Need organized capability for deepwater pipeline repair

Harvey Mohr H. O. Mohr Research & Engineering Gulf of Mexico Leasing The offshore petroleum industry is expanding globally at an unprecedented rate. It is significant that the industry is discovering and developing production in deepwater, 1,000 ft plus, at a record pace. All indications are that the trend to expanding into deeper waters can be projected five and possibly 10 years into the future. This comment is based on two current observations. Lease sales in the Gulf of Mexico during the

Increasing depths pose problems for emergency response

Harvey Mohr
H. O. Mohr Research & Engineering

The offshore petroleum industry is expanding globally at an unprecedented rate. It is significant that the industry is discovering and developing production in deepwater, 1,000 ft plus, at a record pace. All indications are that the trend to expanding into deeper waters can be projected five and possibly 10 years into the future. This comment is based on two current observations.
  • Lease sales in the Gulf of Mexico during the past five years unquestionably reflect this trend and prediction.
  • The trend to deepwater activity is also global. For example, there are 75 deepwater developments under study worldwide. This excludes recently completed projects and projects in progress (excludes predictions). These are deepwater projects under study, indicating that the deepwater activity is global. Many of these projects will include deepwater pipelines.

A distribution of the 75 projects under study is as follows:

  • There have been about 110 deepwater pipelines completed worldwide. Of these, about 60 are in the Gulf of Mexico (GOM). There are about 12 deepwater pipelines under construction or in the advanced planning phase in the GOM, depending on project completions, cancellations, etc.
  • Shell is very active regarding deepwater pipelines in the GOM. Shell has about 20 pipelines completed or under construction in sizes up to 24 inches in diameter. One of the more noteworthy projects is the Mensa 12-in. pipeline in 5,300 ft of water, scheduled for completion early 1997.
  • The technology for laying of the deepwater pipelines, while complex, is reasonably well understood. Different methods have been used - conventional lay barge systems with multiple horizontal weld stations and also vertical J-lay methods. As with any deepwater projects that are on the fringes of technology, there have been some problems with deepwater pipelaying.
  • Hazardous operations (HAZOP) analyses, based on experience, were instrumental in having equipment on stand-by as preparation for problems during the pipelaying operation. This included, as an example, lifting and/or dewatering heads which could be placed over a pipeline end on the seafloor and activated by an ROV.

Unplanned events

Unfortunately, the industry has not responded to possible deepwater, unplanned, emergency pipeline repair after the pipeline is commissioned. An effective response would be for a group of operators to place some essential equipment such as ROV operated repair clamps, mechanical connectors, and ROV operated pipeline cutting and preparation equipment on standby.

Such a project could be fashioned after the RUPE (Response to Underwater Pipeline Emergencies) which was organized in 1977 by H.O. Mohr Research & Engineering on behalf of virtually all the major gas transmission companies operating in the Gulf of Mexico.

RUPE stores and manages in Houston two repair clamps and four mechanical connectors (for two spool piece repairs) for virtually all pipe sizes from 6-in. through 36-in. for the 22 participating companies, which includes six international companies. The diver-assist inventory is valued at $5.4 million.

The industry has had numerous attempts at studying and organizing deepwater pipeline standby repair capability (see accompanying table). Although the SNAM, Sonsub, and the Statoil Norsk Hydro projects (accompanying table) resulted in some support equipment, the equipment is generally available for their own use.

The Sonsub project may be an exception, since they can supply some ROV supported pipeline preparation equipment to anyone. The majority of their equipment is in Norway. HydroTech Systems (accompanying table) has built and tested diverless repair clamps in sizes 12-in., 14-in., and 16-in. for a major operator, and these are on standby. Additionally, the ROV-operated equipment for pipe coating removal has been located and identified, but not on continuous stand-by. There is only one deepwater contingency standby repair capability using repair clamps in existence and owned by a major operator.

A 16-in. diverless repair clamp manufactured by HydroTech Systems incorporates the identical seal system as used on HydroTech's existing product line of clamps. The clamps are designed to open, close, and activate seals by hydraulic power supplied by an ROV. Preparation of the pipe, such as concrete and corrosion coating removal, is done by ROVs which can be supplied by several contributors.

The repair clamps are intended to repair an isolated leak. However, if there is damage that necessitates replacement of some pipe (spool piece installation on bottom), there are currently no complete systems available from any single source. Therefore, the current approach is to make broad base analysis of the basic tasks required and "fill in the blanks" from various suppliers.

Fulfilling tasks

The tasks are based on the concept of a spool piece replacement using mechanical connectors to attach onto the pipeline end. Then, remotely operated collet connectors are used on the spool piece. A table of basic tasks required for making such a spool piece repair installation accompanies this article. There is a growing consensus that various ROV contractors could collectively perform virtually all the tasks listed in the table with a minimum amount of special support equipment having to be constructed.

Mechanical repair clamps and mechanical connector systems are very key components in diverless repair systems. One repair system is being evaluated. All of the components have been used by HydroTech to make diverless connections and repairs.

For example, the inverted U-shaped spool jumper with the collet connector has been used many times to connect flowlines and pipelines in exactly the same manner. Connections were made to 2,200 ft. depths, and another system has been tested and ready for installation to 5,300 ft. The measurements required to fabricate a spool piece on site can be made very accurately by Oceaneering's pre-measurement tool system. Additionally, the hydraulically activated mechanical connectors that can be activated by an ROV are currently available.

As an example, during September, 1996, HydroTech made a repair of a flexible pipe/steel pipe flowline in 1,250 ft depths using its own products and systems. The steel line was cut near the flexible end fitting. The steel line end was retrieved to the surface and a pipeline termination skid (PTS) was installed with an upward looking male hub connection structure. The pipeline and PTS were lowered back to the seafloor.

The flexible pipe was picked up to the surface where the damaged section was removed and the pipe was re-terminated with a new end fitting. A vertical collet connector was attached to the end fitting. The flexible pipe and collet connector were then lowered to the seafloor and stabbed over the connection structure. The diverless collet connector was then actuated by an ROV, completing the connection.

Standby now

The timing and need for organizing a diverless stand-by repair capability is now. A co-ownership program should be considered as a means to reduce the costs of having a standby repair capability, while simultaneously maintaining the ability to accommodate the greatest number of repair scenarios.

The industry appears to have the technological resources in existence without the costly development work associated with earlier attempts to have diverless repair systems. As discussed earlier, there are about 110 deepwater pipelines worldwide with many more planned. This will continue to grow.

For example, there were 36 companies or joint companies that successfully obtained leases in 1,000 ft depths or greater at the September 1996 lease sale in the Gulf of Mexico. When combining the two lease sales in the GOM during 1996, there were over 4.5 million acres leased at these depths, in one year.

AUTHOR

Harvey O. Mohr is president of H.O. Mohr Research & Engineering, a Houston-based mechanical design and research engineering company. The company was recently acquired by HydroTech Systems. Mohr holds a BS in mechanical engineering from Texas A&M. He is a registered professional engineer in Texas and Louisiana.

Area No. of projects Maximum depth (ft)    US Gulf                              40                         7,625    West Africa                      14                         3,000    Brazil                        9                         3,600    Asia/China                      6                          2,700    West. Europe                       6                         4,000    Source: Offshore Data Services
BASIC TASKS FOR MAKING A SPOOL PIECE INSTALLATION

  1. Locate damage.
  2. Abate pollution, if applicable.
  3. Prepare work site.
  4. Rough cut pipe from damaged section.
  5. Remove damaged pipe.
  6. Position/stabilize pipe ends.
  7. Remove concrete and corrosion coating.
  8. Smooth cut pipe ends, if required.
  9. Measurement of spatial relationship between pipe ends.
  10. Fabricate spool piece (to include ends to mate with connectors).
  11. Install mechanical connectors on pipeline ends (test seal integrity).
  12. Lower, position, and connect the spool piece to the mechanical connectors on the pipeline ends.
  13. Pressure test pipeline.
  14. Stabilize the pipeline repair area.

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