Hydraulic Impedance Testing in Water Disposal wells in Oman

1
Hydraulic Impedance Testing in Water Disposal
wells in Oman
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Wellbore Diagram for SH-F3 Wells
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Simulated surface pressure response for a single
diameter wellbore with no fracture. Notice that
surface pressure never rises above its original
value.
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Simulated surface pressure response of an
infinite acting fracture. Notice how the
reflection from the fracture changes from
positive to negative because of the negative
reflection of an open fracture.
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Calculated response of SH-F3 wellbore and
fracture to HIT pulse.
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Surface pressure plot for first shut-in on SH3-1.
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Well SH3-1
Example of recorded HIT data before processing
shows high frequency component caused by hanging
pipe and low frequency oscillation caused by
initial shut-in water hammer.
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Well SH3-1
Example of filtered and de-trended data for the
same pulse - has removed the high frequency
component, and the sinusoidal oscillation -
making the pulse reflections in the signal much
clearer.
9
Plot of pulse from SH3-1 first shut-in showing
location of possible tip reflection.
10
Idealized tip reflection and method for
calculating fracture length using tip reflection.
Time between reflection from fracture mouth and
fracture tip, divided by two, multiplied by wave
velocity in the fracture gives estimate of
fracture length.
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Example pulse from SH3-2 first shut-in, showing
reflection from casing/open-hold interface and
multiple fracture reflections.
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Plot of Reflection Coefficient (ignoring wellbore
attenuation) shows how it is insensitive to the
controlling fracture dimension (either length or
height) once this dimension is greater than about
10 meters. Once that dimension is greater than
10 meters, the hydraulic impedance of the
fracture is so small compared to that of the
wellbore that the reflection coefficient is
almost -1.
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Possible fracture geometries leading to multiple
reflections of the HIT pressure pulse.
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• Summary of results on frac dimensions
• Length 11-12 m (tip reflections)
• Two identified frac initiation points per well
• Upper at ca. 1230 m, lower at ca. 1360 m

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Plot of surface pressure versus reflection
coefficient for SH3-1 fourth shut-in. Closure is
estimated between pulses at 798 and 919 psi.
16
Plot of surface pressure versus reflection
coefficient for SH3-2 third shut-in. Fracture
closure estimated to at 1165 to 1220 psi.
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• Closure stresses as measured by HIT
• Well 1 858, 898, 901, 859 psi. Av. 0.63
  psi/ft
• Well 2 1183, 1255, 1193 psi. Av. 0.74
  psi/ft
• Closure stresses as measured by pressure fall-off
  analysis
• Well 1 880 psi
• Well 2 1210 psi