Pete 324 L19 1

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Pressure Build-up analysisLate time effects
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(No Transcript)
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Build-up derivative goes down
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p4577 psia

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Recall that

• Recall that pore volume of a bounded reservoir
  (no-flow outer boundary) can be estimated from
  the late time portion of a flow (drawdown) test
• Pore volume is in ft3, q is in stb/d and time is
  in hr
• Recall that from late time portion of a build-up
  test we can obtain initial pressure (if
  non-depleted) or average area pressure
  (modified Muskat)
• Question What else?

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Distance to Fault

• Well in an "infinite acting" reservoir, located
  near to a no-flow boundary (fault)

L
L
well
image well
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Analysis
midtime slope m
Late time slope 2m
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Conclusion

• If on the Horner plot of the build-up test there
  are two straight lines one with slope m another
  with slope 2m, then we can conclude that there is
  fault at distance L
• The distance L can be obtained from the time of
  intersection of the two lines, denoted by Dtx
• L has to be not too large and "2m" has to be
  exactly two times "m"

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Estimating distance to a fault from Horner plot
pws
2m
intersection
m
Log of Horner Time Ratio
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Example

• Assume that h 50 ft
• production time before a build-up test was 500
  hr,
• production rate 250 stb/d,
• (? B?)1 (cp resb/stb)
• (? ? ct?) 1x10-6 (cp / psi)
• There are two straight lines on the Horner plot,
  one with m11 psi/cycle the other with 22
  psi/cycle
• They intersect at Horner-time ratio 251
• Question what is the distance to the fault?

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Solution

• Estimate permeability from the first straight
  line (m 11 psi/cycle)
• Estimate ?tx from the Value of Horner time ratio
  at intersection
• Estimate L from formula

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