Subsea Well Intervention

Riserless light well intervention increases subsea well recovery

A multi-well campaign for Statoil offshore Norway has proven the ability of this technology to provide a cost-effective solution for improving subsea well recovery.

Jan Atle Andresen, FMC Kongsberg Subsea, Kongsberg, Norway

Operating companies are continually looking for ways to make production from subsea installations more cost-effective. To help these firms achieve this goal, FMC Kongsberg Subsea, a business unit of FMC Technologies, has recently developed Riserless Light Well Intervention (RLWI) technology as a solution.

RISERLESS LIGHT WELL INTERVENTION

Offshore oil and gas production continues to grow, and subsea wells are becoming increasingly important. Today, there are roughly 2,000 subsea wells worldwide, in water depths to 2,000 m (6,562 ft). About 400 of these subsea wells are located on the Norwegian Continental Shelf (NCS), and they account for almost half of the oil and gas produced in this region. Installation and maintenance of the world's subsea wells are traditionally performed by costly, moored, semi-submersible drilling rigs.

As maintenance of subsea wells improves recovery rates, reducing the cost of that maintenance is the principal driving force behind the development of RLWI technology. Well maintenance using RLWI technology can be performed more efficiently, and at lower cost, using dynamically positioned (DP) vessels instead of large, anchored drilling rigs. Using a DP vessel allows well intervention without rigid riser connections between vessel and seabed, and it avoids the need to moor the vessel.

INTERVENTION SERVICES

The RLWI system enables oilfield operators to perform wireline and chemical treatment services in their subsea wells. Wireline services available are many, but the services used for subsea wells are typically product-enhancing services:

• Production logging to identify reservoir characteristics and contributions from different, perforated zones
• Installation of plugs and packers to isolate zones in wells
• Perforation of new zones in wells.

Scale squeeze is a typical chemical treatment service that can be performed using the RLWI system. By being able to carry out these types of services at an economical rate, the oil companies can better plan for heavier, workover-type jobs.

SIGNIFICANT IMPACT

According to Norway's Petroleum Safety Authority (PSA), the use of light well intervention in subsea wells on the NCS may provide substantial safety gains and contribute to reducing operating costs, extending field lifetimes and increasing recovery volumes. In terms of safety, well interventions are challenging operations, and they require special expertise and control in all phases of preparation and implementation. The use of light well intervention could provide substantial safety gains, among other benefits, because it avoids hydrocarbon transportation to installations on the sea surface.

RLWI technology increases the potential to recover one billion additional barrels of oil offshore Norway. Statistics from the Norwegian Petroleum Directorate (NPD) state that conventional subsea wells extract 8% less oil than regular sea wells. The intention of the RLWI technology is to close this gap, equivalent to a $30-billion increase in Norway's oil recovery over a 10-year period.

Fig. 1. The RLWI system is operated from a DP vessel.

Increased oil recovery and revenue through use of RLWI technology is not limited to Norway; it can be experienced worldwide. Opinions differ on how high the global recovery rate might rise through increased use of light well intervention in subsea wells. However, tests and experience from other countries' shelves, as well as the industry's own forecasts, indicate that the potential is substantial, according to the PSA.

RLWI technology provides increased access to subsea wells at one-third of the cost of a typical intervention, allowing oil companies to better monitor reservoirs worldwide and gather more information. They can also perform interventions at a much lower cost, enabling oil and gas recovery from smaller marginal fields and facilitating more lucrative tail-end production. RLWI technology also impacts vessel owners and downhole service providers, because they are contributors to the complete system.

THE RLWI SYSTEM

The RLWI system consists of several modules that can be independently installed and retrieved from the seabed, as described in the following paragraphs, Fig. 2.

Fig. 2. Several modules comprise the RLWI system.

Pressure Control Head (PCH). As part of the subsea lubricator system rig-up, the PCH is connected on top of the lubricator, Fig. 3. It functions as a pressure barrier and seal toward the wellbore during wireline operations, allowing intervention access to wells under pressure.

Fig. 3. Technical service personnel perform a final inspection of the Pressure Control Head before installation on a well in Statfjord field.

Upper Lubricator Package (ULP). The ULP assembly serves as the connection between the PCH and the Lubricator. It provides a barrier element during intervention of the well. The shear valve block has the capacity to cut all standard, braided wires.

Lubricator tubular (LUB). The Lubricator Joints provide a temporary storage position for the tool string on the way down into the well, or on the way out.

Umbilical system. The main umbilical (Fig. 4) connects to the Lower Lubricator Package (LLP) with a remotely operated multi-bore connector for the emergency quick-disconnect function. It is lowered to the seabed, along with the LLP/LIP (Lower Intervention Package) assembly, Fig. 5.

Fig. 4. Technical service personnel prepare the umbilical for operation.

Fig. 5. The lower stack is ready to be run through the moonpool.

LLP. The LLP connects the LIP and LUB assemblies in the RLWI stack-up. It acts as the running tool for the LIP and hosts the connection for the control umbilical, well kill hose and control module.

LIP. This assembly provides a well safety barrier during intervention. It is designed to interface both conventional and horizontal subsea trees. Included in the LIP is a shear valve that can cut wireline tools and coiled tubing.

NEW AND INNOVATIVE

FMC Kongsberg Subsea's development of the RLWI technology includes a lubricator system with several patented systems and solutions. The system is deployed through a moonpool from a DP vessel and installed on the subsea production system without the use of anchors or risers, Fig. 6. The system is designed for 7-in., 10,000-psi completion wells and has a combined, direct/ electro-hydraulic control system. Its design premise was flexibility. The RLWI system can perform intervention on both horizontal and conventional subsea trees, as well as interfacing with different subsea suppliers.

Fig. 6. In the handling tower, the Pressure Control Head is ready for deployment through the moonpool.

A method for hydrate prevention and subsea flushing of hydrocarbons back into the well, without return to the surface, is a unique feature of this system. Well intervention is conducted by using traditional wireline technology, with the exception of well barriers that are maintained subsea, Fig. 7.

Fig. 7. Wireline unit with spare cable drums.

PROVEN RESULTS

Using the RLWI technology, a well intervention campaign for Statoil commenced on the NCS during October 2003. Interventions were performed on three different types of wells:

• Statfjord satellite, oil-producing, 5x2 5K subsea system supplied by FMC Technologies
• Visund field, oil-producing, 5K horizontal subsea system supplied by Kvaerner
• Asgard field, high-pressure gas producer, 10K horizontal subsea system supplied by FMC Technologies.

The qualification program was successfully completed during November 2003. Operations were conducted in weather conditions varying from 65 knots and 15-m waves to a calm sea. Wireline operations performed through the RLWI system proved to meet the same level of safety compared with topside systems.

As confirmed by Statoil's RESU manager for the Statfjord satellite, Knut Kviljo, the operator has completed the campaign for qualification of light well intervention on subsea fields. Activities were performed on three wells in the Statfjord Nord, Visund and Asgard fields using the Prosafe-operated MSV Regalia and the RLWI technology developed by FMC Kongsberg Subsea.

“The results are very positive and confirm that the use of this technology leads to a substantial reduction in intervention cost for subsea wells,” said Kviljo. “Lower subsea well intervention cost will facilitate increased data collection in subsea wells, which is important for understanding the reservoirs better, and increasing oil recovery.”

HEALTH, SAFETY AND ENVIRONMENT

An HSE focus was maintained during development of the RLWI system. All components were designed, manufactured and tested under the policies, quality programs and supporting procedures within the certified ISO 9001 Quality System.

HSE excellence was proven throughout development, testing and commercialization of RLWI, with high reporting frequency and no lost-time accidents.

FUTURE DIRECTIONS

By performing wireline services in the wellbore, the lifetimes of the well and field are extended, and more oil and gas is recovered. The RLWI service will help to increase the oil recovery from subsea wells in general, closing the oil recovery gap compared to topside-produced wells. This will make subsea installations even more desirable as field development solutions.

The rapidly growing number of wells located in depths greater than 2,000 m are one of the driving requirements for effective well intervention solutions. In these depths, traditional intervention methods for wireline operations, using drilling rigs, are not an economical solution.

Based on the experience gained throughout the development and qualification of the RLWI system, engineers have identified new ideas and solutions to further improve the services and equipment in use. They will allow for more effective, less expensive and safer deepwater intervention service, enabling increased recovery from deepwater wells.

Today, many of the platforms and rigs resident at subsea fields are not able to meet the requirements of drilling and completion while performing required wireline interventions. Engineers are investigating the possibility of enabling existing platforms and rigs to perform parallel operations by using the RLWI system, in parallel with marine riser operations on subsea installations.

This will increase the efficiency of the platforms and rigs, and lower the cost of the intervention service. In addition, the RLWI system offers a great deal of flexibility, and the parts of the RLWI system can be used as a basis for an EDP/LRP package for 7-in., 10,000-psi systems.

A future system improvement includes the development of composite cable that will reduce system complexity at the seabed. The composite cable will simplify the sealing of the well pressure. It will also enable well intervention to be performed into longer horizontal well paths than current wireline equipment can achieve.

AWARDS

Twice this year, the industry recognized RLWI as an innovative technology. Last May, it earned the “Spotlight on New Technology” award from the Offshore Technology Conference in Houston. In August, the Offshore Northern Seas conference gave the title of “ONS Innovator” to this technology. 

THE AUTHOR
	Jan Atle Andresen is marketing and business development manager for FMC Kongsberg Subsea, and has worked for FMC Technologies since 2001. He received his technical education while serving in the Royal Norwegian Navy. Mr. Andresen has worked in the oil industry since 1986 and has 10 years of offshore experience. He also has served in technical leadership roles for Halliburton, Baker Hughes Inteq and Gyrodata. Mr. Andresen serves on the board of directors for the Bergen, Norway, chapter of SPE.