Search Results (2)

Mineralization of groundwater for drinking purposes is a complex parameter of groundwater chemical composition. In the Shaim oil- and gas-bearing area, as in the whole West Siberian megabasin, the main target horizon for solving the issues of domestic and technical water supply is the Oligocene aquifer. It has significant groundwater reserves to cover the needs of the population and production requirements. However, it also faces a huge anthropogenic load in the form of water withdrawal and possible contamination from the surface with oil products. In Western Siberia, various deviations in the chemical composition of groundwater of the Oligocene horizon are recorded in connection with significant water withdrawal; for example, a sharp increase in chromaticity or total iron concentration, with changes in mineralization acting as a factor necessarily accompanying these deviations. Based on the data obtained in the course of monitoring for the period from 2013 to 2023, the main factors and trends of changes in the components of mineralization of the Oligocene horizon were determined. The lithological and mineralogical peculiarities of the water-bearing rocks of the horizon, the paleogeographic conditions of its formation and their relation to trends in mineralization change were studied. Water withdrawal data were processed for two cluster water withdrawal sites (50 and 5 wells, respectively). Analysis of the results showed that the increase in water withdrawal leads to an increase in infiltration from the overlying Neogene-Quaternary aquifer, which leads to the dilution of groundwater of the Oligocene horizon and a decrease in its mineralization. Here, we show that, during further monitoring, it is necessary to pay attention to the appearance of sites where significant amounts of chloride ions are fixed in the anion composition, which can potentially lead to a sharp deterioration in the quality of drinking groundwater. Full article

This study aimed to identify the nature of variable groundwater salinity from the standpoint of whether natural or man-caused factors have a dominant impact on the modern salinity range of the Lower Jurassic sediments in the Talinskoye oilfield of West Siberia in Russia. As of now, the salinity values of reservoir waters vary from 3.7 to 15.3 g/dm³, with an average of 8.9 g/dm³. Petroleum hydrocarbons are extracted at the oilfield from the Lower Jurassic sediments. The volume of overlying sediments’ waters injected into the pay zones to maintain the formation pressure was more than 8960.3 thousand m³ between 2014 and 2021. In this regard, it is necessary to establish whether anthropogenic factors are critical for the variability in groundwater salinity of the Lower Jurassic sediments, or the complex geologic and hydrogeologic conditions are determinant factors affecting the salinity variability. To achieve this objective, we evaluated the genetic coefficients of various types of waters (inclusive of injected waters) which could contribute to the variability in groundwaters with varying quantities and ratios. The resultant genetic coefficients were compared with those of reservoir waters of the Lower Jurassic hydrogeological complex. This allowed for the conclusion that the major factors currently affecting the variable salinity of the reservoir waters of the Lower Jurassic complex are natural ones. We also assessed the relationship between the groundwater salinity values of the complex under study and basic parameters of the geologic setting, such as porosity, formation pressure, modern temperature and paleotemperature of the basement, and basement depth of burial. A tight association was found between the salinity values and porosity of the sediments (R = 0.87), and a very tight connection between the salinity and formation pressure (R = 0.91), which, we believe, also evidences that natural factors have a dominant effect on the variability in groundwater salinity. The variability in the modern salinity values of the reservoir waters of the complex in question ensues from the continental conditions of the groundwater genesis, expelled-water exchange processes (ingress of the pore waters expelled from argillaceous deposits as geostatic pressure rises), and the intrusion of abyssal fluids along the basement fractures. Full article