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

2. Reservoir Seal Seal Fault (impermeable) Oil/water contact (OWC)
Hydrocarbon
accumulation
in the
reservoir rock
Migration route
Seal
Several conditions must be satisfied for an economic hydrocarbon accumulation to exist. First, there must be sedimentary rocks that have good source rock characteristics and have reached thermal maturity. Second, the hydrocarbons must have migrated from the source rock to a potential reservoir, which must have adequate porosity and permeability. Finally, there must be a trap to arrest the hydrocarbon migration and hold sufficient quantities to make the prospect economic. Hydrocarbon traps usually consist of an impervious layer (seal), such as shale, above the reservoir and barrier such as a fault or facies pinch that terminates the reservoir.
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
Darcy’s 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
Darcy’s 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
Sw*=0
Sw*=1
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 (y=axb) 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 assymptote

11. Sw* Power Law Model
Choosing wrong Swi limits accuracy of determining Pd, l