ABSTRACT: Mechanized Oil-Shale Mining in Southern China
Hugh J. Mitchell-Tapping
Oil-shale is one of the most important direct sources of hydrocarbon in southern China. The term oil-shale refers to organic-rich free-grained rocks that produce oil upon distillation and have a production cut-off value, used to distinguish between oil-shale and marlstone, of greater than 12.5 L per metric tonne. One of the largest oil-shale mining areas of China, and a major source of petroleum in southern China, is situated in Maoming basin, Guangdong Province, about 300 km southwest of Hong Kong. This basin is a Tertiary graben about 50 km long by about 10 km wide and is fault-bounded on its northeastern edge with
the oil-shale mine located at the southwestern edge just outside of the city of Maoming. The Eocene oil-shale stretches from Yangjiao in eastern Dianbai county, through the towns of Xinxu, Jintang, Dishan, Shigu, and as far as Shatian in Huazhou county. Below the oil-shale there is a 0.5 m Paleocene coal bed and thin red sandstones that can be traced throughout the basin. In the basin the outcrop and near-to-surface oil-shale extends about 50 km in a northwest-southeast line and the beds dip about 5 to 10° to the northeast. The present day mine face is about 5 km long and is about 75 m in height. In the immediate area around the mine there are numerous oil seeps especially in local ponds and at foundations of buildings. Mine drill-holes, to test the extent of the oil-shale, have een drilled to a depth of 1000 m and still swabbed oil from oil-shale. The mine was started in 1958 on an automated schedule using power-shovels, hoppers, and electric trains. Present-day excavation continues at a rate of approximately 10 m per year cutback of the mine face. The clay units between the coal beds as well as between the shales are hand-mined and used for medicinal potions as well as for special applications in local brick manufacturing. The oil output from the oil-shale is about 100,000 metric tonnes per year (700,000 barrels of oil) and in 1984 it was estimated that about one-tenth of the recoverable reserves had been mined; that is about 20 MMBO.
All samples taken from the lower oil-shale bed above the Paleocene coal seam, the middle bed, and from the uppermost bed are predominantly type I algal-lacustrine kerogen, and although organic carbon and Rock Eval values show the samples to be extremely rich in kerogen, the Rock Eval Tmax and production index or transformation ratio data indicates that the kerogen content is relatively immature, which is typical of oil-shales. The potential for liquid hydrocarbon recovery for the lowermost bed is approximately twice that of the middle bed as indicated by Rock Eval P2 data, and the large concentration of free hydrocarbons (P1) reflects the high organic content. The lowermost bed is more oil-generative and has greater maturity than the middle bed, based on higher Tmax values, but is sti l above the crude-oil generative window. The high hydrogen (H1) and very low oxygen (O1) indices fall into the range of type I or II kerogen and gas chromatograms confirm the aliphatic nature of the shale, which indicates that this oil-shale can generate a large quantity of liquids because of its high organic richness, even though the kerogen is relatively immature, and if thermally mature it would produce a low sulfur, high wax, high pour point, crude oil typical of lacustrine crude.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990