UPDATE 2-Texas pipeline operator Altus to combine with Blackstone-backed BCP Raptor

(Recasts; adds detail, context)

Oct 21 (Reuters) - Altus Midstream Co said on Thursday it would merge with BCP Raptor, a holding company for pipeline assets in the Permian Basin owned by investment firms, with the combined entity to be valued at $9 billion inclusive of debt.

The transaction, a so-called reverse merger which will allow privately-owned BCP to become a public company, will hand control of Altus to BCP's backers: private equity firm Blackstone Inc and infrastructure-focused investor I Squared Capital.

In exchange, Altus gains greater scale in the Permian, the U.S. shale industry's heart. The resultant company will be the largest integrated midstream operator in the Delaware part of the formation, according to Altus' statement.

The tie-up comes as commodity prices hit multi-year highs, offering confidence to energy companies to pursue transformative actions. Altus, with a market value of $1.4 billion, aims to close the deal in the first quarter of 2022.

For investment firms such as Blackstone, the positive environment offers a pathway to exit long-held bets on energy assets: stock in a public company can be regularly offloaded to ordinary shareholders, instead of needing a buyer for the whole private entity.

Blackstone and I Squared will own 75% of the combination. Apache Corporation, the oil and gas producer from which Altus was carved out in 2018 and merged with a blank-check firm, will slim its holding to 20% from 79%. The remaining 5% will belong to Altus' other investors.

Apache Corp, the U.S. arm of energy producer APA Corp , has agreed to the proposal, the statement said.

BCP owns EagleClaw Midstream, Caprock Midstream and Pinnacle Midstream. It also holds part of the Permian Highway Pipeline, and once joined with Altus' interest, they will be the majority owner of the 430-mile (700km) natural gas pipeline.

EagleClaw Chief Executive Jamie Welch will lead the merged entity.

Credit Suisse and Bracewell provided financial and legal advice, respectively, to Altus. Bankers assisting BCP and its backers were Barclays, Citi, Greenhill, Intrepid, and Jefferies, as well as law firms Vinson & Elkins and Sidley Austin. (Reporting by David French in New York and Noor Zainab Hussain in Bengaluru; Editing by Maju Samuel and Lincoln Feast.)