SPE-170980-MS

Subsea Well Intervention: Recent Developments and Recommendations toIncrease Overall Project Returns

M.E. Nelson, Chevron U.S.A. Inc.; P.G. McLeroy, Texas A&M University

Copyright 2014, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in Amsterdam, The Netherlands, 2729 October 2014.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contentsof 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 reflectany position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the writtenconsent 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 maynot be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

As the subsea industry ages, the number of premature subsea well shut downs are increasing due toinsufficient well intervention programs. In the past, subsea well interventions have not been widely usedbecause of a lack of economic feasibility; however, with appropriate project planning, the recent economicclimate, and advances in well intervention technology, a greater overall project return can be realized byimplementing a proactive well intervention program. While intervention on surface wells is a familiartopic, the benefits and negative consequences of more recent subsea intervention developments, such asriser-less light well intervention, riser-less mud return, and well flow back and testing, are evaluated.These different well intervention methods carry varying amounts of risk with them, with the potential togreatly enhance or diminish well performance and thus affect recoverable hydrocarbons. The risksinvolved with the different well intervention methods are evaluated and recommendations are made as towhich methods are utilized depending on desired return rates and risk aversion levels. Recommendationsare made for implementing a successful well intervention program, such as production monitoring,scenario planning, application of a dedicated multi-disciplinary team, cross-organizational collaboration,and logistical improvements. With an effective well intervention program, reservoirs can be furtherexploited, potentially increasing project return and supplying hydrocarbons to a demanding global market.

IntroductionSecondary Recovery Methods Integral to Initial Field DevelopmentEmploying secondary recovery methods is becoming integral to initial onshore field development in orderto achieve maximum hydrocarbon returns. Original onshore field development practices consisted ofoperators exhausting primary depletion, then installing waterflood facilities and converting producers towater injectors. This caused a protracted period of reservoirs being without pressure support, leading tocomplications with shut-in wells and underutilized pipelines and facilities. An early success in changingthis approach was in the high-risk Arctic development, the Kuparuk River Field (Nelson 2007). Kuparuksinitial production began in 1981 and by the end of 1982, ninety wells were completed, 75 of themproducers. Immediately following the wells being brought online, waterflooding began in January 1983.This increased the expected ultimate recovery from 350-600 million to 1.25-1.5 billion barrels of oil. Theproject faced considerable technical challenges in waterflooding due to the cold temperatures of the North

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Slope, but due to the focus placed on reservoir management rather than just field development, thetechnical challenges were overcome and waterflooding helped the project surpass production levels aheadof schedule. Similar to what was experienced in Kuparuk, secondary recovery methods made integral toinitial subsea well field development could help achieve maximum hydrocarbon production, and thus,maximum project returns.

Remaining Reserves in Subsea WellsA clear picture of the opportunity for improved oil returns in subsea wells is seen in a report discussingimproved oil recovery for deepwater Gulf of Mexico (GOM) reservoirs, prepared for the ResearchPartnership to Secure Energy for America (RPSEA) (Lach 2010). Per the report, for 56 major GOMoil-producing fields that began production from 2000 to 2009, the average remaining oil in place (ROIP)per field is 66 MMBOE. In other terms, the volume-weighted average Return Factor (RF) for majoroil-producing fields in the GOM is 28.9%. For further illustration, the forecasted ROIP for the 45 largestNeogene / Pleistocene reservoirs in deepwater GOM is shown in Fig. 1. There is strong evidence forimproved oil recovery in subsea GOM reservoirs, in addition to improving overall project economics oncethought unachievable. Sunk project costs associated with initial development of the subsea fields are nowfurther covered with subsea interventions that offset production declines; capturing more reservesultimately. By use of a secondary recovery method through subsea well interventions, a greater return canbe achieved.

Operators OptionsAn operator has three fundamental options when a subsea well becomes uneconomical to produce, i.e. thecosts to recover the hydrocarbons are greater than the value of the hydrocarbons produced. One option isto launch a subsea intervention campaign or employ a larger scale secondary recovery method in an effortto increase the production rate of more than one uneconomic well. The second option is to shut-in orpotentially abandon the well. The third option is consideration of selling the well in a package if theoperator is opting to exit. Due to the fact that the well needs intervention work to begin flowing with moreeconomic efficiency no matter the owner, the selling operator would have to sell their working interest at

Figure 1Forecast ROIP at cessation of production for 45 largest developed Neogene fields (Lach 2010, his Fig. 43).

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a discounted price. An economic intervention is likely the best option to produce maximum returns for theoriginal operator; much like performing preventive maintenance in operations to maintain value of theassets. Since subsea well interventions come at a great cost and require extensive coordination betweenmultiple parties, approaching subsea well interventions proactively ensures an operator will achievemaximum returns from their subsea well portfolio.

Overview of Subsea Well Interventions Operations

DefinitionsFor clarity, a few definitions are presented. A subsea well intervention (SSWI) is defined as any instancewhen a physical connection is made to a completed well to alter production. SSWI Methods are the meansused to physically connect to the well. SSWI Operations are the activities performed while re-entering thewell. The purpose of the following sections is to provide the reader an overview of SSWI operations usedand the requirements placed on the most commonly used SSWI methods.

SSWI operations are implemented to alter a wells performance by either physically entering the wellto perform work or pumping fluids into the well. While there are numerous, varying types of well workperformed during interventions, for the purposes of this discussion, the main SSWI operations areclassified into the following categories, explained briefly and identified by their main requirements.

Pumping OperationsPumping into a well is the simplest form of intervention. Production enhancement is achieved by pumpingchemicals downhole in an effort to change the production rate. This type of operation includes wellacidizing to improve fluid flow and using methanol to inhibit hydrate formation. The main requirementfor pumping operations is a connection that enables hydraulic communication.

Wellhead / Christmas Tree Maintenance OperationsA SSWI operation servicing subsea infrastructure varies greatly depending upon the condition of theequipment being serviced and the manufacturers recommended maintenance procedures. This wouldinclude pressure testing the surface and subsurface equipment and performing any necessary greasing.Depending on the severity of the operation, the main requirement for this operation is hydrauliccommunication.

Wireline (Slickline) OperationsA slickline is a single strand wire that enters the wellbore. The purpose of the slickline is to run tools intothe wellbore for placement or removal. Additionally, a slickline can be used to perform different tasksincluding memory logging and gauge cutting (Larimore et al. 1997). The main requirement for a slicklineoperation is hydraulic communication and a conduit by which the slickline may be lowered into thewellbore.

Wireline (Braided line) OperationsA braided line is a more complex version of a slickline and is typically used for heavy fishing operationswhen the slickline is not sufficiently strong enough to safely lower and raise the equipment. It may containinsulated wires, which can be used for logging and perforating purposes. A braided line operation requireshydraulic communication and a conduit, as well as a grease injection system to ensure that the BlowoutPreventer (BOP) can seal around the braided contours of the line. Furthermore, it requires an additionalshear-seal BOP as a tertiary boundary.

Coiled Tubing OperationsCoiled tubing is metal pipe used to carry out operations similar to wireline. It has some benefits overwireline techniques due to the ability to pump chemicals directly to the bottom of the well through thetubing. Likewise, coiled-tubing operations can be used for circulation, logging, drilling and production

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operations. In a subsea environment, coiled tubing requires a hydraulic connection to a mobile drilling unitas well as a rigid conduit through which it can reach the wellbore.

Snubbing OperationsSnubbing, also known as a hydraulic workover, can be performed in live wells. It involves running abottom hole assembly (BHA) on a drill string against wellbore pressure to perform the desired tasks, suchas fishing or milling (Ford et al. 2011). Snubbing is advantageous over other live well interventionmethods due to its small footprint on the rig, ability to reach great depths, and rigidity to apply high weighton bit. Modern snubbing units require complicated hydraulic systems and a rigid conduit to the well.

Tubing Retrieval OperationsTubing retrieval refers to pulling and replacing the tubing hanger and production tubing usually due toperformance deterioration. It is an expensive operation due to the complexity of the procedure. Typicallytubing retrieval is performed on older wells or if the well integrity is severely threatened or due tochanging reservoir conditions which require a new completion. The main requirement for tubing retrievalis full wellbore access.

Overview of Subsea Well Interventions Methods

SSWI Method: Blowout Preventer (BOP)One form of attaching to a well for a SSWI is by using a Mobile Offshore Drilling Unit (MODU) equippedwith a full bore drilling riser and BOP, attaching to a subsea Christmas Tree (XT) to gain well access.BOPs maintain well control during the intervention, containing high wellbore pressures and formationkicks. BOPs are used throughout drilling and completion operations, thus operators and drilling contrac-tors have the greatest familiarity with this SSWI method. The main advantage of using a BOP as anintervention method is full-bore access to the well; however, this comes at a great cost. Day rates ofdeepwater MODUs can be in excess of $1MM USD/day. Pulling the subsea BOP due to performanceissues is a risky and costly operation, requiring several days, if not weeks, depending on the performanceissue and because the well needs to be plugged, requiring the mud column to be evacuated out of the riser.

SSWI Method: Completion / Workover Riser SystemCompletion / workover riser systems are very similar in function to the BOP SSWI method. They containequipment used to maintain well control and emergency disconnect systems; however, they utilize asmaller riser system, supplying a conduit to the well that is smaller than the full wellbore. The use of smallbore BOPs increases this methods well control reliability. This method is most ideally deployed on anintervention vessel, typically demanding smaller operating expenses than full-size MODUs (Kharuna etal. 2003).

Because Marine risers create a direct link between a vessel and the wellhead for intervention, they canbe used for a variety of SSWI operations using coiled tubing and wireline intervention. Coiled tubing isa favored intervention method that allows for mud circulation and chemical injection, making a risersystem very valuable for such operations. However, the riser system can be cost prohibitive whenperforming wireline and e-line tasks, which can be achieved at a smaller cost using riserless interventions.The deeper the riser is placed, the greater risk of failure due to the increased loads placed on the hoistingequipment and greater stress levels on the riser. Also, vessel motion results in cyclic top tension on theriser, which is increased as the size of the riser increases (Ambrose et al 2001).

Ultimately, the costs and risks associated with using the completion / workover riser method is relatedto the specific vessel chosen for operations; using small vessels equipped with a completion / workoverriser system in deepwater environments can be unreliable and using a larger vessel can be on the samelevel of cost as a MODU equipped with a full bore BOP. Risk may be mitigated with the implementationof improved riser design, using with materials lighter than steel, thus reducing cyclical fatigue issues.

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SSWI Method: Riserless Light Well Intervention (RLWI)Riserless light well intervention consists of utilizing a monohull vessel and various intervention packagesdepending on the intervention operation being performed. The variety of operations is extensive,including, but not limited to, running e-line to gather data, re-perforating the well, installing plugs forzonal isolation, tubing and casing leak detection, hardware inspection, well-killing operations, pumpingoperations, and the change-out and repair of subsea XTs. (Fjaertoft et al. 2011)

The costs of this intervention method are greatly reduced, sometimes by more than 50%, becauseintervention work is performed by smaller vessels as opposed to larger, more expensive MODUs orintervention vessels. RLWI vessels have been successful in shallow regions, such as the North Sea, buthave operational limitations in ultra deepwater (5000 ft.) (BSEE 2008). RLWI methods typically havereduced environmental impact compared to larger SSWI methods. They are generally considered a saferintervention method because any fire or explosion threat is significantly reduced as hydrocarbons are notreturned to the vessel during operation. RLWI induces lighter mechanical loading on the wellhead and XTthan BOPs or completion / workover packages by using lightweight intervention packages.

While the small size of the vessels used in RLWI provides a multitude of advantages, it also limits theiroperational functionality. Operational delays due to uncontrollable factors such as weather can be costlyto a SSWI campaign. A significant disadvantage this method is that it lacks rigid conduit to the wellbore,thus eliminating its use from intervention operations such as snubbing and tubing retrieval.

As a relatively new intervention method compared to those previously mentioned, the oil and gasindustry still has a lot to learn about the full limitations of RLWI. With regards to deepwater drilling, theRWLI method can still be improved with respect to productivity, sensitivity to weather phenomena, anddeepwater compatibility. A specific area for improvement in RLWI would be the development of strongerwireline cables, increasing the ability to deploy larger intervention equipment packages (Munkerud et al.2007). RLWI vessels have been used successfully in wells around the world, generating industry wideinterest in the potential cost saving associated with method. As this intervention method matures,experience and technology gaps will be filled, improving the reliability of RLWI.

SSWI Method and Operation CompatibilityThe compatibility of specific SSWI method and operation combinations depend on the technicalrequirements of the operation and the cost effectiveness of the method. In determining basic compatibility,the following method and operational characteristics were taken into consideration:

Drilling vessels demand the highest day-rates of the SSWI methods, therefore are reserved whenfull bore access is required.

The completion / workover riser method is most suitable for coiled tubing operations when a rigidconduit is required, however, it is typically a more expensive and complex operation than wireline.

RLWI vessels are cable of pumping, wireline, flow back, XT retrieval/installation operations; and,RLWI is the most cost efficient method of the wireline operations.

Technical challenges prevent RLWI vessels from performing coiled tubing operations. Researchand development efforts are underway to enable the use of coiled tubing without the use of a risersystem.

Each method and operation combination is designated a compatibility level in Fig. 2. Greenindicates that the method and operation are technically compatible and cost-effective. Redindicates that either using a method with a specific operation would be too cost prohibitive or nottechnically feasible. Yellow indicates that the operation could be performed using this method, butthat there are currently more cost-effective or safer alternatives.

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Proactive Approach: Focus on New TechnologiesAs with most new technologies, the associated risks initially reside with a lack of field experience. Withmore field applications with SSWI specific technologies, the costs associated with the risks in usinginfant technologies will reduce.

The BOP SSWI method has the lowest risks associated with technological familiarity because theequipment is used every day for drilling and completion work; however, this method comes at the highestcost due to the size and capabilities required of the vessels used to employ it (Fjaertoft 2011).

The completion / workover riser method is more established than RLWI methods. The main risks usingthis method are a result from the high pressure, small bore riser used. The riser is exposed to very highstress levels, potentially leading to costly failures. Minimizing the risers weight would have significantbenefits, including the reduction of dynamic stress issues. Using lighter riser would allow the use ofsmaller vessels as possible impact on vessel motion would decrease, which would decrease operationalcosts and increase the ability to run operations at greater depths. (Ambrose et al. 2001).

RLWI has less field experience, so the risks associated with the lack of technical familiarity can beviewed as greater than that for the BOP or completion / workover riser system. To its advantage,operations performed by RWLI methods have proven to be much more cost effective than both BOP onXT and completion / workover riser interventions. RLWI is the most cost effective method for wirelineoperations, increasing in efficiency as stronger wirelines are developed (Munkerud et al. 2007). Thedevelopment of stronger subsea cables would increase the possible size of intervention packages and theability for RWLI vessels to operate in harsher, deeper subseas. Developments in operational technologycould lead to the ability for coil tubing to be deployed from monohull vessels used in RLWI methods,reducing the cost of coil tubing operations traditionally performed from a MODU or by completion /workover riser systems. Weather continues to be a significant challenge for the smaller vessels used inRLWI. To mitigate this cost, strategic planning of interventions to occur during calmer weather seasonscould be cost effective.

Reactive Approach: Missed OpportunitiesRisk analysis and decision making is an integral part of major subsea projects. Before widespreadadaptation of the practice along with stage-gated project management, most problems in the field weretackled as situations arose. Given the time and costs associated with situational analysis, more methodicaldecision analysis was incorporated into major capital projects. Today, the common practice is to prepare

Figure 2While some SSWI methods and operations are compatible, not all are economically advisable.

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contingencies, rehearse emergency plans, and schedule operational staff for round the clock coverage toaddress problems that might arise in the high cost environment of subsea development and production.

Similar proactive decision and risk analysis applied to SSWIs would enable increased interventionreaction time, thus improving projects returns.

For example, results from SSWI campaigns from 2002 to 2007 are charted in Fig. 3 and Fig. 4, referredto as Case 1 and Case 2 (McGennis et al. 2008). These case studies were taken from subsea wells locatedin the United Kingdom sector of the North Sea, where the average water depth is approximately 300 ft.(European Observation Network Territorial Development and Cohesion 2013). The interventions wereperformed with a light well intervention vessel, having an average intervention operation time of 8.5 days.

In Case 1, the cumulative recovered oil from the SSWI was approximately 720,000 bbls. With anaverage crude price of $58/bbl from July 2004 to June 2005, the additional recovered oil from Case 1 isvalued at approximately $41.5MM. (Visual 2012) The reaction time from the well collapsing to theintervention going online was six months. Using a conservative rate of return of 3.5% in a simple TimeValue of Money (TVM) calculation, if the well were intervened in two months, one-third of the time, asavings of $487k would be realized.

In Case 2, the cumulative recovered oil was approximately 345,000 bbls. With an average crude priceof approximately $71/bbl from September 2006 to September 2007, the additional recovered oil fromCase 2 is valued at approximately $24.6MM USD. Using a conservative rate of return of 3.5% in a simpleTVM calculation, if the well were intervened in one- third of the time, a savings of $484k would berealized.

At first, the savings made by improving the response time of the interventions in Case 1 and Case 2might not seem substantial; however, these improvements in production are seen on wells much different

Figure 3Case 1 SSWI with follow-on increase in hydrocarbon production. (McGennis 2008, his Fig. 7)

Figure 4Case 2 SSWI with follow-on production increases. (McGennis 2008, his Fig. 10)

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than modern deepwater wells. Production rates in deepwater subsea wells are orders of magnitude higherand their SSWI intervention reaction times are much longer. The savings realized from a similar reductionin intervention reaction time would be much more substantial on major deepwater subsea well interven-tions.

Proactive Approach: Intervention Planning TeamThe financial analysis indicates that a delay in SSWIs, defined as the time between the identification ofthe problem (unexpected or undesired change in production levels) and the implementation of the solution(physically entering the well) can be costly, potentially leading to a situation where an intervention wouldno longer be economically feasible. The execution of a SSWI can be broken into three general stages,illustrated in Fig. 5.

Recognizing the Problem

Recognizing that theres a drop in production levels is not a simple task. Fig. 3 and Fig. 4 highlightproduction rates can be erratic; therefore, an algorithm, such as a Kalman filter, helps to identify a trend.This could take considerable time before the downward trend is recognized, so the more data monitoredand processed, the more likely time could be reduced. Determining what data should be gathereddownhole and on the XT is decided early in a subsea development project; so, planning for an interventionat the early stage of a project and building in the necessary production monitoring equipment is vital toreducing the time it takes to realize there is a problem in the well.

Developing a SolutionOnce the problem is recognized, a team of the necessary disciplines must be assembled to brainstormsolutions, risk assess options, and follow through with the necessary analysis. The creation of such a teamtakes time due to various commitments and competing projects. Once the team is created, a plan is devisedand vetted, and readied for deployment. This part of the overall three-staged process can take months,further delaying production improvements and potentially affecting project economics.

Deploying the SolutionThe necessary operational support, personnel, equipment, and materials, has been identified when thesolution was developed. Now logistical problems can arise. Manufacturers have considerable lead times,vessels could be tied up with other work, additional personnel might needed, organizational funding andsupport are required - all of these factors can further delay an operator from deploying a SSWI campaignif an operator has not adequately planned and built SSWI costs into their standard operations.

Facing Ambiguity: Managing a Well Intervention PortfolioThe ability of an organization to function in ambiguity is necessary to succeed in fields that contain a greatdeal of unknowns, such as subsea well interventions. Scenario planning, a process that identifies plausible,not probable, future scenarios in an effort to improve organizational flexibility has been in use at large

Figure 5Project economics are greatly affected by lengthy reaction times.

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organizations, such as Royal Dutch Shell, since the 1970s (Wilkinson 2013). These efforts have createddirect economic value when evaluating specific scenarios and have given Industry a greater ability torecognize, decipher, and react to change. Similarly, creating a multidisciplinary team dedicated to subseawell intervention scenario planning could increase an operators response time and thus economic gain insubsea wells. A team consisting of all interested parties- reservoir, completions, operations - could becontinuously developing what if scenarios for SSWIs for an operators portfolio. By continuouslyanalyzing production rates, reservoir conditions, qualities of the producing hydrocarbons, ability tomobilize equipment, a dedicated SSWI team could enhance an operators ability to reduce ROIP througheffective intervention operations.

After experiencing a rapid decline in oil production in Oman fields, the Northern Oil Directorate ofPetroleum Development Oman (PDO) increased its well intervention activity aggressively, doubling wellintervention expenditures in a period of 4 years. The Well Services division of PDO managed this increasein well intervention activity through several project management approaches, including the Interventionand Life Cycle and Feedback loop shown in Fig. 6. This is similar to closed loop processes widely usedthroughout the oil and gas industry, commonly referred to as Lessons Learned of After ActionReviews. By employing similar methodologies, a SSWI planning team could improve an operatorsSSWI portfolio, successfully predicting the need for and properly executing SSWIs. (Aihevba 2004)

SSWI Recommendations Best PracticesAcross Organization CollaborationWhen exploring a new technological frontier, as the oil and gas industry is with SSWI, it is vital tocollaborate with other invested organizations to ensure mutual success. Lasting partnerships betweenoperators and contractors may provide benefits for both parties while sharing rewards and mitigating risksif they are founded on shared trust and cooperation. Such partnerships could guarantee a greater commonknowledge of risk associated with a project and ease misalignment of interest, which increases thedecisions available to mitigate risks effectively. Common issues leading to an increase in risk include alack of communication and information, resulting in a lack of common goals and an unhealthy relationshipbetween business partners. The planning stages of a project are crucial, and when contractors are involved,often they can provide technical advice based on experience, which mitigate risks and decrease costs forthe operator while helping to develop stronger relationships. During planning, important project data anddocuments should be shared between the operator and contractor in order to make specific informationavailable to both parties (Imana et al. 1996). In addition to relationships between industry partners, there

Figure 6Adapted from Aihevba (2004), using a closed loop process would enhance intervention effectiveness and execution.

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have been joint efforts between academia and industry throughout the United States to collaborate onresearch in order to achieve goals as evidenced by the RPSEA and DOE partnership in 2005 to improvedeepwater production, technology, and cost effectiveness and to meet high level industry needs (Schr-oeder et al. 2009).

Improving LogisticsWhile there has been extensive discussion about potential improvements to SSWI execution, logisticalsuccesses between business partners have been previously experienced. One such case study reviews howa SSWI campaign was performed successfully by a RWLI vessel on seven wells from December 2011 toMarch 2012 off the coast of Equatorial Guinea (Bosworth et al. 2013). The operation was planned fromHouston, the vessel contractor was located in Aberdeen, UK, and the vessel was mobilized to operate inWest African waters; therefore, effective project management and efficient logistical execution was vital.Planning started 6 months before the operation mobilized and the project engineers worked with the clientat their corporate office in Houston. During the planning period, weekly conference calls were heldbetween Houston, Aberdeen, and Malabo in order to keep all parties updated and resolve any challenges.Project engineers had to organize and communicate aspects of the operation and maintain constantcommunication with all parties in order to finalize the execution plan, mitigate potential risks, and updateequipment status. Also, several requirements were reviewed to ensure employees had necessary paper-work and vaccinations for working in West Africa, while communication with official shipping agentsallowed for customs clearance for the vessel and equipment to be completed without any setbacks.

The SSWI campaign took 66 days while the total transit time of the vessel from the UK to Africa andback took just 39 days, stressing that the logistical flexibility of RWLI, without need for standby vesselsand reduced helicopter flights, allowed for the operations to be performed more efficiently and costeffectively than if other methods were used. This case study highlights how effective project managementand improved logistics between business partners throughout the planning stages is crucial to determiningthe success of RLWI during the operational stage.

ConclusionsTo attain the great financial rewards from improving the recovery of hydrocarbons from subsea fields,efforts should be focused not only on well development, but improving reservoir performance. Subseawell interventions are a key method to offsetting production declines and potentially improving hydro-carbon recovery. However, proactive efforts are needed to improve the relevant technologies andexecution strategies. Investment needs to be made in improving existing SSWI technologies, fillingtechnological voids that exist in the more affordable intervention methods. Methodical SSWI decision andrisk analysis aligned with stage-gated project management from the initial stages will enable organizationsto respond when unexpected production problems arise. This includes dedicating skilled personnel, tocontinuously evaluate well performance and the ability of an organization to counter declining production.Operators can no longer approach subsea well interventions in a reactive manner if maximum returns areto be gained from the ever increasing number of aging subsea wells.

AcknowledgementsThe authors would like to acknowledge the intensive efforts by Gojko Matovic in assisting with theresearch presented in this paper and to the Texas A&M Harold Vance Department of PetroleumEngineering for providing research support. A specific acknowledgement goes to Professor Priscilla G.McLeroy in recognition of her guidance in shaping and refining the direction and purpose of the paper andinvaluable contributions. The author would also like to give a special acknowledgment to David L.ODonnell for his personal and professional mentorship throughout the authors career.The authors would also like to acknowledge the efforts of the individuals and teams conducting oil and

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gas operations, plus drilling contractors, service providers, equipment manufacturers, academic institu-tions, and others who have made individual and collaborative efforts to advance subsea well interventiontechnology and execution. This is a new and challenging frontier and continued efforts to work togetheras an industry will enable meeting the worlds energy needs for generations to come.

Nomenclature

BHA Bottom hole AssemblyBOP Blowout PreventerDOE United States Department of EnergyGOM Gulf of MexicoMM MillionMODU Mobile Offshore Drilling UnitPDO Petroleum Development OmanRF Recovery FactorRLWI Riserless Well InterventionROIP Remaining Oil in PlaceRPSEA Research Partnership to Secure Energy for AmericaSSWI Subsea Well InterventionTVM Time Value of MoneyUSD United Stated DollarsXT Christmas Tree

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Subsea Well Intervention: Recent Developments and Recommendations to Increase Overall Project Re ...IntroductionSecondary Recovery Methods Integral to Initial Field DevelopmentRemaining Reserves in Subsea WellsOperator's Options

Overview of Subsea Well Interventions OperationsDefinitionsPumping OperationsWellhead / Christmas Tree Maintenance OperationsWireline (Slickline) OperationsWireline (Braided line) OperationsCoiled Tubing OperationsSnubbing OperationsTubing Retrieval Operations

Overview of Subsea Well Interventions MethodsSSWI Method: Blowout Preventer (BOP)SSWI Method: Completion / Workover Riser SystemSSWI Method: Riserless Light Well Intervention (RLWI)

SSWI Method and Operation CompatibilityProactive Approach: Focus on New TechnologiesReactive Approach: Missed OpportunitiesProactive Approach: Intervention Planning TeamRecognizing the ProblemDeveloping a SolutionDeploying the SolutionFacing Ambiguity: Managing a Well Intervention Portfolio

SSWI Recommendations Best PracticesAcross Organization CollaborationImproving Logistics

Conclusions

AcknowledgementsReferences