The future of the offshore oil and gas industry is in deepwater exploration and production. It has been argued, based on energy forecasts and estimated production life of operating fields, that production cannot be sustained unless the industry moves to deeper waters. Fortunately, deeper fields tend to be larger in terms of their production rate, thus making the exercise economically feasible.
Deepwater (defined as water depth exceeding the economic limits of fixed platforms – in and around 400 metres) and ultra-deepwater (> 1,000 metres) production either needs floating or tethered systems, or subsea production with tie-back to a nearby facility. Facilities that support subsea production are seen mainly as real estate out at sea and, consequently, most developments have focused on the subsea components and riser systems. Floating production storage and offloading (FPSO) vessels and semi-submersibles come under this category.
Innovations in Dry Wellhead Platforms
Perhaps the most expressive innovations in deepwater floating system developments have occurred with dry wellhead platforms. From the advent of the tension leg platform in the early 1980s, design and evolution of dry wellhead concepts have come a long way. New designs are products of a complex mix of factors associated with deep water, such as environmental issues, remoteness of location, capital and operating costs. The current fourth generation of tension leg platforms provides for improved performance at lower cost.
Figure 1: Schematic of a Truss Spar
Classic spars are simple cylindrical structures that support topsides. Since the feasibility of the concept was demonstrated by Deep Oil Technology, Inc. in the 1980s, it took the industry over a decade to accept and build the first prototype. In contrast, newer developments have taken a much shorter time to come to fruition. The truss spar (see Figure 1) is a marked improvement over the classic spar, in terms of minimising steel weight to support equivalent topsides. Research has shown that it is the performance of the heave plates that make the truss spar comparable in performance to the classic system.
Figure 2:Schematic of a Cell Spar
Lately, with more competition in the market and the desire to drive costs down, the ‘cell spar’ (see Figure 2) has seen development. The concept proposed less than two years ago has now been selected for deployment in the 5,300-foot Red Hawk field during the later part of 2004. The cell spar is shown to reduce costs by ease of fabrication and consequently transportation. A cell spar with a tube bundle takes in less material than an equivalent-diameter single column spar. .
Category:
Transportation
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