BP BUYS INLONDON, March 1 (Reuters) - BP agreed on Wednesday to buy Clean Energy Fuels Corp's biomethane business for $155 million, expanding its huge gas supply portfolio in the United States and showing its shift to less carbon-intensive projects.Clean Energy captures biomethane gas emitted from landfill waste sites and then processes and purifies it to pump through pipelines. It is mainly used as a fuel for transport.BP said in a strategy update on Tuesday that it was exploring new investments in low-carbon forms of energy, a part of the industry in which it sees significant future business potential.