c/7. 7— The Use of Genetically Engineered Micro-Organisms in the Environment *119 
10 to 100 ppm, v\here nonbiological methods 
ma\ he uneconomical. Organisms such as the 
common \east Saccharonn t'es cerevisiae can ac- 
cumulate uranium up to 20 [)ercent of their 
total weight. 
rhe economic competitiveness of biological 
methods has not yet been proven, hut genetic 
improvements have been attempted only re- 
centlv. The cost of producing the micro-orga- 
nisms has been a major consideration. If it can 
he reduced, however, the approach might he 
useful. 
-As with other biological systems, genetic 
engineering may increase the efficiency of the 
extraction process. In the Saccharomyces sys- 
tem, differences in the ability to recov'er the 
metals have been demonstrated within popula- 
tions of cells. Selection for cells with the genetic 
ability to accumulate large amounts of specific, 
desired metals would he an important step in 
designing a practical system. 
Oil recovery 
V 
Since 1970, oil production in the Lhiited 
States has declined steadily. The supply can he 
increased by: accelerating explorations for new 
oilfields; by mining oil shale and coal and con- 
verting them to liquids; and by developing new 
methods for recov ering oil from existing reser- 
voirs. 
In primary methods of oil recovery, natural 
expulsive forces (such as physical expansion) 
drive the oil out of the formation. In secondary 
methods of recovery, a fluid such as water or 
natural gas is injected into the reservoir to force 
the oil to the well. .Approximately 50 percent of 
domestic crude in recent years has been ob- 
tained through secondary recovery. 
Recently, new methods of oil recovery have 
been added to primary and secondary methods, 
which are called tertiary, improved, or en- 
hanced oil recovery (EOR) techniques. They em- 
ploy chemical and physical methods that in- 
crease the mobility of oil, making it easier for 
other forces to drive it out of the ground. The 
major target for EOR is the oil found in sand- 
stone and limestone formations. It is here that 
applied genetics may play a major role, 
engineering micro-organisms to aid in recovery. 
Oil susceptible to these processes is localized 
in reservoirs and pools at depths ranging from 
100 ft to more than 17,000 ft. In these areas, the 
oil is adsorbed on grains of rock, almost always 
accompanied by water and natural gas. The 
physical association of the trapped oil and the 
surrounding geological formations varies signif- 
icatitly from site to site. The unknown charac- 
teristics of these variations are largely respon- 
sible for the economic risk in an attempted EOR. 
Enhanced oil recovery 
Of the original estimated volume of more 
than 450 billion barrels (hbl) of U.S. oil reserves, 
about 120 billion hbl have been recovered by 
primary and secondary techniques, and another 
30 billion hbl are still accessible by these 
methods. The remaining 300 billion bbl how- 
ever, are probably recoverable only by EOR 
methods. These figures include the oil remain- 
ing in known sandstone and limestone reser- 
voirs and exclude tar sands and oil shale. 
Four EOR processes are currently used. All 
are designed to dislodge the crude oil from its 
natural geological setting: 
• In thermal processes, the oil reservoir is 
heated, which causes the viscosity of the oil 
to decrease, and with the aid of the 
pressure of the air introduced, supports 
the combustion that forces the petroleum 
to the producing well. Thermal processes 
will not be improved by genetic technol- 
ogies. 
• Various crude oils differ in their viscosity- 
ability to flow. Primary and secondary 
methods can easily remove those that flow 
