Gov. Tom Wolf’s administration is planning to ask lawmakers to approve a severance tax on Marcellus Shale natural gas production to finance a multibillion-dollar capital plan for a wide range of projects. Wolf, a Democrat, is unveiling the plan Thursday. The administration wants to use the money to pay down a $4.5 billion bond that it would spend over four years on projects including expanding high-speed internet access, improving flood control and cleaning up brownfields and blight.