GEOLOGICAL CHARACTERISTICS AND SOME PROBLEMS IN DEVELOPMENT FOR OIL SHALE IN NORTHWEST CHINA

Abstract

With the amount of oil resources becoming increasingly scarce, non-conventional resources such as oil shale, oil sands, and heavy oil, have caught our attention. There are abundant oil shale resources in Northwest China. Our analysis of field geological section surveys, standard mining investigations, and the laboratory analysis of important samples indicate that the oil shale in Northwest China is characterized by the following features: oil shale strata is 1–36 m thick, the color of slightly greasy, shiny and flaky oil shale is mostly brown-black, black with light brown streaks, but some oil shale outcrops appear maroon. Oil shale is of layered structure, irregular shape, conchoidal fracture, and low hardness, composed mainly of clay and silt-sized detrital minerals (feldspar and quartz). SiO2 and Al2O3 comprise a total of 52.54% of the rock, this indicates that oil shale is of the medium ash type. Organic carbon content of oil shale is 14% and that of total carbon 16.28%. Oil yield is generally 1.5–13.7%, overall caloric value 1.66–20.98 MJ/kg. Density of oil shale is 1.55–2.46 g/cc. Younger oil shale strata are characterized by progressively higher REE abundances. There are mainly three types of oil shale deposits: the littoral-neritic facies sedimentary deposits of the Middle and Upper Carboniferous – the Lower Permian, remnant lake bay-lacustrine facies sedimentary deposits of the Upper Permian, and shale which formed in inland deep water – half deep water lacustrine facies of the Mesozoic, the latter being of the major industrial type, and its origin is similar to “the Black Sea model.” Oil shale layers are also the main oil source rock in the Ordos Basin. Oil shale layers which formed in deltaic environments in the Middle and Late Carboniferous and the Jurassic are mostly paragenetically related to coal beds. In the area, the total amount of predicted resources of oil shale is at least 31,000×10 8 t which is equivalent to about 2000×10 8 t of shale oil. Oil shale resources in the Ordos Basin account for 99% of the total and can be compared to oil shale resources in the Green River area of western North America. In Northwest China, the identified oil shale deposits are located in