Offshore driller Noble (NYSE:NE) reported fourth-quarter earnings after the market closed today, and the results weren't good enough to impress investors. Revenue grew 20.8% from a year ago to $1.17 billion on the back of three new ultra-deepwater drillships.

Net income was up 36% from a year ago to $174.1 million, or $0.68 per share. After adjusting for one-time items, earnings were $0.82 per share, in line with estimates.

One thing investors are looking for is any sign that the ultra-deepwater rig market is slowing down, and that's where there are some caution flags. Dayrates for drillships were down from $353,278 in the third quarter to $348,702 in the fourth quarter, and management said the first half of this year will include lower utilization rates.

Drilling rig owners play a delicate balancing act with explorers who contract rigs. If supply for rigs is low, then prices can shoot higher, to more than $600,000 per day for new ultra-deepwater rigs. But if the supply of rigs grows too quickly, it will result in falling dayrates and lower utilization. If low demand in early 2014 comes to fruition as management expects, net income could fall for Noble, which is why shares are down nearly 2% after hours today.