Proceedings of the Eleventh (2001) International Offshore and Polar Engineering Conference Stavanger, Norway, June 17-22, 2001 Copyright © 2001 by The International Society of Offshore and Polar Engineers ISBN 1-880653-51-6 (Set); ISBN 1-880653-55-9 (VoL IV); 1SSN 1098-6189 (Set)

Deepwater Production System Risks

E.G. Ward, Texas A&M University, College Station, TX, USA Robert B. Gilbert, University of Texas at Austin, Austin, TX, USA

JihadJaber, GeoSytec Consultant, Atlanta, GA, USA Andrew J. gZolford, EQE International, Houston, TX, USA

ABSTRACT

A comprehensive study of risks associated with deepwater production systems has been completed. The Offshore Technology Research Center (OTRC) undertook the study for the Minerals Management Service (MMS) to compare the risks of FPSO's with exiting deepwater production systems (now operating in the Gulf of Mexico (TLP's, Spars, and Fixed Platforms serving as transportation hubs for deepwater production.). This comparison was needed to assist the MMS decision making and poliey development processes regarding the future permitting of FPSO's in the Gulf of Mexico. FPSO risks were found to be similar to other existing deepwater systems. The OTRC's unique attributes and relationships with both the MMS and the industry contributed greatly to the success of this study.

INTRODUCTION

FPSO's are a potentially attractive system for some deepwater Gulf of Mexico oil and gas developments. While FPSO's have been successfully used in many offshore areas worldwide, none have been used to date in the Gulf. The Minerals Management Service (MMS) is the government regulatory authority for offshore oil and gas development in the United States. The MMS asked the Offshore Technology Research Center (OTRC) to complete a study to compare the risks of an FPSO with risks typical for existing deepwater development systems now operating successfully in the Gulf. Results from this study plus other information will be used by the MMS as a basis for policies and decisions regarding the use of FPSO's in the Gulf.

FPSO risks were compared to those of other existing deepwater production systems that are now successfully operating in the Gulf of Mexico. The existing systems considered were TLP's, Spars, and Fixed Platforms serving as transportation hubs for deepwater production. Risks were compared for similarly sized systems throughout a prescribed 20-year operational lifetime. Risk measures emphasized safety to personnel and the environment. The risks for all four systems were found to be comparable.

The study was a unique collaboration between regulatory agencies, the industry, and academia. The OTRC was able to utilize its relationships with industry and the MMS to provide an effective

interface that facilitated the discussion and resolution of complex issues from the perspectives of both the MMS and the industry. This collaboration contributed greatly to the success of this study.

DESCRIPTIONS OF DEEPWATER PRODUCTION SYSTEMS FOR THIS STUDY

The conceptual designs for each of the generic FPSO, TLP, Spar, and Hub/Host systems studied included both the physical and operational characteristics of the systems, and were developed to ensure the following: 1. The TLP, Spar and Hub/Host Jacket systems should represent

existing systems and technologies that are currently being used in the Gulf of Mexico.

2. The FPSO system should be comparable to that already developed for the base case in the Environmental Impact Statement (EIS) study (Minerals Management Service, 2000).

3. The study systems should be as functionally and operationally as comparable and consistent as possible to one another as to ensure that differences in risks reflect realistic differences in the systems and are not an unintended result of design assumptions. The objective of this study was to evaluate risks during all

aspects of offshore production including oil and gas production and processing offshore; drilling and well intervention during production; export of the oil and gas to shore; and transport of personnel to and from shore. The "lifetime" for each system was defined to start at first production and end when all production ceased. This study did not address the construction, installation, commissioning, decommissioning and removal phases in the life of the systems.

The overall systems included production facility, the pipelines and shuttle tankers used to transport oil to a shore terminal, and the supply vessels and helicopters used to support the production operations, as indicated in Figure 1 and Table 1.

RISK MEASURES

Risk measures for the study systems were developed to: 1. Provide relevant and useful input to MMS in their decision

making process; 2. Be tractable and quantifiable;

654

3. Reflect measures that are currently tracked and recorded to allow available historical data to be used to develop and support the results of this risk analysis and to provide a basis for understanding the future performance of actual systems.

From these criteria, the risk measures listed in Table 2 were adopted for this study. The total number of fatalities is a measure the human safety risks. The total volume of oil released in the lifetime is a measure chronic environmental risk. The maximum volume of oil released in a single incident is a measure acute environmental risk. Each risk measure was treated separately in comparisons and no attempt was made to combine them into a single measure, such as equivalent cost.

O a s Flan.ge ~vc.---.~ O"

I • % Gas ~ Shuttle

' "' FP $0 Spar

Figure 1. Layout for Systems

Table 1. Attributes of Systems

Water Depth (ft) Peak Production

Oil (bopd) Gas (scfpd)

Export Oil (bopd) Gas (scfpd)

Wells Pre-Drill (MODU)

Platform Subsea (MODU)

Manning Production

Marine Drilling (Platform) Drilling (MODU)

Spar TLP Hub/Host Jacket FPSO

4,000 4,000 600 5,000

150,000 150,000 7 5 , 0 0 0 150,000 200,000 200,000 5 0 , 0 0 0 200,000

150,000 200,000

30-45 6 65 65

150,000 200,000

275,000 550,000

30-45 0 50 65

30-45 6 65 65

150,000 200,000

30-45 10 0 65

QUANTITATIVE RISK ASSESSMENT

The objective of the quantitative risk assessment was to quantitatively evaluate and compare the risk measures listed in Table 2 for the four systems. Since there is an extremely limited experience base in the Gulf of Mexico for the types of production systems being evaluated in this study, it is not possible to obtain average values directly from historical data. Thus values for averages these risks had to be predicted for hypothetical systems operated in the future in the Gulf of Mexico. Such predictions are statistical in

nature and expected values, standard deviations, and confidence limits are used to characterize the risks.

Table 2. Risk Measures

Risk Measure of Risk Unit

Total Fatalities over Number of Human Safety Production Lifetime Fatalities

Total Volume of Oil Environmental - Chronic Spilled over Production Bbl of Oil

Lifetime

Environmental Maximum Single Spill Volume in Production bbl of Oil

- Acute Lifetime

The quantitative risk assessments were developed through a process of identifying the hazards, developing preliminary risk assessments and then refining those assessments using the input of the technical experts in a workshop process as shown in Figure 2.

The participation of technical experts from industry was coordinated and facilitated through the DeepStar industry consortium. Over 100 experienced engineers representing all segments of the industry (oil companies, consultants, contractors) plus representatives from the regulatory agencies (MMS and US Coast Guard) actively participated and contributed to this study. They brought a detailed understanding of the risks as well as practical design and operational knowledge and options to manage these risks. These engineers served on teams formed to study the four production systems (FPSO, TLP, Spar, and Hub/Host) and provided detailed information on hazards and risks. The practical experience and perspective that these engineers brought to the study was a critical factor to the success of the study.

The general process for the quantitative risk assessment is described below. Details on the methodology and the data used for this study are published elsewhere (Gilbert, Ward, and Wolford, 2001a; Gilbert, Ward, and Wolford, 2001b; Gilbert and Ward, 2000).

Hazard Identification. Hazards and resulting consequences for the various subsystems (platform and subsea wells, topsides, risers, flowlines, pipelines, FPSO cargo tanks, shuttle tankers) and operations (drilling, production, well intervention, oil and gas transportation, supply, personnel transfer) were evaluated for each of the four systems, i.e. the FPSO, TLP Spar, Hub/Host Platform. Considerable effort and care went into the hazard identification, as this would then become the basis for the risk analyses. There were numerous meetings with industry experts in each of the subsystems and operations. Care was taken to understand the similarities and differences between each subsystem and operation for the four systems to ensure that the comparative risk analysis would reflect meaningful similarities and differences. The relationships between the various subsystems and operations and the risk measures are shown in Table 3. The hazard identification was reviewed and refined by the technical experts in Workshop #2.

Preliminary Risk Assessments Preliminary quantitative risk analyses were developed prior to workshops #3 and #4. These preliminary analyses were then used as a basis to elicit quantitative information from the technical experts during these workshops and maximize the value of the information obtained during the workshops.

6 5 5

Draft System Descriptions

Workshop #1 System Definition I Develop System Descriptions

I Develop Preliminary Event/Outcome Tables

Workshop #2 Hazard Identification Elicit Event/Outcome Information

I Conduct Preliminary QRA

Workshop #3 Quantitative Risk Analysis Elicit Frequency/Consequence Input

I Refine QRA & Perform Additional Studies

I Workshop #4 - Review Review QRA

Figure 2. Flowchart for Quantitative Risk Analysis Process and Workshops

Table 3. Subsystem and Operational Categories Used in Risk Assessment

Risk Sub-System Categories

Measure

Fatalities

Oil Spills

Production System

Transportation System

Production Drilling

Supply Vessels Helicopter Transport Tanker Operations

Major Accident Well Systems - Platform (or

Surface) Well Systems - Subsea

Dry Tree (or Production) Risers Flowlines

Import Flowline Risers (Floating Production Systems)

Topsides Supply Vessels

Drillin[~ and Intervention Pipelines

Export Pipeline Risers (Floating Production Systems)

Shuttle Tanker (Offloading in Field and at Port) FPSO Cargo Tank

The philosophy adopted in developing the preliminary risk assessments was to extrapolate directly from publicly available historical data in the Gulf of Mexico to predict future performance. Since there is no experience and data on FPSO operations in the Gulf nor is there a comprehensive public database on FPSO operations

from other offshore areas where they have been used, data on tanker activity in the Gulf and elsewhere and lightering operations in the Gulf (NRC, 1998; Ward and Scoggins, 1999) were used to characterize FPSO risks.

The methodology used to develop the preliminary risk assessments is summarized as follows. Data sets were first divided into the sub-system and operational categories shown in Table 3. Fatality data were then summarized as the total number of fatalities in the data record for each sub-system. The data for oil spills were further sub-divided into categories by the size of the spill, and the number of incidents for each spill-size category was compiled. The data for oil spills were divided into categories because the range of spill volumes per incident covered five to six orders of magnitude.

Exposure factors were identified for each subsystems and operation based upon the characteristics of the subsystem or operation and the type of information that was available in the historical data records. The exposure factor is a measure of the rate at which - opportunities for a hazard or risk can occur. For example, some of the exposures used in this study were: • Port calls as a measure of shuttle tanker trips • Mile-years as a measure of the transportation ofoil by pipelines • Man-hours as a measure of crew activities during drilling,

production, well intervention, etc. • Passenger-trips as a measure of helicopter travel The exposure factor allows the risk estimates to be applied to each system based on the exposure to the risk for that system.

Estimates for the frequency of occurrence for hazards or incidents for each subsystem or operation relative to its exposure factor were developed statistically and described by their expected value and standard deviation.

The risk measures (fatalities and barrels of oil spilled) for each system's subsystems and operations were then estimated from the exposures and frequencies of hazards, and were characterized by the expected value and standard deviation.

The component subsystem and operational risks were then combined to develop the total or overall risk for each system. These total risks were also described by the expected value and standard deviation. Note that this component approach provided a means of (1) identifying the relative contributions to the total system risk from each subsystem or operation and (2) comparing the relative individual component risks between the four systems.

Final Risk Assessments. The preliminary risk assessments were then refined through the workshops to develop final risk assessments. Refinements included: • Evaluating and refining data sets to ensure that the data

ultimately used to predict future system performance was based on historical data that was relevant and characteristic of current and future practices. For example, the data set for oil spills from tankers in the Gulf of Mexico was limited to years after 1990 to account for the effects that the Oil Protection Act of 1990 (OPA90) will have on future performance.

• Modify estimates and extrapolations of future performance that were based strictly on historical data to better reflect current and future conditions and thUS more accurately characterize future performance. For example, the frequencies for small spills from subsea well systems were increased from the data-based extrapolations to account for differences between subsea well systems and the platform well systems that dominate the data set.

• Modify estimates and extrapolations of future performance that were based strictly on historical data to better reflect physical reality and thus more accurately characterize future performance. For example, the sizes of large pipeline oil spills were limited by physical constraints

656

Account for all sources of uncertainty in the estimates, including the following: • the limited quality and quantity of relevant data records,

especially for rare events; • the sometimes sketchy information available on the

exposures corresponding to the data sets; and • the extrapolation of future performance from historical

performance.

RESULTS

Results for the final quantitative risk assessments for fatalities and oil spills are discussed below. Expected values, standard deviations, and confidence limits are used to characterize the risk results. The expected value represents the predicted value for the actual average, while the standard deviation represents the magnitude of uncertainty in the prediction. The expected value and standard deviation were used to calculate confidence intervals for the predicted risks for this study. The 90-percent confidence intervals are used to describe the results; there is a ninety-percent chance that the expected value will be within the indicated intervals.

Fatality Risks. Results for the average total number of fatalities during the 20-year lifetime are shown in Figure 3 for each system. The total fatality risks are very similar for the four study systems. The expected contributions to the total fatality risk are shown on Figure 4. Production and drilling and well intervention activities dominate the total fatality risks for all four systems, because the bulk of the man-hours or exposure during the 20-year lifetime are devoted to these activities. The risk components for the TLP, Spar, and the Hub/Host are similar.

FPSO risks includes fatalities due to shuttle tanker operation, which are naturally not relevant for the other systems.

The magnitudes of these rates are comparable to those reported for typical industrial activities (e.g., AIChE 1989).

Spar/TL.P B P~o d~lctiea

El ~/llh~ and Iatex~gion

[] Supp b, Vessels

• Hel;¢optcr Tratlsp od

la Ta¢_l "l~r Opcrafionz

== l~'~jo:, Ae~qd©nt

Hub/Host Jacket FPSO

:::::::::::::::::::::::::

Figure 4. Contributions to Fatality Risks

3.0 W

5 ¢. "6 2.0

"~ ,E 1.o

o.o > <

IIII 90% confidence intervals

I I I Hub/Host

Spar TLP Jacket FPSO

System

Figure 3. Fatality Risks

Note that the contribution of drilling and intervention activities to the total fatality risk for the FPSO is smaller than for the other systems. Since all FPSO wells are subsea wells and it was assumed that well intervention would be less frequent due to well design, and difficulty and cost of intervention, the man-hours (exposure) drilling and intervention activities for fatalities is lower. Also note that the

Oil Spill Risks. The annual frequencies of oil spills for various spill volumes are shown in Figure 5. The frequencies decrease and the magnitude of the uncertainty increases with increasing spill volumes. This is natural outcome of the fact that large spills are rare events such that there are few occurrences from which to estimate the frequencies (and volumes) of large spills.

Spills of up to 1,000 barrels are generally dominated by production related activities. The frequencies are generally the same for the TLP, Spar, and FPSO. The frequencies are slightly smaller for the Hub/Host because of the lower production rate for this system.

Spills greater than 1,000 barrels are generally dominated by transportation related activities. The transportation systems for the TLP, Spar, and Hub/Host are all pipelines. The exposure factor for pipeline spill risks is mile-years. Spill frequencies for the TLP and Spar are indistinguishable due to design and operational similarities in the pipeline portions of the systems. Spill frequencies for the Hub/Host are slightly smaller due to the shorter length of the pipeline to shore.

Shuttle tankers are the transportation system for the FPSO, and the exposure factor for oil spills is the number of port calls or trips. For spills between 1,000 and 100,000, the spill frequencies for the FPSO shuttle tanker system are lower than that for pipelines. This is in part due to the fact that the potential for pipeline spills remains constant as long as there is oil in the pipeline regardless of the natural decline in production rate during the system lifetime. The potential for shuttle tanker spills decreases with decreasing production as fewer trips or port calls are required.

Large spills exceeding 100,000 barrels are possible although rare for the FPSO system. A spill in the 100,000 - 500,000 barrel category represents a major loss from a collision or explosion involving a shuttle tanker. A spill larger than 500,000 barrels represents a major loss from a collision or explosion involving the FPSO. Large spills exceeding 100,000 barrels are not considered

657

possible for the pipeline systems due to operational practices and safety systems that would shut in a failed pipeline and physical constraints that limit the volume that would leak out after shut-in.

Results for the average total volume of oil spilled during the 20- year system lifetime are shown on Figure 6 for each system. The total oil spill risks are very similar for the four systems.

1.0E+01

1.0E+00 "E" ~>, 1.0E-01

1.0E-02

~' 1.0E-03 0)

1.0E-04 ii

"~ 1.0E-05 t-

1.0E-06

W.lr, . .

• Spar

# TLP

• Hub/Host Jacket

& FPSO

E ected,alu '"11 tt1, interval II |

e go go

~ q N , . . o

o

Spill Size (bbl)

go go o

o g o - o o g

to

Figure 5. Annual Frequency for Spills from All Sources versus Spill Size

10000 90% confidence intervals 8000

~--~ 0 I I Average/!o T°tal 'Q. ~ 6000 ¢/} •

~6 ~ 4000 Hub st F O

Spar TLP Jacket System

Figure 6. Oil Spill Risks

The total risks for all of the deepwater systems (Spar, TLP and FPSO) are nearly identical even though the frequencies for different spill sizes are not identical, as discussed above and shown in Figure 5. This results because risk is a measure both of frequency and consequence (spill size). Analyses showed that most of the risk for the FPSO resulted from spill sizes ranging from 100,000-500,000 barrels, and that such spills are expected to occur only once every

4,500 years. Most of the risk for the TLP and Spar systems resulted from spill sizes of 10,000-100,000 barrels, which are expect to occur once in 600 years. Thus the larger but rarer FPSO spills and the smaller but more frequent pipeline spills results in comparable risks for the TLP, Spar and FPSO. One effect of the spill risk being dominated by rare, high consequence events is that the confidence intervals in the average oil spill volumes in Figure 6 range over nearly an order of magnitude. This uncertainty reflects the typically limited quantity and quality of historical data available to estimate frequencies for rare events. The risk for the Hub/Host is slightly smaller than the other systems because it has a smaller production rate and a shorter transportation distance to the shore.

The relative contributions to the total oil spill risk from different sub-systems are shown in Figure 7. Transportation activities, which dominate the larger spill sizes, are the main contributors to the total oil spill risk. Production related activities, which tend to dominate the smaller spill sizes, do not contribute substantially to the total risk.

Spar/'rLP

Hub/Host Jacket

In Well Systems - Rafform 13 V~II Systems - Subsea

D Dry Tree Risers I Row lines

• Import Row line Risers El Topsides r-I Export Pipeline Risers

• Rpelines B Shuttle Tanker • FPSO Cargo • Supply Vessels • Drilling and Intervention

FPSO

Figure 7. Contributors to Oil Spill Risks

CONCLUSIONS

Results of this study indicate that the expected risks associated with the FPSO are comparable to those of other deepwater production systems now successfully operating in the Gulf of Mexico, namely TLP's, Spars, and platforms serving as a Hub/Host to deep-water production. Specifically, these results show: • There are no significant differences in the fatality risks between

the four systems. • There are no significant differences in the oil-spill risks between

the four systems. The major contribution to the oil spill risks for all systems is the transportation of oil from the production facility to the shore terminal. Spill risks for pipelines and shuttle tankers are comparable even though the frequencies and sizes of possible spills are different. Rare, large spills rather than frequent, small spills will dominate the average total volume of oil spilled during the facility lifetime.

658

The unique attributes and relationships between the OTRC with the MMS and the industry provided an effective interface and forum to discuss complex issues from both the regulatory and industrial perspectives. This contributed greatly to the success of this study.

This study was performed for deepwater production systems in the Gulf of Mexico, but the approach and methodology are useful for other offshore areas and to support other risk-based decisions.

ACKNOWLEDGMENTS

The authors wish to acknowledge the Minerals Management Service for funding this project. Specific individuals at MMS who have been instrumental in this study are Paul Martin, Charles Smith and James Regg. The DeepStar Consortium was instrumental in coordinating and facilitating the involvement of industry experts i n this study. Allen Verret, now a Private Consultant, was most effective in representing DeepStar and its interface with this study. And finally, the authors gratefully acknowledge the industry experts whose participation and contributions were vital to the success of this study.

REFERENCES

AIChE (1989), "Guidelines for Chemical Process Quantitative Risk Analysis", Center for Chemical Process Safety of the American Institute of Chemical Engineers, New York.

Gilbert, R.B. and Ward, E.G. (2000), "Planned Approach for Comparative Risk Analysis of Deepwater Production Systems in the Gulf of Mexico, ' Proc o f OMAE 2000:19 t~ International Conference on Offshore Mechanics and Arctic Engineering, New Orleans, LA, in press.

Gilbert, R.B., Ward, E.G., and Wolford, A.J. (2001a), "Comparative Risk Analysis for Deepwater Production Systems" final report prepared by the Offshore Technology Research Center for Minerals Management Service (available at http://www.mms.gov and http://otre.tamu.edu).

Gilbert, R.B., Ward, E.G. and Wolford, A.J. (2001b), "Preliminary Results from Comparative Risk Analysis for Deepwater Production Systems," International Conference on Safety, Risk, and Reliability - Trends in Engineering, IABSE, Malta, in press.

Minerals Management Service (2000), "Proposed Use of Floating Production, Storage, and Offloading Systems on the Gulf of Mexico Outer Continental Shelf," Final Environmental Impact Statement prepared for the Minerals Management Service, Gulf of Mexico OCS Region (available at http://www.mms.gov).

National Research Council (1988), "Oil Spill Risks from Tank Vessel Lightering", Washington D.C., National Academy Press

Ward, E.G. and Clark, T. (1999), "Oil Spill Risks from Tanker Vessel Lightering: A Marine Board Report, Proc. Offshore Technology Conference, Paper 10706, Houston, May 1999

659