Page 89 - Reservoir Geomechanics

a.
Drained hydrostatic load cycling
cleaned and dried Wilmington sand
0.04
30

CREEP STRAIN 0.035
25
0.03
Confining pressure (MPa) 15 0.02 0.025 Axial strain (in/in)
INSTANTANEOUS
20
STRAIN

10 0.015
0.01
CONFINING PRESSURE
5
0.005

0
0 10 20 30 40
Time (hour)

b.
0.0025
GOM – Lentic
0.002
Wilmington –
Upper Terminal
Volumetric strain 0.0015 Ottawa Sand – 10%

Montmorillonite
0.001
Ottawa Sand –
5% Montmorillonite
0.0005
Ottawa Sand

0
0 5000 1 × 10 4 1.5 × 10 4 2 × 10 4 2.5 × 10 4 3 × 10 4
Time (seconds)

Figure 3.8. (a) Incremental instantaneous and creep strains corresponding to 5 MPa incremental
increases in pressure. The data plotted at each pressure reflect the increases in strain that occurred
during each increase in pressure. Note that above 15 MPa the incremental creep strain is the same
magnitude as the incremental instantaneous strain from Hagin and Zoback (2004b). (b) Creep
strain is dependent upon the presence of clay minerals and mica. In the synthetic samples, the
amount of creep is seen to increase with clay content. The clay content of the Wilmington sand
samples is approximately 15% (modified from Chang, Moos et al. 1997). Reprinted with
permission of Elsevier.