Capillary Pressure: Reservoir Seal Capillary Pressure / Saturation Relationship (S w * Model)
Seal Reservoir rock Seal Migration route Oil/water contact (OWC) Hydrocarbon accumulation in the reservoir rock Top of maturity Source rock Fault (impermeable) 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
Capillary Pressure Required for Migration is Function of Pore Size used in previous discussion From Levorsen, 1967
Capillary Pressure Required for Migration is Function of Pore Size
S w * Power Law Model Having an equation model for capillary pressure curves is useful –Smoothing of laboratory data –Determination of –Analytic function for integration (future topic) The S w * Power Law Model is an empirical model that has proven to work well –Model parameters: S wi, P d,
S w * rescales x-axis S w * Power Law Model S w *, fraction S w *=0S w *=1
Power Law Equations plot as Log-Log straight line S w * Power Law Model
Straight line models are excellent for –Interpolation and data smoothing –Extrapolation –Self Study: review Power Law Equations (y=ax b ) and how to determine coefficients, a and b given two points on the straight log-log line
S w * Power Law Model Pd, can be determined from Log-Log plot But, S wi can be difficult to determine from Cartesian plot, if data does not clearly show vertical asymptote
Choosing wrong S wi limits accuracy of determining P d, S w * Power Law Model