Natural bitumen refers to organically formed minerals with a primary hydrocarbon basis, which are confined to the subsurface in viscous, visco-plastic and solid states. Such substances form a wide range of compounds from high-carbon differences to individual classes of hydrocarbons containing asphalt-resinous components and metals: malt, asphalts, asphaltites and other analogs. The Osinsky productive horizon of the Lower Cambrian (productive formation B1) in the Irkutsk region is one of the main ones for increasing the hydrocarbon resource base in Rosneft's assets. At present, nine oil deposits have been put in the State Register of Reserves. Production of bitumen and high-viscosity oil in the future will allow optimizing the development system with the most complete recovery of hydrocarbons at maximum economic profitability. In most cases oil of the Osinsky horizon can be classified as light, but at the same time there is a widespread development of very viscous to oxidized bitumen in the sediments. The presence of bitumen and viscous oils is due to the fact that the carbonate sediments under consideration are ancient (low Lower Cambrian) and are characterized by a complex structure. The transformation of sediments considering the long history of formation caused a highness of reservoir properties anisotropy, and also led to the reformation of hydrocarbon accumulations. The proportion of bitumen in the rock is often significant and often affects the assessment of reservoir properties. The article presents the methodology of bitumen estimation in the carbonate reservoirs of the Osinsky productive horizon based on well logging data. The quantitative content of bitumen in the void space is determined by the dependence of pyrolysis data on the transverse relaxation rate according to nuclear magnetic logging data. Consideration of bituminosity in the void space allows estimating its volume by section and by area. For this reason, quantitative assessment of bitumen in open oil deposits was performed.
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