Private equity firm The Blackstone Group said on Thursday that it would buy Royal Dutch Shell Plc’s 50 percent stake in a joint venture in Haynesville Shale, a shale-gas field in Louisiana, for $1.2 billion in cash.

Blackstone will make the investment through Vine Oil & Gas, a new Dallas-based exploration and production company established by the private equity firm earlier this year, and its Blackstone Energy Partners.