SPE 143296

Success From Subsea Riserless Well Interventions L. Fjrtoft, SPE, G. Snstab, SPE, Statoil

Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition held in The Woodlands, Texas, USA, 56 April 2011. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers 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 SPE copyright.

Abstract This paper describes how Statoil, over a period of 10 years, have qualified and implemented Subsea Riserless Light Well Intervention (RLWI) applications as their primary means of intervening in subsea wells. The paper will also demonstrate the value of RLWI in relation to the companys Increased Oil Recovery (IOR) goals. Subsea wells represent the area where least well intervention work has been done, and where the biggest practical and technical challenges also lie. Hence less oil is recovered from subsea completed fields than from those with fixed platforms. RLWI is a cost effective intervention method that allows an operator of subsea wells to increase production and optimize utilization of vessels and rigs. Statoil is a leading exponent of RLWI services, utilizing two specialized and modern vessels on full year contract. A third vessel is currently being considered. The total RLWI activity for 2010 was 671 days, spanning a total of 32 different jobs. This paper will describe the development of these applications from 2000 until today covering a total of 125 individual operations. Statoil has 34 subsea fields, of which 32 are on the Norwegian continental shelf with a total of around 460 individual wells. Light Well intervention has been performed on 11 of these fields. Experience so far indicates that there are no limitations on equipment regarding interface to subsea templates. In this paper the contract philosophy for these services will also be discussed. Further on, the agreement between the different production assets for sharing of resources will also be described. The technical achievements and limitations will be listed and described. Then the needs of the future will be described and prioritized.

Finally, the economic benefit and contribution of introducing Riserless Light Well Intervention will also be highlighted. The following three conclusions on RLWI will be elaborated on in this paper:

Improves HSE in subsea well interventions Improves recovery Intervention cost is cut by more than half compared with anchored rigs and riser systems

Introduction The production on the Norwegian Continental Shelf (NCS) was 115 million Sm3 oil and 103 billion Sm3 gas in 2009. Statoil is the operator for approximately 80 per cent of all oil and gas production on the Norwegian continental shelf with around 45 per cent of this production coming from subsea installations and wells. The general ambition of the Statoil subsea improved oil recovery initiative is to achieve an average recovery factor of 55 per cent for subsea completed fields operated by the company. The companys expertise in subsea operations is the key to greater production efficiency, improved recovery and reduced environmental impact. Intervention in existing wells will normally have a lager impact on production volumes in the short term compared with various injection methods.

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The Increased Oil Recovery (IOR) activities are Statoils most important tool to maintain production on the NCS. There are several different technologies and methods under the IOR umbrella, and well intervention is a large contributor to the recovery factor on subsea fields. Today, Statoil has nine teams performing well interventions on the companys 25 fixed installations on the NCS. These nine teams cover a total of 750 wells and contribute with approximately 4,8 billion Sm3 of oil every year. In addition Statoil employs two dedicated vessels for wireline well intervention on the subsea wells operated by the company. The contribution of these interventions is in the range of 15 billion NOK per year (estimate for the 2010 RLWI campaign). The possibility of solid earning is a result of not just using relatively simple equipment, but also to contribute to a much higher production by adjusting the flow regime of the well. Well interventions give increased return on existing investments. By introducing RLWI the intervention cost per well is lowered dramatically, see Figure 2. Fig. 1. Overview of Statoil subsea fields.

Intervention Cost pr. Well

0

2

4

6

8

10

12

14

Land Platform Rig LWI Vessel

Intervention Cost pr. Well

Cos

t M$

Fig.2. Intervention cost pr well with different techniques.

SPE 143296 3

Riserless Well Intervention Technical information

Occasionally wells have to be re- entered for maintenance and technical purposes. For wells installed on seafloor this can be performed by conventional semi submersible rigs anchored to seabed and attached to the wells by risers. Statoil, however, has performed intervention utilizing monohull interventions vessel. The wireline Blow Out Preventer (BOP) is placed on top of the x-mas tree. The BOP is operated by a multi-bore umbilical. All valves and sensors in the x-mas tree and BOP are controlled by the operator on the vessel. In addition the Tubing Retrievable Surface Controlled Subsurface Safety valve (TRSCVSS) is controlled and monitored by the same system. All operations, including wireline, are run in open sea through the moonpool of the dynamically positioned vessel. The x-mas tree is barrier tested prior to performing the intervention. The primary barrier throughout the intervention is the BOP stack. Barriers in the BOP are tested prior to deploying the toolstring into the subsea lubricator. The lubricator is flushed subsea prior to run in hole with the toolstring. When performing intervention on a subsea well adjacent wells can continue flowing avoiding loss of production during the time of interventions.

Fig. 3. Deploying BOP through moonpool. All wireline activities can be performed. Ordinary well assignment may involve bringing new wells on stream, preparing old wells for sidetrack or re-completion, logging production contributions from various well zones, plugging water production, perforating new production zones or finding and repairing leaks. The system is compatible with both horizontal x-mas tree and conventional x-mas trees. The working pressure of the equipment is 690 bar, and it is able to operate on water depths up to 500 m. It is possible to kill the well by running the kill hose and hook it up via the stack subsea. The ultimate contingency is to run a work over riser, an option not yet required. Utilizing this technology allows the company to quick and easy get access to its subsea wells. The intervention team has an efficient planning process and can be ready on a relatively shorter notice compared to conventional rig operations. The operator team consists of 30 persons including two offshore crews. The offshore operations are supervised by the Company Well Supervisors. The main challenge is to indentify all risks associated with the operation and manage to control these. The operating weather limits are lower on the vessels than on the conventional rigs, and the helicopter landing frequencies are not as reliable as for a rig. The relatively small vessels utilized to support RLWI have a limited frequency due to excessive movements. Last year 16 per cent of operation time was waiting on weather.

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Fig 4. Barriers drawing with wireline in hole. Fig.5.The Blow Out Preventer (BOP) is installed on

the subsea well and the intervention vessel is dynamically position above.

. Integrated operations

To ensure a proper Quality Assurance/Quality Control of logging data and close follow up on well performance suite of communications solutions have been implemented. This enables the logging engineers and other specialists to work in their onshore offices and still provide the hands on follow up that is desired.

Live video feed Live video signover the Internet. Thiopportunity to log video from either thor any other came

X-mas Tree /BOP dataA dedicated monitodeveloped. This giworld, a full live ovsensors in the x-ma

Wireline data The three most imis also transmittedengineers onshoretension and speed o

als are tran

on

ra o

ring system have been ves a he

d

porta ov have access to wire line dept,

tanding in the background. The screen to the

smitted continuously s gives everyone the the server and watch live

e subsea operations (ROV) nboard the vessel.

user anywhere in terview of the valves ans tree and BOP stack.

nt wire line parameters er the link to shore. The

n their office computers.

Fig 6. During a production logging tool (PLT) run operator reservoir engineers onshore follows live the data gathering from the vessel. The screen to the left shows logging

s on vessel, operator supervisor sengineerright displays the BOP and x-mas tree valves- and sensor status and real time logging data.

SPE 143296 5

The sum of these features together with dedicated operational rooms onshore enables the operator to have an offshore ternative would be to send these people offshore, and

h I concept does not have any hydrocarbons back to surface, hence the fire & explosion risk onboard the intervention ced. Further on, the well pressure is contained subsea, so there is a limited amount of pressurized

WI p until 2000, RLWI in live subsea wells on Norwegian sector was unknown. One operator had utilized the available

m abandonment activities on suspended wells in 1997, but with no under balance situation and no

&A) activities on the field. In the North Sea, this method was only known and field proven

ble rig to only mechanical work. No under balanced operation had to be

ouraged Statoil to perform a re-perforation of e procedure and equipment. This was the first ever diverless RLWI

nd Frontier and Island Wellserver) on a 365 days/year basis.

Fig. 7. Overview of the intervention vessels on contract for Statoil the last decade.

operation supported with specialists and decision makers onshore. The alrisk having them stuck on the vessel for two weeks due bad weather and no helicopter landings.

ncrease HSE focus I

T e RLWvessel is highly reduequipment topside. In conjunction with the absence of pipe handling, this makes RLWI a very safe intervention method HSE wise. In addition the equipment used is considerable lower weight than equipment utilized on conventional rigs. This contributes to a lower risk regards to lifting and handling of equipment in general and particular when handling equipment above templates. Finally all equipment is handled with wire, no jointed pipes are used, which lower the risk regarding falling objects.

0 years of RL1Utechnology to perforexposure to reservoir conditions. Statoils partners for the Tommeliten field asked the operator to evaluate the use of a monohull vessel and riserless technology

r the Plug and Abandonment (Pfoon UK sector. The operation was planned and performed according to the operators and Norwegian legislation and the Tommeliten P&A had the following highlights:

First riserless well intervention on a subsea well in Norwegian sector Reduced the scope for the semisubmersi

performed. Operation performed using vessel and experienced contractor from UK Employed a lump sum-all inclusive contract

pThe experience gained from the Tommeliten P&A cam

o subsea wells on the Heidrun field using the samaign, motivated and enc

twoperation (divers is not even an option on 350 m water depth on the Norwegian Continental Shelf). For the first time, a wire line tractor was also utilized in a subsea lubricator. A longer term contract was established, and that was the beginning of the regular operations with monohull vessels and iserless technology. Today Statoil operates two vessels (Islar

MSV Seawell (2000)

MSV Regalia (2003)

Island Frontier (2006 )

Island Wellserver (2009 )

MSV Seawell (2004 - 2005)

6 SPE 143296

Status Up to this day Statoil has performed more than 125 Subsea Riserless Interventions in water depths down to 400 meter. This has become the standard method for wirel on subsea wells, and has also he available information up front for planning heavier semisubmersi ions. Applications Over the last 10 years, Statoil has together with the suppliers developed and qualified new applications for this service. In the beginning only simple data gathering and down hole mechanical work was qualified, but tod everything that can be deployed using conventional wire line tec qualified and field proven.

Data gathering (PLT) Subsea fields does not have the same accessibility as dry wells, hence data gathering has traditionally been very expensive and in practical terms not available due to the requirement for a semi submersible rig. The RLWI concept has made the access to production data more cost efficient and Production Logging has become a large part of the work performed. These data enables the reservoir engineers to better optimize the production and highlight the need for production stimulation activit

Perforating/ re perforation n ption that further perf ations later in the

e availability of a cost efficient

Zone isolation (plug/ straddle) breakthrough will very often be a limited factor for the life of a well. A large portion of the work performed,

Subsea wells on the NCS is normally completed with Tubing Retrievable Surface controlled subsea safety valve. an insert valves, but when they fail, a re-completion or an insert valve is required. After the

illing of short scale bridges ll to the extent that production is choked or plug installation is made impossible, has

lls have , to

ing areas for plug setting in scaled up tubing.

ubing and Casing leak detection ation

trees &A operations of subsea wells

s some

ine interventionsble ent

improved t rig interv

ay almosthnology has been

ies.

Traditio ally the perforation strategy of subsea wells was made on the assumwell life was very costly, and making the initial perforations sub-optimal. Th

or

intervention method enables the development project to stage the perforations over time to increase the recovery factor.

Waterhas been to isolate water producing zones. Plugs can easily be installed and pulled based on updated logging data.

Inspection/repair/installation of insert TRSCSSV. They are more reliable thintroduction of RLWI services, a growing number of subsea wells have now been brought back in production by locking open the TRSCSSV and installing an insert. Normally these insert valves have a much shorter lifetime, but the OPEX impact of installing such insert valves have now been reduced since a Semi Submersible rig is no longer required to replace the valves.

MBuildup of scale in a subsea wenormally required an intervention by semi submersible rig. By utilizing scale milling equipment on wire line in combination with a wire line tractor, smaller scale bridges have been milled out and full bore access to the webeen reinstated. Also the deployment of so called strings shots have been performed through the subsea lubricatorclear tub

In addition, the intervention activities below have been successfully deployed from the RLWI vessels: T Hardware inspection: Camera and ultrasonic visualiz Well killing operation Pumping operations/Scale treatments Selective tracer injection or sampling Change-out of gas lift valves Sleeve operations DIACS valves Change out and repair of subsea P

Further on RLWI has been utilized to deal with reduced wellhead fatigue capacity wells. The RLWI equipment induces lesloads on the wellhead and the x-mas tree.. The equipment used has a considerable lower weight than rig equipment. Incases RLWI has been used to secure the wells with these fatigues capacities issues with a deep barrier prior to rig operation. When the conventional workover system for mobile rigs was out of business due to re-classification, RLWI could secure the

SPE 143296 7

wells prior to the rig intervention. The rig could then operate ithe workove

n balanced condition and perform jobs as planned without the use of r system. Commercial considerations

n the Norwegian Continental Shelf. Each of these production assets consists of the history the volume of work was not sufficient to justify a

o be able to secure availability of a vessel, the different production assets needed to cooperate r period of five years. The operator established a steering committee consisting p of partners managed to secure enough commitment to contract a vessel. A r the contracted vessel in terms of prioritizing wells, distribution of common ntervention plan is made for each year, and the basis for prioritizing is the

e original contract. Over time, more assets have joined in the contract and this ssel and when.

tem, a subsea lubricator system and ROV services all packed in one contract.

ed flexibility for the operation.

to reduced cable strength.

ng time been a field proven technology deployed from a RLWI vessel. Recent needs on a former

y of performing a complete P&A of a subsea well on NCS.

Statoil operates a number of subsea fields ooperator and a number of partners. In the beginning of the RLWI separate vessel for every asset. Tand commit a number of intervention days oveof representatives from the partners. This grou

ibility fopartner agreement defines the responscosts and distribution of weather waiting. An inumber of wells committed by each asset in th

the vePartner Agreement regulates who will get An operation team, located in Stavanger, is responsible for this activity for all Statoil operated assets on the Norwegian Shelf. This secures a good flexibility, continuity and a competence center available for the whole company. Further on, it improves the communication and day to day work with the supplier. The contract utilized for these vessels is of an all inclusive type. The contractor has the responsibility for planning and executing the interventions on the supplier. In other words, Statoil gets an intervention service consisting of a vessel with all equired crew, a wire line sysr

Needs for the Future To be able to further develop the application of monohull vessel deployed RLWI, the following methods, procedures and equipment should be developed:

Annulus access Availability to fast switch wireline access between main bore and annulus bore without re-running the intervention stack. Reduces time and cost significantly, and in the same time minimize heavy lift over well.

Tool deployment systems for longer tool strings The system currently in use has a limitation of 22 meter tool strings. To increase this length more forces has to be transferred into the structure of the lubricator and/or x-mas tree. Subsea deployment systems were longer tool strings could be built inside the well, would give a much improv

Stronger and slimmer cables for heavier tool strings and increased forces down hole Due to the limitation of the lubricator length a large diameter cable will fill up more of the lubricator with weights compared to a smaller cable. The consequence is that either one need more runs to get the scope completed or one has to reduce the maximum pulling force/payload due

Deep water Development and qualification of a riserless deep water intervention system will enable cost efficient wire line operations also on wells currently beyond economic feasible interventions.

Partial P&A has for a loStatoil asset in the South China Sea, demonstrated feasibility of a complete and permanent P&A method without using a semi submersible drilling rig. There is still a need to verify this method towards Norwegian legislation, but technically this should be a s ient wafea ible and cost effic

8 SPE 143296

CategorThe com gory A with wireline application only and have no riser attached to the well. Category B rigs/vessels have high pressure small bore riser and are able to perform heavy

terventions like coil tubing. In addition through tubing drilling is feasible with this type of vessel/rig. Conventional rigs with

ig is a smaller semi-submersible rig hull type with full Dynamic Position (DP) or mooring assisted station keeping options. It is capable to handle live well returns.

Fig. 8. Illustrate the main difference regarding RLWI, heavy intervention rig and conventional rigs.

Ambitions for Category B

The topside system would be sized for through tubing operation with 2 7/8 and 3 inch drill pipe. The coil tubing could be integrated in the rig avoiding use of riding belts and minimize heavy lifting. This will improve health, safety and environmental conditions performing these types of inventions. Compared with a conventional rig, the planned unit will be simpler to operate and need less power, will drill slimhole wells and will connect more easily to a seabed wellhead. The crew will be cross train and the rig can easily switch between the different modes of operation. Being able to pursue all three methods with a single crew eliminates the need to go to shore for modifications and to replace a specialized team trained in only one application.

y B rig pany has split the rig portfolio in three categories. RLWI vessels are in cate

inlow pressure riser are category C. These rigs also have workover equipment to perform interventions on the wells with high pressure riser. At times heavier interventions methods are required on subsea wells like coil tubing. The driving force to introduce Category B rig to the company is the cut in cost compare to conventional rigs. Category B rig is build for purpose capable of performing Through Tubing Rotary Drilling, coil tubing and wireline work. The r

Category A RLWI

Category B Heavy intervention &

TTD

Fig.9. Illustrates the operation cost per category.

Category C Drilling and completion

Wire line / tractor only Limited BHA length

Full range of through tubing services

Limited live well through tubing services

High pressure

small bore (7) riser standard

Low pressure marine riser (21) standard HP concentric riser and SSTT required for live well intervention

Category A RLWI

SPE 143296 9

Conclusions RLWI has been performed on a regular basis on NCS with high HSE standard since 2003. Two RLWI vessels are currently in operation full time for Statoil in Norway More than 125 subsea RLWI interventions since 2000 using four different vessels with high degree of success RLWI has become a routine operation with increasing demands and continuously improved operational efficiency as

an ongoing activity to meet the overall ambitions for RLWI RLWI is one of the key elements to reach Statoil IOR ambition increase oil recovery from the 463 subsea completed

wells RLWI is giving reduced operational costs (OPEX) for subsea completed fields compared with the costly alternatives Utilize category A for wireline work, and release conventional rigs to drill new wells.

Acknowledgements The authors would like to thank Statoil for permission to publish this paper. We would also like to give particular thanks to the offshore crews involved in these RLWI operations for their vital input to the successes described in this paper. They have a challenging workplace on a moving deck of a relatively small vessel operating in of the worlds most hostile environmental conditions. Nomenclature BHA Bottom Hole Assembly BOP Blow Out Preventer DP Dynamic Position DIACS Downhole Instrumentation And Co tem HP High Pressure HSE Health, Safety and Environment IOR Increased Oil Recovery NCS Norwegian Continental Shelf OPEX Operating expendit oing costs for a product/system for running it P&A Plug and AbandonmPLT Production Loggin l RLWI Riser Less Well Intervention

R SSV Tubing Retrievable Surface Controlled Subsurface Safety Valve TT ing Drilling

ntrol Sys

ures ongent

g Too

ROV Remote Operated Vehicle STT Subsea test tree S

T SCD Through Tub

UK United Kingdom References

1. Frode Martin Nordvik (Ministry of Petroleum and Energy), Signe Berg Verlo and Evy Zenker (Norwegian Petroleum Directorate) Facts 2010 - The Norwegian petroleum sector, June 2010.

2. http://www.statoil.com/en/ouroperations/pages/default.aspx

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