The Organic Geochemical Characteristics And Reservoir Forming Pattern Of Palaeogene And Neogene Oil Sands In Western Qaidam Basin

Because of higher rate of oil imports in China, the exploration and development of oilsands, which is an unconventional energy resources, is concerning. China has rich oil sandsresources. Qaidam basin is one of the earlier explored basins in our country. According toinformation statistics, the oil sands geological resource extent up to31595×104t of oil within500m in Western Qaidam Basin. In Western Qaidam Basin, there are a lot of exposed LowerGanchaigou formation oil sands in Ganchaigou, and there are also a lot of exposed LowerYoushashan formation oil sands in Youshashan. This thesis depends on field observation andindoor analysis which is based on the regional tectonic evolution characteristics andsedimentary characteristics, by using the test of physical property, and organic geochemicalanalysis. This thesis explores the reservoir physical property, the origin of parent materialsand the environment of forming of oil sands. This thesis provides clues to the ore genesis ofoil sands, and provides the basis for the exploration and development of oil sands resources inthis area.Lower Ganchaigou formation in Ganchaigou deposited sublacustrine fan facies. Thelithology of upper part in this formation is a suit of coarse alternating with fine clastic rock,and the lower part is a suit of coarse clastic rocks. It’s a low porosity and very lowpermeability sandstone reservoir. It’s a poor reservoir property. Lower Youshashan formationin Youshashan deposited braided river delta and shallow lake facies. The lithology is mainlymedium sandstone, calcareous sandstone and argillaceous siltstone with interlayers ofconglomerate and marl. It’s a low porosity and permeability sandstone reservoir. It’s a poorreservoir property. But it’s better than Lower Ganchaigou formation.The oil sands organic geochemical analysis shows that the saturated hydrocarbon content inLower Ganchaigou formation reached up to14.74%, aromatics content reached up to3.89%.And the saturated hydrocarbon content in Lower Youshashan formation reached up to35.85%,aromatics content reached up to2.52%. The saturated hydrocarbon content in LowerYoushashan formation is higher than it in Lower Ganchaigou formation. And the contentabout aromatics is opposite.The characteristic of biomarkers shows that the hydrocarbons ofoil sand formed in a strong reducing saline lacustrine depositional environment. The type oforganic matter is mainly Ⅰ kerogen. And the organic matter is derived from lower aquaticplants. The maturity level is low mature and mature crude oil migration into the reservoir. Thehydrocarbon in oil sands once endured heavy biodegradation and some other secondary alterations. Comparing with Lower Ganchaigou formation the alterations in LowerYoushashan formation is stronger.The source rocks of Lower Ganchaigou formation and Lower Youshashan formation oilsand come from the dark shale. Oil sands in Lower Ganchaigou and Lower Youshashanformation is that hydrocarbon migration into the reservoir, when the hydrocarbon is lowmature. In the late Himalayan age, strong faulting resulted in adjusting and altering of oilreservoirs, and also resulted in the formation of secondary oil reservoirs in shallow layers. Itformed a wide range of exposed oil sands. So the exploitation method of oil sands in this areais open pit mining, and the oil can be extracted by ATP cracking process.