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Unconventional Reservoir Services

Pulse Decay Permeametry

When unconventional resource plug samples can be tested for permeability, the pulse decay method provides a rapid, accurate result for very low permeability cores (down to approximately 1 nd). Measurements are made at representative confining stress up to 10,000 psi. Equipment designs are available for either gas or liquid flow and follow the improvements indicated by Jones in SPE 28450. Shale/mudrocks are often tested at as-received water saturation resulting in effective kg or effective ko. The method represents the key part of the combined-method, stationary-liquid, approach for relative permeability in tight gas sands (Dacy, SPE 135427). Generally the pulse decay method requires a fraction of the time needed by the steady-state plug method.

Pulse Decay Permeability (plug) method:
  • Accurate and comparatively rapid (fraction of the time required by steady-state method)
  • Perm range: ~1 nd to 0.1 md
  • Net confining stress to 10,000 psi
  • Designs for both gas perm and liquid perm
  • Gas perms at high pore pressure, thus greatly-reduced klinkenberg slippage
  • Low delta pressure used, thus no inertial effects
  • Low effective flow rates cause no damage to structure
  • Test conditions optimal for no change in magnitude or position of lesser phase
  • Used for effective oil perm of as-received oil-productive shale/mudrock
  • Used for tight gas sand stationary-liquid relative permeability

Pulse Decay Equipment Design
Pulse decay equipment design facilitates a rapid permeability determination.

High Mean Pore Pressure Chart

At high mean pore pressure a small pressure drop is established and monitored providing permeability as the pressure pulse decays. For demonstration, the data set in the figure shows near complete depletion of the pulse approaching 5000 seconds. Note, however, that computed permeability was stable by 1000 seconds.

Pulse Decay Permeability Method

The pulse decay permeability method represents the key part of the combined-method, stationary-liquid, approach for relative permeability in tight gas sands. Effective kg (md) values annotate the data points between the end points in the graph above indicating measured kg at 70% Sw of 6 nanodarcies and at 19% Sw of 353 nanodarcies.

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