The owner of the Pike River coal mine, Solid Energy, says the first phase of work to re-enter the West Coast mine is nearly finished.
The mine exploded in November 2010, killing 29 men who were underground at the time.
The Government last year approved funding of a staged plan to re-enter and explore the main entry tunnel up to a rockfall just over 2km in from the mine portal.
Solid Energy says most of the ventilation shaft has been filled and expanding foam is being placed in it to fully seal it - an essential step in the project to allow exploration of the mine's main entry tunnel.
However, work has been delayed by wet weather this summer, which has allowed fewer work days on the vent shaft platform that can only be reached by helicopter.
Solid Energy said challenges with the materials being used have also made progress slower than hoped, but preparation for the next stage - cutting extra drill holes - is well advanced.
A spokesperson for the men's families, Carol Rose, says they have been told that the company had allowed for weather contingencies and a re-entry is still on track to take place in April this year.