Estimate of a spatially variable reservoir compressibility
by assimilation of ground surface displacement data
C. Zoccarato, M. Ferronato, G. Gambolati, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Italy
D. Bał
Dept. of Civil & Structural Engineering, The University of Sheffield, UK
F. Bottazzi, S. Mantica
Development, Operations & Technology, eni S. p. A., San Donato Milanese, Italy
ABSTRACT
Fluid extraction from producing hydrocarbon reservoirs can cause anthropogenic land subsidence. In
this work, a 3-D finite-element (FE) geomechanical model is used to predict the land surface displacements above
a gas field where displacement observations are available. An ensemble-based data assimilation (DA) algorithm
is implemented that incorporates these observations into the response of the FE geomechanical model, thus
reducing the uncertainty on the geomechanical parameters of the sedimentary basin embedding the reservoir. The
calibration focuses on the uniaxial vertical compressibility cM,
which is often the geomechanical parameter to
which the model response is most sensitive. The partition of the reservoir into blocks delimited by faults moti-
vates the assumption of a heterogeneous spatial distribution of cM
within the reservoir. A preliminary synthetic
test case is here used to evaluate the effectiveness of the DA algorithm in reducing the parameter uncertainty
associated with a heterogeneous cM
distribution. A significant improvement in matching the observed data is
obtained with respect to the case in which a homogeneous cM
is hypothesized. These preliminary results are
quite encouraging and call for the application of the procedure to real gas fields.
