Saudi Aramco's Amin Nasser, CEO of the world's largest oil company, says he does not spend much time worrying about booming production from U.S. shale fields.

One reason, says Nasser, is that shale drillers will eventually deplete the low-cost, high-quality "sweet spots" they've focused on throughout much of the three-year oil price downturn. American energy companies have driven down the cost of producing a barrel of crude, staved off bankruptcy and prevented output declines by tapping their best oil fields first.

"The concentration that we are seeing today is on the sweet spot of shale, and this will not last forever," Nasser said in an exclusive interview on CNBC's "Squawk Box."

"You can concentrate for some time on the sweet spots and produce more oil. But ultimately you need to venture downward, and that's where you have less quality and you require more cost to produce these barrels," Nasser said Sunday from the command center at Saudi Aramco headquarters in Dhahran.