Global petroleum occurrence considered in relation to reservoir depth versus reservoir temperature

The majority of produced plus remaining conventionally recoverable oil and gas (estimated ultimate recovery = EUR) occurs within the range of 60-120°C (140-248°F) reservoir temperature. Previous studies documenting this “Golden Zone” (GZ) for petroleum exploration have, however, largely ignored the factor of reservoir depth. The present paper addresses this omission by comparing cumulative plots of global EUR versus temperature and versus depth and calculating P10, P50, and P90 values, referring to the 10th, 50th, and 90th percentiles of total EUR with respect to original (pre-production) reservoir temperature and present reservoir depth, respectively. It is found that the P90-P10 interval for depth (80% of EUR occurrence) varies considerably between areas of higher and lower temperature/depth ratio, whereas the P90-P10 interval for temperature is relatively invariant. This difference is interpreted as confirming that temperature is the more fundamental factor controlling global oil and gas occurrence. Earlier studies have explained how the combination of temperature-controlled diagenetic processes results in petroleum loss both below 60°C (by oil degradation and seal leakage) and above 120°C (by porosity loss, seal failure, and consequent remigration).