Experimental modeling of CO₂‐fluid‐rock interaction: The evolution of the composition and properties of host rocks in the Baltic Region

Abstract

The objective of this study was to determine the influence of the possible CO 2 geological storage in the Baltic Region on the composition and properties of host rocks to support more reliable petrophysical and geophysical models of CO 2 plume. The geochemical, mineralogical, and petrophysical evolution of reservoir sandstones of Cambrian Series 3 Deimena Formation and transitional clayey carbonate caprocks of Lower Ordovician Zebre Formation from two offshore structures in Latvia and Lithuania and two onshore structures in Latvia, induced by laboratory-simulated CO 2 geological storage, was studied for the first time in the Baltic Region. The geochemical, mineralogical, and petrophysical parameters were measured in 15 rock samples, before and after the alteration experiment. The diagenetic alterations of reservoir rocks were represented by carbonate cementation in the top of the onshore South Kandava structure, and quartz cementation and compaction, reducing the reservoir quality, in the deepest offshore E7 structure in Lithuania. The shallowest E6 structure offshore Latvia was least affected by diagenetic processes and had the best reservoir quality that was mainly preserved during the experiment. Carbonate cement was represented by calcite and ankerite in the transitional reservoir sandstones of very low initial permeability in the upper part of the South Kandava structure. Its dissolution caused a significant increase in the effective porosity and permeability of sandstones, a decrease in the weight of samples, bulk and matrix density, and P and S wave velocities, demonstrating short-term dissolution processes. Only slight geochemical changes occurred during the experiment in offshore reservoir sandstones. Minor dissolution of carbonate and clay cements, feldspar and some accessory minerals, and possible minor precipitation of pore-filling secondary minerals associated with slight variations in rock properties, demonstrating both short-term and long-term processes, were suggested. As a novelty, this research shows the relationship between diagenetic alterations of the Cambrian Series 3 Deimena Formation reservoir sandstones and their changes caused by the CO 2 injection-like experiment.

A modelling study to evaluate the effect of impure CO2 on reservoir performance in a sandstone saline aquifer

“…From a geochemical perspective, CO 2 and impurities can influence the storage system in basically three ways: formation of carbonic acid or bicarbonates by dissolution of CO 2 in formation water (Equations (9) and (10) ); production of weak or strong acids due to the effects of impurities; and dissolution and/or precipitation of calcite as cementing material [ 13 , 58 , 59 ]. CO 2 + H 2 O ↔ H 2 CO 3 CO 2 + H 2 O ↔ H + + HCO 3 - …”

CO2-brine-rock interactions: The effect of impurities on grain size distribution and reservoir permeability

“…Previous studies (Aminu et al, 2017;Gilfillan et al, 2009;Liu et al, 2012Liu et al, , 2011Shogenov et al, 2015) report that the acidification of formation waters, due to the dissolution of CO2, leads to brine-rock interaction and triggers dissolution or precipitation of rock minerals and cementation of the rocks which hold the rock grains together. Consequently, it can alter the reservoir rock grain-size characteristics and result in changing the permeability.…”

“…Depending on the impurities and pH of the formation water, quartz can react with carbonic acid, hydrogen ion or bicarbonates, which had already formed from the dissolution of CO2 in water, Equation 4 to Equation 8 (Rathnaweera et al, 2016;Shogenov et al, 2015).…”

Potential of the Middle Cambrian Aquifer for Carbon Dioxide Storage in the Baltic States

“…The sandstone consists of approximately 82% quartz, about 9% feldspar, 6% mica, and 3% various heavy metals, such as zircon, tourmaline, and rutile [44]. The reaction of Ca-and Mg-bearing aluminosilicates in the composition of the sandstone with the injected CO 2 has a potential to form calcite, dolomite, and MgCO 3 [77,78]. However, the interaction among aluminosilicates, carbonic acid, and newly formed carbonate minerals can reduce the overall salinity of the water and thus increase CO 2 solubility [77,79].…”

“…The reaction of Ca-and Mg-bearing aluminosilicates in the composition of the sandstone with the injected CO2 has a potential to form calcite, dolomite, and MgCO3 [77,78]. However, the interaction among aluminosilicates, carbonic acid, and newly formed carbonate minerals can reduce the overall salinity of the water and thus increase CO2 solubility [77,79]. Wet density of the sandstone within the Dobele structure increases with depth, the average being approximately 2300 kg/m 3 .…”