MOBILE JACKUP PLATFORMSPAST, PRESENT AND FUTURE

In November 1955, the first electromechanical, three-legged offshore s e l f - e l e v a t i n g drilling platform was launched from what was then R.G. LeTourneau's manufacturing facility on the Mississippi River south of Vicksburg.

Christened Scorpion by its owner, Zapata Offshore Company, this self-elevating offshore drilling platform was designed to operate in 80 feet of water.

That first-generation mobile offshore jackup rig was a giant step in the evolution of the offshore oil and gas industry. Earlier "mobile" offshore drilling platforms were often inland barges and drilling tenders, limited to the marshes and relatively safe shallow c o a s t a l w a t e r s of the Gulf of Mexico and Lake Maracaibo.

Although the triangularleg Scorpion's 80-foot operating depth is far less than the 300- to 350-foot capabilities of today's jackups, from another perspective it was a remarkable technological breakthrough. Scorpion's operating depth was twice that of its predecessors.

The decade f r om the mid-fifties to mid-sixties saw a remarkable spurt of inventiveness in design and manufacturing t e c h n o l o gy for jackup rigs. Like most technological revolutions, the rapid and successful development of the jackup was tied directly to economic conditions. Vast amounts of offshore oil and gas were known to exist. These energy reserves were in demand and return on investment in offshore exploration and production was attractive.

What had been missing was an economical, mobile, sturdy offshore d r i l l i n g p l a t f o r m from which experienced drilling contractors could exploit known offshore reserves. That piece of equipment had to be a true openwater vessel that could be safely towed to a drilling site, position itself securely, get the job done, then move on to the next location.

Once those initial engineering and fabrication challenges were overcome, the trend in jackup design took the direction of expanding water depth, drilling depth and operating environment capabilities.

This trend continues to dominate jackup technology today.

The improvements that have taken place in jackup capability have historically been stimulated by the need to find and produce a d d i t i o n a l offshore energy reserves.

Important desigri changes that increased operating water depths came d u r i n g t h e midsixties.

A unit was developed t h a t could operate in 250 feet of water. This j a c k u p had slanted legs. This change was based on two factors: first, the types of steel then readily available could not withstand the calculated combined loads when the spud legs were in a vertical configuration; second, the slanted legs increased the rig's overturning moment without requiring a larger and heavier hull.

These first slant leg jackups extended operating water depths by 100 feet. Later models of the slant leg self-elevating drilling platform could operate in over 300 feet of water.

By the early seventies, the use of higher strength steels made it possible to build jackups with vertical legs that could operate in water depths up to 350 feet.

Looking at the history of the offshore energy industry from our present perspective, it is accurate to say that the jackup is the success story of that industry.

It provides the offshore drilling contractor with the essential advantage of a stable, fixed area from which to work. Once a jackup is on location, it also provides important time and cost advantages over floating drilling equipment.

Of the several types of deepwater mobile offshore drilling units in use, jackups have proven they can drill more foot of hole per dollar spent.

Statistics bear out the jackup's dominant role in offshore operations.

At the start of 1981, there were 549 mobile offshore drilling rigs of all types. Of that total, 270 were jackups. Of the 204 mobile rigs on order or under construction at the start of the year, 152 were jackups. Jackups make up more than half of the total mobile offshore rig fleet. By the end of the eighties, the total number of jackups may well be 600.

The current state-of-the-art in jackup design and manufacture c o n s i s t s of building versatile units that meet the wide variety of drilling contractor requirements while at the same time satisfying the guidelines of regulatory agencies. Offshore exploration and development drilling now takes place in a number of areas that have a variety of meteorological and other environmental characteristics. There are jackups specifically designed for remote, deeper water areas where weather conditions such as frequency of storms, excessive wind and wave heights must be taken into account. A totally different class of self-elevating platform is specifically designed for accessible areas where weather, water depth or remoteness from supply sources are not major obstacles.

Between these two extremes of offshore operating environments are a number of other situations that call for jackups with different operating capabilities.

In addition to providing units tailored for specific environments, the rig construction industry took a major step toward meeting operator requirements with the introduction of the cantilever drilling jackup. This feature is now found on shallow water, moderate environment units as well as on large, deepwater units that can withstand wave heights up to 88 feet.

The incorporation of cantilever drilling into the jackup design concept added a remarkable degree of versatility. In rough waters, jackups provide a stable base so t h a t the cantilevered drilling package can remain extended and drilling operations continued.

In addition, the cantilever lets the s e l f - e l e v a t i n g offshore drilling platform p e r f o r m p r o d u c t i on drilling and well servicing functions in addition to exploratory drilling. In those areas where there are a number of bottomsupported production platforms, a cantilever jackup can take up position next to such a permanent structure, cantilever its drilling package over the structure without placing any weight on the platform, and carry out whatever drilling and well servicing activities are called for. When working on very large production platforms, it is feasible to move the drilling structure onto the permanent platform and use the mobile platform as a tender. The cantilever jackup has thus become a valuable and economic tool for extending the productive lives of older offshore wells.

In deeper waters, where there are fixed platforms that provide for multiple wells, cantilever jackups can drill exploratory or development wells in rough weather conditions that previously would have shut down drilling operations.

They can do this without exerting dead or static loads normally brought to bear on sea floor units by package drilling units resting entirely on the fixed platform.

This capability is extremely important in exploiting offshore oil and gas fields that previously had been judged as economically marginal. In such fields, the estimated recoverable reserves were not great enough to j u s t i fy large permanent, and costly, bottomsupported platforms from which to drill, complete and service multiple wells.

Such a situation offers a glimpse of what the future may hold for jackup rig application. For example, a North Sea operator plans to cut development costs of the Morecambe Bay offshore gas field by approximately $240 million.

Key elements in this plan are the use of jackup drilling platforms, a derrick package designed for slant drilling and a number of minimal fixed platforms.

These bottom-supported, fixed platforms will be strategically placed so as to permit depletion of as much of the field's reserves as possible. These platforms will be smaller, less expensive and quicker to construct than if conventional drilling techniques were used from large fixed drilling platforms.

The Morecambe Bay development plan calls for the self-elevating drilling platforms to be positioned alongside each of the minimal platforms. The drilling packages with slant drilling capabilities will then be skidded onto or cantilevered over the fixed platforms. Flexible control and drilling fluids lines will extend from the mobile platform to the drilling floor. With the mobile platform serving as tender, the jackup can move from fixed platform to fixed platform drilling and completing development wells to bring the field on stream and generate early cash flow.

Another innovative use of jackup drilling rigs presently under c o n s i d e r a t i o n is a mobile, retrievable early production system.

Such a system would be made up of a sea-floor concrete and steel storage unit, the jackup with a portable drilling template, and sea-floor as well as surface controls. The mobile p l a t f o rm would carry the drilling and production hardware.

Again, worldwide energy supply and demand factors will play a key role in the acceptance of such a system. This kind of retrievable, "reusable" system may well meet offshore requirements for lower total investment in early development of marginal fields. The system could be used to develop fields estimated at less than 500,000 barrels per day of crude production over a productive life of less than 10 years.

More immediately, a definite trend in jackup design is toward increasing not only the operating water depth but also the jackup's capacity to store consumable items such as fuel, cement, pipe, drilling mud, potable and nonpotable water, etc. Three criteria, namely operating water depth, drilling depth, and variable load capacity are directly related to environments in which the new "super" jackups will be operating.

This new generation of super jackups includes a massive unit that can operate under those extremely hostile c o n d i t i o n s of weather, water depth and remoteness which presently constitute the major frontiers of offshore operations. This "hostile environment" jackup can not only operate in these regions but can be safely towed from location to location under sea conditions that previously would have prohibited relocation. Such conditions exist in the North Sea, off the coasts of southern Africa and eastern Asia, both coasts of North and South America, and the Bering Sea. On location wave heights up to 88 feet combined with wind speeds of 100 knots were some of the factors that had to be accounted for in designing such a rig.

An important factor in the development of a jackup with these capabilities has been the effective use of higher strength steels to keep hull weight to a minimum and at the same time provide maximum strength.

The newest member of the jackup family is a unit specifically designed for those offshore areas where conditions are labeled "harsh" rather than "hostile." This unit's strong suit is its greater capacity to store more consumable items necessary for offshore drilling at greater distances from supply bases. This capability is a necessity because in most harsh offshore areas, frequent scheduled re-supply of consumables is impractical and unpredictable.

Speculation about the f u t u r e of any facet of offshore operations is risky. As for f u r t h e r development of the self-elevating offshore drilling platform, there will p r o b a b l y not be any radical changes in the basic jackup design in the near future. However, the proven and tested elements of this design will probably be f u r t h e r refined under the stimulus of worldwide demand for oil and gas. As a result, we may see operating water depths reach beyond the 300-400 foot maximums of the present. Storm rat- New York Office: JOTUN-Baltimore Copper Paint 74 Trinity Place/Suite 402 New York, N.Y 10006 (212)962-6500 Telex 8-7549 ings may increase and new techniques may permit the jackup to go on and off location in greater wave heights than permissible today.

Any of these developments are contingent on a number of economic and geopolitical factors.

One certainty is that the established jackup rig builders have demonstrated the expertise and capacity to build units that will go anywhere drilling contractors search for offshore oil and gas.