Under-relaxed iterations for coupled finite element solution to gas and water
dynamics in depleted reservoirs
D. Bau', G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
Residual land subsidence over depleted gas fields may still
occur for quite a long time after field abandonment if the reservoir is
confined laterally by an active waterdrive (or aquifer) of large extent.
Prediction of the post-production occurrence requires the numerical solution to
the system dynamics which is described by a coupled non-linear water-gas model.
This is solved by a mixed finite element (FE)-analytical approach enhanced with
an effective under-relaxed iterative technique. The results from a major gas
field in the Upper Adriatic basin show that convergence depends primarily on the
geological setting and hydromechanical properties of the waterdrive and
reservoir and may be greatly accelerated under difficult conditions by the use
of a proper under-relaxation factor with a substantial reduction of the
computational cost.
