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Overestimation of OGIP in water-Drive gas reservoirs due to a misleading linear p/z plot. M.H. El-Ahmady, R.A. Wattenbarger, Texas A&M University, and T.T. Pham, El-Paso Production Company June 13, 2001. Outline of Presentation. The uniqueness problem.

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overestimation of ogip in water drive gas reservoirs due to a misleading linear p z plot

Overestimation of OGIP in water-Drive gas reservoirs due to a misleading linear p/z plot

M.H. El-Ahmady, R.A. Wattenbarger, Texas A&M University, and T.T. Pham, El-Paso Production Company

June 13, 2001

outline of presentation
Outline of Presentation
  • The uniqueness problem
slide5

What is the OGIP?

p/z

False straight line

OGIP

G’

Gp

non uniqueness problem
Non-Uniqueness Problem

Early data may indicate - (a) large OGIP with no water influx or(b) smaller OGIP with water influx

outline of presentation7
Outline of Presentation
  • The uniqueness problem
  • A Field example
field a gulf of mexico
Field A (Gulf Of Mexico)
  • Early production data shows OGIP = 270 Bscf without water drive
  • Aquifer analysis showsOGIP = 110 Bscf with water drive
field a gulf of mexico12
Field A (Gulf Of Mexico)

After more production:

  • p/z showed lower OGIP
  • One well “watered out”
  • The current estimate of OGIP is 120 Bcf , close to the early aquifer analysis (110 Bcf)
outline of presentation13
Outline of Presentation
  • The uniqueness problem
  • A Field example
  • Simulation, const. prod. rate
outline of presentation18
Outline of Presentation
  • The uniqueness problem
  • A Field example
  • Simulation, const. prod. rate
  • Simulation, false straight line
what rates cause the false straight line simulation
What rates cause the false straight line? (simulation)
  • We give a value of G’
  • Assume constant production rate for the first 6 months
  • p/z plot gives a perfect straight-line after 6 months.
slide21

Simulation of

false straight line

p/z

False straight line

OGIP

G’

Gp

outline of presentation24
Outline of Presentation
  • The uniqueness problem
  • A Field example
  • Simulation, const. prod. rate
  • Simulation, false straight line
  • Conclusions
conclusions
Conclusions
  • At very early times, the p/z plot extrapolates to the correct OGIP, even with water drive.

(However, this is probably not practical because of data errors and lack of data at very early times).

conclusions26
Conclusions
  • A false linear p/z plot may occur for a particular production rate schedule. This makes it impossible to determine OGIP with this rate schedule.
conclusions27
Conclusions
  • The “non-uniqueness” production rate schedule generally increases, then peaks and decreases.
overestimation of ogip in water drive gas reservoirs due to a misleading linear p z plot28

Overestimation of OGIP in water-Drive gas reservoirs due to a misleading linear p/z plot

M.H. El-Ahmady, R.A. Wattenbarger, Texas A&M University, and T.T. Pham, El-Paso Production Company

June 13, 2001