Casing influence while measuring in situ reservoir compaction

In situ measurements of soil and rock compressibility through radioactive marker techniques (RMT) are here discussed. Compressibility is the main parameter governing compaction of sediments undergoing stress state variations, particularly when fluid withdrawal is considered. Numerical analyses of land subsidence phenomena from underground fluid extraction are strictly linked to the material parameters adopted, and consequently the results are strongly affected by the compressibility values used in the mathematical model. It is here proved that the presence of a fully cased hole generates perturbations of the deformations in a large area around the borehole, even accepting an elastic behaviour of the surrounding rocks. Additionally, elasto-plasticity is taken into account to further confirm the statement.