Patents protect deepwater platform concepts

Sandeep Khurana
Paragon Engineering Services Inc.
Houston

Numerous deepwater platform concepts have patents that provide an inventor protection for his new ideas.

But an inventor should not be discouraged by the fact that many patents exist. In fact, it may be advantageous to build on existing patents and prior art, and patent new ideas and concepts for reducing costs.

Challenges still remain such as for optimizing drilling and production operations simultaneously on deepwater platforms.

Deepwater development

One major component in developing deepwater fields is the work platform for accessing and producing oil and gas reserves. Some work platforms handle only producing operations while others have both producing and drilling capabilities.

A floating production tanker may be the ideal choice for a large deepwater production facility with subsea wells but without drilling capabilities. But integrating drilling with a production facility on a deepwater work platform requires new concepts.

Deepwater work platforms with both producing and drilling capabilities eliminate the need for mobile deepwater drilling rigs, which are limited in number and expensive to contract. Also, well maintenance costs will be less if the work platform accommodates dry wellhead trees instead of subsea wet trees.

Patented deepwater platforms

The market today includes deepwater platform concepts that allow drilling and production from the same platform. The two most common deepwater concepts are compliant towers and tension-leg platforms (Fig. 1 [50,439 bytes]). These concepts have been researched for decades and are being installed in deepwater fields.

Compliant towers have their niche in 1,500-2,000 ft water depths, while the tension-leg platforms (TLPs) have been developed for water depths of up to 4,000 ft. Both concepts have high capital costs, and therefore, need relatively large recoverable oil and gas reserves to make them economic.

A new generation of deepwater platform concepts is now being proposed for the Gulf of Mexico that will challenge these two concepts. These concepts can improve deepwater development economics.

These concepts, which are patented by the companies marketing them, include spars, mini-TLPs, and buoyant towers (Fig. 2 [58,295 bytes]).

The term "patented concept" generates a number of questions. One commonly asked questions is, "How can technology like spars and TLPs be patented, if it existed in the 1960s?" But technology is not static. As deepwater fields are being developed, inventors use the experience to invent newer aspects or variations of the same concept that can be patented.

The challenge is to reduce deepwater field development costs.

Concept basis

To comprehend the patented aspects of spars, mini-TLPs, and buoyant towers, it is important to understand the concepts in relation to production and drilling operations.

The motion characteristics and the available buoyancy define the extent of drilling and production activities possible from these platforms. Note, the strength or structural design of these concepts is based on survival or storm wave conditions that have an occurrence of once in 100 years.

No drilling or production activities occur during the storm conditions. However, the motions for day to day normal operating conditions govern the drilling and production operations.

A free-floating body has six degrees of freedom of motion. These include three displacements (linear movements) and three rotations (angular movements).

The displacements are sway, surge, and heave. The corresponding rotations are pitch, roll, and yaw (Fig. 3 [33,522 bytes]).

The production facility design is limited by the motion characteristics of the vessel.¹

FPS tankers

For floating production system (FPS) tankers, the mooring arrangement restrains only surge, sway, and yaw. This leaves the FPS with pitch, roll, and some heave. The excessive motion in pitch, roll, and heave under Gulf of Mexico normal sea conditions makes drilling from an FPS impossible.

The maximum FPS topside facility weight is a function of available buoyancy for supporting the weight.

Spar

A spar (Fig. 2a) is a deep-draft cylindrical hull (steel caisson). The deep draft reduces heave and pitch/roll. The mooring arrangement restrains surge, sway, and yaw motions. Therefore, spars can be designed to accommodate drilling.

For drilling operations, the idea is to have an acceptable "watch circle," which defines the maximum limits of the lateral movements, so that drilling can be done under normal day-to-day operations.

The production facility must be designed for the platform motion characteristics. In the case of a deep-draft hull, it can provide enough buoyancy to support the topside weight of both drilling and production equipment.

Mini-TLPs

The mini-TLPs (Fig. 2b) or conventional TLPs (Fig. 1b) are constrained for heave by tension tethers. The tension tethers are placed at the corners to assist in resisting platform pitch and roll.

The tension tethers also act as the mooring system that restrains platform surge, sway, and yaw. Therefore, drilling can be done from the platform.

Again, the production facility has to be designed for the motion characteristics.

The mini-TLPs are not only the "scaled down" version of the conventional TLPs, but also have the hull portion optimized to reduce wave loads.

The main issue for the mini-TLPs is the limited buoyancy available to support the topside weight. Therefore, it cannot accommodate a large drilling rig and production facility.

Buoyant towers

Buoyant towers (Fig. 2c) are a hybrid between TLPs and the spars. These concepts have a cylindrical hull with the keel depth in between the shallow-draft TLPs and deep-draft spars.

The hull is restrained for heave (vertical movement) like TLPs. The tension members that restrain heave also assist in reducing pitch and roll.

Tension members also serve as the mooring system that restrains platform surge, sway, and yaw. The motion characteristics are somewhere between TLPs and spars.

Buoyant towers can be designed to accommodate drilling. Similarly, the production facility must be designed for the motion characteristics.

Patented aspects

For a long time, spar-shaped buoys have been installed as navigation aids. Various modifications from the basic concept have allowed the spar to hold progressively heavier equipment or be used for liquid storage.

For example, the U.S. Navy used spars in the 1960s and the Shell Brent spar was installed in 1976. However, spars for deepwater oil and gas drilling, production, and storage warranted several modifications to the concept.

Spars Inc. markets a spar concept patented in 1987 with the following combined elements:²

• Deeper spar hull draft with ballast that reduces heave and allows storage
• New drilling riser concept that decouples hull motions from riser motions
• New hull mooring system.

In September 1996, this spar concept was installed in 1,930 ft of water in the Oryx Energy Co.-operated Neptune field in the Gulf of Mexico, Viosca Knoll Block 826.

Later in 1998, the Genesis spar will be installed in Green Canyon Block 205, in 2,590 ft of water. Chevron USA Production Co. is the operator.

Spars Inc., in 1997, patented a modification to its original concept.³ This modification reduces the spar hull length by including a space frame attached below the hull. This concept will be used for developing the Amoco Production Co.-operated King Project in Mississippi Canyon Block 84. Water depth is 5,400 ft.

Meanwhile, Exxon Corp. is planning to use a deep-draft caisson vessel (DDCV). The DDCV includes several modifications to the spar concept. These modifications were developed by Exxon's in-house research.

Exxon will install the DDCV in 4,700 ft of water to produce its Hoover discovery in Alaminos Canyon Block 25. Its Diana field in East Breaks Block 945, completed with subsea wells, will be tied back to the DDCV.

A mini-TLP has a smaller hull, but its tensioned tethers and basic concepts are similar to a conventional TLP. However, the mini-TLP's surface piercing central flotation column with attached buoyancy, and its tensioned tethers, have a series of patents.⁴ Atlantia Inc. markets this concept.

This concept will be used by British-Borneo Petroleum Syndicate plc to produce the Morpeth field in Ewing Bank Block 921. The Block is in 1,710 ft of water.

Modec Inc. markets another version of mini-TLP. This concept has an optimized hull configuration that has a series of patents.⁵

As discussed previously, the mini-TLPs have a limited topside weight capacity; therefore, the mini-TLP can only carry lightweight modular drilling/workover rigs.

Optimization of the drilling and the production facilities is the key to making mini-TLPs economical.

Several buoyant-tower concepts have patents. One such concept is a tension buoyant tower (TBT) that has been examined in numerous joint-industry studies. The TBT, patented in 1988,⁶ has not yet been installed on any deepwater projects.

The TBT patent proposes a deep-draft hull restrained by multiple tendons. The tensioned risers serve as structural members.

Another similar concept is the buoyant-leg structure (BLS) that was first patented in 1992 and with several modifications patented again in 1997.⁷ One version of the BLS uses a deep-draft hull restrained for heave by a single tubular leg with flexural rigidity.

The first phase of the joint-industry study on this concept was completed in 1997. A second phase is scheduled to start in 1998.

Another version of the BLS is a drilling unit with a retractable gravity base. It has a patent-pending status.⁸

Patents

The discussion of various patented deepwater concepts leads to the question of "What is patentable?"

Two of the most important requirements for patents are that the concept has novelty, and it is not obvious. Both requirements must be satisfied to obtain a patent.⁹

A patent should pass the "novelty test" so that it has an aspect that is different from all previous inventions and knowledge (that is, the relevant prior art).

The prior art includes all the existing patents even if they have expired, and all the relevant published research papers.

After passing the "novelty test," the invention needs to pass the "non-obvious" test. The invention must not be obvious to one with ordinary skills in the field. This is the area that many new concepts fail to address, and therefore, the concept is not patentable.

For example, a conventional TLP with three instead of four legs can be a new concept but it can be considered an obvious extension of the conventional TLP, and therefore, may not be patentable.

Patent law

The word "patented" and its implication can be understood from basic knowledge of patent law.

A patent is a disclosure of the invention by an inventor in return for legal protection. The disclosure is made public through the publication of the patent.

The published patent must satisfy the statuary requirement that it includes "...a written description of the invention, and of the manner of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same."¹⁰

In addition to this so-called "enabling" requirement, the published patent should also have the "best mode" contemplated way for carrying out the invention.

In short, patents are easy to comprehend, and reading patents is one of the best ways to keep abreast of the latest technology.

A key part of the patent is its claims, always found at the end of the patent document. The claims define the legal extent of the patent and determine who would infringe on the patent and who would not.

The claims must define an invention that is novel and one that is not obvious to persons with ordinary skill in the relevant art.

The claims in the patents encompass the patented aspects, as discussed previously, for the various for deepwater platform concepts.

The legal protection the inventor gains is exclusive rights on the patented invention for a limited time. A U.S. patent is a legal right that permits the patent owner to prevent someone from making, using, selling, or offering to sell the patented invention in the U.S.

A patent is an offensive tool, and assists an inventor to stop infringement or obtain damages because of the infringement. On the other hand, one must be aware that patenting does not automatically give the patent owner a right to use his own invention. It is critical to understand that a patent may actually infringe upon a previously issued patent.

This could be merely because the inventor and the patent examiner were unaware of the existence of the prior art.

In short, if the patent is granted and someone can prove later on that the idea existed in a prior art or was obvious from the prior art, the patent cannot be enforceable and can be revoked.

U.S. patents give exclusive rights to the invention only in the U.S. If the invention is important enough to create exclusive rights in a foreign country, one can obtain a patent in that country. Otherwise, anyone in the foreign country could make, use, and sell the invention with impunity.

However, they cannot bring it into the U.S., otherwise it would infringe on the U.S. patent.

Patent advantages

This leads us to the question of "Why patent?"

The most basic reason is to protect ones invention. Another possible reason is to have a portfolio of patents that can be used for cross-licensing arrangements between companies.

A secondary aim is to prevent another business in your industry from patenting a concept and blocking your company from using the concept in the future.

For a patent application filed after June 8, 1995, the term of the patent is 20 years from the filing date. One needs to determine if it is better to seek a patent on a particular technology or to keep the idea as a trade secret. The decision must be made on whether the disclosure of that technology in return for the limited life of patent protection would outweigh the possible advantages of keeping the technology a trade secret for a longer time.

However, if one decides not to patent the technology and someone else develops the same concept either independently or by copying your design, one cannot prevent anyone from using it without a patent.

Acknowledgment

This article is based on deepwater development studies performed by Paragon Engineering Services Inc.

References

1. Muller, Wayne, "How FPSO motion affect separator performance and controls," Paragon Engineering Services quarterly newsletter, April 1997.
2. Horton, Ed, Deep Water Offshore Apparatus, U.S. Patent 5,558,467, Sept. 24, 1996
3. Horton, Ed, Drilling, production and oil storage caisson for deep water, U.S. Patent 4,702,321, Oct. 27, 1987.
4. Blandford, Joeseph W., Method and apparatus for production of subsea hydrocarbon formations, U.S. Patents 5,117,914, 5,297,632, 5,381,865, 5,433,273, and 5,549,164.
5. Wybro, Pieter G., Tension Leg Platform and method of installation thereof, U.S. Patents 5,421,676, and 5,551,802.
6. Horton, Ed, Multiple Tendon Compliant Tower Construction, U.S. Patent 4,740,109, Apr. 26, 1988.
7. Copple, Robert W., Deep water platform with buoyant flexible piles, U.S. Patent 5,683,206, Nov. 4, 1997.
8. Copple, Robert W., and Cuneyt C. Capanoglu, A new generation of mobile drilling unit (MODU-BLS with retractable base), U.S. Patent Pending, Sept. 30 1997.
9. Pressman, David, Patent it Yourself, 6th Edition.
10. Title 35 of the U.S. Code, Section 102.

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