geological framework of basin analysis, they form the observational backbone for predicting detailed sedimentary structure and stratigraphy.
Oil and gas exploration, development, and production proceeded rapidly in the United States by comparison with the rest of the world. Consequently, the oil fields of the conterminous states are now more depleted than their counterparts elsewhere. Most U.S. oil reserves are in discovered fields and are considered to be nonrecoverable resources. This presents a unique opportunity and challenge for improved technology, because recovery from most hydrocarbon fields in the world today ranges from only 15 to 55 percent. An immediate need to develop a better understanding of reservoir heterogeneity, in situ rock and fluid properties, and enhanced oil recovery techniques is apparent.
The most significant trend in the U.S. oil industry has been the shift in effort toward recovery of a maximum amount from existing fields and established areas. In the major oil companies a majority of earth scientists are now engaged in production-or exploitation-related activities instead of the more traditional exploration-related areas. New giant fields—those with recoverable reserves greater than 100 million barrels—in the United States are likely to be found only in remote areas and have associated greater costs. However, there are numerous old giant fields that have yielded only a fraction of their original oil. Hence, billions of barrels of domestic reserves could be added by the use of enhanced recovery techniques. Horizontal drilling has increased reserves in some areas. Complemented by discoveries from more detailed exploration within existing producing regions, the motivation for the shift of effort to established areas is clear.
New types of well-logging tools and interpretational techniques are developing constantly. These developments now allow the location of previously unrecognized oil and gas zones in both actively producing and abandoned wells. The potential for increasing reserves is enormous. The current focus of the domestic oil industry is commonly referred to as reservoir management, and most major companies have actually restructured their organizations in this direction—establishing interdisciplinary teams that include geologists, geophysicists, and reservoir engineers. The teams are charged with characterizing the established fields and reservoirs and then using the information to manage further development drilling and the application of enhanced recovery techniques. In addition, such teams explore for untapped reserves that become economically viable because of their proximity to existing producing facilities.
The most significant technological development in the past decade supporting reservoir management has been the advance of three-dimensional seismology. The large investment for three-dimensional seismic acquisition and processing is often easily justified on economic grounds because of its leverage against the much larger costs of development and field production. The technical base for three-dimensional seismology should continue to grow, along with the capability to record ever larger surveys and produce more detailed images with ever larger computers.
Entirely new seismic technologies are also now in the research and development phase. The most promising is the area of cross-well seismology, in which the active seismic experiment is carried on between wells instead of on the surface. Producing an image from these data is conceptually similar to medical CAT scan technology. The key advantages of the technique are that much higher seismic frequencies can be propagated between wells than from the surface, and measurements can be made within an existing and operating oil field. Moreover, time-lapse repeat measurements can be made with great precision and have been tested for monitoring the advance of hot steam fronts in enhanced production projects that attempt to flush extra hydrocarbons from an otherwise depleted field. Although still in the research phase, an entirely new industrial application of seismology is developing.
Characterization of complex reservoirs for the development of geological and fluid behavior models could lead to optimal hydrocarbon recovery from existing reservoirs. The problems are not different from those generally addressed in modern oil field research and embrace such general considerations as the flow of fluids through porous media. General practice has been to expect such research to be conducted by the 10 or so major oil companies. However, major companies are focusing increasingly on larger targets, and the needed research is lagging.
The United States is rich in coal and its reserves are sufficient to support consumption at the present rate for centuries. Most U.S. coal is used in the generation of electricity; it accounts for more than