A discovery in the deep waters of the Gulf of Mexico is the first for a partnership that includes a spinoff of China's state oil company, Shell announced.

Shell announced a discovery in the Rydberg area of the Norphlet play in the deep waters of the Gulf of Mexico. It's the third major discovery in Norphlet for Shell and the first for the partnership that includes the U.S. subsidiary of Colombian energy company Ecoptrol and Nexen, a subsidiary of China National Offshore Oil Corp.

Shell said Tuesday it's still assessing the data from the exploratory well in the Rydeberg area but expects it to hold about 100 million barrels of oil equivalent. Together with the two other discoveries in the Norphlet play -- Appomattox and Vicksburg -- Shell says the region holds at least 700 million boe.

Shell and Nexen are planning another exploratory well inside the Rydberg discovery, about 10 miles away from Appomattox. Rydberg is located 75 miles offshore.

"The Rydberg discovery builds upon our leadership position in the Eastern Gulf of Mexico and its proximity to our other discoveries in the area make Rydberg particularly exciting," Marvin Odum, Shell's director of upstream activity in the Americas, said in a statement.