Oil and gas operators gained confidence in deepwater activity over the years as many large reservoirs that can produce at high flow rates have been discovered. And as happens with most challenges, many advances in technology were needed to keep up with the opportunities. Significant advances in exploration, drilling, and development have been necessary to support the industry. Fortunately, the economic and safety benefits have been sufficient to justify the efforts. Water depth is one of the many factors that impact the methods of oilfield development, and its cost.
Some people consider a particular water depth to define the boundary of deepwater, which is a simple way to view it. Deepwater has also been defined by some people based on “maximum” diver depths, which is subjective based on safety considerations. This would generally set the limit between 750’ and 1,000’, though there have been successful dives beyond 1,000’ water depth. Another means of defining deepwater is the maximum depth of bottom-supported rigs and platforms, with the deepest being Bullwinkle, set in 1,353’ water depth in 1988 in the U.S. Gulf of Mexico.
The best method of distinction for the oil and gas industry is to focus on the technologies, such as whether the rigs and platforms are bottom-supported or floating. Note that bottom supported drilling rigs cannot reach the depth of the largest fixed platforms, so the exploration and initial drilling may use deepwater technology while development for production may use offshore “shelf” technology.
All available technology should be considered for any development without a pre-conception of whether it is deepwater or not. For example, there are floating platforms in water depths shallower than 1,353’ and even 1,000’, but the technology is sufficiently different to consider them deepwater developments. On the other hand, there are many subsea trees of all types in shallower water depths, with the simpler all-hydraulic vertical trees (“mudline” trees) set near fixed platforms in a few hundred feet of water. Fields with these mudline trees that are hooked up by divers are generally considered subsea but not deepwater.
The U.S. BSEE apparently agrees with that deepwater is defined by technology, in that the Code of Federal Regulations requires a deepwater operations plan for “any non-conventional production or completion technology, regardless of water depth” (30CFR250).
Ocean Flow International