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USGS1982

Assessment of the petroleum, coal, and geothermal resources of the Economic Community of West African States (ECOWAS) region

Approximately 85 percent of the land area of the ECOWAS (Economic Community of West African States) region is covered by basement rocks (igneous and highly metamorphosed rocks) or relatively thin layers of Paleozoic, Upper Precambrian, and 'Continental Intercalaire? sedimentary rocks. These areas have little or no petroleum potential. Areas of the ECOWAS region that have potential for petroleum production or potential for increased petroleum production include the narrow belt of sedimentary rocks that stretches along the continental margin from Mauritania to Nigeria and the Niger Delta and the Benue depression. The Senegal Basin, located on the continental margin of Mauritania, Senegal, Gambia, Guinea Bissau, and Guinea, has been intensely explored by the oil industry and most of the larger structures onshore and on the shelf probably have been tested by drilling with little or no resulting commercial production. Unless basic ideas pertaining to the petroleum geology of the Senegal Basin are revised, future discoveries are expected to be limited to small fields overlooked by industry at a time when petroleum prices were low. On the continental shelf of Sierra Leone and the continental shelf of northeast and central Liberia, the sedimentary rocks are relatively thin, and industry has shown little interest in the area. On the continental rise of these countries, however, the sedimentary section, deposited in a complex fault-block system, increases in thickness. A renewal of industry interest in this deep-water area will probably follow further development of deep-water production technology. A recent oil discovery on the continental slope off the Ivory Coast is expected to spur further exploration offshore of southeastern Liberia, Ivory Coast, Ghana, Togo, and Benin. This relatively unexplored area in the Gulf of Guinea has good possibilities .for the discovery of giant oil fields. Nigeria's oil development from the Niger Delta may have peaked, as 13 of 14 giant oil fields were discovered prior to 1969 and the greatest number of fields were discovered in the period 1965 through 1967. Like delta regions in other parts of the world, individual oil fields of the Niger Delta are small to medium by world standards and future discoveries, therefore, are likely to reflect this reality. The natural gas resources of the Niger Delta, unlike its oil resources, are comparatively underdeveloped. Parts of the Benue depression in Nigeria and Niger could contain significant deposits of petroleum. The lower Benue depression, immediately north of the Niger Delta, has been extensively explored by drilling. Except for noncommercial discoveries of oil and gas and traces of oil and gas on the ground surface, the results of exploration in the lower Benue depression were negative. However, in the Lake Chad area of Chad and in southern Chad near the Central African Republic boundary, oil and gas discoveries were made just prior to the cessation of all drilling and exploration activity in early 1979. It is rumored that these discoveries may be large although little information is available. The relation between the two areas in Chad and their overall relation to the Benue depression is poorly understood; however, the possibility of thick sedimentary sections containing Cretaceous marine source rock and Tertiary reservoir beds-all contained within grabens in a highly faulted failed-arm system subjected to high heat flow--is attractive. Of the ECOWAS countries, only Nigeria and Niger produce coal commercially. Nigeria produces subbituminous coal from Paleocene-Maestrichtian and Maestrichtian (Late Cretaceous) age rocks of the Niger Delta region; reserves are estimated, on the basis of extensive drilling, to be 350 million tons (standard coal equivalent). In addition, lignite deposits of the Niger Delta appear to be large but have not been developed. Niger produces small amounts of coal used locally by uranium mine and mill operations from C

Open-File Report↗
USGS1983

Montana; basic data for thermal springs and wells as recorded in Geotherm

Changes in ground-water withdrawals, water levels, and quality of water occurred in the artesian aquifers of the Sevier Desert, Utah during 1963-81. Ground-water withdrawals increased from an average of 9,500 acre-feet (11.7 cubic hectometers) per year between 1951 and 1963 to an average of 27,500 acre-feet (33.9 cubic hectometers) per year between 1964 and 1981. Most of the increased withdrawal was from the deep artesian aquifer. Water levels declined as much as 19 feet (5.8 meters) in the deep artesian aquifer and as much as 13 feet (4.0 meters) in the shallow artesian aquifer between 1963 and 1981. The declines probably are due to increased ground-water withdrawals for irrigation and municipal use. Quality of water in parts of the shallow artesian aquifer is deteriorating. The deterioration probably is the result of recharge of poor quality from the overlying water-table aquifer. A digital-computer model was constructed to predict water-level changes resulting from changes in recharge and discharge for 20 years (1981-2000) at one-half, one, and two times the 1977-79 average rate. The model computer water-level declines of more than 80 feet (24 meters) in the deep artesian aquifer with withdrawals twice the 1977-79 average, declines of more than 40 feet (12 meters) if withdrawals were equal to the 1977-79 average, and declines of more than 15 feet (4.6 meters) if withdrawals were one-half the 1977-79 average. Computer water-level declines after 20 years in the shallow artesian aquifer were more than 50 feet (15 meters) at two times the 1977-79 average rate, more than 15 feet (4.6 meters) at the 1977-79 average, and less than 4 feet (1.2 meters) at one-half the 1977-79 average. The model also was used to predict the effects of approximate changes in ground-water withdrawals related to the Intermountain Power Project. Water-level declines in the deep artesian aquifer of more than 15 feet (4.6 meters), and only small changes in water levels in the shallow artesian aquifer after 20 years. These changes are in addition to changes computed for 20 years of withdrawals at the 1977-79 rate. (USGS)

Open-File Report↗