Page 205 - Applied Petroleum Geomechanics

200 Applied Petroleum Geomechanics

very similar to the LOT, and interpretation of the closure pressure is the
same as the methods introduced in the previous sections. The major dif-
ference between LOT and DFIT is that the DFIT uses a larger injection rate
(volume) and creates a much longer hydraulic fracture. The formation
breakdown pressure may be measured larger for a higher pumping rate. It
should be noted that the recorded pressure in the DFIT normally is the
gauge pressure. The mud pressure in the borehole should be added for the
purpose of calculating in situ stresses (refer to Eq. 6.25).

6.2.5 Case example of in situ minimum stress measurement
The MWX was sponsored by the US Department of Energy to increase
natural gas production from low-permeability sandstone reservoirs. Three
vertical wells, MWX-1, MWX-2, and MWX-3, spaced several hundred
feet apart were drilled in the Piceance Basin of northwestern Colorado.
The MWX involved strata of the Mesaverde Group, which comprises the
Cretaceous Iles and the Williams Fork Formations (Nelson, 2003). The
major stress measurement techniques used were small-volume hydraulic
fractures and anelastic strain recovery (ASR) (Warpinski and Teufel, 1989).

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Measured pore pressure
Measured pore pressure
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165° F F F I Interpreted pore pressure r e
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Depth (ft) 7000 Sandstone Shale 200° F F
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Pressure and minimum stress (psi)
Figure 6.7 Pore pressure and minimum horizontal stress (S h ) measurements as a
function of depth at the MWX site in the Piceance Basin of Colorado. (Modified from
Nelson (2003) courtesy of the U.S. Geological Survey, data from Spencer (1989) and
Warpinski et al. (1985))