Final answer:
Unmineable coal seams are advantageous for CO₂ storage due to their large capacity, low cost, and high integrity for securely containing CO₂.
Step-by-step explanation:
The advantages of using unmineable coal seams for CO₂ storage include large capacity, low cost, and high storage integrity. Unmineable coal seams are beneficial for CO₂ storage because they can hold large volumes of carbon dioxide; this represents their large capacity for storage. The storage process incurs lower costs compared to other methods, as the infrastructure for deep geological storage already exists from previous mining operations, contributing to the low cost. Moreover, unmineable coal seams typically have geological characteristics that make them effective at securely containing the stored CO₂, which is indicative of their high storage integrity. While unmineable coal seams are advantageous in many locations, their availability is not uniform, and they are not present in all regions.