The target object of the research is the industrial oil and gas interval of the second Verkhnechonsky horizon of the Lower Nepa sub-suite of the Nepa suite. The results of the work are presented in order to demonstrate the diversity of the material composition and forms of manifestation of evaporites in the section of the Vendian terrigenous sediments of the Nepa arch of Eastern Siberia. First of all, evaporites are understood to mean chemogenic formations, groups of sulphates and chlorides, commonly manifested at different levels of the productive horizon. Of course, processes of secondary rock transformation play a significant role in the formation of these deposits. However, it seems that evaporite strata could also have been formed in Vendian time. This is indicated by the results of a complex of laboratory studies of cores of a number of wells in the study area. First, anhydrite-dolomitic seams, relatively matured in thickness, were recorded, lying above the basal layer. From the average 25-m thickness of the target horizon at the site, the thickness of the layer of high content of anhydrite and dolomite can reach 5 m. Secondly, the observed vertical sequence of evaporites is compared with mineral associations of lagoon origin in arid climate conditions. Thirdly, the group of chlorides, halite and sylvite, is found both in association with sulphates and locally along the section. Relatively high content is observed in the near-gravel, and in the covering of fine-medium-grained sandstones. The variety of salts represented suggests various formation models.
References
1. Konoval'tseva E.S., Usloviya formirovaniya i zakonomernosti rasprostraneniya porod-kollektorov nizhnevendskikh neftegazonosnykh otlozheniy tsentral'noy chasti nepsko-botuobinskoy anteklizy (Formation conditions and distribution patterns of reservoir rocks of the Lower Vendian oil and gas deposits in the central part of the Nepa-Botuobinsky anteclise): candidate of geological and mineralogical science, Moscow, 2014, 158 р.
2. Kuznetsov V.G., Litologiya. Osadochnye gornye porody i ikh izuchenie (Lithology. Sedimentary rocks and their study), Moscow: Nedra Publ., 2007, 511 p.
