For all intents and purposes, earnings season for the fourth quarter of 2011 is history. And since the process of examining quarterly results is essentially a rearview mirror exercise anyway, our task now -- especially in energy -- is to combine what we learned about each company's recent strengths with our beliefs about what lies ahead technologically, competitively, and geopolitically for the sector.

Ideally, the result will be improved ideas about relative corporate prospects. Below is a foursome of oilfield services stocks that appear eminently capable of becoming stronger and making money for Fools, even amid major changes in the world of energy.

The oil-field services stock everyone should own: Schlumberger (NYSE: SLB). I'm beginning with Schlumberger not because it's the largest member of the group, but because, as I've previously noted to Fools, it's the one stock without which any portfolio is underserved. Indeed, you may recall that as 2011 came to an end, I touted the company as being firmly ensconced among our five top energy stocks for this year.

Since that time, I've hardly altered my opinion. In fact, with 110,000 employees operating in approximately 80 countries -- certainly including all of the world's major hydrocarbon-producing venues -- Schlumberger appears ideally suited for the long haul as conditions in one after another of the world's exporting nations (read: Iran, Nigeria, Mexico, Venezuela, Russia, etc.) become steadily more unstable.

To Schlumberger's blanket geographic reach, you can add its major presence in such key energy centers as Brazil and Saudi Arabia. Add to that its technological leadership -- largely born of a research budget that last year topped a lofty $1 billion -- and you have a company that quite simply may be indispensible to the vital world of oil and gas.

As technology grows, so goes the importance of National Oilwell Varco (NYSE: NOV). Perhaps you're focusing on the horizontal drilling-hydraulic fracturing combination that has expanded natural gas and oil reserves in North America. Or maybe it's the movement into deeper waters offshore that has your attention. In either case, National Oilwell Varco has played an important role in producing the equipment that has propelled these advances.

The company's products include key mechanical components for both land and offshore rigs. In addition, it provides both land and well-servicing rig packages, inspection and coating of tubular goods, and drilling equipment that includes down-hole motors, bits, and tools. From a macro perspective, I'm convinced that, for years to come, the company will be a key beneficiary of increasing crude prices and natural gas utilization.

Don't ignore the soon-to-expand Kinder Morgan (NYSE: KMI). I must confess to being a "management freak." While it's impossible to quantify managerial competence, I endeavor to be attentive to my visceral feelings about the competence of the leadership of the companies I follow. On that basis, I find midstream energy company Kinder Morgan to be tough to top.

As you probably know, Kinder Morgan is a midstream company (read: pipelines and storage) that currently operates 37,000 miles of lines across North America. Further, it is in the process of acquiring El Paso (NYSE: EP), its fellow Houston-based midstream giant. The combination, which is expected to be completed during the coming quarter, will cost Kinder about $38 billion, including the assumption of El Paso debt. Of that amount, approximately $7 billion is likely to be recovered through the sale of El Paso's exploration and production operation.

Kinder Morgan CEO Richard Kinder has built his company from a $40 million pipeline that he acquired when (to his credit) he bid adieu to the late Enron Corporation 15 years ago. It'll be well worth watching whether he can keep working his magic with El Paso.

Deeper drilling is raising Oceaneering International (NYSE: OII). Nearly two years ago, when the Deepwater Horizon tragedy hit and sullied the Gulf of Mexico, Oceaneering-manufactured remotely operated vehicles (ROVs) were significant actors in the response process. Starting as a diving company in 1964, Oceaneering has steadily expanded to become a technology-based company that plays a crucial role worldwide in deepwater applications, primarily for the oil and gas industry.

It's clear that the steady expansion of deepwater drilling in the Gulf of Mexico, in Brazil's Santos Basin, offshore West Africa, and in an increasing number of additional global locations is unlikely to abate. That, it seems to me, bodes extremely well for Oceaneering, which operates essentially without competition in its vital services niche.  

Foolish takeaway
While I'm convinced that the energy industry is easily among the crucial sectors for Fools to examine as they construct their portfolios, there are numerous other companies in a plethora of industries that merit your attention. Find out about 11 possible ideas by obtaining The Fool's special free report "Secure Your Future With 11 Rock-Solid Dividend Stocks."