My understanding is that Chase Pay replaces the use of physical cards – in this case, both credit card and Fuel Rewards card – as both card numbers are registered in your Chase Pay preferences (linked CC and merchant “Shell”), @gatorj.
If your preferred linked CC is a MasterCard, you should additionally be able to take advantage of a MC promo offering a $0.15/gal. discount when you register your MC number with your Fuel Rewards card by March 31, 2018:
https://www.fuelrewards.com/fuelrewards/mymastercard
…which is in addition to the:
$0.15/gal. discount per $100 spent on groceries that you can earn when using your registered MC, or the
$0.10/gal. discount per $50 dining,
$0.05/gal. discount per $50 travel,
$0.05/gal. discount per $50 spend with a linked MC, Visa, or AmEx card, and
other shopping offers that accompany the Fuel Rewards card.
https://www.fuelrewards.com/fuelrewards/frequently-asked-questions