Clara Rojas and Consuelo Gonzalez had also been held for six years.
On board the helicopters are Ramon Rodriguez Chacin, the Venezuelan justice minister, as well as four Red Cross representatives and doctors to treat the hostages.
The Revolutionary Armed Forces of Colombia (Farc) had offered on February 2 to hand over to the Venezuelan president three of the hostages, while Gechem was later added to the list on health grounds.
The hostages are part of a group of about 40 foreign captives whom the Farc want to swap in exchange for 500 of their fighters being held in Colombian prisons.
The imminent release of the four comes days after protests were held in France and Colombia to mark the six-year detention by the Farc of Ingrid Betancourt, the French-Colombian former politician.
The Farc, in addition to demanding that its fighters be released, has called for the demilitarisation of two zones in the south of Colombia.
Alvaro Uribe, the Colombian president, has indicated a willingness to negotiate an exchange of prisoners, but has ruled out demilitarisation of such a large and populated part of the country - suggesting a smaller, less inhabited zone instead.
Tensions had earlier arisen between Uribe and Chavez over the hostage negotiations, which worsened when Chavez said the Farc should not be designated a "terrorist" group.