Shihong Chi's thesis
by
Shihong Chi, MSE
University of Texas at Austin, 1999
Supervisor: K. E. Gray
Fluid production from reservoirs over time affects the petrophysical
properties of producing formations, due to changes in formation
pressure. The formation pressure decline may cause subsidence and
compaction of the reservoir.
This work investigated changes in resistivity, porosity, permeability
and other rock mechanical properties under effective hydrostatic
pressures and uniaxial pressures. The data used in this study were
obtained from experiments carried on samples extracted from geothermal,
geopressured reservoirs in Brazoria County, Texas. All experiments were
conducted under conditions which simulated in situ reservoir conditions
except the temperature. From microscopic modeling and petrographical
studies, the observed phenomena during the experiments were modeled and
interpreted.
It was shown that microfractures or flow paths of similar structures
existed in the rocks and dominated permeability variations. The opening
and closing of these structures were very important to understanding
changes in petrophysical parameters under varying effective stress. The
mechanical parameters and stress-strain curves were influenced by
fracture-type structures.
The matrix compressibility was mainly affected by fine matrix materials
and weak grain contacts in rocks in lower stress levels. In higher
stress levels, the matrix compressibility was almost linear and it was
repeated in the unloading cycle.
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