Numerical modelling of case sliding in radioactive marker boreholes of
the Northern Adriatic basin, Italy
N. Castelletto, M. Ferronato, G. Gambolati, C. Janna,
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
The possible influence of the well casing in reservoir defomation
measurements by the radioactive-marker tecnique (RMT) is investigated. The
issue is quite important as RMT data may be used for a most-representative
estimate of the in-situ vertical rock compressibility cM
(i.e., a basic parameter to predict the land
settlement due to gas-/oilfield development or the land uplift due to
underground fluid injection). A geomechanical finite-element (FE) model is
implemented to evaluate the disturbance caused by the stiffness of the steel
casing and the surrounding cement on the amount of deformation around the
borehole as detected by RMT. The FE model is integrated by a class of
elasto-plastic interface FEs (IFEs) specifically designed to account
for the potential sliding of the different materials (i.e., along the contact
surfaces between the steel casing and the cement, and the cement and the
exploited formation). The numerical simulations make use of real casing data
and geomechanical information from the Northern Adriatic basin,
Italy.
The results show that sliding is not likely to occur along the contact surfaces
and RMT appears to be a reliable tool for assessing the actual geomechanical
properties of the depleted formation at a depth larger than
1000 m> where the in-situ
deformation is negligibly affected by the casing stiffness.
In shallow softer units
the compaction as measured by RMT is progressively influenced by casing, with a
corresponding likely underestimate of cM.
