01 - spe 53974 - 1120 gulf coast blowouts

Copyright 1999, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the 1999 SPE Latin American and CaribbeanPetroleum Engineering Conference held in Caracas, Venezuela, 21–23 April 1999.

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AbstractThis paper focuses on what happened after wells are out ofcontrol by analyzing statistically a database that containsabout 1120 blowout events from the Gulf Coast and adjoiningstates covering the period 1960-1996. The trends areextracted, including blowing fluid type, mode of control,duration of blowout, pollution, fire and explosion, andfatalities. Detailed differences between Outer Continentalshelf (OCS) and Texas are given. A report form of blowoutevents is recommended in order to improve the data qualityand standardize reporting.

IntroductionDrilling engineers and fire-fighting specialists never stopinvestigating blowouts because of the cost of blowouts, theloss of life and pollution incurred from blowouts. One logicalcounter measure is to analyze statistical data, revealed theweakest points and attack them. Blowout databases have beendeveloped to extract trends from blowout events since 1990.Kato and Adams set up a database containing 905 blowoutsand analyzed the trends1,2. Their data were mainly collectedfrom Alberta, Canada, Texas, USA, and the Gulf of Mexico.They investigated statistically the pollution possibilities fromblowouts, causes, duration and kill methods. Danenberger3 putspecial attention to Outer Continental Shelf (OCS) drillingBlowouts by 87 events from 1971-1991. He found that most ofblowouts were attributable to shallow gas influx, and were ofshort duration.

Hughes, Podio and Sepehrnoori4 initially developed adatabase in 1990, which is updated regularly. The data aremainly from Texas, OCS as well as Louisiana. This databasecontains almost all blowouts in Texas and OCS. Partialtrends were extracted from the updated database in a previouspaper5, including blowout depth, blowout causes, operation in

progress and etc. Present paper is a follow up of a recentpaper, which focuses on what happened after the blowoutswere underway.

The updated database contains 1120 blowout events fromthe period between 1960 and 1996, geographically distributedas follows: 826 in Texas, and 187 in the Outer ContinentalShelf (OCS). The remaining 110 from Louisiana, Mississippiand Alabama are incomplete and not included in this paper.Five agencies contributed the blowout data: State Oil and GasBoard of Alabama, Louisiana Office of Concervation,Mississippi State Oil and Gas Board, Texas RailroadCommission (RRC) and Minerals Management Service(MMS.).

This article analyses the following aspects: blowing fluidtype, mode of control, blowout duration, pollution, fire andexplosion, and fatalities.

No systematic method to report blowout existed before1973. Although it has been mandatory to report the events inUnited States since 1973, a more detailed and standardreporting is needed, and a blowout report form isrecommended.

Blowing Fluid TypeThe blowing fluids are categorized into 11 groups as shown inTable 1. Shallow gas is defined as gas which comes fromdepths shallower than 2000 ft or for wells with the last casingset at only 200 ft. There are 22 wells (2.7%) and 6 wells(3.2%) where fluid type are missing in Texas and OCSrespectively.

Pure gas blowouts account for 76.4% in OCS, including57.7% gas and 18.7% shallow gas. Flow of liquids occur in10.6 % blowouts, and 9.6% events compound to a mixture ofGas and liquids. In Texas, the blowout occurrences caused bypure gas (as well as shallow gas), liquids, and mixtures of gasand liquids are 50.3%, 8% and 39%, respectively. Obviously,gas is by far the most dangerous kick medium. It is noted that89.3% and 86% of the blowouts contain gas in some forms inTexas and OCS.

Figure 1 shows the clear difference in fluid types betweenOCS and Texas. It is apparent that there are more dangerousgas blowouts in OCS than in Texas. Especially in OCS exist35 (18.7%) shallow gas events, but only 2 wells (0.2%) inTexas. It is only in OCS that oil blowouts (9 wells, 4.8%) andcondensate blowouts (7 wells, 3.7%) were reported. In Texasoccurrences are characterized by 198 wells (24%) blowing

SPE 53974

Killing Methods and Consequences of 1120 Gulf Coast Blowouts During 1960-1996Skalle, P./NTNU, Trondheim, Jinjun H./Southwest Petroleum Institute, Nanchong, Podio, A.L./UT, Austin

2 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974

mixtures of gas and water, as well as 3.6% mud. Thisdifference is real, but partly caused by an imprecise reportingform.

Mode of ControlBlowout control methods are divided into 8 categories:Collapse of open hole wellbore (Bridging), Closing theblowout preventer (BOP), Pumping Cement slurry (Cement),Capping, Depletion of small reservoirs, Install equipment,Pumping Mud, and Drilling Relief wells. Figure 2 and 3 givethe modes of control in OCS and Texas respectively.

Figure 4 compares the two areas. In OCS, bridging is themost common control of blowouts with 39.6%. Killing withweighted mud ranks second with 19%. In Texas, mud is thefavorite method, accounting for 41% of total killing events,while bridging ranges second with 19%. 11% of Blowoutswere killed by means of cement in both areas. Other modesof control such as BOP, depletion, install equipment andrelief well, have almost same importance in OCS and Texas.

DurationBlowout duration has a wide range from 0.0 to 10800 hours(about one and half years) according to the database. Figure 5shows the proportion of blowouts vs duration. In OCS, 12%more occurrences (15%-3%) than in Texas ceased in lessthan one hour, which means that significantly more blowoutswere controlled quicker in OCS. A little bit more blowoutslasted in 1-24 hours in Texas than in OCS. Only about 4% ofblowouts continued blowing in more than one month in bothareas.

A cumulative percentage of blowouts vs duration isshown in Figure 6. Suffice it to say that the majority of theevents were of short duration. 52.4 % and 44.9 % of theoccurrences were controlled in one day or less in OCS and inTexas respectively, which demonstrated that duration in OCSwas obviously shorter than in Texas. About 80% of blowoutsstopped blowing in one week or less. In other words, only 20% of blowouts continued blowing after one week.

Some record about formations in which blowoutsoccurred. It is, however, only in Texas where enough recordsare available to extract trends statistically (see Table 2). InTexas, 189 blowout events took place reportedly in sand, 80in lime and 11 in other rocks. The further studies are made insand and lime.

Table 3 and Figure 7 give the duration distribution indifferent rocks. Totally 51.1% of events ceased in less than24 hours in sand, but only 43% in lime.

Table 4 and 5 and Figure 8 show the relationshipbetween duration and depth in two rocks. In sand, averageduration of blowouts increases with depth. In shallowformation (< 1000 ft), the average duration is 58 hours. Theaverage duration is 519.6 hours for each blowout when thedepth is over 10000 ft.

By comparison, the correlation in lime is not as clear as insand. A partial reason may be the relative shortage of data inlime. In the column of < 1000 ft, there was only one recordwith a blowout of 300 hours. Blowouts happening in the

depth from 1000-2500 ft lasted in average 19.5 hours. At theaverage depth of 4067 ft, the average blowing period was114.9 hours. When the depth was over 10000 ft, the durationwas 83 hours without counting the longest duration of 10800hours.

PollutionBlowout pollution is divided in 4 levels according to thespills: Enormous (>10000 bbls), Large (≤10000 bbls), medial(≤1000 bbls) and Small (≤100 bbls). Statistics are shown inTable 6. Pollution Rate is defined as number of pollutioncases in 100 blowouts. It is clearly shown that 17.6%pollution rate is highest in OCS, while only 7.5% in Texas.As regard to the pollution size, most cases (24 of 33 in OCS,44 of 62 in Texas, and 9 of 14 in Louisiana) are among thesmall size. Only in OCS we found cases (2) of enormoussize in which spills are over 10000 bbls. It is concluded thatblowouts in OCS have a higher risk of polluting theenvironment than in Texas.

Besides oil, hydrogen sulfide (H2S) is dangerous as an airpollutant. So far, there have been only 9 cases of blowouts inTexas that contained reportedly H2S. The concentration ofH2S ranged from 300 PPM to 12,000 PPM. The data are notenough to obtain trends. More attention should be paid toH2S pollution.

According to data available, pollution rates are low andpollution sizes are small in all three investigated areas. Thesame conclusion as Kato1 can be reached that a lowprobability exists for a blowout resulting in pollution.

Fire and ExplosionIn some cases, blowout may cause fire and explosions,especially in gas blowouts. Table 7 gives the number ofblowouts with fire or explosion in 3 areas. In the last columnis the term, Fire Rate, which is defined as number of fire andexplosion in each 100 blowouts (usually explosion incursfire). Fire rate in OCS was 6.95%, which is twice as high asin Texas or in Louisiana. The main reason may be muchhigher percentage of gas (including shallow gas) blowouts asmentioned in Table 1.

As the fire is dangerous to personnel and equipment, it ispredicted that blowouts in OCS is much easier to cause lossof life than in Texas and in Louisiana, which has beendemonstrated by the past casualties shown in Table 8.

FatalitiesTable 8 gives the data about deaths associated with blowoutdisasters. In OCS, 65 people died from 11 blowout events. Itwas gas blowouts that caused 60 fatalities. Oil rushing outfrom wellbore caused 4 persons to die. Therefore, gasblowing was extremely dangerous in OCS and contingencyplanning should be improved.

In Texas, 14 casualties resulted from 9 blowouts. 4 peopleunfortunately died of blowing gas, while 10 deaths were fromthe mixture of gas and oil / gas and water.

Number of fatalities in OCS was more than triplecompared to Texas although the total number of blowouts

SPE 53974 KILLING METHODS AND CONSEQUENCES OF 1120 GUL COAST BLOWOUTS DURING 1960-1996 3

was less than one forth of the number of blowouts in Texas.The observed trend that blowout events in OCS was muchlikely to cause casualties than in Texas is partly explainedthrough the higher fire rate (especially explosion) in OCS.

Figure 9 compares the number of death during differentdecades. 34 people died of blowouts in the 1960's. Thefatalities decreased to 14 in the 1970´s. The number of deathsincreased again during 1980-1989 because the number ofwells drilled were at a peak. A decreasing trend in fatalitiesis seen over the 36 year’s period. This trend we believe iscaused by ever improving alertness precautions. May thistrend continue!

Blowout reportingToday, all blowouts (and kicks) are reported to officialagencies, e.g., The Railroad Commission (RRC) in Texas.But the different reporting forms are designed to meet specialneeds. The RRC puts their emphasis on safety and surfacepollution. No reporting form is designed to really find thedetailed reasons behind the accidents. Useful information waslost forever, although it could have been included in thereporting form with no much extra effort. Therefore aworldwide acceptable Blowout Reporting Form is suggested,as shown in the Appendix. Its main objective is to savevaluable information for future investigation.

ConclusionFollowing conclusions can be drawn from this analysis:

1. Two thirds of fluids rushing out of well were pure gasin OCS; by contrast, about 50% of the blowout were gas inTexas, while 39% were a mixture of gas and liquids.

2. The dominating method of controlling OCS blowoutswas bridging (39.6%), while weighted mud and cementslurries accounted totally for 29% of killing events; In Texas,weighted fluids have been the prior method to controlblowouts (40%); Bridging and cement rank the second andthe third with 16% and 10.6% respectively.

3. About one half of all blowouts ceased in less than oneday while only 20% of all blowouts continued blowing formore than one week. The duration in sand is a little bitlonger than in lime. Duration of blowouts seem to increasewith drilled depth.

4. A low probability exists for pollution resulting fromblowout; Pollution rate and fire rate in OCS weresignificantly higher than in Texas. Although casualties aredecreasing and fire rate is low, an ever improvingcontingency planning should be worked out to further reducethe probability and to guarantee personnel safety.

5. A Blowout Reporting Form is suggested.

NomenclatureSubscriptAV = averageBO = blowoutBOP = blowout PreventerCOND = condensateDURA = duration

GOW = gas plus oil plus waterGW = gas plus waterOW = oil plus waterOCS = outer continental shelfNo = numberShG = shallow gas

AcknowledgmentsThe authors wish to thank Belinda Wolf at the TexasRailroad Commission for granting us access to all thecompiled files of blowouts in Texas. Thanks are also given tofollowing agencies: State Oil and Gas Board of Alabama,Louisiana Office of Concervation, Mississippi State Oil andGas Board, Texas Railroad Commission (RRC) and MineralsManagement Service (MMS) (OCS).

References

1. Kato S. and Adams N.J., “ Quantitative Assessment ofBlowout Data as It Relate to Pollution Potential, “ paperSPE 23289 presented at the First International Conferenceon Health, Safety and Environment, The Hague, TheNetherlands, November 10-14,1991.

2. Adam N.J. and Kuhlman L.G., “ What Can Go Wrongand How To Deal With It: One Company’s Experiences,“ paper OTC 7099 presented at the 25th Annual OTC,Houston, Texas, May 3-6, 1993.

3. Danenberger E.P., “ Outer Continental Shelf DrillingBlowouts, 1971-1991, “ paper OTC 7248 presented at the25th Annual OTC, Houston, Texas, May 3-6, 1993.

4. Hughes V.M.P., Podio A.L., and Sepehrnoori K., “Computer-Assisted Analysis of Trends Among GulfCoast Blowouts, “ In Situ, 14(2)(1990)201-228.

5. Skalle P. and Podio A.L., “ Trends Extracted from 1200Gulf Coast Blowouts During 1960-1996, “ paper SPE39354 presented at the IADC/SPE Drilling Conference,Dallas, USA, March 3-6,1998.


Table 1. Number of Blowouts With Different Blowing FluidsFLUID TYPE TEXAS % OCS %GAS 414 50.1 108 57.7SHALLOW GAS 2 0.2 35 18.7GAS+OIL 76 9.2 14 7.5GAS+WATER 198 24.0 4 2.1GAS+COND 19 2.4GAS+OIL+WATER 28 3.4COND 7 3.7OIL 9 4.8OIL+WATER 6 0.7WATER 31 3.7 3 1.6MUD 30 3.6 1 0.5MISSING DATA 22 2.7 6 3.2TOTAL 826 100 187 100

Table 2. Number of Blowouts in RocksROCK TYPE SAND LIMETEXAS 189 80OCS 10LOUISIANA 7

Table 3. Duration Distribution in Rocks in TexasDURATION 0- 1 hr 1-24 hr 1-2 days 2-3 days 3-7 days 7-30days>30 daysNo.of BO in Sand 5 89 32 15 15 15 9 % 2.7 48.4 17.4 8.2 8.2 8.2 4.8No.of BO in Lime 2 32 18 7 8 7 3 % 2.5 40.5 22.8 8.9 10.1 8.9 3.8

Table 4. Duration vs Depth in Sand in TexasDEPTH kft < 1 hr 1.0-2.5 2.5-5.0 5.0-10 > 10No. of BO 9 29 54 54 24AV DEPTH ft 549 1784 3680 7110 12400AV DURA hr 58 120 82.6 238.6 519.6

Table 5. Duration vs Depth in Lime in TexasDEPTH kft < 1 hr 1.0-2.5 2.5-5.0 5.0-10 > 10No. of BO 1 7 23 23 22AV DEPTH ft 316 1754 4067 7540 12120AV DURA hr 300 19.5 114.9 52 83

Consequences of Blowout Events

Table 6. No. of Blowouts with Pollution SizePOLLUTIONSIZE

ENORMOUS(>10000bbls)

LARGE(≤10000bbls)

MEDIAL(≤1000bbls)

SMALL(≤ 100bbls)

TOTALCASES

POLLUTIONRATE %

TEXAS 5 13 44 62 7.5OCS 2 4 3 24 33 17.6LOUISIANA 5 9 14 14.5

Pollution Rate = Number of pollution cases / Number of blowouts × 100 (%)


Table 7. Number of Blowouts with Fire and ExplosionLOCATION FIRE EXPLOSION FIRE RATE %TEXAS 21 6 3.27OCS 4 9 6.95LOUISIANA 2 1 3.15

Fire Rate = Number of fire and explosion/Number of blowouts×100 (%)

Table 8. Fatalities Caused by Blowing FluidsBLOWING FLUIDS OCS

No. of Disasters FatalitiesTEXAS

No. of Disasters FatalitiesGAS 9 60 4 4GAS+OIL 1 1 3 7GAS+WATER 2 3OIL 1 4TOTAL 11 65 9 14


Figure1 Blowing Fluids in Texas and OCS

0

10

20

30

40

50

60

Gas ShG G+Cond OilFLUID TYPE

BLO

WO

UT

%

OCSTexas

Figure 2 Kill Methods Applied to Texas

Depletion5%

Install equipment

6%

Mud41%

Relief well3%

missing5%

Bridging16%

BOP9%cement

11%Capping

4%

Figure 3 Kill Met hods Applied to OCS

missing3 %Mud

19 %

Relief well5 %

Depletion9 %

Install equipment

5 % cement11 %

BOP9 %

Bridging39 %


Figure 4 Comparison of Kill Methods Between Texas and OCS

0 5 10 15 20 25 30 35 40 45

Bridging

BOP

cement

Capping

Depletion

Install equipment

Mud

Relief well

missing

PERCENTAGE OF KILL METHODS

TexasOCS

Figure 5 Blowout Duration

0

5

10

15

20

25

30

35

40

45

0-1 hr 1-3days

1week-1month

missdata

DURATION

PE

RC

EN

TA

GE

OCS

Texas


Figure 6 Blowout Duration

0

10

20

30

40

50

60

70

80

90

100

1 hr. 3 days 1monthDURATION

CU

MU

LAT

IVE

PE

RC

EN

TA

G

OCS

Texas

Figure 7 Duration in Sand and Lime In Texas

0

10

20

30

40

50

60

0-1 hr 1-2days

3-7days

over30days

DURATION

PE

RC

EN

TA

GE

%

Lime

Sand


Figure 8 Duration vs Depth

0

100

200

300

400

500

600

0 5000 10000 15000

AVERAGE DEPTH

AV

ER

AG

E D

UR

AT

ION lime

sand

Figure 9 Fatalities vs Decades

0

0,5

1

1,5

2

2,5

3

1960´s 1970´s 1980´s 1990´s

YEAR

No.

of F

atal

ities

per

100

00

wel

ls d

rille

d


Appendix: BLOWOUT REPORT FORM: PAGE 1: Before blowout

REPORT DATE NAME OF REPORTER TEL. No.Date of Blowout e-mail:

WELL LOCATION

RIG TYPE Land rig Drilling ship Semisub Juckup +?

County /Block Field Well Number Operator Contractor Well Name

OPERATION IN PROGRESS

Eploratory Drilling Development Drilling

O Trip out O Actual drilling

O Coring O Circulation

O Well testing O Other

Completion

O WOC O Nipple Down BOP

O Running well equipment

O Well testing O Other

Production

O Gas production O Oil production

O Closed in well O Other

Work Over

O Pull tubing O Runing tubing

O Pull/Drill out well plugs

O Install BOP

O Other

Water Depth:

MD of last casing TVD of last casing Size of last casing MD of well Inclination at Bottom

Bit size Mud weight Name of formation Formation Type

O Sand O Lime

REASONS FOR KICK (PRIMARY BARRIER)

O Swabbing OGeopressure OLow mud weight OGas cut mud

O Fmtn Breakdown OOther

EXPLAIN IN DETAIL:

DETAILED DESCRIPTION OFOPERATION IN PROGRESS

SURFACEEQUIPMENT OFINTEREST

X-mas tree

BOP


Appendix: BLOWOUT REPORT FORM: PAGE 2: After blowout

BLOWING FLUIDS gas+ oil+ water+ mud+ condensate DETAILS?

Release Point of Blowout

Ignition Delay(hr):Fire Duration (hr):Duration of Blowout (hr)Explosion? Yes /No:DETAILS?

Material Losses(US$):

Fatalities:Injuries:Pollution(bbl): [H2S] (PPM):DETAILS?

MODE of KILLING the WELL: Please explain in detail

Bridging: O Passive O Active

Kill with weighted mud: O Mud Density

Kill with cement slurry: O Slurry Density Depletion BOP / Diverter: Capping: Install Equipment

REASONS FOR LOSS OF CONTROL (SECONDARY BARRIER):

O Failed to close BOP O BOP Failed after Closure

O BOP not in place O Diverted/choked-no problem

O Fractured at casing shoe

PLEASE EXPLAIN IN DETAIL:

01 - spe 53974 - 1120 gulf coast blowouts

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