Shell, the world’s second-largest publicly traded energy company, is making a high-stakes bet that it can take highly efficient technology and processes perfected onshore and deploy it in deep-sea production. It hopes to squeeze more oil out of existing undersea wells, like those that ring the platform, which weighs 82 million pounds and floats in 3,000 feet of water over the Mars oil field in the Gulf of Mexico. It also wants to make new deep-water projects cheaper and faster, especially in Brazil, where it acquired a bevy of offshore prospects as part of its $50 billion purchase of BG Group PLC last year. It is a strategy born of necessity. Big oil companies have traditionally needed prices of $70 a barrel or more just to break even on new deep-water projects, which take years to begin paying off. But with onshore shale oil flooding the market, Shell executives aren’t sure when crude, currently around $50 a barrel, will fetch more again. And with electric cars and other technologies threatening to eat into demand, they believe the world’s thirst for oil may peak as soon as the end of next decade.