Mr Watchorn worked as the company's Production/Facility manager from April 2011 until July 2012 when he resigned.
He then began work at NZEC, a direct competitor to his former company, TAG Oil said.
Andrew Cadenhead, chief operating officer of TAG Oil, told the ERA the oil and gas industry was fiercely competitive, and geotechnical information would be of incalculable value to a competitor such as Mr Watchorn's new employer.
He said any damage caused by a leak in information could take years to become apparent.
The ERA ruled that Mr Watchorn was "deceptive" and his actions breached contract, but found no evidence to prove he passed information on to his new employer.
Mr Watchorn was ordered to pay $65,567 in damages to TAG Oil, and $12,000 in penalties, half of which to be paid to the Crown and half to TAG Oil.