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

Abstract

AbstractThe objective of this study was to determine the influence of the possible CO2 geological storage in the Baltic Region on the composition and properties of host rocks to support more reliable petrophysical and geophysical models of CO2 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 CO2 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 CO2 injection‐like experiment.