We have all seen pictures of a "gusher," the spurt of black oil that sometimes erupts from an oil well when it first penetrates the oil-bearing stratum in the rock below. This oil is under great pressure and will continue to flow up the well pipe on its own accord until the pressure equalizes. Once this happens, the oil can still be pumped out, using enormous pumps that look like bobbing birds. Eventually, no more oil can be pumped, but at that point there is still plenty of oil down in the porous rock stratum.

Once the pumps have run dry, the oil companies use "secondary" recovery processes—pumping water into the well to displace the oil upward, for example. But water injection does not recover most of the oil that is still down below. The water, being thin and runny, does not push the thick, viscous oil very well. Instead, the water flows around and past the oil, which stubbornly clings to the rock. On average worldwide, only about 25 percent of the oil in a stratum is recoverable by primary and secondary means, although in some cases the yield can be as high as 50 percent.

Sometime around 1960, somebody suggested that adding a water-soluble polymer to the water to increase its viscosity might help it push the oil along ahead of it. Sure enough, the thickened water can no longer flow around the oil, and another 10 to 20 percent of the oil in the rock can be recovered. A partially hydrolyzed form of the polymer polyacrylamide is usually used, although xanthan gum—a biopolymer more commonly found as an additive in foods—is also employed. Other polymers are also being developed whose properties are especially designed for enhanced oil recovery. As world oil reserves are depleted, these polymers will become more and more important in the oil companies' quest to get the most from every well.

Extension of range and payload will occur for each pound of polymer-based material that is substituted for a greater weight of aluminum or titanium. Failure of the airframe material is a significant concern, but polymer matrix and polymer-or carbon-reinforced composites offer a wide range of behavior that could provide an optimal mix of properties. The high skin temperatures that are generated at supersonic speeds present another challenge, but there are many new high-temperature matrices that, used with carbon fibers, could provide novel solutions.

The leverage obtained by using polymers is greater for ground-based military vehicles than for aircraft, because polymer-based composites are being substituted for steel, which is about 5 to 7 times as dense as the composites. Military design philosophy has been strongly influenced by the need for protective armor plates. But the advent of armor-piercing artillery shells suggests shifting to a protective strategy based on light weight for range and speed, coupled with deflection of antitank and antivehicle missiles by features of vehicle architecture, such as low-angle surfaces.

Military marine structures and vehicles are still built largely of steel, which demands heroic defenses against corrosion and very heavy (nonplaning) hull structures. Polymer-based substitution could be highly advantageous in many

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