Video game publisher THQ Inc. said Tuesday it has formed a joint venture to launch casual online games in North America and China with ICE Entertainment, a Shanghai online game operator.

The companies’ first project will be to launch a casual online version of the game “Dragonica,” developed by Barunson Interactive Co., which is based in Korea. ICE has the rights to operate the game in China. The game is scheduled to be released in North America next year.

Revenues will be based on a micro-transactions model, in which the game is offered online for free and players pay small amounts of money for in-game items and other extras that enhance playing, said Agoura Hills-based THQ.

Financial terms of the deal were not disclosed.

The market opportunity for online casual gaming in North America is estimated to be $2.2 billion by 2013, according to DFC Intelligence. China’s market was valued at $1.7 billion in 2007, according to Niko Partners, and is expected to grow to 4.2 billion by 2010.

Shares of THQ were down 35 cents, or 3 percent, to $12.24 in morning trading on the Nasdaq.