Deepwater Technology

Eleven short-length, full-diameter production casing riser samples have been constructed for testing (photo courtesy Lincoln Composites).

• This composite drilling riser will eventually be tested as part of an actual drilling riser (photo courtesy Northrop Grumman).
• Composite choke and kill lines have held 22,500 psi for an hour (photo courtesy Northrop Grumman).

PART I:

This is the first in a two-part series on composite material applications for the offshore oil industry. Part I discusses the government-backed composite materials research and development efforts for risers, drill pipe, and line pipe. Part II will look at ongoing, privately- and publicly-funded, composite coiled tubing R&D efforts.

In the deepwater world, where production platforms must float at the ends of tethers anchored to the ocean floor, weight saved is money earned. And the money earned can be considerable. For example, for every ton removed from the deck of a tension leg platform, an estimated $250,000 is saved for each meter of water depth in which the platform will be moored. In a mere 600 meters of water that translates to $150 million.

No wonder the prospect of replacing steel parts with composite materials is high on the wish list of operators banking their futures on reserves that lie miles beneath the ocean surface. Saving weight with composites is hardly a new concept. Some deck sections of Shell's latest floating production behemoth, Ram/Powell, are of composite material.

But composites have been slow to enter the offshore oil industry. For one reason, weight was less significant when all platforms were fixed to the ocean floor. And steel - strong, familiar, and the material of choice around the oil industry - is generally less costly than composites. Too, while composites have come a long way in recent years, they have rarely been considered for use in situations as demanding as drilling or production operations, where failure can be catastrophic.

Those attitudes are quickly changing, however, as weight becomes the single most important driver of tension leg platform (TLP) design. Still, even as the industry acknowledges the need to reduce its dependence on heavy steel construction, the risk and cost of composite research is prohibitive in an industry forced to work with short term-minded shareholders for whom the future is but a fiscal quarter away.

Research requires millions of dollars spent over years before manufacturers can hope for a marketable product. And even then, there is no guarantee composites can be manufactured and distributed at a cost end-users are willing to pay if the financial benefits are perceived as too indirect or delayed.

The US Commerce Department's National Institute of Standards & Technology (NIST), through their Advanced Technology Program (ATP), has sought to alleviate some of the research and development financial burden by providing matching funds to private industry consortiums whose work in composites shows promise.

To date, ATP money has gone towards sharing the cost of research into such potential composite material components as production and drilling risers, drill pipe, facility piping, and coiled tubing. All these products are near market-ready and all hold the promise of significantly extending the industry's ability to increase the US domestic oil and gas reserve base - the petroleum-related ATP program's ultimate raison d'Itre.

Production riser

The quest for an economic, lightweight composite production riser (CPR) is not a new idea. France's Institut Francais du Petrol (IFP) began such a quest in 1985. They had designed, by the time they concluded their work, a CPR with an internal pressure of greater than 15,000 psi and an ultimate axial tension capability of more than one million pounds. The pipe could also handle an external pressure differential of about 1,430 psi, or a hydrostatic head equal to about 3,000 ft of water. But the project ended as it was readying for a field test, joint interest partners having at that time determined the cost would be too high, compared to standard steel risers. At that time, the offshore industry had yet to see the current recovery and was driven by immediate cost-savings, not long term investment payouts.

An industry collaboration of end-users, service companies, and composite material and manufacturing companies, has been awarded ATP money to build on the IFP work, and to design a composite production riser for use with TLPs in 3,000-5,000-ft waters. "IFP did what I call proof-of-concept," said Doug Johnson, of Lincoln Composites and program co-technical manager, "They built a handful of joints and proved that they could meet the design requirements of the time."

Though testing is preliminary, the project team appears to have succeeded in addressing the issues left outstanding by their predecessors of risk mitigation and cost reduction. They also appear to have met the technical and manufacturing challenges to an affordable CPR through development of a composite tubular design, a composite-to-metal interface design, and a metal connector design.

Constructed of carbon and E-glass fiber, it will be marketable at less than twice the cost of steel, a reasonable tradeoff for the kind of savings and water-depth extension such a tool promises.

The composite tube is of hybrid composite construction with carbon and glass fiber reinforcements in an epoxy matrix. Its lighter weight means lower loads to be supported by the platform because of less riser top tension. And the more compliant CPR could help reduce or even eliminate the need for the top tensioner system - a considerable weight and investment saving.

In actual application, it is expected that concessions will be made to steel's superior ability to handle bending loads and the bottom- and top-most joints will be of traditional steel composition. The arrangement will also keep all composite material below the waterline, safe from fire.

The preliminary composite tube body designs were for a 10 3/4-in. single/dual casing riser, a 9 5/8-in. single casing riser, and a 10 3/4-in. dual casing riser. Since it was the most demanding, the 10 3/4-in. single/dual casing configuration was chosen for prototype testing. The loading imposed on the riser by SIWHP and buckling requirements, both hoop stresses, will directly determine the amount of circumferential carbon fiber required. The current CPR is capable of withstanding external collapse pressures of about 3,600 psi and internal burst pressures of 6,000 psi - the program-mandated working pressures.

A challenge that has long plagued the use of composite tubulars is the inevitable necessity to join orthotropic, filament-wound composites to isotropic, steel connectors. Such mating is particularly problematic when axial and torsional loads must be considered simultaneously. But since only insignificant torsional loads are imposed on production risers, Lincoln engineers chose for the interface configuration a system known as a multiple traplock, in which one-piece end fittings are incorporated into each of the composite tube ends during the filament winding process.

The traplock configuration is, relative to other interface methods, inexpensive, since the fittings are manufactured with standard machine tools and tolerances, and only one piece is needed on either end. Also, none of the dimensional or surface finishes require match-machining or special tooling.

The riser uses a metal, 12 3/4-in., 94.20 lb/ft, Hydril MAC-II steel threaded connector. The total weight of the 62-ft long joint, with couplings, is about 1736 lbs and is handled with standard drill floor makeup equipment. The coupling offers internal and external metal-to-metal seals and a reverse angle intermediate torque shoulder for positive torque stop.

Eleven, 12-ft long, full-diameter prototypes have been produced and several samples have been tested. One sample failed at a tensile load of 824,500 lbs - 10% higher than required. Prototype samples have been subjected to impact at their midpoint and at the composite-to-metal interface through a drop test designed to similate actual rig working conditions. Engineers have concluded that, not unlike standard production risers, damaged riser joints should be set aside for inspection before being run as damage is not always obvious to visual inspection.

Drilling riser

Northrop Grumman is leading a $4.8 million, 3-year ATP program to develop a composite drilling riser and choke and kill lines. ABB Vetco Gray is responsible for providing metallic components and onshore prototype testing. The DeepStar consortium is providing design requirements and program coordination. Drilling contractor Reading & Bates will provide a real world, offshore drilling test by including a composite pup joint in an otherwise steel drilling riser on an actual drilling program. Hexcel Carbon Fibers is supplying carbon fibers and technical consultation and the Offshore Technology Research Center is doing non-destructive testing and materials characterization.

Though prototype testing remains, the objective of building a riser joint compatible with existing, API Class D steel riser and connector designs, and that has a 1.5 million lb axial tension rating, is essentially accomplished. The pipe has a 19.5-in. drift diameter, two wound-in-place steel tailpieces on either end which can be welded to standard riser connections, and has an internal working pressure of 3,000 psi. The choke and kill lines have a 3 1/4-in. ID and a 15,000 psi working pressure, though it has held 22,500 psi for an hour.

Like its steel counterparts, syntactic foam flotation is attached as needed, though it is half what a steel riser would require. In fact, studies indicate that when equipped for work in 6,000-ft waters, a composite riser represents about 40% less on-deck weight than a steel riser and 50% less at 10,000 ft depths. It is expected actual costs will be less than half that of a comparable titanium system.

The riser is fitted with an internal liner that has tested as more wear resistant to drillpipe collars than steel and that also seals the composite material of the riser when under high internal pressures. The first full-diameter prototype is a main tube body only, tested for collapse. The latest prototype has inserts for connectors and is ready for full onshore testing. When those on-land tests are done, it will be added to a steel drilling riser on a Reading & Bates drilling operation.

Northrop Grumman's Bill Andersen, project manager, is reluctant to predict when his riser will be ready for the acid test offshore. Although all earlier successes were predicted by the same software predicting success for the remaining trials, he is a cautious man by nature. "Let's just say the offshore test is forthcoming," he said. "You never know what is going to happen in this business."

Composite drill pipe

In the popular perception of the material, few things seem as unlikely a candidate for composites as does drill pipe. But, composites' high torsional strength, stiffness, and lightweight are particularly applicable to long reach drilling - a fast growing practice in the offshore industry. In fact, in OTC paper 8434, "Composite Drill Pipe For Extended Reach Horizontal Drilling" by Alex Y. Lou and Chris Lundberg, delivered at the 1997 Offshore Technical Conference in Houston in May, the authors estimate that such a drill pipe, where light weight reduces drag and stiffness resists initiation of sinusoidal buckling, could improve reach by 40%, to 35,000 ft.

Besides reaching more oil from a single location, the reduced weight could allow use of smaller drill motors and reduce the hookload and the size of the derrick, motor, and substructure.

Earlier attempts have been made to develop composite drill pipe, attractive for its light torsional loads at the surface. In 1990, the Harwell Laboratory in the UK and Rogalandsforskning in Norway completed a feasibility phase, but the remaining effort was underfunded and abandoned. And in fact, Brunswick has commercially produced three sizes of a flexible composite drill pipe for use in short-radius lateral drilling operations. But it is high-priced and has limited applications.

The prototypes, already field-tested in a drilling well, are of a hybrid composite with carbon fiber for stiffness and E-glass fiber for strength. It uses an interior liner to shield the composite and to provide pressure integrity and an external abrasion resistant coating. They are made in 30-ft sections compatible with current drilling practices and equipment. The manufacturing process has been designed to eventually produce 500,000 ft per year economically. The proprietary, metal tool joint has standard API thread patterns that transition the torque, tension, compression, and pressure loads from the metal component to the composite. The weight of the pipe in 8.7 ppg mud is 3.6 lb/ft.

The 4-year/$2.87 million ATP project has completed the first field test phase at Amoco's Catoosa drill test facility. The drill string used for the test incorporated 500 ft of 6 1/4-in. drill collars, 850 ft of 4 1/2-in. standard drill pipe above three joints of 4 1/2-in. composite drill pipe. To accommodate conditions at Catoosa 4 1/2-in. composite drill pipe was used but the project is to design 5 1/2-in.

Below the composite was 890 ft of 4 1/2-in. standard drill pipe, a near bit sub and an 8 1/2-in. bit. The composite pipe operated in a 10-12 deg/100 ft curve with about 1,000 psi internal pressure and 16,000 to 30,000 lbs weight on the pipe.

After nine hours of drilling in two days at about 80 rpm with a 20,000-30,000-lb hookload, the three joints of composite were retrieved with only non-destructive scratches on the outside coating. Two of the joints were equipped with centralizers and had substantially less damage evident than the one without centralizers.

Marketing of composite drill pipe will at least await the end of the ATP project, and then it will be something of a niche market. "Composite drill pipe cannot match steel cost one for one," said Phillips' Lou. "Our target is two times the cost of steel pipe and initially it will be more. If steel can do the job, that is what (operators) will use. They will only use composite when steel cannot do it."

Nonetheless, progress is encouraging for composite drill pipe, and as wells are drilled in deeper water and longer reaches are necessary to justify project economics, it will probably find its commercial place. Meanwhile, such serious issues as defining torsion and fatigue numbers remain, as does the search for a more refined design and a more compliant external coating.

Facilities piping

For years, Specialty Plastics president, Dick Lea, often felt like something of a second-class citizen when he arrived at operators' offices to talk composites. He seemed to wait longer in their outer offices than purveyors of the traditional steel products the oil industry has long been built on.

"The rap against composite pipe for years was the unreliability of their connections," Lea said. "And with fixed platforms, weight was not a big deal." With floating platforms, weight is more than a big deal - it is the main deal. And Lea and his company are fast becoming first-class citizens.

Connecting composite ends to each other and to alloys and steels while maintaining a 300-psi internal pressure rating was the mandate of Baton Rouge, Louisiana-based Specialty Plastics when they accepted a $1.8 million, three-year grant from ATP. The state of Louisiana and NASA are also involved in the project, as are 11 oil companies, interested in the huge savings to be realized by replacing miles of deck level, low-pressure steel line pipe with lightweight composites.

The decks and subdecks of TLPs are awash in such piping for saltwater cooling applications, drains, fire water transportation, and fire deluge piping. It represents an immense amount of weight-saving potential. For example, a six-inch, schedule-40 steel line pipe, the most commonly used such pipe grade, weighs about 20 lb/ft. A comparable composite pipe weighs about 4 lb/ft. The weight savings are obvious, but without a reliable connection, the risk is unacceptable.

About half-way through its program, Specialty Plastics has produced a Fiberbond heat-coupling, a pre-preg (fiberglass with resin coating ready for hardening) material that is wrapped over the ends of abutted pipes and heat cured in place. Since it works with equal reliability on composite-to-composite pipe ends or on composite-to-metal joining, the heat-activated coupling opens the possibilities of lighter weight piping not only to newbuilds, but also as a means to replace as much of the existing steel piping as desired. The connecting wrap is ready for two-in. to six-in. pipe and the company expects to go to 24 in. pipe.

Supplies and Congress

If the oil industry is to venture much farther past the world's continental shelves, as it seems bent on doing, lightweight, composite substitutes for steel components may offer a key means to do so. The industry has demonstrated an eagerness to use them and manufacturers, with prudently-administered government assistance, have demonstrated their ability to respond. But threats exist that must be overcome before the technology is brought to market.

"Something everyone knows is that carbon supplies are tight until early 1998" Doug Johnson said. "When this industry takes off, when the product goes to market, the demands are going to be increased. Fiber suppliers may have to put additional facilities on line. Many carbon fiber suppliers have already announced significant expansion plans for 1998 and 1999. We are pleased by their commitments of capitol, but we want the industry to carefully compare total carbon fiber demand vs. capacity projections for 2000 to 2005." Johnson said his company experienced supply deficiencies even while simply trying to build demonstration hardware.

But market-based obstacles are surmountable and the profit motive for all involved should be large enough to move fiber makers to make the capital investments they must. As a consequence, composite components will almost certainly play an important role in the deepwater offshore industry in the very near future.

How quickly that role is assumed and its origin may be as much a political question as a technical one. Currently the breakthroughs are being made in the US, due in large part to the government's cost-sharing ATP program. But the program is subjected to attack each year as it goes before the US Congress for funding.

The chairman of the congressional oversight committee that controls its funding, Rep. Harold Rogers (R-Ky.) was quoted in the April 28, 1997 issue of C&EN magazine as saying it was his intention to "zero out this program." Detractors have said such work could be done as well by the private sector.

But the oil industry has long ago sworn off basic research. Almost certainly, without government funding, such high-risk, long-range research and development programs would go the way of the 1990 IFP CPR program, because few private companies can afford them on their own.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.