Rapidly cooling a geologic formation in which a wellbore is formed

A method comprising:

• positioning a first chamber comprising a cooling fluid downhole relative to a second chamber comprising a cold source at a first sub-zero temperature, the cooling fluid configured to be cooled upon contacting the cold source, the cold source separated by the cooling fluid by a separation member, the first chamber and the second chamber lowered to a position within a wellbore formed in a formation;
• causing the cold source to contact the cooling fluid by activating the separation member, wherein a combination of the cold source and the cooling fluid cools to a second sub-zero temperature;
• and
• transferring at least a portion of the combination to the formation at the position.

A system comprising:

• a canister configured to be positioned at a downhole location within a wellbore, the canister comprising:
• a cold source at a first sub-zero temperature;
• a cooling fluid configured to be cooled to a second sub-zero temperature in response to being contacted by the cold source;
• and
• a separation device that prevents the cold source from contacting the cooling fluid;
• and
• an activation mechanism connected to the canister, wherein, in response to a signal, the activation mechanism is configured to:
• cause the separation device to permit the cold source to contact the cooling fluid, and
• transfer at least a portion of a combination of the cold source and the cooling fluid to a wellbore wall at the downhole location.