Deepwater wells in the Gulf of Mexico may have been producing since 1979, but the potential in the area is still significant. Today 99% of proved reserves in the Gulf of Mexico are in Neogene-age (1.8 million to 24 million years ago) and younger reservoirs. Recent discoveries include a new type of reservoir from the Paleogene age (24 million to 65 million years ago) with significantly deeper wells.

The Paleogene-era reservoirs are a promising exploration target. However, there is no guarantee that the design approaches and technologies behind current successful production will be appropriate in the new reservoirs, whose production challenges have yet to be fully understood.

Similarly, it cannot be assumed that current technologies will be fully extendable into the 3,281-ft- (1,000-m-) deep Miocene and the ultradeep water and deep-drilled lower Tertiary wells.

Emerging challenges

The Paleogene, Wilcox play stretches from Walker Ridge to Alaminos Canyon. A number of phenomena characterize this play, shaped by the Paleogene period’s onset of convergence between North and South America as well as mass wasting and failure of continental margins, with flexural effects of sediment redistribution during forced regressions and marginal failure.

By mid October, 10 discoveries had been reported in the play. Tests are ongoing to determine its geologic potential and permeability. In envisaging the challenges presented by these ongoing discoveries in the Gulf of Mexico, two emerging technologies stand out as having particular relevance for the future: subsea processing and multiphase pumping.

Subsea processing

Subsea processing began experimental deployment offshore Abu Dhabi more than 30 years ago, but serious interest in the technology has only grown over the last 5 years or so. Why the sudden rise in interest?

Part of the reason is a better appreciation of the benefits subsea processing can deliver. By

Multiphase pump systems aid increased production and recovery in several field developments around the world. (Photo courtesy of Framo Engineering AS)
separating or pressure-boosting well fluids on the sea bed, it is possible to significantly reduce expenditure on the fixed platform or floating vessels; it could conceivably eliminate the need for a platform altogether by enabling significantly extended tieback distances to shelf- or even shore-based process facilities. Subsea separation and re-injection of produced water and gas can increase production and allow flow lines and topside processing equipment to be used more efficiently.

While subsea pumping is quite well established, the risk factors involved in designing, qualifying and incorporating the new technologies involved in subsea separation have delayed its deployment. Additional issues around cost and reliability contributed to the delay. By 2004, there were still only two subsea separation stations installed: the Troll Pilot for water separation and re-injection, operated by Norsk Hydro in the North Sea; and the VASP system for gas-liquid separation and boosting, operated by Petrobras in Brazil.

The Statoil Tordis project illustrates at least one of the challenges facing the use of subsea processing in deep or ultradeep water. This improved oil recovery project will be the first in the world to adopt full-scale subsea separation. The main module for subsea separation — in 656 ft (200 m) of water — weighs about 1,000 tonnes and therefore requires one of the handful of heavy lift vessels for installation. The separator alone weighs in the region of 180 tonnes. Extending this technology to deep water, where equipment needs to be thicker-walled and hence heavier (typically by a factor of about 1.5), will raise serious weight issues affecting installation, reliability and maintenance of a project.

Multiphase pumping

Multiphase pumping is a technology for artificial lift that has grown rapidly in popularity over the last decade. It contributes to improved production at lower costs. By boosting the volumetric flow of produced fluids, the technology allows for lower wellhead pressures and increased production rates while reducing the need for separators, compressors, heaters, separate flow lines and other equipment.

Gas flaring and venting are also reduced or eliminated; this, combined with the small footprint of the equipment, adds environmental benefits to the mix. Moreover, because multiphase pumps can handle very low inlet pressures and pressure-boost the well flow to remote centralized processing units, they can have a significant impact on the viability of marginal fields or the development of two or more fields located close to one another, say, 20 miles to 30 miles (32 km to 48 km) apart in a remote deepwater region — such as in the instance of Chevron’s Jack and St. Malo prospects in the Gulf of Mexico.

Multiphase pumping is one of the more proven technologies for providing the artificial lift solutions required in the deeper waters of the Miocene and lower Tertiary plays. Its potential for ultradeepwater and older reservoirs may be considerable. However, in addition to the technical feasibility of the technology, developers and operators need to be conscious of issues that may arise around contractual liability: some of the companies that supply multiphase pumping equipment may not be in a position to take on the contractual liability for such a vital component in the overall flow path, in which case innovative and collaborative thinking will certainly be required.

Ancillary technologies

It is also important not to lose sight of the ancillary technologies that need to be developed if emerging technologies for deepwater use such as subsea processing and multiphase pumping are to be effectively installed and used. Some of the ancillary technologies needed include deepwater power cables and greater-capacity deep water lifting equipment.

Although power cables for use along the seabed are available, there is not yet a deepwater power cable installed in a dynamic application. Copper cable is only suitable for such applications when it has benefited from significant strengthening from steel or other armoring (such as carbon fiber for ultradeep water); this is because of copper’s low strength and stiffness-to-weight ratio and the exposure to dynamic loading when hanging over the side of a vessel.

There are a number of directions that could be taken with respect to lifting gear. This facet of installation and operation has several dimensions. For example, when specifying components for deep and ultradeep water systems, designers need to take account of the fact that a large part of the crane capacity is consumed by the wire rope.

Vessels available and currently being commissioned for deployment of seabed equipment and light construction work typically offer 100 tonnes heave compensated lifting capacity in depths up to 9,843 ft (3,000 m). For operators to take advantage of these smaller, more available and lower-day-rate vessels, an integrated, installation-aware philosophy needs to be adopted at the earliest stages of field development layout and subsea architecture selection.

Should designers of the ever larger, heavier systems needed in deep water go the route of increasing modularity so that the individual modules can be installed and retrieved using commonly available lifting equipment capacity (although this may increase the complexity, and duration, of installation)? Or should the focus be on progressing the capacity of lift equipment (requiring new technologies that will need to be proved)?

From the operator’s perspective, there will always be a desire for modularity because of the additional robustness it gives the system. But installation issues must be factored in also, as they will play a prominent role in the success or failure of the development. Installing five such modular systems over the next few years will be much less logistically challenging than attempting to install 30 such systems in the same length of time. Unless careful thought is given to this issue now, the requirement to develop new technologies for the lifting equipment as well as the processing equipment could become much more urgent in order to meet project specifications and deadlines.

The Deepwater Installation of Subsea Hardware (DISH) Joint Industry Project — aimed at understanding better the existing technical limitations and developing feasible, globally acceptable solutions for water of 6,562 ft (2,000 m) depth or more — has successfully demonstrated the use of fiber ropes for deepwater lifting of up to 50-tonne loads. The research and development needed to extend the lift capacity at the necessary depths is still ongoing. Economics is likely to be a major driver in any solution reached.

Integrated approach

In addressing these and other emerging technology challenges, DeepSea argues that developers and their partners need to keep the “complete picture” in view at all times to ensure reliability and provide a cost-effective transportation system from wellhead to production facility. For example, in choosing a specific multiphase pump for a given application, a wide range of parameters need to be considered to ensure that the pumps will not only provide the required boost when in place but that they can also be installed and maintained as easily as possible and can be replaced straightforwardly in the event of damage, failure or routine maintenance.

The “complete picture” can be maintained throughout a project by adopting a systems approach to designing, planning and implementing new technologies. This approach applies critical path analysis and processes for evaluating and optimizing options — e.g., whether to use a J-lay, S-lay or reel lay installation approach — at every stage from design and planning, through procurement, to installation and operation, in an integrated way.

It contrasts with traditional approaches in which the relevant disciplines — flow assurance, system design, etc. — are not usually as integrated as they need to be, leading to questions like the title of a recent SPE Forum (17-22 September, Croatia): “Who owns the deepwater riser and who owns its production problems?” at which many of these topics were discussed and explored in detail by some of the industry’s leading experts in risers and flow assurance.

Given that as many problems with technology applications tend to occur at the interfaces between elements of the system as in the elements themselves, this integrated holistic approach will have increasing relevance as the complexity and variety of deepwater exploration and development in the Gulf of Mexico and elsewhere continue to grow.
Understanding and applying an integrated approach is particularly vital during times of high activity, as the industry is experiencing now, for attaining the necessary accuracy in costing from the concept/FEED stage to bid receipt/project sanction for subsea developments, particularly given the range of installation/offshore construction options available in the marketplace over the coming 2 to 3 years.

Comments