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

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

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 s used in previous discussion From Levorsen, 1967

Capillary Pressure Required for Migration is Function of Pore Size From Levorsen, 1967

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

Sw* Power Law Model Sw* rescales x-axis Sw*=0 Sw*=1 Sw*, fraction

Sw* Power Law Model Power Law Equations plot as Log-Log straight line

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

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

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