CALGARY - The oil companies behind the $7-billion Mackenzie Valley natural gas pipeline announced Thursday they had stopped most work on the project, saying there hasn't been enough progress in resolving several key issues, including access. The pipeline partners said they remain committed to the project, but said progress has been so slow on bridging some differences that they are unwilling – at least for the time being – to commit more money. Imperial Oil leads four companies in Mackenzie Valley project The oil companies said they would stop project execution work like geotechnical data gathering, the start of...