Model Parameters

Proppant Model Parameters

The Proppant Model Parameters tab on the MODEL PARAMETERS screen contains parameters that determine the effects of proppant in the fracture.

Fracture Area is Considered Propped for Proppant Concentration Greater Than:

This number is the threshold value for in-fracture proppant concentration that must be exceeded in order for the fracture area to be considered propped. The default value is 0.2 pounds/square-foot, which corresponds approximately to a solid monolayer of 20/40 proppant.

Proppant Diameter Greater than (to ignore FLAs as Proppant):

This is the threshold diameter that the proppant you pump must exceed in order for it to be considered a true proppant in the fracture. This feature allows FIELDPRO Modules to ignore particulate fluid-loss additives (FLA's, including 100-mesh sand) as proppant, while still accounting for the effect on hydrostatic head and wellbore friction. This feature is also very useful for ‘neglecting’ early proppant slugs that you may wish to ignore in the fracture. The default value is 0.008 inches.

Immobile Proppant Bank Formed at Volume Fraction of Proppant in Slurry:

This number specifies the level of slurry dehydration where an immobile proppant bank forms. Volume fraction of proppant is defined as

VP / (VP + Vf)

VP - volume of proppant VF - volume of fluid

The default value of 0.6 implies that slurry becomes immobile when only 40% of its volume is fluid and 60% is proppant. Changing this value alters all proppant effects because they depend on the relative state of the slurry between no proppant effects (i.e., at proppant volume fraction of zero) and maximum proppant effects of a completely immobile slurry (i.e., at the value entered here).

Proppant Drag Effect Exponent

This parameter adjusts the magnitude of the proppant effect on the in-fracture drag (or friction) due to the slurry fluid. RES has found that values between 4.0 and 12.0 typically match observed data. A higher number causes greater increases in net fracturing pressure due to the pumping of proppant.

Proppant Radial Weighting Exponent

This parameter controls the relative contribution of the proppant effects at different positions in the fracture. Decreasing this number increases the relative proppant effects at the fracture tip and decreases the proppant effects near the wellbore. The default value is 0.25.

Proppant Convection Coefficient

This coefficient determines the overall speed of the convective process. Increasing this number increases the speed of convection. The default value is 10.0.

Proppant Settling Coefficient

This coefficient determines the overall speed of the settling process. Enter 1.0 for ‘ideal’ settling, or 0.0 for no settling.

Quadratic Backfill Model

When this option is selected, the Quadratic Backfill Coefficient is set to its default value of 0.5. The quadratic backfill model will exhibit a steeper than linear increase in net pressure resulting from a tip screenout. If this option is not selected, a linear rise in net pressure will be exhibited. Most of the field data that RES has seen exhibits a slightly faster than linear rise.

Quadratic Backfill Coefficient

This coefficient controls the behavior of the Quadratic Backfill Model. The default value is 0.5. Entering 0.0 is equivalent of turning the quadratic backfill model off. Using a larger number makes the pressure increase more rapidly once the proppant starts to ‘pack’ in the fracture.

Stop Model When Proppant Packs at Wellbore (Screenout)

This option should normally be selected. One possible exception is for simulations where high concentrations of proppant are pumped into very small fractures. In those cases, FIELDPRO Modules may indicate a wellbore screenout when your own field experience indicates otherwise.

Reset Proppant in Fracture if there is additional pumping after Closure on Proppant

Select this option if you want to ignore the presence of proppant from, for example, a slug or mini-frac or even previous fracture, if the fluid that carried this proppant has been completely leaked off (the fracture is completely closed). In other words, you assume that the fractures do not ‘see’ each other.