A new well design for the Waitangi Valley-1 site was needed, using worldwide expertise, "which is going to take some time".
The well had shown "the hydrocarbon kitchen is definitely working" but even greater pressures were expected at lower depths.
"We will be drilling that well deeper - we are excited to get down and see what's down below," Mr Cadenhead said.
Taranaki production would sustain the financial viability of high-risk East Coast drilling "but eventually one of these is going to come in", he added.
In contrast to Waitangi, maximum pressure at Tag's well near Dannevirke was successfully predicted and matched with appropriate design.
"We had no problems reaching our intended total depth at that well, but we're 250km away at Waitangi Hill, with little to no drilling data in this area, and we encountered something no drilling engineer could have predicted. We'll learn from that and come back with an appropriate plan," Mr Cadenhead said.
Tag could have kept drilling at Waitangi "but we wanted to step back, make sure we are totally confident that if the trends we saw in the first 900m of drilling continued for the rest of the well and we had a well design that could handle it", he said, adding that belief in the potential for Waipawa black shale and Whangai formations was as strong as ever.
"High pressures can actually be a production bonus once we design our wells to deal with the drilling difficulties," said Mr Cadenhead.
CEO Garth Johnson said the decision to plug the well was made after consulting worldwide drilling experts.
"The well will be abandoned following all regulatory requirements and with no environmental issues encountered to date."
The drilling rig would return to Taranaki, where TAG has enjoyed unmatched New Zealand success in finding commercial gas and oil reserves.
Mr Johnson said the company remained excited about East Coast prospects.