Enbridge Energy has started drilling on property it owns on the north and south sides of Line 5, the oil and gas pipeline it owns under the Mackinac Straits.
Spokesman Michael Barnes says the company has agreed to look at ways to replace the aging pipeline.
That could mean a new pipeline in a tunnel, inside a horizontally drilled tube, or in a trench.
"It tell us what the composition of the rock is, and so that will help both the state and us analyze what alternatives may be best possible for that area," says Barnes.
Enbridge -- a supporter of Michigan Radio -- agreed to submit its analysis to the state by June.
Environmental groups want the pipeline shut down, not replaced. They want the pipeline shut down, saying the potential for an underwater pipeline to cause an environmental disaster in the Great Lakes is too great.