Three-dimensional reconstruction of diagenetic geobodies for geological carbon dioxide storage

Abstract

Geological storage of carbon dioxide (CO2) may help in mitigating greenhouse gas emissions, the main cause of global warming. Deep saline aquifers form ideal storage sites for CO2, but these are often complex due to differences in porosity and permeability, referring to heterogeneity, especially in carbonate reservoirs. Diagenetic heterogeneities, such as the presence of less reactive dolomite bodies in a more reactive limestone host rock, have huge impacts on CO2 storage. As upscaling still poses a challenge, we bridge the gap between micrometre–centimetre lab experimental scale and reservoir scale by documenting heterogeneity at the inter-well, subseismic scale. We developed a method using satellite images, field pictures, GPS data and distance measurements to reconstruct diagenetic dolomite geobodies in three dimensions from outcrops (in Picos de Europa, northern Spain). The dolomite bodies studied have higher porosity than the limestone host rock, which is also observed in CO2 reservoir targets. The geobodies are elongated in the direction of the main faults and their length/width ratio is about 2.5 in the Picos de Europa Formation. Geobodies hosted in different formations seem to vary in dimension. We suggest that large dolomite bodies are favoured in zones with large fluid input and flow rate slow enough to allow for extensive chemical reaction based on the disconnected dolomite body distribution and inferred fluid migration from the source. Understanding how these diagenetic bodies form helps with prediction of heterogeneity crucial in CO2 storage reservoir modelling.