Radioactive marker measurements in heterogeneous reservoirs
M. Ferronato, G. Gambolati, P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
D. Bau'
Dept. Geological and Mining Engineering and Sciences, Michigan Technological
University, Houghton, Michigan, USA
ABSTRACT
A numerical study is performed to simulate the vertical deformation of a
depth interval representing a marker spacing ~10.5 m! located in a deep
heterogeneous sedimentary reservoir. Realistic lithostratigraphic sequences
typical of the Northern Adriatic basin are used. A number of scenarios are
addressed consistent with the available data. In particular two basic
geologic scenarios at the marker scale are simulated, one where sands
prevail within the marker spacing (SD), and another where thin sandy and
clayey layers alternate (CL). The sensitivity of the marker response is
investigated in relation to clay and sand permeability and compressibility
contrast, Biot's coefficient, and respective position of monitoring and fluid
pumping wells. The modeling results show that rock may indeed expand above
and below depleted layers. Depending on the marker position the expansion
may partially offset the compaction, especially in the CL scenario with a
very low permeable clay. To obtain a representative field compaction the
markers should span a depth interval made mostly by sand and entirely
depleted, and should be installed in a test hole far from producing wells.
Compressibility contrast and the Biot coefficient play a secondary role.
Very critical measurements are provided by two markers which incorporate
a thin (≈1 m) depleted level overlain and underlain by almost
impermeable clay layers.
