Completion is expected by the fourth quarter of this year.
Balang is a part of the China Changcheng Natural Gas Power Group, which has investments in the natural gas and power sectors in the Asia Pacific Region, including China.
Repsol says the business will continue to be operated by Repsol until the completion of the transaction, prioritising the well-being of staff and safe and reliable operations.
Balang chairman Dai Ying Xiang said: "Balang is committed to develop the discovered resources in these assets, with the potential for PNG's next LNG project to be a reality in the very near future. This deal is great news for PNG, and for the people of the Western Province in particular."
Repsol owns mineral rights to nine blocks in Papua New Guinea: four exploration blocks with a net surface area of 7,418 square kilometres and five development blocks with a net surface area of 1303 square kilometres.