Can Diagenetic Processes Influence the Short Term Hydraulic Behaviour Evolution of a Fault?
Résumé
The scope of this work is to quantify the impact of calcite cementation on the hydraulic behaviour of an active fault in carbonate rocks. In the studied context, the permeability mainly depends on the fracture network. Therefore the hydraulic regime depends on the way fractures become sealed by vein deposits. The work is based on the study of cores and groundwater recovered from an active normal fault in the Gulf of Corinth, the Aigion fault, in the framework of the Corinth Rift Laboratory Project. The data set includes cores, borehole images, pumping tests and in situ fluid samples. The cores show numerous recent fractures partially, or completely, sealed by recent carbonate crystals. We modelled the fluid-rock interaction to quantify the growth rate of calcite in the veins of this specific geological context. Modelling was carried out with Diaphore, a software designed to study the diagenetic evolution of porosity in hydrocarbon reservoirs. The required time to seal a 1 mm thick fracture in the case of the Aigion fault at 760 m depth was calculated to be within the range of a few hundred years, considering the composition of water sampled at this depth. As a conclusion, diagenetic processes are likely to have a key influence on the fault hydraulic behaviour over the time scale of seismic cycles. However, the possibility of calcite growth strongly depends on the composition of the fluid. Tests were made with seawater and slightly higher values of pCO2, a fluid that could also be present around the Aigion fault. In this case dissolution, and therefore opening of the fractures, happens.
Domaines
Physique [physics]
Origine : Publication financée par une institution
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