Correct energy conservation in geothermal wellbore simulation

•A simple test that a geothermal wellbore simulator conserves energy is proposed.•In two-phase flow it is important to distinguish between flowing and static enthalpy.•Some simulators confuse flowing steam quality and static steam dryness.•The change in flowing enthalpy should approximately match change in potential energy.•We explore some consequences of not conserving energy in wellbore simulations.

A fundamental error of interpretation of static steam dryness versus flowing steam quality in the coding of the simulator GWELL has been found, that means it does not correctly conserve energy or momentum. GWELL, or the energy and momentum subroutines from it, may have formed a basis for other geothermal wellbore simulator codes in existence, prompting this note on how to quickly check if your favorite geothermal wellbore simulator is actually conserving energy. The possible consequences of using a simulator that does not conserve momentum or energy as presumed, are also briefly explored.