The project is northeast of the $3.3-billion Golden Eagle development, which is under construction.
Solitaire is expected to produce eight million barrels of oil.
Detailed design and engineering will begin immediately and field installation is expected to begin toward the middle of next year.
First oil from solitaire is expected in 2015.
Nexen is in the final stages of being acquired by Chinese state-owned firm CNOOC Ltd. for $15.1 billion.