Local rock expansion in non-homogeneous productive gas/oil fields
D. Bau', M. Ferronato, G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
The reliability of in situ compaction measurements
performed by radioactive markers for the evaluation of the mechanical
properties of productive gas/oil fields is investigated with a finite element
model applied to a typical Plio-Pleistocene sequence of the Northern Adriatic
sedimentary basin, Italy.
Preliminary results show that with particular layering configurations within
the recorded depth interval some low permeable levels may initially expand
after the inception of fluid withdrawal thus providing a measurement where
the overall compaction may be partially or also totally offset by the local
expansion. If such a measurement is used to estimate the in situ rock
vertical compressibility large errors may arise which are not due to the
instrument inaccuracy as at a first glance it might appear.
This would suggest that great care must be paid to the detailed lithology of
each monitored depth relative to the depleted levels before the marker data may
be used to evaluate the actual stiffness of a reservoir.
