The industry's greatest achievements in recent years are probably in drilling and subsea technologies. Drilling techniques have been refined to levels that make this technology the instrument required for the industry to achieve its ultimate goal: optimum depletion of the reservoir. Subsea technology has contributed the same, and is giving the industry access to the remaining most prospective petroleum basins of the world, i.e. in deep and ultradeepwater.
But still, the industry has not yet reached a state of perfection in reservoir depletion technology. And it has no alternative but to strive for perfection in this particular area. The reservoir - or the well for that matter - is still both the boss and the customer in the upstream industry. It has to be treated accordingly.
Should we, at any time, not be entirely convinced that the subsea well is what best serves the purpose of reservoir depletion in deepwater, then there are still major challenges ahead for the industry. In fact we know that these challenges exist.
Admittedly, there is nothing wrong with subsea technology. Bringing the state of the art in subsea know-how to its current level is still one of the greatest achievements made by the offshore sector in recent years.
Optimum reservoir depletion means, however, maximum recovery of oil at affordable costs. And the indications are that maximum recovery is not always achievable with subsea-completed wells in very deep water.
There is still a lot of difference between a well completed on land or on a platform, and the well completed subsea in deep water. The difference is basically in the physical and cost problems of accessing that well, whether for the purpose of drilling, completion or workover.
A few of the very big platforms in the North Sea, like the Brent, Ekofisk and Statfjord installations, for instance, are still producing at exceptionally high rates after 20 to 25 years of production. Oil recovery rates are building toward the 50% mark. The smallest pockets of remaining oil can be reached by deviated wells, and they can be tapped economically. All this would not have been possible without the achievements made in drilling technology in recent years, and not without the availability on these installations of permanent, depreciated - fully paid for - drilling facilities.
The problem with subsea is the substantial cost of drilling and completing a subsea well, and later working over that well, using a US $200,000 per day deepwater rig.
The number of rigs capable of operating in 5,000ft (1,524m) or more of water stands at 64 units, including those under construction or being upgraded. Demand for units with such water depth capabilities will reach about 80 by 2004. The effect of such an imbalance between demand and supply is likely to be rig rates soaring beyond $200,000 per day. Add the further expenditure involved in such operations, and you are likely to come up with costs that will not justify the drilling or workover of a well that could very well exceed the economic gains of doing it in the first place.
Not that the time of subsea completed wells is over - far from it. Not only will subsea wells be extensively used, but they will become an integral part of extended wellstream processing on the seabed.
But at the moment the industry seems to be looking to the dry completion unit for a solution to the problem, knowing that the availability of a permanent drilling facility and dry completions are the best means to ensure proper depletion of deepwater fields.
Most importantly, the problem of costs related to accessing the deepwater subsea well with a drill bit or workover tool needs to be addressed. Whatever the solution, this challenge is probably what will end up resulting in the next step on the road toward the perfection of offshore technology.

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