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

Sw* Power Law Model Power Law Model (log-log straight line) “Best fit” of any data set with a straight line model can be used to determine two unknown parameters. For this case: slope gives l intercept gives Pd Swi must be determined independently it can be difficult to estimate the value of Swi from cartesian Pc vs. Sw plot, if the data set does not clearly show asymptotic behavior

Type Curves A Type Curve is a dimensionless solution or relationship Dimensionless means that it applies for any values of specific case parameters Petroleum Engineers often use type curves to determine model parameters well test analysis well log analysis production data analysis analysis of capillary pressure data

Type Curves Process of type curve matching Step 1: observed data is plotted using an appropriate format The data and type curve must be plotted using the same sized grid (ie. 1 log cycle = 1 log cycle) Step 2: a “match” is found between observed data and a dimensionless solution by sliding the data plot over the type curve plot (horizontal and vertical sliding only) Step 3: the “match” is used to determine model parameters for the observed data Often values are recorded from an arbitrary “match point” on both the data plot and type curve plot

Brooks and Corey Type Curve Dimensionless variable definitions Dimensionless Capillary Pressure Dimensionless Wetting Phase Saturation Restating Sw* Model (Type Curve Plot)

Brooks and Corey Type Curve Type Curve Plot By matching the type curve, we can solve for all three Sw* Model parameters: Pd , Swi , and l curve matched gives, l vertical slide gives: Pd horizontal slide gives: Swi

Brooks and Corey Type Curve Data Plot, Pc vs. (1-Sw ) Grid must be same size as Type Curve Plot Any pressure unit can be used for plotting Pc Pd will be in same unit

Brooks and Corey Type Curve Example Data, Cottage Grove #5 Well lithology: sandstone porosity: 0.28 fraction permeability: 127 md fluid system: brine/air swg: 72 dyne/cm

Brooks and Corey Type Curve Step 1: Plot data on same sized grid Plots are shown overlayed

Brooks and Corey Type Curve Step 2: Slide data plot to obtain the best match Only horizontal and vertical sliding is allowed Best match is with the l=1.0 curve Actual value of l is slightly less than 1.0

Brooks and Corey Type Curve Step 3: Pick an arbitrary match point and record values from both curves For this particular type curve, the “best” arbitrary match point is where PcD=1 and SwD=1 At this match point, Pc=2.0 psia and (1–Sw)=0.77 Match Point

Brooks and Corey Type Curve Using dimensionless variable definitions Dimensionless Capillary Pressure When PcD = 1.0, from match point Pc=2.0 Since by definition, PcD=Pc/Pd , then Pd=2.0 Dimensionless Wetting Phase Saturation When SwD = 1.0, from match point (1-Sw)=0.77 Since by definition, SwD=(1-Sw)/(1-Swi), then (1-Swi)=0.77 Therefore, Swi=0.23 Model Parameters: l=1.0, Pd=2.0, Swi=0.23 The Sw* log-log plot should be used to verify these values This would allow a more precise determination of l than “slightly less than 1.0”