Woodside Petroleum is testing the patience of investors as its much-vaunted "year of the deal" races towards a conclusion and decisions crucial to the opening up of two giant gas fields off the Western Australian coast are pushed into 2020.

A multibillion-dollar deal to bring in a new partner to help fund the Scarborough project in Western Australia is no longer an immediate prospect because a 52 per cent increase in the size of the gas field has prompted Woodside to rethink whether to keep all of its 75 per cent stake.