even though the official documentation does not seem to specify
whether the specified heat capacities of the SPECROCK and SPECHEAT
keywords are for constant pressure or for constant volume, the
implicitly seem to be for the latter: pressure dependent heat
capacites cannot be specified, yet the enthalpy for an incompressible
fluid *is* pressure dependent, so the specified heat capacities must
be for constant volume and they specify the internal energy instead of
the enthalpy.
