SAKHALIN RMR-Conclusion: Riserless mud-recovery system used in Sakhalin wells

In 2006, Russia’s CJSC Elvary Neftegaz, a joint venture between OAO Rosneft and BP Exploration Operating Co. Ltd., drilled the top hole sections of two wells off Sakhalin Island using a riserless mud-recovery system from a semisubmersible rig.

Part 1 of this series, published Apr. 23, describes how the RMR system was designed and organized. This concluding part reviews the permitting process, operations, and lessons learned during the 2006 drilling season and presents future plans.

Rig systems integration

Although the system does not have a large deck footprint, it was essential to identify a suitable location to avoid conflict with other deck-space intensive applications such as skip and ship of drilled cuttings. The RMR service provider, AGR Subsea AS, visited the Transocean Legend semisubmersible drilling rig in South Korea in July 2005 during mobilization. The visit identified the optimum location starboard aft, close to the shaker house. Further discussions clarified that the location presented no risk or obstruction to personnel access, especially with respect to the aft lifeboat stations and fast rescue craft.

Transocean appointed a single point of contact to ensure that all the right operations and engineering personnel were involved in the project. This allowed full consultation concerning the RMR equipment interfacing with the rig systems, especially the routing of the return line to the shaker house. Transocean Inc.’s engineering department reviewed several options before deciding to hard pipe the line from the landing platform, through the BOP control area, and through the bulkhead of the adjoining shaker room. This routing satisfied classification requirements, including hazardous zone certification, given that there could be gas in the return flow.

Previous operations in Norway and the Caspian had been powered from the rigs’ power distribution systems. Limitations of the Legend’s system, however, suggested that an independent power source would be required. A 300-kw mobile generator set was procured in Singapore, shipped to South Korea, and installed on board the rig during the 2006 refit.

New equipment introduced to a rig may affect many of the rig systems and third-party services. Full involvement of all concerned is critically important to successful installation and operation. In this case, in addition to Transocean, it was necessary to engage other equipment manufacturers, including the wellhead manufacturer and the remotely operated vehicle contractor. The ROV unit would play a major part in the deployment, makeup, and operation of the RMR system. The operator’s drilling supervisors would be responsible for overseeing the operation.

The project group held a meeting in Busan, South Korea, in November 2005 during demobilization from Sakhalin. The group, including AGR Subsea’s project manager and Elvary Neftegaz personnel, gathered to review the system, its deployment, and operations in order to identify risks and engineering interface issues. The result was an outline plan of actions relating to modifications of the permanent guide base, ROV procedures, topside handling, moon-pool handling, and overall safety management.

A senior drilling supervisor spent time on board a semisubmersible in the Caspian Sea to witness deployment and operation of the system on another company-operated exploration well. This first-hand experience provided valuable input to the detailed planning and safety reviews.

The project team also undertook an integrated hazard and operability review. The aim was to consider and review potential risks associated with running and operating the system. A risk-engineering consultancy planned and facilitated the exercise. The risk workshop reviewed the four stages of operating the system: installation, deployment, operation, and recovery. Each stage was broken down into discrete activities and considered from the points of view of safety, feasibility, and optimum performance.

The hazop review produced a list of more than 50 recommendations and actions. These were subsequently assigned to individuals charged with closing out the action items. These activities were in addition to those risks and actions previously identified in the project risk register and actions tracker.

This workshop provided the service provider, AGR Subsea, with information needed to finalize deployment, operating, and recovery procedures. The procedures were incorporated into the detailed hole section instructions prepared by the operations team. These documents were subjected to a critical review in order to finalize the shallow gas procedures.

Russian certification

As with other jurisdictions, the Russian Federation has detailed verification and certification procedures for new or foreign equipment. Timely action is required to ensure trouble-free importation, use, and export of a new system. “Technical passports” must be prepared for each piece of equipment so that it can be reviewed against the relevant GOST standards to enable the issue of certificates of conformity to Gosstandart of the Russian Federation.

Once the equipment is certified as meeting Russian Federation standards, it is then submitted to RostechNadzor (RTN), the Russian Federation ministry responsible for industrial safety. RTN reviews the submission and, if it is accepted, will issue a “permit to use” the equipment in the Russian Federation. There are no clearly defined rules as to the amount of information and data required for each submission. Current regulatory guidance is wide in scope and open to interpretation. The most important documents are:

• Copy of the contract between the operating company and service provider.
• Copy of all equipment technical specifications, drawings, and process flow diagrams.
• ISO 9000 certification of the manufacturer.
• Certificates of compliance from original manufacturer, including Ex0 [IEC area-of-use designation standard for electrical components subject to oil immersion] certificates for electrical equipment where appropriate.
• Factory acceptance test reports.
• Details of operating environment.
• System description and operating procedures.

The result is a “technical passport” containing almost enough design information to enable a system to be manufactured. Most of the documentation had to be translated into Russian. Due to the large amount of information and data required, it was the service provider’s responsibility to obtain the necessary certification and permit. There are several well-qualified engineering consultancies familiar with certification and permitting that can assist foreign companies in developing the required packages of documentation.

The certification process took almost 4 months including the RTN permit for use. Although this was a somewhat protracted process, involving numerous clarifications, it resulted in a trouble-free import and export. The exercise demonstrated the need to allow adequate time for the certification process within the overall project schedule.

Fabrication, mobilization

With concept and potential benefits firmly established and peer review completed, focus moved to detailed engineering design and with emphasis on the possible risk of hose failure in the strong current conditions.

Hydraulics modeling of the recovery hose and pump performance based on actual surface-hole geometry, drilling fluids, and water depth concluded that a single 300 kw pump unit would suffice. Using a variable-speed drive, the system was capable of a range of flow rates up to 1,100 gpm, which was deemed sufficient for surface-hole drilling.

Elvary Neftegaz took a contract with the RMR service provider in late 2005. Procurement and manufacturing commenced during fourth-quarter 2005, with a target completion of late January 2006. Although the timing was tight, AGR Subsea met the schedule, and factory acceptance testing commenced early February 2006 in Bergen.

A key aspect of the acceptance test was to run the pump continuously for a 48-hr endurance run while recording flow rates and motor performance throughout. The motor was submerged in water for the test to dissipate the heat it generated. Power supply and data acquisition were managed through the control cabin. The pump and motor had to meet a predetermined range of parameters to confirm acceptance.

The complete program lasted 1 week. The equipment was then prepared for shipment to Busan, where the drilling rig was to be released back to Elvary Neftegaz having worked for another operator during the winter of 2005-06.

Operational experience

The system was deployed on the top-hole section of the two exploration wells drilled during summer 2006, in the Kaigansky-Vasuykansky license area, in the south of the Sakhalin V area. The system functioned as planned and was virtually trouble-free. There were moderate seas but the currents were low to negligible for the first well, thus avoiding the risks of problems with the hose or the capabilities of the ROV. In 2006, authorities permitted use of the system on a trial basis, and contingency plans were made to revert to the conventional method should the system suffer a major failure.

Vasukanskaya-1

The suction module was run on drill pipe with a stand of drill collars below the running tool to help stabilize and centralize for engagement onto the 30-in. wellhead housing. The operation was monitored throughout by the ROV. The pump module and return hose were then deployed from the starboard aft of the rig. This activity had no impact on drilling operations as the rig crew was making up the 17½-in. drilling assembly concurrently.

The pump was landed on the seabed about 30 m from the well and the ROV made up the suction hose and umbilical jumper cable to the suction module with no difficulty. The total installation time was less than 15 hr, but due to the concurrent operations, only 7 hr of rig time lay on the critical path.

The team held meetings on the rig before drilling commenced to review shallow gas and system operating procedures to ensure full understanding of specific roles and responsibilities, particularly under emergency conditions. The ROV was deployed to maintain a continuous watch on the system and provide an additional visual aid for monitoring the mud level in the suction module.

Under steady-state conditions, the system is normally operated in automatic mode with the pump speed, and hence the mud level, controlled by the pressure sensor in the suction module housing. At the beginning of the section, however, seawater and high-viscosity (hi-vis) pills were used. The operator had to maintain control of the fluid level by monitoring the fluid level using the subsea cameras and lights mounted on the housing and adjusting pump speed manually. Before starting to drill, a 100 bbl hi-vis pill was circulated at 950 gpm to help the operator establish the subsea pump speed and aid visual identification of the mud cap level.

After drilling 7 m, the pump started to cutout as a result of generator fuel starvation. The problem was traced to a fuel line blockage due to rust and sediments in the fuel tank. After cleaning and restarting, there were still no returns at the shakers. The trouble was determined to be a blockage of the return hose with sand and cuttings settling down after the pump cut out. Workers unblocked the hose and flushed it clean by opening the pump bypass valve and pumping seawater via a 2-in. connection on the return hose manifold at deck level.

After the start-up problems were resolved, the system worked faultlessly and the section drilled at an average rate of 18 m/hr with a maximum of 40 m/hr and flow rates of 900-1,050 gpm. Because the section was sandier than expected, it took longer to mud up with native clays. The 17½-in. section was drilled to 1,000 m TVD, a total of 763 m in 41 hr.

Notwithstanding the 3½ hr lost due to the generator cutout and return hose blockage, the section was drilled in a half day less than originally planned, to which must be added the 4 days saved through elimination of drilling and abandonment of the pilot hole. Credit was given to the system for improved hole cleaning and reduced waste at surface. Improved hole condition contributed to the reduced casing running time.

The ROV disconnected the suction hose and power umbilical, and the suction module was recovered before the 13 3/8-in. casing was run. The running tool was installed in the bottomhole assembly while pulling out of hole and the suction module was easily recovered. The ROV then connected the suction hose to the permanent guide base manifold outlet so that mud returns could be taken back to the rig while running casing. It also enabled the casing to be washed down without mud loss should this have been required.

The pump and return hose were recovered after cementing the 13 3/8-in. casing, while the BOP stack was being run. By this time, the current had strengthened to 2-3 knots, and the return hose had wrapped itself around the winch umbilical. This complication did not seriously affect recovery nor was any damage to the hose visible.

Savitskaya-1

Although the currents were stronger at this location, the operation went smoothly. The crew ran the pump while waiting for cement and landed on the seabed without incident, although the current ranged from 2 knots at surface to 1.5 knots at the seabed.

After drilling and cleaning out the 30-in. conductor, the crew attempted to engage the suction module. After several failures, the rig had to be winched over 8 m before the suction module could be placed over the 30-in. wellhead housing. The current was sufficiently strong to create difficulties for the ROV when making up the suction hose and umbilical jumper cable but this was achieved while the rig crew made up the drilling assembly.

The 17½-in. hole section commenced without incident and progressed down to 479 m, where mud returns were lost. ROV inspection of the hose showed that it had been caught around the pump frame and kinked. Several attempts to release the hose failed due to the strong currents. The current at the time was 1.8 knots and had changed direction by 180º in a short period. After a wait of 7½ hr for slack water, the hose was cleared and operations recommenced.

Drilling continued from 479 m until reaching section TD at 967 m. Performance in this section exceeded expectations, and it was completed in 17 hr at an average ROP of 28 m/hr. The total interval took 33 hr including the time lost due to the kinked hose. The improvement in hole condition and penetration rate was attributed to use of a 1.12-sp gr bentonite mud system. Hole conditions at casing point were sufficiently good to eliminate a wiper trip before running the 13 3/8-in. casing. This saved a further half day over past performance.

The crew recovered the suction module without difficulty before running casing. Although the current did not abate, the ROV successfully disconnected the suction hose and jumper cable from the suction module in just 45 min. The suction hose was transferred to the permanent guide base to capture mud returns. The pump and return hose were recovered without problems during the running of the BOP and marine riser.

Lessons learned, plan

Table 1 compares the performance achieved in the 2006 wells with operations in 2004 and 2005. The overall saving of about 9 days/well from the average of the 2004-05 wells results from:

• Eliminating a pilot hole and attendant abandonment problems.
• Avoiding running and recovering the riser and hydraulic latch connector.
• Improved performance resulting from drilling a single 17½-in. section as opposed to a 26-in. hole in two passes.

If a full sized 26-in. hole were to be drilled in future, without any improvement in drilling performance and allowing 5½ days to drill a 750-m interval, the time savings with the riserless mud-recovery system would still be 7 days over the alternative method.