reservoir geomecanics

417 Effects of reservoir depletion
Figure 12.19. Cumulative subsidence and horizontal displacement calculated from superposition of
many disk-shaped reservoirs in the Lapeyrouse field using the solution (Geertsma 1973) and DARS
(with a viscoplastic rheology) for calculating the total reservoir compaction (after Chan and Zoback
2006). The predicted displacement U X , U Y and U Z are measured in cm. The predicted subsidence
(d) is comparable to the measured elevation change from the leveling survey (red line) in the middle
of the field but underpredicts the apparent subsidence at north end of the field near benchmark M.
However, the reservoirs are relatively deep (∼4.5 km) and thin (individual sands are
∼10 m thick), but as many as five reservoirs (ranging in diameter from ∼1 to2.5 km)
are stacked upon each other in some places. Hence, D/R is quite large (ranging from
about 3 to 9) and the subsidence and surface displacements are expected to be small
despite the appreciable depletion. As shown in Figure 12.19, about 12 cm of subsidence
is expected over the center of the reservoir and horizontal surface displacements are as
much as 5 cm near the edges of the field.
Figure 12.19d compares the predicted cumulative subsidence from all reservoirs
(modeled as individual circular reservoirs of constant thickness) with that measured