Title Hydrothermal fluid flow in Silurian carbonates in Lithuania and cold-water injection impact on long-term reservoir performance /
Authors Kaminskaitė-Baranauskienė, Ieva ; Aydin, Hakki ; Liu, Zhida
DOI 10.1016/j.geoen.2025.213704
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Is Part of Geoenergy science and engineering.. Amsterdam : Elsevier B.V.. 2025, vol. 247, art. no. 213704, p. [1-18].. ISSN 2949-8929. eISSN 2949-8910
Keywords [eng] CO2-water-rock interaction ; hydrothermal alteration ; PHREEQC ; pore evolution ; TOUGHREACT
Abstract [eng] The narrow barrier reef zone has been identified within the Silurian succession of the Baltic basin that stretches for hundreds of kilometres in a north-south orientation across central Lithuania. The reefs have been widely explored by drilling due to accumulations of oil. Even though the oil production proved economically unfeasible, infrastructure of over 70 wells is left behind that could be reused for geothermal purposes. In this study, hydrothermal fluid flow products were examined across the Silurian column to identify natural deformation mechanisms affecting petrophysical properties of the rocks. The cores showing hydrothermal alteration have been analysed by macro- and microscopic petrography, cathodoluminescence and SEM microscopy, XRD, C and O stable isotope and liquid-vapour inclusion analyses. Then, thermo-chemical numerical models were run of cold-water injection and low enthalpy geothermal energy extraction from the reef reservoirs within the Silurian section. CO2-water-rock interaction simulations were performed for three different cases to capture different rock and formation water types observed in the wells, including 1) calcite-rich reef interval within the largest Kudirka structure; 2) dolomitized Kudirka reef interval; and 3) interval within the Pavasaris structure in the central part of the barrier reef zone. The results show that during a cold-water injection, a decline in temperature coincided with a decrease in pH. This combined effect resulted in the dissolution of dolomite and calcite minerals, evident from the observed decrease in their volume fraction and the corresponding rise in the concentration of Ca2+ and Mg2+ ions. This had a positive effect on porosity. Petrographic analysis of Silurian carbonate rocks and manifestations of hydrothermal processes within them also indicate that porosity of the rocks was maintained through several stages of dissolution. Hydrothermal alteration products as well as oil stains were found within the vugs, solution-enlarged fractures, stylolitic surfaces as well as tension-gashes associated to stylolites, suggesting that they acted as conduits to fluid flow. The largest porosity losses of the Silurian reefs are associated with the two largest thermal events that have taken place during the Late Silurian-Devonian continent-continent collision as well as the Carboniferous-Permian rifting and magmatism, that provided external heat sources (temperatures reaching 70–140 °C) creating suitable conditions for cementation. Therefore, low temperatures of the reservoirs and cold-water injection may act in advantage to sustainable water production.
Published Amsterdam : Elsevier B.V
Type Journal article
Language English
Publication date 2025
CC license CC license description