshwater into the subterranean formation;
• and
• causing the CO2 circulation system to circulate, subsequent to circulation of the determined volume of freshwater, an amount of the CO2 fluid into the subterranean formation into which the predetermined volume of freshwater was injected for sequestration.

A method, comprising:

• identifying a wellbore that extends from a terranean surface and to a subterranean formation that comprises a saline aquifer;
• determining a volume of freshwater based on a plurality of geometric characteristics of the wellbore and the subterranean formation, wherein the plurality of geometric characteristics of the wellbore and the subterranean formation comprise a geometric characteristic of the wellbore, a first geometric characteristic of the subterranean formation, and a second geometric characteristic of the subterranean formation;
• injecting, through the wellbore, the predetermined volume of freshwater into a portion of the saline aquifer adjacent the wellbore to create a freshwater ring about the wellbore in the subterranean formation, the geometric characteristic of the wellbore comprising a radius of the wellbore, the first geometric characteristic of the subterranean formation comprising a radius of the freshwater ring, and the second geometric characteristic of the subterranean formation comprising a thickness of the subterranean formation;
• and
• subsequent to injecting the predetermined volume of freshwater, injecting a carbon dioxide (CO2) fluid, through the wellbore, and into the subterranean formation for sequestration.