Rare Earth Elements as Geochemical Criteria of the Oil-bearing Capacity of the Formations

Abstract

The REE studies in the formations of clastic and carbonate type with the presence of hydrocarbon oil and gas showed that components of bitumen and oil accordingly did not only have a significant impact on REE fractionation between the formations of oil and gas deposits, but also became the main differentiation cause (factor) in the behavior of the individual lanthanides being a part of REE of the formations’ mineral and organic complexes. As exemplified by the study of the South Pyzhinskaya 1 parametric well’s section (Western Siberia), the 12 th Kokdumalak oil and gas deposits’ well (Uzbekistan) and the Krapivinskoye oil and gas field (Western Siberia), there were shown the variations of the full REE composition spectra. There were specified the differences in the behavior of individual lanthanides in REE composition of formations and their factions - the acid extract (1.8% HCl), taken as a movable mineral complex (MMC), and the organic part of the alcohol-benzene mixture (OP ABM). Reasons for fractionation and differentiation in the lanthanide behavior are considered from the standpoint of the oil and gas hydrocarbons of petroleum fluids impact on the redox conditions of the environment, impact of their stabilizing properties on the lanthanide valence states and REE isomorphism. The results of the formation studies taken from the South Pyzhinskaya 1 well were compared with the changes in the isotopic composition of carbon and oxygen in the well section. There was provided a comparison of the ratios Ce4+/Ce3+ in various samples of insoluble residue 1.8% HCl and OP ABM, as well as the ratio of Eu 2+ /Eu 3+ in oil from the zone of OM generation. As a result, there were revealed significant differences in the REE behavior within oil and gas deposits, enabling to interpret REE as geochemical criteria of the oil-bearing formations.