Sustainability 2011 , 3 1849
Figure 8. Estimated energy return ratios for the California oil industry, 1955–2005.
Functions used to generate energy return ratios are presented in Table 2, while input data
(for low case) are presented in Table 4.0!20!40!60!80!100!120!140!1950! 1960! 1970! 1980! 1990! 2000! 2010!Point of extraction energy return ratios!(NER/EROI and EER)!Year!NER/EROI (POE)!
EER (POE)!(a) Point of extraction (POE) energy return ratios (excludes refining).0.0!2.5!5.0!7.5!10.0!12.5!15.0!1950! 1960! 1970! 1980! 1990! 2000! 2010!Full fuel cycle energy ratios (NER/EROI and EER)!Year!NER/EROI!
EER!(b) Full fuel cycle energy return ratios (includes refining).Figure 8 shows a closing of the gap between NER and EER beginning in the mid-1980s. This is
due to changing of the primary energy source for California TEOR steam production. Originally, steam
for EOR was generated using produced heavy crude. Producers switched to natural gas for generating
steam, thus the internal energy usexc 1 drops significantly by 1985, reducing the gap between NER and
EER. TEOR ceased to be a largely self-fueled process at this time.