Hydrogeochemistry of Pre-Jurassic Aquifers in West Siberia

Abstract

––For the first time in the last 35 years, hydrogeochemical data on pre-Jurassic complexes in West Siberia have been generalized. Groundwater and brines of Cl–Na and Cl–HCO3–Na type with total salinity (TDS) varying from 4 to 330 g/L are found to be widespread in the area under study, with the former type dominating. A detailed analysis of the hydrogeochemical data allowed us to assume the presence of three genetic groups of groundwater and brines in the hydrogeologic section: (1) sedimentogenic, (2) lithogenic (revived) and ancient infiltrogenic, and (3) condensatogenic. An integrated analysis of coefficients rNa/rCl, Ca/Cl, (Br/Cl)·10–3, and (Sr/Cl)·10–3 and integrated index S of brine metamorphization in the Siberian sedimentary basins has corroborated the fact that groundwater and brines in West Siberia are at the initial stage of metamorphization of their chemical composition. Groundwater and brines in the studied Siberian sedimentary basins show an increase in the degree of metamorphization (catagenetic changes) of their chemical composition in transition from the areas of igneous and metamorphic deposits at the base of the Meso–Cenozoic sedimentary cover of the young West Siberian sedimentary basin to the structures of the ancient Siberian Platform, where ultrastrong Ca–Na and Ca chloride brines are widespread.

Causes of Variability in Groundwater Salinity of the Lower Jurassic Sediments in the Talinskoye Oilfield of West Siberia

“…The Jurassic sediment groundwaters as a hydrologic object in West Siberia were explored by many researchers [3,18,[20][21][22][23] but their genetic sources and the role of various geologic factors in the genesis of the chemical composition remain unclear so far. The data generalized herein allows us to refine these issues that are of importance in terms of theoretic and application aspects.…”

“…The constant value of the rNa/rCl coefficient in the ocean is 0.87, and in the case that coefficient is in excess of 0.87 (as in the event of the UY10 and UY11 pore waters), the water solutions are considered as either low-metamorphic waters of infiltration genesis or sediment waters from desalted basins [33,36]. For the other coefficients listed, there are no classifications commonly acknowledged in petroleum hydrogeology; however, based on the experience of deep horizon testing, it is generally recognized that the higher the rCa/rNa, rCl/rHCO 3 , and rCa+rMg/rHCO 3 coefficients, the more metamorphic or anthro-pogenically altered the water composition [3,18,20,22,33,[36][37][38]. The most significant in that case are the rNa/rCl and rCa/rNa coefficients that reflect the water transformation degree.…”