Capillary Pressure: Reservoir Seal Capillary Pressure / Saturation Relationship (Sw* Model)

1
Capillary Pressure Reservoir SealCapillary
Pressure / Saturation Relationship (Sw Model)
2
Reservoir Seal
Seal
Seal
Fault (impermeable)
Oil/water contact (OWC)
Migration route
Reservoir rock
Hydrocarbon accumulation in the reservoir rock
Top of maturity
Source rock
3
Reservoir Seal

• The seal for a reservoir is usually provided by a
  water wet zone with low (but finite) permeability
• Typically a shale
• Darcys Law would indicate that with a finite
  permeability, gravity effect alone would cause
  petroleum to pass upward through the seal due to
  density difference, over a long (geologic) time
  period
• Darcys Law is a Rate Process (ENGR 112)
• For multiple phases flowing, the Darcy flow
  potential includes pressure, gravity, and
  capillary pressure terms
• Effect of displacement pressure of seal halts
  upward migration of petroleum in trap
• Displacement pressure of seal can limit total
  height of reservoir, from free water level to
  highest elevation in reservoir

4
Capillary Pressure Required for Migration
is Function of Pore Size
s used in previous discussion
From Levorsen, 1967
5
Capillary Pressure Required for Migration
is Function of Pore Size
From Levorsen, 1967
6
Sw Power Law Model

• Having an equation model for capillary pressure
  curves is useful
• Smoothing of laboratory data
• Determination of l
• Analytic function for integration (future topic)
• The Sw Power Law Model is an empirical model
  that has proven to work well
• Model parameters Swi, Pd, l

7
Sw Power Law Model

• Sw rescales x-axis

Sw0
Sw1
Sw, fraction
8
Sw Power Law Model

• Power Law Equations plot as Log-Log straight line

9
Sw Power Law Model

• Straight line models are excellent for
• Interpolation and data smoothing
• Extrapolation
• Self Study review Power Law Equations (yaxb)
  and how to determine coefficients, a and b given
  two points on the straight log-log line

10
Sw Power Law Model

• Pd, l can be determined from Log-Log plot
• But, Swi can be difficult to determine from
  Cartesian plot, if data does not clearly show
  vertical asymptote

11
Sw Power Law Model

• Choosing wrong Swi limits accuracy of determining
  Pd, l