Page 230 - Reservoir Geomechanics

211 Determination of S 3 from mini-fracs

Pressure FBP

FPP
LOP
ISIP
LT = Limit test
LT FCP
(FIT) LOP = Leak-off point
FIT = Formation integrity test
FBP = Formation breakdown pressure
FPP = Fracture propagation pressure
ISIP = Instantaneous shut-in pressure
FCP = Fracture closure pressure

FLOWRATE

Volume (or time if constant flowrate)

Figure 7.2. A schematic mini-frac or extended leak-off test showing pressure as a function of
volume, or equivalently time (if the flow rate is constant). Modified after Gaarenstroom, Tromp
et al.(1993). The significance of the various points indicated on the pressure record is discussed in
the text.

the pressure in the wellbore due to the column of wellbore fluid. In fact, it is always
preferable to measure pressure downhole during such tests.
If the LOP is not reached, a limit test, or formation integrity test (LT, or FIT), is said to
have been conducted. Such tests merely indicate that at the maximum pressure achieved,
the fluid pressure did not propagate away from the wellbore wall, either because the
maximumwellborepressuredidnotexceedtheleastprincipalstressorwasnotsufficient
to initiate a fracture of the wellbore wall in the case of an open-hole test. The peak
pressure reached during a LOT or mini-frac is termed the formation breakdown pressure
(FBP) and represents the pressure at which unstable fracture propagation away from a
wellbore occurs (fluid flows into the fracture faster from the wellbore than the pump