Houston-based independent Noble Energy Inc. (NYSE: NBL) plans to divest certain noncore U.S. onshore assets, representing 5,700 BOE per day and some 29 million BOE of reserves, for approximately $550 million.

The package includes higher-cost assets in the Midcontinent and Illinois Basin.

Noble’s U.S. onshore resource base now exceeds 2.5 million net acres, with net-risked resource potential of some 1.6 billion bbl. equivalent. Specifically, Noble has more than 750,000 net acres in the Denver-Julesburg Basin in Colorado, with total net-unrisked potential of more than 1 billion bbl. equivalent (360 million bbl. equivalent risked).

In the emerging Niobrara play, Noble has been encouraged by early horizontal drilling results within Wattenberg Field, which includes Gemini, the field’s most successful well to date. In Wattenberg, the company’s first four horizontal Niobrara wells have indicated strong projected returns. Noble anticipates ultimate recoveries from the wells to be approximately seven times those of a typical vertical well in the field.

Noble expects to grow its onshore production by more than 50% from 2009 to 2015. As of year-end 2009, estimated reserves were 820 million bbl. equivalent, with U.S. assets comprising 55% of total reserve additions. The company has set a capex of $2.6 billion per year for the next five years.

The sale is expected to close in third-quarter 2010.

The effective date is April 1.