Final answer:
The ratio of swept oil volume to the oil volume in place before EOR signifies the efficiency of the EOR process in recovering additional oil. It is akin to the concept of EROEI which measures energy output versus energy input, reflecting process effectiveness.
Step-by-step explanation:
The ratio of swept oil volume to the oil volume in place before the Enhanced Oil Recovery (EOR) process represents the efficiency of the EOR technique being used to extract additional oil from a reservoir. This ratio is crucial in determining how effectively an EOR process is able to mobilize and recover the oil that was initially unrecoverable using conventional methods. For instance, an EOR process that manages to sweep and extract a significant proportion of the oil in place would be considered more efficient than one that recovers a lesser volume. This efficiency can be likened to the concept of Energy Returned on Energy Invested (EROEI), which measures the amount of energy obtained from an energy source compared to the amount of energy invested to harness it. For example, during early oil extraction times when 'gushers' were common, a high EROEI of 100:1 indicated a very efficient process, where only a small amount of energy was needed to extract a large amount of oil.