Pseudopressure Function General Equation Pseudopressure Function or qg = surface gas rate a = units conversion factor (see next slide) k = permeability h = total thickness re = external radius rw = wellbore radius s = steady-state total skin D = rate-dependent skin coefficient pwf = wellbore flowing pressure pR = volumetric average reservoir pressure m = gas viscosity Z = gas Z factor Bg = gas formation volume factor

Gas Rate Equation in Field Units qg = surface gas rate, scf/d k = permeability, md h = total thickness, ft re = external radius, ft rw = wellbore radius, ft s = steady-state total skin D = rate-dependent skin coefficient, 1/(scf/d) TR = reservoir temperature, deg R pwf = wellbore flowing pressure, psi pR = volumetric average reservoir pressure, psi m = gas viscosity, cp Z = gas Z factor Bg = gas formation volume factor, res.bbl/scf

Pseudopressure integral Gas rate is proportional to area under curve Pwf Pr Gas rate is proportional to area under curve