Horizontal Multifrac – General Model

Subtopics:

This model is the most generalized model in Fekete's suite of analytical multifrac models. Individual fracture properties can be specified, the wellbore can be activated, the reservoir dimensions are not constrained by the dimensions of the completion, and it is not built upon the presumption of linear flow. As a result, it calculates relatively slowly.

This model is a homogeneous, single-phase, rectangular reservoir model consisting of a horizontal wellbore and transverse fractures. You may specify the reservoir dimensions and well position, provided that the entire wellbore and all fractures fit within the reservoir boundaries.  In addition, each fracture can be situated anywhere along the horizontal wellbore and configured to have a unique fracture half-length and conductivity.  Thus, it is possible to model the combined effects of the horizontal wellbore and multiple fractures, as well as the transition into middle-time flow regimes and boundary-dominated flow for any number of different geometrical configurations. Depending on the configuration, pseudo-radial flow can be observed with this model.

Damage skin is applied along the length of the horizontal wellbore and a turbulence factor may be specified.

 

Parameters

Pi = initial pressure

sd = skin on horizontal well

Lex = effective horizontal well length in the x-direction

Activate Hz Well: When selected, direct flow from the reservoir to the horizontal well (not just from the fractures) is assumed.

xfy = fracture half-length in the y-direction

FCD = dimensionless finite conductivity

#Fracs = the number of fractures that intersect the horizontal well.

kx = permeability in the x-direction

ky = permeability in the y-direction

kz = permeability in the z-direction

h = net pay

Φt = total porosity

Sg = gas saturation

So = oil saturation

Sw = water saturation

cf = formation compressibility

 [Dual Porosity Parameters]

PSS = Transfer from secondary porosity to primary porosity is modeled as pseudo-steady state (PSS).

Transient Slabs = Transfer from secondary porosity to primary porosity is modeled as transient, using a slab shape factor.

Transient Cubes = Transfer from secondary porosity to primary porosity is modeled as transient, using a cube shape factor.

Transient Sticks = Transfer from secondary porosity to primary porosity is modeled as transient, using a stick shape factor.

ω = storativity ratio

λ = interporosity coefficient

sdΦ = interporosity skin (for transient dual-porosity only)

Xe = reservoir length

Ye = reservoir width

OGIP = original gas in place

Zw = z position of well within reservoir

Xw = x position of well within reservoir

Yw = y position of well within reservoir

rw = wellbore radius

CD1 = dimensionless wellbore storage (may be left blank)

CD2 = dimensionless wellbore storage 2

CpD = dimensionless storage pressure

D = turbulence factor (may be left blank)

AD = areal extent of reservoir

Eavg = average error

Itr = number of iterations

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