Remaining Potential for Growth of Oil Reserves in Discovered Fields in Two High-Growth U.S. Regions: San Joaquin and Permian Basins
A recently completed U.S. Geological Survey assessment probabilistically quantified potential additions to reserves in about forty major U.S. oil fields. Estimates are of technically recoverable reserve additions without regard to economic constraints. Two regions showing high rates of growth of reserves and significant potential for future increases are the San Joaquin Basin in California and the Permian Basin in Texas and New Mexico. Additions to reserves in these basins result mostly from improving recovery efficiency. Increases take place primarily in reservoirs with either low permeability or heavy oil, from intensive application of technology that allows oil to flow more readily through low-permeability reservoirs, such as fracturing, or that reduces oil viscosity, such as thermal recovery or miscible gas flooding. Such additions are likely to continue, although the easiest gains have been made. Approaches such as directed drilling and improvements in seismic technology have helped harvest bypassed oil, but they have not resulted in the volumes that come from improving overall recovery efficiency in large reservoirs.
In the San Joaquin Basin, where 8 billion barrels of oil were added to reserves in existing fields between 1965 and 2005, growth will continue from thermal recovery of low-gravity oil in shallow, high-porosity, high-permeability reservoirs, in which recovery efficiency can reach values over 60 percent. An increasing component of growth should come from expansion and intensification of fracturing and waterflood projects that recover oil from low-permeability, high-porosity diatomite reservoirs. Recovery efficiency in diatomite is typically only about 15 percent, but it may improve as technology evolves. Diatomites may account for much of the several billion barrels of additions possible from the San Joaquin Basin. A modest contribution may come from CO2 floods in deep sandstone reservoirs.
Reserves in the Permian Basin have grown from increasingly complex waterflood, infill, and CO2 flood projects in heterogeneous carbonate reservoirs with generally low permeability. This technology has been quite successful; recovery efficiency in a few major reservoirs now exceeds 50 percent. There is only limited potential for further reserve additions in the largest fields. As advanced technology spreads to smaller, lower-quality reservoirs, reserves will continue to grow, but not as markedly as they have in the last few decades.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California