Typical geological characteristics of the new energy resource of oil shale and some problems concerning its development and utilization

Abstract：With the gradual decrease of oil resources in China, non-conventional resources such as oil shale, oil sands and heavy oil have aroused much attention among geologists. There are abundant oil shale resources in northwest China, which have been preliminary studied in this paper. Field geological section survey, standard mining investigation, and laboratory analysis of important samples indicate that the oil shale in northwest China has the following features： 1) Oil shale strata 1- 36m thick exist in this region. 2) The color of the oil shale is mostly brown-black, black, whereas the color of some oil shale outcrops is maroon. Oil shale is characterized by slightly greasy luster, flaky layered structure, irregular conchoidal fracture, small hardness and light brown streak. 3) In hand specimen, oil shale is mainly composed of clay minerals and silt-sized detrital minerals (feldspar and quartz). 4) The main chemical components of oil shale are SiO2 and Al2O3, which possess 65.44% of the rock, indicating that the shale is of the medium ash type. The organic carbon possess 14% of the oil shale, total carbon poesses16.28%, and oil yield is generally 1.5%-13.7%, for an overall caloric value of 1.66-20.98 MJ/kg. The density of the shale is 1.55-2.46 g/cc. Younger oil shale strata have progressively higher REE abundances. 5) Oil shale deposits can be mainly divided into 3 types: littoral-neritic facies sedimentary deposits in middle and late Carboniferous-early Permian strata, remnant lake bay-lacustrine facies sedimentary deposits in late Permian strata, and inland lacustrine–delta facies sedimentary deposits in Mesozoic strata. Oil shale formed in Mesozoic inland deep water-half deep water lacustrine facies is the major industrial type and its origin is similar to “the Black Sea Model.” Oil shale layers are also the main oil source rocks in Ordos basin. Oil shale formed in the deltaic environment in middle and late Carboniferous and Jurassic strata are mostly related to coal beds in genesis. 6) In this region, the total amount of predicted resources of oil shale is at least 30000×108 t , which is equivalent to about 2100×108 t shale oil; among them, oil shale resources in Ordos basin accounts for 99% and can be compared with oil shale resources in Green River area of western North American. 7) In northwest China, identified oil shale deposits are located in the vicinity of large and medium-sized cities, with good development prospects . As long as the problem of environmental pollution has been solved and the appropriate technologies have been used, immense economic benefits are likely to be obtained.