A downhole tool system includes a downhole tool string configured to couple to a downhole conveyance. The downhole conveyance extends into a wellbore, from a terranean surface, through at least a portion of a subterranean zone. The subterranean zone includes a geologic formation. The downhole tool system also includes a heating device coupled with the downhole tool string. The heating device is configured to transfer heat to the geologic formation in the wellbore at a specified temperature sufficient to adjust a quality of the geologic formation associated with a fluid absorption capacity of the geologic formation.