![ISOPE-2010- Lessons Learnt from Recent Deepwater Riser Projects
Jean-François Saint-Marcoux,
Acergy, London, UK
Marin Abelanet
Acergy, Singapore, Singapore
Stéphane Bombino
Acergy, Paris, France
ABSTRACT
Major Risers development Projects have been launched recently (Total
CLOV and Petrobras Pre-salt to name a few). The Business strategy of
major Oil and Gas companies with regards to Subsea Umbilicals
Flowlines and Risers is evolving towards a more segmented approach
requiring optimization of each individual element of the SURF
package. This in turn requires a thorough review of the capabilities of
the concept of each segment to a level that was not considered before.
Acergy has gathered experience in all types of flowlines (rigid,
flexibles, bundles) and risers (SCR’s, Flexibles, single and bundle
Hybrid riser Towers). In particular, Acergy has pioneered the use of
Hybrid Riser Towers and have completed in 2007 the largest bundle
HRT to-date.
The paper will focus on how Risers become industrialized products
with their components being systematically organized through a
technical hierarchy. This in turns allow a detailed FMECA and a
structured detailed engineering package. From the structured
engineering package, result robust interfaces for material sourcing and
Fabrication.
KEY WORDS: Risers, FMECA, Hybrid Riser Towers, Risers,
Ultra-deepwater, Industrial model
NOMENCLATURE
ANSI: American National Standard Institute
API: American Petroleum Institute
BT: Buoyancy Tank
CRA: Corrosion Resistant Alloys
FEED: Front End Engineering Design
FJC: Field Joint Coating
FMECA: Failure Modes, Effects and Criticality Analysis
FPSO: Floating Production Storage and Offloading [unit]
FPU: Floating Production Unit
GOM: Gulf of Mexico
HRT: Hybrid Riser Towers
IMR: Inspection, Maintenance, Repair
ISO: International Standard Organization
LRA: Lower riser assembly
NACE: National Association of Corrosion Engineers
OHTC: Overall Heat Transfer Coefficient
OREDA: Offshore Reliability Data
PIP: Pipe in Pipe
PLET: Pipeline End Termination
SCM: Supply Chain Management
SCR: Steel Catenary Risers
SLOR: Single Line offset Risers
SURF: Subsea Umbilicals Flowlines and Risers
URA: Upper Riser Assembly
INTRODUCTION
As ultra deepwater1
fields are being developed, it becomes more and
more clear that, with the notable exception of the Gulf of Mexico,
FPSO based field architecture with wet Xmas trees is becoming the
norm. Typical examples are Total Angola CLOV development and
Petrobras Brazil Tupi area fields.
Operators, to a large extent, handle themselves directly or through
engineering companies their overall field developments. These field
developments include: Flowlines, Risers, and Floating Production
Units. They expect cost effective solutions and, as they have done for
other areas of petroleum industry, they split their ultra-deepwater scope
of work into segments: Flowlines, Risers and Umbilicals. Therefore it
is for the contractors as they provide any of these segments to adapt
their offer accordingly. As has been well known for centuries,
industrialization is the only solution to achieve a step change in cost-
effectiveness. This paper specifically deals with ultra-deepwater risers
as one of these segments.
STAKES
Industrialization brings cost-effectiveness and reliability through
standardization and repeatable processes. For a basically tailor-made
equipment such as HRT, this implies adapting methods that are of
frequent use in serial manufacturing industries, for instance System
Engineering and Value Analysis concepts.
The main stake is to find relevant tools, among general industrial
engineering methodologies, that can apply to this specific problem, and
that meet operators needs.
The frame to this industrialization / standardization is given by the
following complementary objectives:
1) Structured feedback and lessons learnt through a standardized
description of studied equipment:
- Conceptual description, functional approach;
- Physical description, organized list of equipments and
technologies, maturity approach;
- Organizational description (packages and suppliers tiers
1
Taken as deeper than 1800m per ANSI/API 17A](https://image.slidesharecdn.com/f762fede-a043-4f24-9565-f9d1ecce0848-150824204407-lva1-app6891/85/ISOPE-2010-TCP-0462-Lessons-Learnt-from-deepwater-Riser-Projects-1-320.jpg)
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
- 1. ISOPE-2010- Lessons Learnt from Recent Deepwater Riser Projects Jean-François Saint-Marcoux, Acergy, London, UK Marin Abelanet Acergy, Singapore, Singapore Stéphane Bombino Acergy, Paris, France ABSTRACT Major Risers development Projects have been launched recently (Total CLOV and Petrobras Pre-salt to name a few). The Business strategy of major Oil and Gas companies with regards to Subsea Umbilicals Flowlines and Risers is evolving towards a more segmented approach requiring optimization of each individual element of the SURF package. This in turn requires a thorough review of the capabilities of the concept of each segment to a level that was not considered before. Acergy has gathered experience in all types of flowlines (rigid, flexibles, bundles) and risers (SCR’s, Flexibles, single and bundle Hybrid riser Towers). In particular, Acergy has pioneered the use of Hybrid Riser Towers and have completed in 2007 the largest bundle HRT to-date. The paper will focus on how Risers become industrialized products with their components being systematically organized through a technical hierarchy. This in turns allow a detailed FMECA and a structured detailed engineering package. From the structured engineering package, result robust interfaces for material sourcing and Fabrication. KEY WORDS: Risers, FMECA, Hybrid Riser Towers, Risers, Ultra-deepwater, Industrial model NOMENCLATURE ANSI: American National Standard Institute API: American Petroleum Institute BT: Buoyancy Tank CRA: Corrosion Resistant Alloys FEED: Front End Engineering Design FJC: Field Joint Coating FMECA: Failure Modes, Effects and Criticality Analysis FPSO: Floating Production Storage and Offloading [unit] FPU: Floating Production Unit GOM: Gulf of Mexico HRT: Hybrid Riser Towers IMR: Inspection, Maintenance, Repair ISO: International Standard Organization LRA: Lower riser assembly NACE: National Association of Corrosion Engineers OHTC: Overall Heat Transfer Coefficient OREDA: Offshore Reliability Data PIP: Pipe in Pipe PLET: Pipeline End Termination SCM: Supply Chain Management SCR: Steel Catenary Risers SLOR: Single Line offset Risers SURF: Subsea Umbilicals Flowlines and Risers URA: Upper Riser Assembly INTRODUCTION As ultra deepwater1 fields are being developed, it becomes more and more clear that, with the notable exception of the Gulf of Mexico, FPSO based field architecture with wet Xmas trees is becoming the norm. Typical examples are Total Angola CLOV development and Petrobras Brazil Tupi area fields. Operators, to a large extent, handle themselves directly or through engineering companies their overall field developments. These field developments include: Flowlines, Risers, and Floating Production Units. They expect cost effective solutions and, as they have done for other areas of petroleum industry, they split their ultra-deepwater scope of work into segments: Flowlines, Risers and Umbilicals. Therefore it is for the contractors as they provide any of these segments to adapt their offer accordingly. As has been well known for centuries, industrialization is the only solution to achieve a step change in cost- effectiveness. This paper specifically deals with ultra-deepwater risers as one of these segments. STAKES Industrialization brings cost-effectiveness and reliability through standardization and repeatable processes. For a basically tailor-made equipment such as HRT, this implies adapting methods that are of frequent use in serial manufacturing industries, for instance System Engineering and Value Analysis concepts. The main stake is to find relevant tools, among general industrial engineering methodologies, that can apply to this specific problem, and that meet operators needs. The frame to this industrialization / standardization is given by the following complementary objectives: 1) Structured feedback and lessons learnt through a standardized description of studied equipment: - Conceptual description, functional approach; - Physical description, organized list of equipments and technologies, maturity approach; - Organizational description (packages and suppliers tiers 1 Taken as deeper than 1800m per ANSI/API 17A
- 2. models). 2) Assess failures: - Record what went wrong or can go wrong - Better identify where effort must apply to avoid critical dysfunctions - Complete functional knowledge of equipment through dysfunctional approach Dysfunctional modes Functional modes Unknown Known Dysfunctional modes Functional modes Standards scope Unknown Known Fig. 1 Failures assessment role in standardization As described in Fig.1 failure phenomena and scenarios knowledge improves general knowledge of behavior of equipment, hence allowing better standardization of products and methods. AN EXAMPLE OF METHODOLGY John Milton remarked “Truth and understanding are not such wares as to be monopolized and traded in by tickets and statutes and standards”. Yet in spite of this early recognized difficulty, there has been a continuous push to make available the firmer part of current understanding into codes and standards and the ANSI-API 17/ISO 13628 series of recommended practices can be seen as the most recent attempt to do so in the deepwater offshore industry. This effort is further carried out internally by companies and contractors. The Fig.2 delineates the simplified workflow process of new concepts as they are being developed. The deliverable of the first phase is a functional analysis whereby the various requirements, from operational to construction (fabrication and installation) are clearly identified. The major drivers are: - Flow assurance requirements - Met ocean conditions - Site location - Yard fabrication procedure - Offshore construction The second phase consists of the Front End Engineering Design. This starts with the definition of a concept consistent with the functional requirements. This is validated with: - Pre-design analyses - FMECA The third and final phase is the delivery of the documents required for Supply Chain Management (procurement services and their associated management) and then for construction (fabrication and installation procedures) Of course, this straightforward scheme is in reality much more complex because of overlaps between the phases, different owners of the phases, not to mention changes along the duration of a particular project. Fig. 2 Workflow of new riser concept development To a certain extent it may be said that deepwater risers such as flexible risers or SCR are single bore units and therefore do not require as much standardization as HRT’s. By its inherent flexibility in design (selection of the number of conduits HRT’s in a field and selection of the number of HRT’s) it lends itself to fit for purpose solution for each field. Therefore the remaining of the paper will concentrate on HRT’s.
- 3. The figures 3 and 4 below respectively describe - a turret-moored FPSO in ultra deepwater with two HRT’s (Fig.3) - an HRT fabrication yard (Fig.4) Fig. 3 Deepwater FPSO based development with HRT’s Fig. 4 Deepwater HRT fabrication HRT FUNCTIONAL ANALYSIS AND STANDARDIZATION Industrialization means that pragmatic choices have to be made, and that those choices must be robust with intended projects and with regards to potential changes. Functional analysis allows making those choices judiciously. Flow Assurance Pressure containment at design temperature is usually the driver and requires high strength steel. However because of the potential for reservoir souring API 5L grade X65 is usually the highest grade used because of its compliance with NACE MR-01-75. It is therefore reasonable to standardize on API 5LX65, and to consider CRA as an option in presence of high CO2. If CRA is justified it will require less buoyancy and therefore will be even more cost effective compared to other riser types. Wet insulation cover a wide range of Overall Heat Transfer Coefficient and long cool down time. Unlike other riser systems, HRT risers can be coated with a large thickness of wet insulation without the limitation on installation squeeze pressure of flexibles, or the limitation of w/D ratio of dynamic risers. If an OHTC-value of less than 1.5 W/m2 .K is required, Pipe-in-Pipe solutions are feasible. Therefore Wet insulation is the selected standard with PIP as an option. With regards to the number of risers per tower it can be seen that one riser per tower (SLOR) may lead to layout difficulties whereas large number of risers may lead to impractical sizes of buoyancy tank. Standard sizes would be from 4 to 8 main risers2 . Site location and Met ocean Conditions The current ultra-deepwater field developments appear to target areas with a maximum water depth of 3000 to 3500m. This is about the maximum water depth encountered in the GOM, and in the Mediterranean Sea. And therefore the concept should be acceptable to these depths. This is the case because buoyancy foam which provides buoyancy along the bundle has been already qualified by drillers. The in-place dynamics of an HRT is low and therefore a wide range of met ocean conditions can be accommodated. Met ocean conditions affect essentially: - Towing (surface current and waves period and directionality) - Depth of the buoyancy tank (depth at which the current is still significant) Fabrication and Installation The basic principle is that under usual conditions onshore fabrication is more cost effective. Additionally quality control techniques are more easily implemented onshore or even inshore. Still onshore construction can be adapted to the locally available constructions site: - Complete onshore construction of the full length of the tower - Construction segments with inshore jointing (patent pending) 2 This number refers to Production,, Water Injection, and Gas Injection or export risers. Gas lift risers are smaller and not a driver of the bundle architecture and therefore not included in these figures.
- 4. The same standard design with minor differences can accommodate onshore or inshore construction. Reversible installation operations allow simpler de-commissioning or re-location. This feature was used as early as in 1995 (Fisher and Berner 1988; Fisher, Holley, and Brashier 1995). TECHNICAL HIERARCHY As HRT’s (both monobore –SLOR- and multibore) are becoming more and more known a standardization of the HRT has appeared: - Jumper - Buoyancy Tank (BT) - Upper Tower Assembly (URA) - Bundle - Lower Tower Assembly (LRA) - Suction piles - Spool The HRT being considered a system, these elements are called “sub- systems” as shown in Fig. 5 Sub-system Bundle BUN Riser base RBA Buoyancy tank BTA URA URA LRA LRA Jumpers/spools JPS Others OTH Fig.5 Identifiers of sub-systems of an HRT. With the introduction of a technical hierarchy of system, sub-system, unit, equipment, part, and component it becomes feasible to identify completely all elements of the “System HRT”. As an example Fig. 6 shows the full decomposition of the production riser down to the individual weld. System Sub-system Unit Equipment Part Component Name 2 3 4 5 6 7 x Hybrid riser tower x Bundle x Production riser x Rigid risers x DJ x Joint x Weld Fig. 6 Use of the Technical Hierarchy levels to describe the HRT down to its lowest level The Technical Hierarchy provides the frame to identify each component of the system down to the individual fabrication operation. It allows both a top-down and a bottom-up view. As such it allows answering the following example questions: - which part, unit or system can be affected by the failure of a particular weld? - Which welds would be affected by a change in service conditions? The Technical Hierarchy provides a mean of tracking each individual element from engineering, to procurement, fabrication and installation. In particular: - Engineering documents can be referred to a particular level of the technical hierarchy - Interfaces are readily identified - Procurement can be performed at the most cost effective level with regards to cost and delivery - Quality Control can be tracked to the same level Besides the Technical Hierarchy allows proceeding with the FMECA. HRT FAILURE MODES, EFFECTS AND CRITICALITY ANALYSIS The FMECA was conducted by Acergy on its preferred “standard” architecture. Principles The FMECA covers all stages of the life of the HRT: - Installation of the suction anchor - Fabrication in the yard, and inshore as applicable - Installation towing - Installation upending - Spools and jumper connections - Pre-commissioning - Service life The following assumptions were made: - Design is compliant with codes and industry standards - Design is compliant with specific design analyses developed by Acergy for similar systems (Total Angola Girassol, BP Angola Greater Plutonio, ExxonMobil Angola Block 15 Gas Gathering) - Extreme and operating conditions as provided by operators are not exceeded - Causes originating in Fabrication that may affect service conditions are included - Detailed risk analyses will be performed for each specific project - Suitable maintenance is provided during service life - Failures are mutually independent, but common mode failures are included where necessary - All parts are manufactured by qualified suppliers with an approved quality control system Fabrication Fabrication risks are related to lifting and handling of parts and sections of the bundles.
- 5. Connections can be monitored through onshore quality control and hydrotest. It is easier to consider the fabrication and the sheltered water assembly as a single phase because the same tools are available there. The Fig. 7 is a diagram of the fabrication process. To the left is the yard fabrication of the sub-systems: buoyancy tank, upper riser assembly, bundle, lower riser assembly and flexibles. To the right is the sheltered water area where the bundle is assembled to the URA and the LRA. Fig. 7 Location of Risks at Fabrication phase (low risks omitted for clarity) Towing Upending Main risks are localised at interfaces between the various sub-systems in particular at URA and LRA where moment and loads are concentrated. Unexpected human intervention should be minimized: contingency plan should detail tasks to a sufficient level, in order to be able to anticipate contingency risks assessment. Normally the suction anchor will have been installed long before to allow settling of the soil. The Fig. 8 shows both the towing and upending configurations. Those two operations re performed in a relatively short period of time, typically a week, by a dedicated fleet of vessels and crew. During tow care should be exercised to minimize fatigue. This is achieved by a proper selection of the route and depth of tow. The upending operation is conducted in a matter of hours. Fig. 8 Risks at towing and upending phase (low risks omitted for clarity) Service Risks can be grouped as per functions, as follows: - Loss of containment which can be mitigated by pressure and temperature monitoring - Structural integrity: in particular tension provided by the buoyancy tank; This is the rationale behind the monitoring of the HRT. Monitoring can also include the position of the top of the HRT for early assessment of undesired trend. The Fig. 9 shows the risks in service. The risks are essentially: - loss of buoyancy of the buoyancy tank - tether connection - erosion in the goosenecks - loss of permanent buoyancy of the bundle due to water creep - integrity of the risers weld - rotolatch connection - integrity of the spools All of these risks are well identified and mitigated through engineering per design codes specialized material qualifications. Such facilities have been in service for ten years and this contributes greatly to the assessment of the risks. Through the OREDA database it is possible to quantitatively assess the risks of various subsea components and in particular connectors.
- 6. Fig. 9 Risks in service (low risks omitted for clarity) Summary Risk criticality is assessed from consequence severity and causes frequency. See Tab.1. It would be difficult to cascade FMECA into a detailed quantitative RAM analysis, because it covers a huge variety of concepts, but a few quantitative parameters could be analyzed: - frequency provided by OREDA database - number of failure causes reviewed - relative proportion of high severity cases Tab. 1 Table of frequency vs. severity Frequency Severity 1 Very unlikely 2 Unlikely 3 Possible 4 Likely 5 Very likely 5 Very serious M M H H H 4 Serious L M M H H 3 Moderate L L M M H 2 Slight L L L M M 1 Negligible L L L L M The results of the FMECA are as follows: - 2 High severity risks - 194 Medium severity risks - 437 Low severity risks These results are summarized in Fig. 11 Total 0% 31% 69% H M L Fig. 10 distribution of risks for an HRT It is interesting to note that the two high risks identified are the connection at the top and bottom of the HRT, as resulting from the OREDA (2002) database. These connections are of course inevitable, and therefore it can be concluded that the proposed design of the HRT does not provide any additional high risk. PRACTICAL IMPLICATIONS First immediate outcome of FMECA is a sorted list of critical failure scenarios that are mitigated throughout detailed design phase. In other words, it is a qualitative reliability and availability assessment. Then, a check-list can be extracted from tables to improve technical risk management in design: Tab. 2 : Example of check list of failure modes coverage. Standard or spec Part Failure mode Cause / phenomenon, Ref § Comments Joint Crack Overpressure ANSI/API… Another classical outcome of a FMECA is IMR support dossier. It justifies the preventative inspection and maintenance actions, and corrective actions. It allows issuing a preliminary list of spare parts, to be optimized by operating Company from own feedback and policy. This justified, anticipated approach can simplify spare standardization. CONCLUSIONS The recent deepwater projects have fostered an independent review of HRT concepts. This is opening the door to their industrialization. It also can be seen that the level of risks of HRT is acceptable as not significant risk is added by a carefully selected architecture. Further standardization of engineering will allow shorter delivery and improved costs.
- 7. ACKNOWLEDGMENTS The authors acknowledge Acergy for allowing them to prepare this paper. The contribution of Jean Pierre Branchut, Jean-Luc Legras, Gregoire de Roux, Blaise Seguin and Johann Declerq to several aspects of the subject of this paper is gratefully acknowledged. Nevertheless this paper only reflects the opinion of its authors and does not imply endorsement by the company to which acknowledgements are made. REFERENCES ANSI/API RP 17 A (ISO 13628-1) Design and Operation of Subsea Production Systems – General Requirements and Recommendations. January 2006 ANSI/API RP 17 N Recommended Practice for Subsea Production System Reliability and Technical Risk Management, March 2009 DNV RP-A203 Qualification Procedure for New Technology Fisher, E., A., Berner, P., C. (1988), “Non-integral Production riser for Green Canyon Block 29 Development”, OTC 5846, Houston, TX Fisher, E., A., Holley, P., Brashier, S. (1995), “Development and Deployment of a Free-standing Production Riser in the Gulf of Mexico”, OTC 7770, Houston, TX ISO IEC Guide 73 (2002) Risk Management – Vocabulary Guideline for use in Standards ISO 20815 (2008) Petroleum and Natural Gas Industries – Production Assurance and Reliability Management OREDA (2002) Offshore Reliability Data Handbook, 4th edition, DNV