Page 48 - Reservoir Geomechanics

32 Reservoir geomechanics

Pressure (psi)
2000 4000 6000 8000 10000
0
LATE PLIOCENE-RECENT hydrostatic gradient 0.44 psi/ft MUD WEIGHT 20 in csg

REPEAT FORMATION TEST (RFT)
DRILLSTEM TEST
PLIOCENE LEAK-OFF TEST 16 in csg
LOSS OF CIRCULATION
WELL FLOW (GAIN)
5000 Seal O m
MIOCENE

OLIG
Seal D e 13 3/8 in csg
EOCENE/U.CRET Seal C e COMP IVC

0.73 psi/ft
10000 APTIAN ALBIAN Seal B COMP IIIC LOSS
NEOCOML-BARREM-APTIAN e COMP IIC 0.8 psi/ft GAIN 9 5/8 in csg

GAIN
BATH-CALLONIAN COMP IJ
15000 OXFORD Seal “AJ” 0.84 psi/ft /LOSS

Figure 2.4. Pore pressure, mud weight and related parameters in the Mango-1 well in northern
Egypt (after Nashaat 1998). The pore pressure measurements in compartments IIC and IIIC
confirm that pore pressure increases with a local hydrostatic gradient within a compartment even
though the absolute value of pore pressure is well above normal pressure values. AAPG C 1998
reprinted by permission of the AAPG whose permission is required for futher use.

Pore pressures in the reservoirs of the South Eugene Island (SEI) Block 330 field
in the Gulf of Mexico provide a good illustration of pressure compartments. The sand
reservoirs of the South Eugene Island field are quite young (Plio-Pleistocene in age,
<4 million years) and are found mostly in a salt-withdrawal mini-basin bounded by
the southwest-dipping normal faults shown in Figure 2.5 (Alexander and Flemings
1995). Localized subsidence and sedimentation (and slip along the normal fault shown)
occurred when salt at depth was extruded to the southeast (Hart, Flemings et al. 1995).