ogp_434-2_blowoutfrequency

Risk Assessment Data Directory

Report No. 434 – 2March 2010

I n t e r n a t i o n a l A s s o c i a t i o n o f O i l & G a s P r o d u c e r s

Blowout frequencies

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RADD – Blowout frequencies

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contents

1.0 Scope and Definitions ........................................................... 1 1.1 Application ...................................................................................................... 1 1.2 Definitions ....................................................................................................... 1

2.0 Summary of Recommended Data ............................................ 2 3.0 Guidance on use of data ........................................................ 6 3.1 General validity ............................................................................................... 6 3.2 Uncertainties ................................................................................................... 6 3.3 Example ........................................................................................................... 6 4.0 Review of data sources ......................................................... 7 4.1 Basis of data presented ................................................................................. 7 4.2 Onshore blowouts ........................................................................................ 11 4.3 Other data sources ....................................................................................... 12 5.0 Recommended data sources for further information ............ 12

6.0 References .......................................................................... 13


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Abbreviations: BOP Blowout Preventer DNV Det Norske Veritas EUB Alberta Energy and Utilities Board GoM Gulf of Mexico HPHT High Pressure High Temperature NSS North Sea Standard OCS (US) Outer Continental Shelf UKCS United Kingdom Continental Shelf


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1.0 Scope and Definitions 1.1 Application This datasheet presents (Section 2.0) frequencies of blowouts and well control incidents. They are intended to be applied to well operations worldwide, both offshore and onshore, as indicated in the table headings.

1.2 Definitions The following definitions are taken from [1]: • Blowout An incident where formation fluid flows out of the well or

between formation layers after all the predefined technical well barriers or the activation of the same have failed.

• Well release An incident where hydrocarbons flow from the well at some point where flow was not intended and the flow was stopped by use of the barrier system that was available on the well at the time of the incident,

• Shallow gas release

An incident where shallow gas is released from the well after a gas zone has been penetrated before the BOP has been installed (any zone penetrated after the BOP is installed is not a shallow gas incidents)

• Oil well A well where the formation has an estimated gas/oil ratio (GOR) less than 1,000

• Gas well A well where the formation has an estimated gas/oil ratio (GOR) exceeding 1,000

• HPHT well A well with an expected shut-in pressure equal to or above 690 bar (10,000 psi) and/or bottom hole temperatures equal to or above 150°C (300°F)

• North Sea Standard (NSS) operation

Operation performed with BOP installed including shear ram and two barrier principle followed

• Production Production, injection and closed in production wells • Well intervention Completion, wireline, coiled tubing, snubbing and other

workover operations • Wireline Wireline operations in production or injection wells (i.e. not

wireline operations carried out as part of drilling and completion operations)

• Workover Workover activities (not including wireline, snubbing or coiled tubing operations). Often referred to as "heavy workover"


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2.0 Summary of Recommended Data For well operations in the North Sea and in other offshore areas where the equipment is of North Sea Standard (see Section 1.2), Scandpower’s analysis [2] of SINTEF’s blowout database is recommended. For well operations in other areas of the world, SINTEF’s own analysis [1] of the database is recommended. Both sets of data are tabulated below. In the original reports [1,2] they are presented in different ways, however so far as possible the tables below are consistent in layout for easy comparison. For North Sea Standard operations, [2] does not give separate frequencies for topside and subsea releases, except for shallow gas releases. DNV have estimated the fractions of subsea releases where applicable; these are also included in the table below. For onshore operations, comparable data were not found. It is recommended to use the offshore data presented here. Some possibly indicative values are presented in Section 4.2.


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Blowout and Well Release Frequencies for Offshore Operations of North Sea Standard

Frequency Operation Category Averag

e Gas Oil Unit

Fraction

Subsea Topside Blowout 6.0 × 10-4 - per drilled

well

Diverted Well Release 8.3 × 10-4 - per drilled well

Well Release 9.3 × 10-5 - per drilled well

Exploration Drilling, shallow gas

Subsea Blowout 9.8 × 10-4 - per drilled well

Topside Blowout 4.7 × 10-4 - per drilled well

Diverted Well Release 6.5 × 10-4 - per drilled well

Well Release 7.3 × 10-5 - per drilled well

Development Drilling, shallow gas

Subsea Blowout 7.4 × 10-4 - per drilled well

Blowout 3.1 × 10-4 3.6 × 10-4 2.5 × 10-4 per drilled well

0.39 Exploration Drilling, deep (normal wells)

Well Release 2.5 × 10-3 2.9 × 10-3 2.0 × 10-3 per drilled well

0.39


0.39 Exploration Drilling, deep (HPHT wells)


0.39


0.33 Development Drilling, deep (normal wells)


0.33


0.33 Development Drilling, deep (HPHT wells)


0.33

Blowout 9.7 × 10-5 1.4 × 10-4 5.4 × 10-5 per operation 0 Completion Well Release 3.9 × 10-4 5.8 × 10-4 2.2 × 10-4 per operation 0 Blowout 6.5 × 10-6 9.4 × 10-6 3.6 × 10-6 per operation 0 Wirelining Well Release 1.1 × 10-5 1.6 × 10-5 6.1 × 10-6 per operation 0 Blowout 1.4 × 10-4 2.0 × 10-4 7.8 × 10-5 per operation 0 Coiled Tubing Well Release 2.3 × 10-4 3.4 × 10-4 1.3 × 10-4 per operation 0 Blowout 3.4 × 10-4 4.9 × 10-4 1.9 × 10-4 per operation 0 Snubbing Well Release 1.8 × 10-4 2.6 × 10-4 1.0 × 10-4 per operation 0 Blowout 1.8 × 10-4 2.6 × 10-4 1.0 × 10-4 per operation 0 Workover Well Release 5.8 × 10-4 8.3 × 10-4 3.2 × 10-4 per operation 0 Blowout 9.7 × 10-6 1.8 × 10-5 2.6 × 10-6 per well year 0.125 Producing Wells

(excluding external causes) Well Release 1.1 × 10-5 2.0 × 10-5 2.9 × 10-6 per well year 0.125 Blowout 3.9 × 10-5 3.9 × 10-5 3.9 × 10-5 per well year 0.125 Producing Wells, external

causes Well Release - - - per well year - Blowout - 1.8 × 10-5 - per well year 0.125 Gas Injection Wells Well Release - 2.0 × 10-5 - per well year 0.125 Blowout 2.4 × 10-6 - - per well year 0.125 Water Injection Wells Well Release - - - per well year -


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Blowout and Well Release Frequencies for Offshore Operations Not of North Sea Standard

Operation Category Well Type

Frequency Fraction

Subsea Appraisal 1.3 × 10-3 per drilled

well 0.59 Blowout (surface flow)

Wildcat 1.9 × 10-3 per drilled well

0.59

Appraisal 01 per drilled well

02 Blowout (underground flow)

Wildcat 01 per drilled well

02

Appraisal 3.2 × 10-4 per drilled well

0 Diverted well release


0


1.0


Well release


1.0

Blowout (surface flow) - 9.6 × 10-4 per drilled well

0.18

Blowout (underground flow) - 4.4 × 10-5 per drilled well

02

Diverted well release - 7.0 × 10-4 per drilled well

0


Well release - 8.8 × 10-5 per drilled well

0


0.41 Blowout (surface flow)


0.41


- Blowout (underground flow)


0.172


- Diverted well release


-


1.03

Exploration Drilling, deep

Well release


1.03

Blowout (surface flow) - 3.5 × 10-4 per drilled well

0.14

Blowout (underground flow) - 1.3 × 10-4 per drilled well

02

Diverted well release - 01 per drilled well

-

Development Drilling, deep

Well release - 2.2 × 10-4 per drilled well

0.25

Blowout (surface flow) - 4.6 × 10-4 per completion

0

Blowout (underground flow) - 01 per completion

0

Diverted well release - 3.1 × 10-4 per completion

0

Completion

Well release - 01 per completion

0


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Blowout and Well Release Frequencies for Offshore Operations Not of North Sea Standard


Frequency Fraction

Subsea Blowout (surface flow) - 3.3 × 10-5 per well year 0.43 Blowout (underground flow) - 4.7 × 10-6 per well year 02 Diverted well release - 01 per well year 0

Production

Well release - 9.5 × 10-6 per well year 0 Blowout (surface flow) - 1.0 × 10-3 per workover 0.05 Blowout (underground flow) - 01 per workover 02 Diverted well release - 01 per workover 0

Workover

Well release - 8.5 × 10-4 per workover 0 Blowout (surface flow) - 1.1 × 10-5 per wireline

job 0

Blowout (underground flow) - 01 per wireline job

0

Diverted well release - 01 per wireline job

0

Wireline

Well release - 1.1 × 10-5 per wireline job

0

Notes

1. Based on no incidents to date. However, these scenarios are considered credible. Table 4.1 gives population data, from which estimates can be made of these frequencies if required.

2. For underground flow releases there are no topsides releases. For all other releases, fractions of releases occurring at topsides = (1 - fraction subsea).

3. Only 2 occurrences, both located at subsea wellhead (see Section 4.1). Subsea fraction = 0 if wellheads are located at topsides.


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3.0 Guidance on use of data 3.1 General validity The data presented in Section 2.0 should be considered valid for the North Sea and US GoM OCS. They can also be applied to other areas of the world, according to whether or not standards are considered to be equivalent to those in the North Sea. For onshore operations it is recommended to use the offshore data presented in Section 2.0.

3.2 Uncertainties As in any analysis of historical frequencies, there are uncertainties in: • The population (in this case, wells drilled, well operations or well years) • The incident data In particular, where incidents are infrequent, another incident just after the data period may significantly increase the statistical frequency, especially when no incidents have been recorded to date but are nevertheless credible (as is the case with some of the SINTEF category – well type combinations). The SINTEF database [1] has been extensively reviewed to ensure that it is as complete as possible in regard both to population and incidents, minimising so far as possible these uncertainties. According to [1]:

“It is SINTEF’s belief that from 1980-01-01 most blowouts occurring in the US Gulf of Mexico (GoM) Outer Continental Shelf (OCS), the UK and Norway have been included in the database.”

Therefore, they present frequencies based on this period and these geographical areas. Neither SINTEF [1] nor Scandpower [2] have, in their reports, quantified these uncertainties in the way that, for example, OREDA [5] does for equipment reliability; instead they have focused on data quality. Further potential uncertainties arise where the frequencies are used outside the context of the data, for example, in other areas of the world. SINTEF present data for all blowouts in their database, covering 49 countries/areas, and incident data for 4 other countries/waters. However, the populations and numbers of blowouts in each case are small, and hence SINTEF do not recommend using frequency estimates obtained from these data in preference to the data used to obtain the frequencies presented in Section 2.0 (see Section 4.1). Hence there is greater uncertainty in using the data for other countries/waters but no quantification of this uncertainty is available. Using the frequencies for operations not of North Sea Standard will introduce an element of conservatism to any analysis.

3.3 Example A hypothetical North Sea platform has 8 oil producing wells and 2 gas injection wells. There are one workover and two wireline jobs per year on the platform oil wells. The following extract from Section 2.0 highlights the relevant frequencies:


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Frequency Operation Category Averag

e Gas Oil Unit

Fraction

Subsea

Blowout 6.5 × 10-6 9.4 × 10-6 3.6 × 10-6 per operation

0 Wirelining

Well Release 1.1 × 10-5 1.6 × 10-5 6.1 × 10-6 per operation

0

Blowout 1.8 × 10-4 2.6 × 10-4 1.0 × 10-4 per

operation 0 Workover

Well Release 5.8 × 10-4 8.3 × 10-4 3.2 × 10-4 per operation

0

Blowout 9.7 × 10-6 1.8 × 10-5 2.6 × 10-6 per well year

0.125 Producing Wells (excluding external causes)

Well Release 1.1 × 10-5 2.0 × 10-5 2.9 × 10-6 per well year

0.125

Blowout - 1.8 × 10-5 - per well

year 0.125 Gas Injection Wells

Well Release - 2.0 × 10-5 - per well year

0.125

The annual frequencies of blowouts and well releases are then: Blowouts: (8 × 2.6 × 10-6) + (2 × 1.8 × 10-5) + (1 × 1.0 × 10-4) + (2 × 3.6 × 10-6) ≈ 1.6 × 10-4 Well releases: (8 × 2.9 × 10-6) + (2 × 2.0 × 10-5) + (1 × 3.2 × 10-4) + (2 × 6.1 × 10-6) ≈ 4.0 × 10-4 The annual frequencies of topsides and subsea blowouts are: Topsides Blowouts: (0.875 × 8 × 2.6 × 10-6) + (0.875 ×2 × 1.8 × 10-5) + (1 × 1.0 × 10-4) + (2 × 3.6 × 10-6) ≈ 1.6 × 10-4 Subsea Blowouts: (0.125 × 8 × 2.6 × 10-6) + (0.125 ×2 × 1.8 × 10-5) ≈ 7.1 × 10-6 Topsides Well releases: (0.875 × 8 × 2.9 × 10-6) + (0.875 × 2 × 2.0 × 10-5) + (1 × 3.2 × 10-4) + (2 × 6.1 × 10-6) ≈ 3.9 × 10-4 Subsea Well releases: (0.125 × 8 × 2.9 × 10-6) + (0.125 × 2 × 2.0 × 10-5) ≈ 7.9 × 10-6

4.0 Review of data sources 4.1 Basis of data presented The key data source is the SINTEF Offshore Blowout Database, described in [1]. SINTEF have performed their own analysis of this database, updated annually, in order to obtain the frequencies set out in Section 2.0. These are based on blowout data from the US Gulf of Mexico OCS, UKCS and Norwegian waters for the period 1st January 1980 to 1st January 2005. Table 4.1 gives the numbers of wells and incidents in the database for these areas and period. Scandpower [2] annually review the SINTEF database and analyse it further to obtain blowout frequencies applicable specifically to the North Sea (and other places where equipment standards are comparable). They use the most recent 20 years’ data


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available. Their report explains how the analysis is done, however two key elements of this are: • Elimination of irrelevant incidents • Adjustment due to trend over time Table 4.2 sets out the numbers of wells and incidents used in their analysis. [4] provides the basis for the HPHT well frequencies, concluding that the blowout frequency for an HPHT well is 12.3 times higher than for a normal well (including underground blowouts).


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Table 4.1 Numbers of Wells and Incidents in SINTEF Offshore Blowout Database [1]


No. of Wells/

Incidents Appraisal 6,257 Wells Number of Exploration

Wells Dri l led Wildcat 7,505 Wells Appraisal 8 Blowout (surface flow) Wildcat 14

Appraisal 0 Blowout (underground flow) Wildcat 0

Appraisal 2 Diverted well release Wildcat 7

Appraisal 2


Well release Wildcat 2

Number of Development Wells Dri l led

- 22,833 Wells

Blowout (surface flow) - 22 Blowout (underground flow)

- 1

Diverted well release - 16


Well release - 2 Appraisal 6,257 Wells Number of Exploration

Wells Dri l led Wildcat 7,505 Wells Appraisal 9 Blowout (surface flow) Wildcat 13

Appraisal 0 Blowout (underground flow) Wildcat 7

Appraisal 01 Diverted well release Wildcat 01

Appraisal 3

Exploration Drilling, deep

Well release Wildcat 3

Number of Development Wells Dri l led

22,833 Wells


- 3


Development Drilling, deep

Well release - 5 Number of Completions 20,328 Wells Blowout (surface flow) - 9 Blowout (underground flow)

- 0


Completion

Well release - 0 Number of Well Years in Service

211,142 Well Years


- 1


Production

Well release - 2 Number of Workovers 19,920

Workovers Blowout (surface flow) - 20 Blowout (underground flow)

- 0


Workover

Well release - 17 Wirelining Number of Wirel ine Jobs 358,941


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No. of Wells/

Incidents Wireline Jobs


- 0

Diverted well release - 0 Well release - 4

Table 4.2 Numbers of Wells and Incidents in Scandpower Blowout Analysis [2]

Operation Category No. of Wells/

Incidents Number of Wells Dri l led 9,172 Wells Exploration Drilling

(shallow gas) Incidents 26 Number of Wells Dri l led 13,022 Wells Development Drilling

(shallow gas) Incidents 29 Number of Wells Dri l led 9,744 Wells Blowout 2 Number of Wells Dri l led 2,854 Wells

Drilling (deep)

Well release 4 Number of Oil Well Years in Service

95,270 Wells Years

All Well Interventions

Number of Gas Well Years in Service

82,204 Wells Years

Number of Completions 16,381 Completions

Blowout 4

Completion

Well release 4 Number of Wirel ine Ops Per Year2

1.7 Ops/Year

Blowout 4

Wireline

Well release 2 Number of Coiled Tubing Ops3 358 Ops Number of Well Years2 4,214 Well

Years Blowout 2

Coiled Tubing

Well release 2 Number of Snubbing Operations3 196 Ops Number of Well Years2 4,214 well

years Blowout 3

Snubbing

Well release 1 Workover Interval – Oil Wells [3] 5 years Workover Interval – Gas Wells [3]

7 years

Blowout 8

Workover

Well release 11 Number of Well Years in Service 177,474 Well

Years Blowout – external causes 7 Blowout – not external causes 5

Production

Well release 2

Notes to Table 4.1 and Table 4.2

1. No number of incidents is given in the report for this scenario. It has been assumed that there have been 0 such incidents to date.

2. Assumed based on feedback from oil companies.


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3. Norwegian Sector only used as basis for frequency estimates.

The basis for the subsea fractions for North Sea Standard operations are as follows: • Exploration drilling, deep blowouts: 12 out of 31 from outside casing or underground

− Assumed also to apply to exploration drilling, deep well releases − Assumed to be the same for HPHT wells as for normal wells

• Development drilling, deep blowouts: 5 out of 15 from outside casing or underground − Assumed also to apply to development drilling, deep well releases − Assumed to be the same for HPHT wells as for normal wells

• Production well releases (excluding external causes): assumed to be the same as for production blowouts (excluding external causes) − Assumed also to apply to production well releases, external causes − Assumed also to apply to gas and water injection wells

From the SINTEF report [1], Tables 4.5 to 4.7, the basis for the subsea fractions for operations not of North Sea Standard are as follows: • Exploration drilling, shallow gas blowouts:

− Surface flow: 13 out of 22 with known location − Diverted well release: 9, assumed to have been topsides − Well release: 2 out of 2 at subsea wellhead − All assumed to be same for appraisal and wildcat wells

• Development drilling, shallow gas blowouts: − Surface flow: 4 out of 22 − Underground: 1 at wellhead, assumed topsides − Diverted well release: 16 at wellhead, assumed topsides − Well release: 1 at subsea wellhead

• Exploration drilling, deep blowouts: − Surface flow: 9 out of 22 with known location − Underground: 1 out of 6 with known location (remainder no surface flow) − Diverted well release, well release: all topsides

• Development drilling, deep blowouts: − Surface flow: 1 out of 7 with known location − Underground: 3 out of 3 no surface flow − Well release: 1 out of 4 with known location

• Completion blowouts: 0 out of 15 subsea • Production blowouts:

− Surface flow: 3 out of 7 with known location − Underground: 1 out of 1 no surface flow − Well release: 0 out of 2 with known location

• Workover blowouts: − Surface flow: 1 out of 19 with known location − Well release: 0 out of 17

• Wireline blowouts: 0 out of 7 with known location

4.2 Onshore blowouts For onshore blowouts, the Alberta Energy and Utilities Board (EUB) maintains a database of onshore drilling incidents [6]. This database includes drilling occurrence


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data for Alberta from 1975 till 1990 with a total of 87,944 wells drilled. The database contains incident reports for individual well control occurrences. The occurrence data are presented below. Category Number of Occurrences Frequency (per well drilled) Blow* 53 6.0 x 10-4 Blowout 43 4.9 x 10-4 Total 96 1.1 x 10-3 * A category of well control incident defined as an uncontrolled release of wellbore fluids to atmosphere that can be shut-in or diverted to flare in a short period of time. They are assumed here to be equivalent to well releases as defined in the SINTEF and Scandpower work.

The total frequency is about 40% of the corresponding value for offshore drilling blowouts. During 2002 – 2006 there were 39 blowouts and 88,856 wells drilled (blows no longer being recorded). Of the 39 blowouts, 7 involved release of gas, the remainder released only fresh water. Taking the full number of blowouts gives a frequency of 4.4 × 10-4 blowouts per well drilled, about 10% smaller than the frequency above from 1975 – 1990 data and hence not significantly lower. For comparison, this is about 40% of the corresponding value for offshore drilling blowouts and well releases presented in Section 2.0. However it should be noted that Alberta wells are believed to be sour, with precautions being taken accordingly to minimise the likelihood of releases. Hence use of the above frequencies is not recommended except in a similar context. EUB also records the numbers of blowouts during well interventions and other blowouts (from producing or suspended wells) but they do not record the corresponding population data (numbers of well interventions, producing wells and suspended wells).

4.3 Other data sources Other databases previously used have been: • BLOWOUT, an internal DNV compilation of blowouts and well control incidents from

the North Sea and US waters during 1970-89. • WOAD (World Offshore Accident Databank), a public-domain database maintained

by DNV covering all offshore hazards. The data from both of these are now included in the SINTEF database and hence are superseded.

5.0 Recommended data sources for further information The SINTEF and Scandpower reports [1,2] should be consulted for further information. In particular, the Scandpower report [2] explains how the frequencies presented in Section 2.0 are derived from the statistics in Table 4.2.


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6.0 References 1. SINTEF 2006. Blowout and Well Release Characteristics and Frequencies, 2006, Report

No. STF50 F06112. 2. Scandpower Risk Management AS 2006. Blowout and Well Release Frequencies –

Based on SINTEF Offshore Blowout Database, 2006, Report No. 90.005.001/R2. 3. Nilsen, E F 1999. Basis utblåsningsfrekvenser 1999, internal technical memo, Statoil

HMS T&T SIK. 4. SINTEF Safety and Reliability, Alliance Technology, Scandpower 1998. Estimation of

Blowout Probability of HPHT Wells, Report No. STF38 F98420. 5. OREDA 2002. 6. Alberta Energy and Utilities Board. Oil and Gas Well Blowout Reports.

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