Copyright 2003, Offshore Technology Conference This paper was prepared for presentation at the 2003 Offshore Technology Conference held in Houston, Texas, U.S.A., 58 May 2003. This paper was selected for presentation by an OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Offshore Technology Conference or officers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented.

Abstract This paper provides a detailed account of the successful salvage operation aboard the Saipem 10000 through the months of September, October and November, 2001. The target of this operation was the recovery of a Subsea Blowout Preventer Stack which was buried below the sedimentary mudline in 6673 feet of water depth. (2034 metres) The salvage operation involved the Saipem 10000 for 56 days. The equipment and human resources used in the operation were predominantly belonging to the Saipem Group. Wherever applicable, the contribution of external resources is acknowledged. The loss of the Subsea system was the result of a hoist system failure and occurred at the completion of an exploratory well drilled by Total Fina Elf (TFE) offshore Equatorial Guinea. The hook weight at the time of the loss was 575 metric tonnes. The associated marine riser string was also lost to the sea. Innovative techniques, many empirical by nature, were used during the salvage operation. The success of methods used was achieved thanks to repetitive trial and error. Persistence paid off and two separate world records were broken during the salvage operation. One record was set for the water depth in which high torque hydraulic tooling was used to disconnect the joints of a marine drilling riser. The other record, since then broken by 151 feet, was the water depth from which the Blowout Preventer Stack (BOP) was retrieved. Introduction and Background The Saipem 10000 is an ultra deepwater drillship which can operate in water depths of 10 000 feet, has a Class III

Dynamic Positioning system which allows it to keep its position at all times and a drilling capability which extends to 30 000 feet from the Rotary Kelly Bushings (RKB) Its functions include: Drilling Activities Extended Well Testing Early Production Crude Oil Storage (140 000 Bbls) Crude Oil Export Well Completion Activities

The topsides drilling equipment package is outfitted with the latest integrated control and management systems and two drill centres, configured A and B are installed within a single derrick structure with the following specifications:- Type: Dynamic Base Dimensions: 80 x 60 feet Top Dimensions: 60 x 20 feet Height: 200 feet Static Hook Load: 2 000 000 lbs per rig. Rated Maximum: 5 000 000 lbs The supplementary rig centre, located foremost, provides facilities for riserless drilling and other activities that require a full hoist system without riser and diverter capabilities.

OTC 15086

Saipem 10000 Deepwater Salvage Operation R.Cesaroni Saipem S.p.A. P.A.Potter Saipem S.p.A. SPE Members

2 OTC 15086

The main rig centre, located aft, is a fully equipped riser drill centre. The simultaneous setback and hook load for the substructure of each rig floor is 2 600 000 lbs. The mud system has been designed such that cross connections exist between the two drill centres to maximize flexibility of operations involving drilling fluids. Table 1 compares the core specifications with other offshore mobile drilling units. (MODUs)

At the time of the event, approximately 2/3rds of the marine riser inventory was deployed in the riser string. Although part of the string was recovered, none of the joints, following the vendors survey, were deemed fit for reuse. Some subcomponents were found to be suitable for reuse with recertification where applicable. Specifically, some of the marine riser buoyancy modules and a middle section of the instrumented riser joint have been utilized in the refurbishment of the Subsea System. Figure 1 shows schematically the marine riser string configuration at the time of the accident. The initial condition of the Subsea System at the moment of failure of the hoist system was such that the Riser Tensioning Ring (hereafter referred to as the Support Ring) had been stowed in its storage position, engaged on the bottom leading edge of the Diverter Housing and the assembly was being hoisted to engage the Termination Hydraulic Ring beneath the Support Ring. During this phase of BOP Retrieval operations, the riser string and BOP stack are supported solely by the topsides hoist system. Figures 2 and 3 provide pictorial representation of the topsides configuration before and after the event. Following detailed internal post analysis, the following sequence of events involving the the Subsea System can be described thus

1) Riser Handling Tool fractures and opens within the Diverter Housing.

2) The riser string and the BOP stack descends vertically towards the seafloor.

3) As the BOP Stack decelerates through the sedimentary mud layer the riser string rapidly goes into severe compression which immediately exceeds the limit for buckling.

4) The top section of the string is now the dominant mass and the string leans from the top culminating in a dive led by the telescopic slip joint.

5) Meanwhile, the BOP stack has decelerated to a halt beneath the sedimentary mudline and remains virtually upright whilst the riser string joints immediately above the riser adapter are subject to a buckling condition as the top section continues to dive subsea.

It should be noted that the sequence described here was only known after several days duration of salvaging. At the time of the event, the attitude of the BOP stack could only be surmised. Naturally, optimistically it was hoped that the BOP stack would be found to be vertical. At this time, nothing but speculation could be offered to describe the attitude of the BOP stack below the mudline. The final static configuration of the marine riser string when the event was completed is shown in Figure 4. The configuration can be attributed to the net buoyant effect of the composition of the differently rated buoyancy riser joints in the string. The calculated net buoyant effect of the string is shown in Figure 5. The joint cumulative number shown on the y axis of the graph describes the position in the string with reference to the riser running sequence listing used by the Saipem 10000. No.1 is the instrumented joint, No.2 the 15 ft. pup joint and so on as shown in Figure 1. The entire string consisted of a total of 80 joints which included the special joints and the short pup joints. It can be seen that the analysis shown here displays only half of that amount. That half that is not accounted for in this graph is that portion of the riser string which is shown as Riser Debris in Figure 4. This fact demonstrates the significant impact of the top heavy portion of the string as it plunged subsea and into the mudline. The graph, Figure 6, is the result of an in-depth series of surveys by the Sonsub Innovator ROV of the distribution of the riser loop detected through the water column as shown in Figure 4. During this preliminary stage of the salvage operation, options regarding the abondonment of the riser string became important in the planning to commence a salvage operation to secure the BOP stack back to surface.

Parameter Semi

Submersible

Standard DP Drillship

Large DP Drillship

Saipem 10000

Displacement (mT) 37000 22000 100000 96455 Engines, Horse Power ~ 18000 ~ 22000 52800 59400 Fuel Storage (barrels) 10 500 19000 25000 39890 Length (feet) ~ 330 534 835 747.4 Thrusters, Horse Power 2 at 3500 6 at 3000 6 at 7000 6 at 5440 Variable Deck Load (short tons) 4080 6000 20000 22046 Width (feet) ~ 285 80 125 138 Drilling Fluid (barrrels) 5600 4200 15000 18157 Riser (total length, inv, feet) 5000 6000 20000 11340 Substructure Height (feet) 42 35 60 39.4 Moonpool dimensions (ft x ft) 21.5 x 42 26 diameter 80 x 30 84 x 34 Personnel 100 128 200 172

Table 1

OTC 15086 3

Buoyancy of dropped Riser

05000

100001500020000250003000035000400004500050000550006000065000700007500080000850009000095000

100000105000110000115000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Joint cumulative number

Wei

ght [

kg]

Total Optimistic wet weight [kg] cumulative Total Pessimistic wet weight [kg] cumulative

Some of the buoyancy modules through the length of the riser string had exceeded their maximum water depth rating and these effectively imploded, their syntactic foam macro-spheres being crushed by the hydrostatic pressure. A number of such modules were revealed through the eyes of the ROV cameras during the numerous surveys having sunk onto the mudline in the general area of riser debris shown in Figure 4. Other modules, notably green and black (2000 and 6000 feet rated respectively) escaped their parent riser joints as main tube sections buckled during the string dive and these surfaced in the moonpool and around the rig. These are shown in Photographs 1 and 2. Extensive meetings were held by Saipem 10000 management, head office and third party organisations which included representatives from the Insurance company, underwater demolition, remotely operated vehicles (ROVs),

soil excavation company and additional assistance and advice was offered by a competitor, to whom a similar catastrophic loss had befallen them. The final decision was to use of the Saipem 10000 as the salvage vessel due to the fact that one complete, suitably rated hoist system, was still intact on the forwards supplementary drill centre. The other decision, which later proved to be 100% correct was the choice of soil excavation techniques in preference to explosives. (as a means of separation) Preparations Prior to Commencement of the Salvage Operation The salvage team were faced with main problems. Firstly, the disposition of the flotation suspended loop of damaged

Wet weight per joint

-2000

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

15000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Joint cumulative number

Wei

ght [

kg]

Optimistic wet weight [kg] per joint Pessimistic wet weight [kg] per joint

Figure 5

Figure 6

4 OTC 15086

marine riser relative to the position of the BOP stack and secondly the position and depth below mudline of the BOP stack. The approximate position of the buried BOP stack was known with an optimistic degree of certainty. This was ascertained by repeated views, both visual and via the medium of sonar scans of the considerable depression in the mudline that could have only mass of the BOP stack freefalling through the mudline from a distance of 130 200 feet. (The approximate distance of the supported string at the time of event) One of the early ROV surveys provided this image (Photograph 3) of the most inversely prominent mud displacements on the seabed. Further, the presence of a 15 foot pup joint and the top of the instrumented joint reinforced suspicions that this indeed was the site of the buried BOP stack.

This image gives some impression of the considerable depth of the crater and the overall width in consideration of the 90 foot length slick joint that overlies the crater. First analysis of this image then spawned a number of speculative proposals as to the attitude of the BOP. The worst case scenario is shown pictorially in Figure 7. This particular BOP Stack was not fitted with any form of emergency recovery system which, if the worst case scenario transpired to be reality, would have serious consequences as to the likelihood of retrieving the BOP stack. To explain this, some historical background into BOP stack design is given here. 10 years ago and earlier, deepwater drilling had not been attempted simply because the technology minimum requirements were not in place. As the technology, which today we accept as industry standards, evolved, it became clear that one of the severe limiting factors was both the landing weight of the BOP stack in deep and ultra deepwater and also the MODU payload capability coupled with the hoist system limitations. A number of methods have been employed to reduce the landing weight of the BOP stack in deepwater, however the starting point of weight reduction was the design of the BOP stack as a whole entity. The blowout preventers have been reduced in weight and size using modern metallurgy to produce high pressure, compact and ultralight BOP preventer components. Further the enveloping framework design of the BOP stackup was revised which resulted in an ultralight frame classified fitfor purpose. While todays technology has provided us with compact BOP stacks, commonly rated at 15 000 psi wellbore pressure, the frameworks simply support the auxiliary lines, valves and stack auxiliaries and unlike their earlier predecessors are not capable of withstanding the side loading regimes that would be experienced should a stack be hauled out the mud on the seafloor using grappling techniques on the BOP frame. As the picture of the hardware distribution became clearer, it became evident that the buoyant riser water- suspended loop some 1970 feet (600 metres) high off the mudline would have to be handled in a careful and safe

Photograph No.1

Buoyancy Modules surfacing around the Saipem

Buoyancy Modules surfacing in the moonpool

Photograph No.2

Photograph No. 3

OTC 15086 5

ML

11 xx SSlliicckk TTyyppee BB

BBOOPP

11 xx SSlliicckk

TTyyppee BB

11 xx SSlliicckk

TTyyppee BB

11 xx SSlliicckk

TTyyppee BB

11 xx SSlliicckk

TTyyppee BB

11 xx SSlliicckk

TTyyppee BB

11 xx SSlliicckk TTyyppee

11 xx 1155fftt PPuupp

IInnsstt.. JJooiinntt

NNoottee TThhiiss ssppeeccuullaattiioonn iiss bbaasseedd oonn tthhee uunnsseeeenn rriisseerr ssttrriinngg jjooiinnttss aannddtthhee ffaacctt tthhaatt tthhee VVeettccoo HHMMFF rriisseerr jjooiinntt ccoonnnneeccttiioonnss aarreessiiggnniiffiiccaannttllyy ssttrroonnggeerr tthhaann aannyy ootthheerr ccoonnssttiittuueenntt ccoommppoonneenntt oofftthhee rriisseerr jjooiinntt((ss)).. IItt iiss kknnoowwnn tthhaatt aa rriisseerr mmaaiinn ttuubbee sseeccttiioonn wwiillll ccrreeaassee iinn bbeennddiinnggaa lloott eeaarrlliieerr tthhaann ffaaiilluurree ooff tthhee ppiinn // bbooxx ccoonnnneeccttiioonn ooff HHMMFFrriisseerr..

PPrroobbaabbiilliittyy && SSppeeccuullaattiioonn HHyyppootthheessiiss ooff BBOOPP AAttttiittuuddee,, ffoolllloowwiinngg ddrroopp eevveenntt....

Figure 7

manner, further the slick joints lying transversely over the sunken BOP stack site would require displacement to gain uninterrupted access to the bottom of the crater. Figure 8 provides a view of a generated plot of the disposition of the riser using bridge instrumentation taking coordinate fixes from the ROV. The uppermost and underlying priority at this stage was to ascertain the exact orientation of the BOP stack. A secondary question that could be crucial in the salvage operation was at what depth below the bottom of the crater had the BOP Stack sunk in the sedimentary mud layer. A question of sedimentary mud composition was addressed by conducting an empirical seafloor penetration test. The test was conducted from the supplementary rig centre using a constant value of 5 metric tonnes weightonbit down to a maximum penetration of 151 feet (46 metres). The results are shown graphically in Figure 9.

This data showed that the top layer of sediment down to a level of approximately 89 feet (27 metres) was very soft and thereafter the density increased almost exponentially with depth. These results were interpreted optimistically following

Figure 8

SEABED HARDNESS TEST CHART

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45 50

depth below m.l. (meters)

time

( 1/4

of m

inut

e)

depth below mudlinew.o.b.

Figure 9

6 OTC 15086

estimation of the depth of the BOP stack from crater depth and the partially visible instrument joint and 15 foot pup joint. Representatives from the derrick builder surveyed the damaged structure to establish the extent of deformation through the derrick structure with consideration to the estimated highest value load that would be imposed during the forthcoming salvage. It was considered that the structure encompassing the supplementary drill centre was unaffected then allowing operations to proceed. An excavation company: formerly called Copipe Systems Ltd (since renamed PSL Group) was contracted to supply suitable excavation machines and their operating personnel to assist in the salvage operation. Further preparations included the use of a sub bottom profiler sonar surveying instrument deployed from the Sonsub Innovator ROVs. (2 identical spreads positioned residentially port and starboard on the after deck of the Saipem 10000) This instrument was largely unsuccessful, the visual plots on surface being extremely difficult to interpret. Adjustments and recalibration procedures proved to be ineffective. Certainly the device provided very little information concerning hardware that was buried beneath the seafloor. At the request of the excavation company, a precursory sonar scan of the crater was performed by the ROVs and plotted on the bridge Nav screen. Figure 10 provides a sketch of the relation of the crater boundaries to the BOP position as indicated by the instrument joint at the site of disappearance into the mudline. Soil Excavation and Removal Equipment and Methodologies Following consultation with the PSL, the Saipem 10000 was supplied with JetProp and CTS (Cuttings Transport System) machines. These were configured onboard the vessel, in accordance with the equipment operators advice to suit the specific requirements for this salvage operation. The various modifications that were performed on the equipment were as a result of empirical test runs to the seafloor and equipment operation. Each of the two machines used in the excavation and removal of soil used in this salvage operation are described below. THE JET PROP The machine acts on the principle of the single stage impulse turbine which induces seawater downwards effectively excavating the sedimentary layer hydrodynamically. The hydrodynamic force required (3000 psi at a flowrate of 660.4 galls min-1 [207 bar at a flowrate of 2500 litres min-1] ) to create the low pressure beneath the machine is supplied from the surface via the rig high pressure mud pumps pumping seawater. In satisfying the supply requirements, the turbine rotates at a rate of 350 rpm and induces a descending water column moving at a rate of 19.7 ft sec-1 (6 m sec-1) The JetProp machine is deployed on drill string and is illustrated here in Figure 11.

Figure 11

7mt

5mt

10mt

Crater top view

Sonar View

South

North

Figure 10

OTC 15086 7

The JetProp machine, although highly effective, proved to be a major contributor to reduce visibility conditions causing time delays and hampered the progress of excavation. It was found that the current velocity at the mudline level was very low or nonexistent and this provided no assistance in the removal of the clouds of suspended sedimentary particles. The problems of poor visibility caused by the suction excavation activities of the JetProp in the area of the main crater were somewhat alleviated by employing the machine for intermittent periods at a specific elevation above the mudline. A number of distance elevations were used to best establish the polluted opaque seawater displacement effect. (98 164 feet [30 50m.] above the mudline) The optimum height of the JetProp above the excavation site was 9.8 feet. (3 m.) CTS Machine (Cuttings Transport System) This machine displaces sedimentary mass from the extent of its suction hose to the extent of its discharge hose using an inductor operating on the principle of the pitot tube. Formerly, the machine was provided with power from an electricallydriven subsea pump though for this salvage operation, the unit was adapted to use the pressure and flowrate supplied via the running drill string from the rig high pressure mud pumps. Initial trials showed that the suction hose length was too great at the length of 262 feet (80m.) and was subsequently shortened to half this length. In order to manoeuvre the machine around the excavation site, hooks were furnished on the running string to facilitate stowage of both hoses by ROV prior to movements. Photographs Nos. 4 and 5 show the final preparations for the machine prior to deployment subsea and the commencement of deployment. This machine requires a greater flowrate than the JetProp though less delivery pressure topsides. (1717 galls min-1 at 1160 psi [6500 litres min-1 at 80 bar] ) The maximum debris removal rate is 10594 ft.3 (300 m3) per hour using a 6in. diameter suction hose and a 10in. diameter discharge hose.

The PSL Group technicians worked continuously with the Saipem 10000 personnel and Sonsub ROV operators throughout the extensive excavation operations. Once excavation operations had commenced it became quickly apparent, that in order to reach an appropriate depth in the crater at the BOP Stack location, a large volume of sedimentary matter would require removal effectively increasing the overall size of the crater depression. Without such removal, it was seen that neither of the excavation machines could get close enough to the bottom of the crater to perform their function effectively. During the excavation, readings were obtained from the Acoustic Postioning System (HIPAP) mounted on the Lower Marine Riser Package (LMRP) and the Riser Instrumented Joint. Essentially, the system consists of two sets of transponders. (Refer to Figure 1.) The pair mounted on the instrumented riser joint make differential comparison of readings with the pair mounted on the LMRP which, unlike the x and y units on the instrumented joint, are static. The detection of these readings provided the first indication as to the attitude of the BOP Stack buried beneath the mud but also presented a means of precise location fixing when running the many assorted strings that were employed through the long process of salvage. Figure 12 shows a readout taken from the system instrumentation on surface. Subsequent operations using the excavation machines utilized a positioning transponder incorporated into the running string to aid positioning. Whilst enlarging the delimiting boundary of the crater, it was necessary to soften the sedimentary surrounding material with a side entry jet sub. It was recognised that the crater site would require further clearing of riser string debris that constituted an obstruction to a clear access to the BOP Stack beneath the mudline.

Photograph No.4

Rig Crew members assisting PSL Operator Technician with the preparation prior to deployment of the CTS

Machine.

Photograph No.5

Machine being deployed on drill string

8 OTC 15086

Figure 13 shows the initial perceived situation as of the end of September 2001, some two weeks after the event.

The following figures from 14 - 18, detail the progress of the excavation works and illustrates the process and method used to dig an extensive crater centred on the BOP Stack co-ordinates.

Figure 12

This acoustic positioning plot provided the first quantatitive value for vertical defletion. The plot shows that the extension tube of the LMRP flex joint, the riser adapter and the instrumented jont were around

9.7 degrees from the vertical plane.

SE 146 DEG

MUX CABLE

ONLY LINES CONNECTED

ONLY LINES CONNECTED

BLACK BOOSTER RUBBER HOSE

LIKELY BROKEN !

PARTIALLY COVERED BY MUD

CRATER

Figure 13

5m 30 min

Transponder 25m above JetProp to aid position

SStteepp 11

Figure 14 Phase One

SStteepp 22

6m 15 min

7m 15 min

SStteepp 33

SStteepp 44

10m 15 min

SStteepp 55

30m Visibility

RROOVV

OTC 15086 9

At this point, visibility became a real problem due to the minimal bottom current and the fine sedimentary deposition. This phase commenced the agreed enlargement of the overall extents of the crater depression.

Figure 15 Phase Two Soft Seabed

HP Jetting with jetting sub/side entry subs. Breaks up hard clay then removed

by JetProp

Phase Two Hard Seabed

Assumed position of

wellhead, 20m from existing

crater.

Existing Crater, approx dims. 15m x 15m

25m

5m

3mVessel to move a 1m min-1during excavation. At end of each run,pumps will be shut off & vessel to return to next way point at 10m

min-1

Figure 16 Phase Three: Extending the crater limits..

Approx North

1

5

6

4

3

2

7

8

1c1a

2a

Step 1.2m from riser, 3m. from crater edge Step 2.3m from Step 1, 3m from crater edge

Step 3.3m from crater edge, 2m from riser(assuming no obstructions)

Step 4.3m from Step 3, 2m from riser (assuming on obstructions)

Step 5.2m from crater edge,2m from riser (assuming no obstructions)

Step 6.3m from Step 3, 2m from riser (assuming on obstructions)

NOTE All other steps performed using identical methodology

Figure 17 Phase Four: Excavation Plan

Size of excavation dictated by soil angle

repose

10 OTC 15086

The following bulleted paragraphs indicate the detailed instruction formulated by the excavation operator as a result of exhaustive debate of methodologies between the drilling contractor, the operator, the ROV company and the excavation company. The JetProp will be orientated above the riser

pup flange at a height of 9.8ft. (3m.) above seabed. This will be confirmed by ROV prior to lowering the tool.

On completion of positioning the JetProp above the riser the excavation supervisor will request the vessel DP operator offsets the JetProp 10-19.7ft.(3-6m.) to the start position (this start position will be determined using ROV survey data).

When the DP operator confirms that the JetProp is in position the ROV Supervisor will observe the lowering of the JetProp into position at the base of the crater. The ROV should then be positioned at a vantage point located at the North end of the crater to observe the planned excavation runs to facilitate accurate monitoring of the JetProp during transit.

Note: At this time it is expected that the transit distance will be around 49-65ft.(15-20m.) again this will be clarified on receiving ROV survey data on completion of the third excavation pattern.

When the ROV is in a secure position the excavation Supv will instruct the driller to bring the pumps up to 634 galls min-1 (2400 litres min.-1) steadily over 4 minutes.

On receiving confirmation that the required flow is as requested the excavation Supv will request the DP operator transits the vessel along the pre-determined route North at a vessel speed of 3.3 ft.min-1 for a distance of 49-65 ft. (15-20m.).On reaching the end of the run the DP operator will confirm to the excavation Supv that the run has ended.

On receipt of confirmation from the DP operator that the run has ended the excavation Supv will instruct the driller to lower the flow to 79 galls min.-1 (300 litres min-1).On receipt from the driller that the flow is as requested the excavation Supv will request the DP operator transits back along the route at a vessel speed of no more than 16.4 ft min--1

On receipt that the vessel has reached the start point the excavation Supv will request the DP operator offsets the vessel 9.8 ft.(3m)either East or west of the riser at the original start point.

R

4 of 15 m. Runs

Start position for South excavation pattern, 6 metres

East of the riser. 3 metres

180 swathe heading due West

SSoouutthh

NNoorrtthh

WWeesstt EEaasstt

Figure 18 Phase Five: Excavation Plan #1, Riser Pup Ref.

R

4 of 15 m. Runs

Start position for South excavation pattern, 6 metres

East of the riser.

3 metre steps

180 swathe heading due West

SSoouutthh

NNoorrtthh

WWeesstt EEaasstt

Phase Five: Excavation Plan #2, Riser Pup Ref.

R

6 of 25 m. Runs

Start position for South excavation pattern, 6 metres

West of the riser.

3 metre steps

180 swathe heading due West

SSoouutthh

NNoorrtthh

WWeesstt EEaasstt

Phase Five: Excavation Plan #3, Riser Pup Ref.

BBOOPP

Transit distances, steps and runs to be confirmed following

analysis of ROV survey data.

SSoouutthh

NNoorrtthh

WWeesstt EEaasstt

Phase Five: Excavation Plan #4, Riser Pup Ref.

OTC 15086 11

During this phase of excavation of the crater, close liaison was achieved between the interacting groups, namely PSL, Saipem 10000 personnel and the ROV operators. Specific survey requirements were requested by PSL. These operators emphasised the importance of an accurate picture of the excavation site to optimise the efficiency of the excavation periods. At this stage, in late October 2001, a comprehensive sonar survey was conducted using the ROVs in accordance with PSLs instructions. Their survey programme called for 9 discrete sonar grabs, orientated in an ordered pattern. Figures 19 ~ 24, following, shows this schematically..

Due South Riser Pup Joint

180 swathe grab South

RROOVV

Due North

1st grabs at the base of the crater. Grab South 180 Grab North 180

Figure 19. ROV Sonar Mapping # 1

Due South Riser Pup Joint

180 swathe grab North

RROOVV

Due North

ROV Sonar Mapping # 2

240

30 mt

Crater dwg. after last jet-prop opt.22.10.2001

30 mt

Vertical Riser Pup

Joint

Bare Joint, type A crack

FFiigguurree 2200

-7m

-12 m

0.0m - Mud

LMRP

STACK

-16 m

45

37 m

W E10 m

West-East Section -28.10.01

Figure 21

- 7 m

-12 m

0.0m -Mud Line

LMRP STACK

-16m

41

52 m

N S

North-South Section - 31.10.01

10 m 5 m

Figure 22

12 OTC15086

-7m

-12 m

0.0m- Mud Line

LMRP

STACK

-16 m

45

37 m

W E

10m

West-East Section - 5.NOV.01

9

3.5m

1155 mm ttoo

bboottttoomm ooff ccrraatteerr

2.5m

Figure 24

Controlled Descent of the Riser Buoyant Loop As shown in Figure 4, the buoyed loop of marine riser rose some 1970 ft. (600m.) above the mudline. While this did not present a near surface underwater hazard to shipping, it was clear that such a structure had to be removed to restore a safe condition. It should be noted here that the buoyancy modules are attached to the riser joints by means of kevlar straps secured by stainless steel tensioning fasteners. Whilst in normal service they provide more than adequate restraint against the possibility of the modules escaping from their position in the dressed joint. In the buoyed loop however, this was not the case. As can be seen in Annex 1: Dropped Riser Configuration and

Buoyancy Analysis, the majority of the buoyed loop was composed of 90 ft. riser joints that had plastically deformed hence imposing excessive stress on the kevlar banding securing the buoyancy modules. In the scenario of a freely ascending module, the terminal velocity with which it breaks surface can be considerable and the associated inertia of such a body is capable of causing extreme impact damage to any object it might collide with. The surfacing velocity of such buoyancy modules was witnessed immediately following the event and it is clear that the potential dangers of such an uncontrolled ascent is an extreme hazard. A series of calculations were performed by Saipem engineers to quantify the escape and terminal velocity of all buoyancy modules, dealing with each riser joint set of 10 modules on a case by case basis with respect to water depth and buoyancy rating.

Clearly, the 6000 foot rated buoyancy riser joints, colour coded black, acted as the dominant buoyant contributor providing the accumulated net uplift of the loop and supporting it in the water column as seen in figure 4 and Annex 1 In simple terms, the evolving plan that was agreed within the organisation was to selectively release specific buoyancy modules to facilitate a controlled descent of the entire loop which would finally come to rest on its side on the mudline. The emerging hazard and risk assessment associated with this operation centred on the potential danger presented by the free ascent of released modules. Two equipment and system features of the Saipem 10000 would minimize this risk of impact from surfacing modules.

1) The design of the ROV spreads which afforded a substantial seafloor operational footprint, an

-7m

-12 m

-16 m

45

37 m

W E

10 m

West-East Section - 31.10.01

7m

9

0.0m- Mud Line

Figure 23

OTC 15086 13

appreciable lateral distance from the vessel topsides winching and reeled ROV tether system.

2) The overall maneouvreability of the vessel, using

its six azimuthing thrusters, both in manual propulsive mode and station keeping capabilities in dynamic positioning (DP) mode.

The assessment of the entire loop prompted a decision to disconnect either end of the loop. The ends were examined as different entities. At the end of the bare joints that disappearanced into the mud and bridged the crater depression, it was decided that the connection between No.3 and No.4 should be disconnected (shown in Annex 1). This then would enable, later in the salvage operation, movement of the length comprising joints, Nos. 1,2 and 3 thereby providing clear access to the entire crater depression and the buried BOP stack. To achieve a disconnection between joints Nos. 3 and 4, a proposal was formulated which involved adaptation of the riser joint hydraulic tooling to operate subsea, supported and functioned by the workhorse ROV. This tooling is normally operated by the rig crews when running and pulling riser, its hydraulic power being supplied by a dedicated power pack. Photograph No. 6 shows the normal usage of this equipment whilst Figure 25 shows the outline of the tooling.

After several modifications to the tooling and ROV capability, 4 of the 6 HMF riser bolts were successfully broke beyond their makeup torque setting and unscrewed from the threaded boxes. The following images show this feat which later was recognised as a world record for operation of such hydraulic tooling in this water depth.

Photograph No.6

Francis hydraulic tooling in use whilst pulling

riser The break out torque required to be generated to break out these bolts is in the order of 33 000

ftlbf.

Figure 25

Photograph No.7

Image showing HMF Riser Pin / Box connection in the region of joints 2,3 or 4 in Figure 6. This

was the orientation of the riser connection which was disconnected by the ROV adapted

riser bolt hydraulic tooling.

14 OTC15086

The other end of the loop showed the greatest degree of damage and that was attributed to two reasons. Firstly, this portion had been the uppermost portion in the deployed marine riser string and it was seen that most of the 4000 foot rated buoyancy had suffered fatally from the excessive hydrostatic pressure and secondly this section had suffered considerable impact damage as the top heavy section drove itself into the mudline. It was seen from visual examination that joint No.12 was the most damaged with its main tube creased and lines broken. It was at this location that the decision was made to effect a disconnection by using cutting equipment via ROV intervention. This was successful. Prior to the calculations performed to quantify the ascent velocity of the modules that were to be selectively released, a detailed inventory of the entire loop was made and formulated in a table. The table gave the following information:

Joint numbering (per Annex 1) No. of complete pairs buoyancy modules remaining

on each joint (dressed with 5 pairs per 27.43m joint [90 ft])

Nos. of missing buoyancy module restraining straps missing.

Optimistic buoyancy wet weight per joint. Pessimistic buoyancy wet weight per joint. Steel weight per joint. (in seawater) Optimistic net weight per joint Pessimistic net weight per joint Cumulative optimistic net weight Culmulative pessimistic net weight

A formula was derived and the drag force experienced by an ascending buoyancy module can be given by: Net uplift mass = ( Cr x x A x V2 ) / 2

Where: Cr Coefficient of drag (friction, wake & added mass) p Density of seawater (1027 kgm-3) A Cross sectional area, buoyancy module V2 Velocity squared The division by 2 is derived from the kinetic energy formula (1/2mv2) A spreadsheet was devised whose parameters are shown below in the Table 2.

Joint Velocity

Cr 0.5

Cr 0.6

Cr 0.7

Cr 0.8

Cr 0.9

Cr 1.0

Known Net Uplift

Const. Const.

Zero, increments ms-1 ascending

Const.

The numerical values in each cell were analysed following application of the above formula and highlighted for each value of Cr to the nearest match to the constant in the right hand column: the known uplift value for black or yellow buoyancy. From this was derived the maximum expected ascent velocity of each type of buoyancy module in the buoyed loop. To validate the accuracy of the calculations, an empirical test was performed by releasing an undamaged module from the debris pile of riser joints. The planned release and rate of ascent were measured using a straight-forward time distance calculation and a stop watch to record the time from release to surfacing. The measured ascent velocity was found to be a close approximation to the calculated values. These were:-

Black Vertical Case: 1.8 m.s-1 (6 ft.s-1) Black Horizontal Case: 0.33 m.s-1 (1 ft.s-1) Yellow Vertical Case: 2.1 m.s-1 (7 ft.s-1)

A final table was constructed in which modules were selected for release, spaced equidistantly four joints apart commencing at No.2 black and culminating at No.6 yellow travelling counterclockwise around the loop. The table tabulated increasing net weight in water of the loop as each module pair were released. A total of 9 pairs were selected although the 9th did not require removal since the buoyed loop attained negative buoyancy after the 8th pair were released. Figures 26 and 27 show the distributed weight of the loop before and after intervention.

Photograph No.8

ROV adapted HMF riser bolt hydraulic tooling backing out a riser bolt

Table 2

OTC 15086 15

Final Clearance for unimpeded access to the BOP stack. With the crater excavation accomplished to the extent required for uninterrupted access to the top of the BOP stack and the buoyed riser string loop lowered to the safety of the mudline, the salvage operation proceeded with the final preparations to clear the crater area and ready the riser adapter atop the BOP stack for the core activity of this salvage: recovering the entire BOP stack to surface. The ROV cameras now provided us with comprehensive views of the status of hardware immediately above the BOP stack. Photograph No. 9 illustrates this view.

The main tasks that dominated this phase of the salvage operation were: i) The removal of the 15ft. pup joint from the instrumented joint. ii) The removal of the instrumented joint from the riser adapter. iii) Grappling and moving the obstructive bare joints bridging over the crater top. This was achieved by a combination of techniques including the use of the ROVadapted HMF riser hydraulic tooling, cutting and the use of a grappling assembly for lifting and dragging. Using the information obtained from the early and kind co-operation from another drilling contractor: Pride International (Technical Paper: SPE / IADC 67808: Pride Africa Successful BOP and Riser Recovery Offshore Angola) and other external sources of consultation, grappling and lasso assemblies were made up and subsequently deployed subsea for the use in the clearance operations. The assemblies are shown in photographs Nos. 10 and 11.

Joint Number

Net weight (kg)

Weight before Intervention

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

1 3 5 7 9 11

13

15

17

19

21

23

25

27

29

31

33

35

Figure 26

Figure 27

Photograph No.9

A 90 ft. slick (bare) riser joint can be seen bridging the expanded crater

depression at the top of this image and the greater excavated depth has revealed the severly damaged 15 ft. riser pup joint immediately above the riser instrumented

joint.

11

13

15

17

19

21

23

25

27

29

31

33

35

Weight after Intervention

0

5000

10000

15000

20000

2500030000

35000

40000

45000

50000

1 3 5 7 9

Joint Number

Net Weight(kg)

16 OTC15086

Upon completion of the disconnection of the 15ft. pup joint from the instrumented riser joint, the grappling assembly was secured to the remains of the pup joint and it was recovered to surface.

Photograph No.11

The grappling and recovery assembly made up, ready for deployment subsea beneath the rig floor

Photograph No.10

Lasso Assembly ready for deployment subsea, shown suspended in moonpool from the rig

floor.

The subsequent disconnection of the instrumented riser joint from the riser adapter flange finally gave free access to the BOP stack.

All that remained to be done at this stage prior to commencement of the BOP stack recovery attempt was the lateral displacement of the bridging slick joints across the excavated crater.

The grappling and lassoing technique is shown in the next photograph.

Photograph No.13

The riser instrumented joint arriving on surface supported by recovery slings. Note the position transponder on the right hand side of the IRJ.

Photograph No.12

The disconnection of the 15ft. pup joint from the instrumented riser joint

OTC 15086 SAIPEM 10000 DEEPWATER SALVAGE OPERATION 17

A jetting and wash tool was run into the BOP wellbore to both establish a throughbore of the full extent of the BOP stack and agitate the packed off and compacted mud at the base of the BOP wellhead connector. This operation also provided confirmation of the attitude of the BOP stack providing assuredness that the LMRP flex joint was not unduly cocked. Photograph No.16 shows the angular deviation of the BOP stack. The Development of the Recovery Tooling

The design of a proper recovery tool was made through an evolution of suggestions, ideas and proposals that led to a final configuration as shown in Figure 28.

One factor emerged which strongly influenced the final choice of recovery tooling assembly. The booster line isolation valve which is located directly below the riser adapter flange at the top of the BOP stack was known to be in the open position. This valve is a ball type valve, operated by a hydraulic actuator. Unlike all the other valves on the BOP stack which move to the close or open position on loss of hydraulic supply, this valve remains in the last position it was functioned. During the operation of retrieving the BOP stack this valve is left open to ensure that the booster line drains as the riser is pulled.

Photograph No.14

A view, through the eyes of the ROV camera of the successful grapple of joints of slick riser.

Photograph No.15

ROV assistance stabbing into wellbore with wash tool ..

Photograph No.16

The angular inclination of the top of the BOP Stack.

51/2 F.H.

Side Entry & Circ. Sub w/ 2 Weco

Union 6 5/8 F.H. Box 6 5/8 F.H.

Pin

6 5/8 34.02# S135 D.P. Used pipe.

(Tensile Strength 4727.7 kN)

C/O 6 5/8 F.H Box 6 5/8 Reg. Pin

Saver Sub 5 F.H.Pin -7 5/8 Reg Pin

C/O 6 5/8 Reg Box 7 5/8

Reg Box

2in. Chicksan Line or 2in.

Flexible Hose

Fitting to circulate into the booster

line

All listed in stock

onboard

STRING FOR BOP RECOVERY #2 S10000 18/10/01

RISER HYDR. RUNNING TOOL 500 /750 TON

Figure 28

18 OTC 15086

Photograph No.18

This image, recorded after the BOP stack was successfully recovered, shows the detail of the tooling

pictorially described in Figure 28. Additional appurtenances are a reaction post (white) for the ROV assistance and a ROV operated hydraulic control panel

and manifold.

Another factor influencing the choice of the tooling assembly was the near vertical attitude of the BOP stack beneath the mudline. The following photograph shows the assembly made up after use.

This modified handling tool is one of the standard riser handling tools belonging to the Saipem 10000 riser inventory capital equipment outfit.

Its basic specifications follow. Manufacturer: ABBVetco Gray Description: Tool CDE Riser Handling / Test Tool, HMF, Class H, nom. 21in. Test Pins: 2 each Choke & Kill, nom. 6in. 15K psi MWP --------------------- 1 each Booster Line, nom. 5in. 5K psi MWP -------------------- 2 each Hydraulic

Lines. nom. 2 7/8in. 5K psi MWP --------------------- 1each Glycol line nom. 3in. 15K psi MWP

The hydraulic locking dogs which engage a

profile within the boxes of the riser joints and riser adapter are normally operated via a hydraulic supply and control panel on the rig floor where the tool is normally used when running and pulling the marine riser.

For this salvage operation, the tool was

modified in three ways:- A vertical reaction post to enable the ROV to remain

on station during recovery tool engagement. The use of a modified booster line pin to provide

hydraulic communication between the chicksan hard piping (shown red in the previous photograph) and the booster valve on the riser adapter and thence the BOP stack wellbore.

A custom made hydraulic manifold to enable ROV intervention to connect, operate and supply hydraulic usable volume to operate the riser handling tool locking dogs.

The Salvage Operation of the BOP Stack

The operation comprised two phases. The first was the deployment subsea of the equipment

described in the previous section and the successful positive engagement of that assembly into the riser adapter atop the BOP stack. The second was the simultaneous activities of circulating through the wellbore via the running string, sideentry sub, chicksan hardpiping and hence through the mud booster valve into the BOP stack wellbore whilst maintaining an overpull on the running string and recovery assembly in this first attempt to free the BOP stack from beneath the mud

Photograph No. 17

View of the mud booster line valve from beneath the riser adapter flange. (Other kick outs seen in

this image are one stainless hydraulic conduit and a choke / kill)

OTC 15086 19

and retrieve it to surface. The following ROVgenerated

images display the stabbingin of the modified riser handling tool to the flanged connection at the top of the riser adapter.

What is clear to see in these images is the 9 inclination of the BOP stack from the vertical in relation to the vertically suspended load of the recovery tool assembly.

Photograph No.19

Final approach of the modified riser handling tool to the riser adapter flange

Photograph No.20

Stabbing in Note the angular difference due to slight stack

deviation from the vertical.

Photograph No.21

View of the top of the modified riser handling tool showing the ROV reaction post and the custom made

hydraulic manifold for locking dog control.

Photograph No.22

View of ROV wet mateable connector stabbing into the hydraulic control panel to provide the usable volume of hydraulic pressure from the ROV onboard hydraulic accumulator to operate the

riser handling locking dogs.

20 OTC 15086

Prior to running the recovery tool assembly, a circulation test was performed using the mud pumps at a flowrate of 1189 galls. min-1 and a pump discharge pressure of 2277 psi.(4500 litres min.-1 at 157 bar.)

Finally, before deployment subsea, a bullseye slope indicator was installed on the subsea Stack to provide accurate measurement of verticality change during the circulating and overpulling operations.

With 750 mT bales fitted, the stabbingin operation required the assistance of both ROV vehicles operating subsea simultaneously and a controlled change in vessel heading and position.

The subsequent salvage operation to free the BOP stack from beneath the mud consumed 4 days of rig time.

Figure 29 and Figure 30 provide an insight into the methodology and the natural progression of events.

W/H Conn

LPR

MPR

S/B Rams

Lower Ann

Riser Conn

Upper Ann.

Flx .Jt

Riser Adapter

UPR

CS Rams

Modified Riser

Handling Tool

Side Entry

Blue representscirculation

h

Applied Hook Load

Note OPEN Valve CLOSED Valve

Figure 29

OTC 15086 21

The BOP stack emerged through the moonpool splash zone at 2300 hours on 14th November 2001. The following images show the emergence of the BOP stack and the initial jetwashing of the equipment prior to a total disassembly and rebuild in the following months.

Final events depicted diagrammatically over a period of 4 days.

Figure 30

Day 4 Circulate at 5200 lt.min-1 and overpull 500 mT. Spot with 30MC Hi. Vis. Bentonite pill. Displace out 2nd Hi. Vis. 33MC pill. Stack moves at 445 mT

Day 2 Circulate at 4900 lt.min-1 increasing to 5200 lt.min-1. Overpull varying between a min. of 200 mT and a max. of

495 mT. Day 1 Circulate at 2400 lt.min-1, vary overpull between 170 495 mT.Work string every 1 hours. Increase flowrate to 4000 lt.min-1 Note returns SW side of BOP stack. Monitor Slope

Indicator

Photograph No.23

The BOP Stack emerging from the moonpool. Substantial packed sedimentary mud required removal during this retrieval to the BOP carrier seen in the background.

Day 3 Circulate at 4000 lt.min-1 increasing to 4900 lt.min-1. Overpull varying between a min. of 200 mT and a max. of

495 mT

Photograph No.24

Photograph No.25

22 OTC 15086

Summary and Conclusion It is true to say here that whenever an unplanned event of this magnitude occurs in this industry, a unique energy invariably takes over to provide the motivation, resolution and capabilities required to accomplish the seemingly impossible. At the outset of the consultations following this event of the Loss of this Subsea System in ultra deepwater, some external sources expressed serious reservations as to the suitability of the Saipem 10000 drilling vessel with its crews to attempt such a salvage operation. Contrary to these doubts, it was proved conclusively that the Saipem 10000 was the most appropriate salvage vessel platform for this operation and achieved its task in only 56 days after the accident occurred. This may be attributed to a number of factors: Primarily, the twin drill centres capability meant that the second drill centre not involved in the event was immediately available, as it remained undamaged by the chaos caused at the other rig centre. This fact, coupled with the dynamic positioning capability of the Saipem 10000, proved to be an ideal platform from which to conduct this salvage operation. Furthermore, the load rating capabilities of the components of the hoist system, together with a comprehensive inventory of suitable tubular goods and tools, provided an array of feasible options with which to approach

the salvage task. Less obvious, but nonetheless, an important issue in a salvage attempt of this type, is the matter of handling the BOP Stack on surface once retrieved. Clearly, the drilling vessels own dedicated BOP Handling System must be the most appropriate and in fact it should be noted that mishandling of this type of modern BOP Stack [by a salvage vessel] could potentially cause significant damage to the structure considered as a single entity. Finally, for the personnel involved in this salvage operation, not enough credit can be afforded because, had it not been for their resolve, innovation, perseverance and unswerving willingness to work as a team, this success story could not be related. Saipem are indebted to all those external companies and individuals that offered their assistance and help in this operation. The level of co-operation and mutual respect remained high throughout this period and without their willingness to work together as a team, this operation and its chances of success would have been seriously jeopardized. Despite the geographical remoteness of the location of this salvage operation, the policies and practices of the Health & Safety Executive (HSE) were at no time compromised throughout the 56 day operation and this is borne out by the fact there were no Lost Time Accidents. (LTAs) for the entire period.

View of the BOP Stack following jet washing, supported in the BOP Carrier..

Photograph No.26

Acknowledgements The authors would like to thank the SaipemManagement for their kind permission to enable thepublication of this paper. Furthermore, the authors would like to thank the PSLGroup for providing an insight into their equipment andoperational methods.

OTC 15086 23

11 22 33

44

55

6677

88

99ML

SSAAIIPPEEMM 1100000000 DDrrooppppeedd RRiisseerr CCoonnffiigguurraattiioonn,, CCoommppoossiittiioonn && BBuuooyyaannccyy AAnnaallyyssiiss 2244 SSeepptteemmbbeerr 22000011

1

6

7

8

10

9

11

12

13

14

5

4

3

2

1 432 51

1

2

7

8

6

5

4

3

9

11

10

12

13

14

151617

19

18

20

Remnant HP Hose, Termination Joint Hyd. Ring

Riser Joints Debris Pile

Annex 1

Note: Black Arrows indicate Optimistic values, buoyancy Blue Arrows indicate Pessimistic values, buoyancy

Spaces indicate HMF riser Box / Pin Connections

Initial Disconnection of HMF Pin / Box

Remnants of deformed joint cut with ROV tooling

24 OTC 15086

18 w/h datum

LPR

MPR

UPR

CSR

SBR

UA

LA

Receiver Plates:LBOP / LMRP

FJ

RA

H A R H 4

H D H 4

MNL

W/H

SAIPEM 10000 BOP STACK 18in. 15K Configuration Aft Side, Looking Forwards SPRING 2001

Riser Adapter Vetco.18in. 10M BX-164 flange & inconel 635 ring groove down. Fitted for Vetco HMF Class H 21in. riser. Fitted with: 2 ea. 15K C/K kickouts, nom.6in. w/#6 CIW clamp hub: BX 154 r/groove, 2 ea. 5K rigid conduits kickouts: nom. 24in.w/#1 CIW clamp hub: BX 152 r/groove. 1 ea glycol inj kickout: nom. 3in. 15K w/#6 CIW clamp hub: BX 154. 1 ea. mud boost line kickout w/ 5K hydraulic ball valve: line nom. 5in. 5K. Fitted with 18in. integral NBP SFI Code No. 3D31209

Flex Joint Oilstates 18in. 5M. Max. deflection: 10. BX - 164 flange top & bottom. SFI Code No. 3D31208 Max. applied tensile load: 2 x 106 lbf Rated Spring Load Rate: 40K lbf / degree deflection.

Upper Annular Preventer Shaffer S by F Spherical 18in. 10M w / 18in. 10M BX - 164 Studded top, 15M BX - 164 Flange down. 2 ea. side outlets, one blanked, other fitted with dual block hyd. operated 31/16in. 15K Shaffer HB with BX - 154 flanged outlets. Short sea chest. NC VvsElement: Nitrile, type SL, rated at 10M. SFI Code No. 3D31204

Riser Connector Vetco E x F high angle release. 18in. 10M, fitted with 18in. 15M studded top, BX - 164. Rated for 3000m water depth. SFI Code No. 3D31201

Mandrel Vetco high angle release 18in. 15M with 18in. 10M BX - 164 Flange down. SFI Code No. 3D31111

Retractable Stabs Shaffer 15M. nom. 3in. female: internal retract

Isolation Valves Shaffer 15M. nom. 3in. T - HB straight, H2S trim. For High temperature service, CRA, PSL 3, NO Valves

Lower Annular Shaffer S by F Spherical 18in. 10M w / 18in. 10M BX - 164 Studded top, 15M BX - 164 Flange down. Element: Nitrile, type SL, rated at 10M.Low Temp service: -26F SFI Code No. 3D31110

Double Ram Type BOP Assembly Shaffer 18in. 15M S x F. NXT door mechanisms. CRA, fitted with Poslock ram locking mechanisms. 15M BX - 164 studded top; 15M BX - 164 flange down H2S Trim SFI Code No. 3D31105

Pressure Temp. Sensor

3in. ~ 5in

3in~5in

5in. ~ 7in.

Triple Ram Type BOP Assembly Shaffer 18in. 15M S x F. NXT door mechanisms. CRA, fitted with Ultralock II ram locking mechanisms. 15M BX - 164 studded top; 15M BX - 164 flange down. H2S Trim. SFI Code No. 3D31103

BOP Connector Vetco Heavy Duty, rated for 3000m water depth. with extended neck to fit Vetco SG5 wellhead profile. 18in. 15M BX - 164 flange top. SFI Code No. 3D31101

Pipe Ram Hang - Off Capacities 3in. ~ 5in. 3in. 200 000 lbs 5in. 600 000 lbs 5in. ~ 7in. 5in. 300 000 lbs 6 5/8in. 600 000 lbs

LIC LOC

IGI OGI

LOK LIK

UOK UIK

UIC UOC

MBV

OGR IGRKI

CI

GI

Notice of Modification December 2000. Shear / Blind rams fitted with tandem piston booster operators.. Poslocks adjusted Jan 01

Mud Boost Valve 2in. ball. 5 1/2in. nom. Dia. kick in. 5K MWP

Annex 2

OTC 15086 25

LMRP

LBOP

1188iinn.. WWeellllhheeaadd

RRKKBB DDaattuummRotary Housing / Diverter A blFlexible Joint

Slip Joint Inner

Slip Joint Outer Barrel

Riser Fill - Up Joint

Intermediate Flex.

Auxiliary Lines Termination Joint & Hydraulic Ring

Buoyancy Joints 6000 ft.

Slick Joint 13/16in. wall. Type B

Slick Joint 1in. wall, Type A

15ft. Pup

Riser Instrumentation Joint

6.33 20.77

6.1 20.0

1 x 4.572 1x 15

1 x 27.43 1 x 90

6 x 27.43 6 x 90

22x 27.43 22 x 90 ft

1 x 4.27 m 1 x 14.0 ft.

4.57 m 1 x 15.0 ft.

1 x 3.26 m 1 x 10.7 ft.

Mid - Stroke

1 x 38.86 m 1 x 127.5 ft.

1 x 6.43 m 1 x 21.10 ft.

Keel Joint

20 x 27.43

20 x 90

7.85 25.76

Mud Line ~ 3.8 m

~ 0.8 m

~ 3.0 m 18in. W/H Housing

Conductor Pipe 30in. Housing / GRA

14.18 46.53

1 x 27.43 1 x 90

Buoyancy Joints 4000 ft.

1 x 6.1 1 x 20

Pup Joints: 1 x 20 ft., 1 x 15 1 x 6.1m 1 x 4.6m 1 x 20 ft. 1 x 15 ft.

24.38 80.0

3.048 10.0

11.43 37.50

Buoyancy Joints 10000 ft.

Tensioner Ring

10 x 27.43 10 x 90 ft

Slick Joint 13/16in. type B3x 27.43 3 x 90 ft

Slick Joint 1in. type A

Buoyancy Joints 2000 ft.

3 x 27.43 3 x 90 ft

Slick Joint 1 in. type A 2 x 27.43 2 x 90 ft

3 x 27.43 3 x 90

Buoyancy Joints 10000 ft.

Figure 1 Riser String at time of Loss of Subsea System

Static x & y inclinometers

Dynamic x & y inclinometers

26 OTC 15086

RRoottaarryy KKeellllyy

RRiisseerr GGiimmbbaallSShhoocckk

AAbbssoorrbbeerrss

SSuuppppoorrtt RRiinngg

Rig

LLaannddiinngg JJooiinntt

TTeelleessccooppiicc SSlliipp JJooiinntt

DDiivveerrtteerr HHoouussiinngg

RRiisseerr HHaannddlliinngg

TTooooll

EElleevvaattoorr

TToopp DDrriivvee UU iitt

BBaalleess

TTrraavveelllliinngg BBlloocckk wwiitthh 1122 lliinnee rreeeevvee -- uupp

Figure 2 Topsides arrangement prior to event: Loss of Subsea System

RRiisseerr SSppiiddee

RRiisseerr GGiimmbbaa

ll

KKeeeell JJ ii tt

IInntteerrmmeeddiiaattee FFlleexx JJooiinntt

AAuuxxiilliiaarryy LLiinneess TTeerrmmiinnaattiioonn

TTeerrmmiinnaattiioonn JJooiinntt

RRiisseerr KKeeeell JJooiinntt sshhoowwnn mmiiss--aalliiggnneedd

wwiitthh tthhee tthhrroouugghh bboorree iinntteerrnnaall

ddiiaammeetteerr ooff tthhee DDiivveerrtteerr HHoouussiinngg

Sea

Notes

Not to Scale Topsides hoist arrangement

shown immediately prior to the event.

Note that Riser Spider is open to facilitate continued hoisting.

Keel Joint shown mis aligned with underside of Diverter Housing.

Next step in this BOP Retrieval Procedure is capture and store the Auxiliary Lines Termination Joint Hydraulic Ring beneath the Support Ring.

Though not schematically shown here, Keel Joint cladding overlap with the through bore of the Diverter Housing actually caused by an out of trim condition of the vessel.

OTC 15086 27

RRoottaarryy KKeellllyy

RRiisseerr GGiimmbbaall SShhoocckk

SSuuppppoorrtt RRiinngg

Rig DDiivveerrtteerr HHoouussiinngg

TToopp DDrriivvee UUnniitt

BBaalleess

TTrraavveelllliinngg BBlloocckk wwiitthh 1122 lliinnee rreeeevvee uupp.. WWiirreelliinnee ppaarrtteedd aaddjjaacceenntt ttoo ddrruumm wwiirree aanncchhoorr.. LLiinnee

ffrreeee

RRiisseerr SSppiiddeerr

RRiisseerr GGiimmbb

ll

Sea

EElleevvaattoorrss ffrraaccttuurreedd aanndd ooppeenn wwiitthhiinn

ccoonnffiinneess ooff tthhee DDiivveerrtteerrHHoouussiinngg

DDeerrrriicckk SSttrruuccttuurree

PPoorrtt

Figure 3 Topsides Arrangement immediately following event, Loss of Subsea System

Notes

Not to Scale Top Drive impacted on top of

Riser Spider & Riser Gimbal Assembly.

Riser Gimbal shock absorbers compressed to various reduced heights.

Wireline torn loose of anchor and free.

Elevators fractured, remains left within the Diverter Housing, held by Bales.

Angle is shown inclined to the Port side of the vessel.

28 OTC 15086

NORTH

GRA

Slick to BlackBlack to Yellow

Slick

Suspected Site of Sunken BOP

11 SSqquuaarree == 1100 mmeettrreess

TTrraacckkeedd RRiisseerr SSttrriinngg ffoolllloowwiinngg DDrrooppppeedd SSttaacckk EEvveenntt..

1

2

6

4

3

5

7

8

9

Riser Debris and Site of

MUX Cables

1 Grey middle

Mini crater with one C/K/Glycol hose visible. Co-ordinates 30m S of Fix 9 110m WSW of GRA Suspected site of Hyraulic Termination Joint & Ring

Figure 4 Initial Static Configuration Riser Sting.

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