SPE 53974 Killing Methods and Consequences of 112 Gulf Coast Blowouts During 196-1996 Skalle, P./NTNU, Trondheim, Jinjun H./Southwest Petroleum Institute, Nanchong, Podio, A.L./UT, Austin Copyright 1999, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 1999 SPE Latin American and Caribbean Petroleum Engineering Conference held in Caracas, Venezuela, 21 23 April 1999. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 3 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 7583-3836, U.S.A., fax 1-972-952-9435. Abstract This paper focuses on what happened after wells are out of control by analyzing statistically a database that contains about 112 blowout events from the Gulf Coast and adjoining states covering the period 196-1996. The trends are extracted, including blowing fluid type, mode of control, duration of blowout, pollution, fire and explosion, and fatalities. Detailed differences between Outer Continental shelf () and Texas are given. A report form of blowout events is recommended in order to improve the data quality and standardize reporting. Introduction Drilling engineers and fire-fighting specialists never stop investigating blowouts because of the cost of blowouts, the loss of life and pollution incurred from blowouts. One logical counter measure is to analyze statistical data, revealed the weakest points and attack them. Blowout databases have been developed to extract trends from blowout events since 199. Kato and Adams set up a database containing 95 blowouts and analyzed the trends 1,2. Their data were mainly collected from Alberta, Canada, Texas, USA, and the Gulf of Mexico. They investigated statistically the pollution possibilities from blowouts, causes, duration and kill methods. Danenberger 3 put special attention to Outer Continental Shelf () drilling Blowouts by 87 events from 1971-1991. He found that most of blowouts were attributable to shallow gas influx, and were of short duration. Hughes, Podio and Sepehrnoori 4 initially developed a database in 199, which is updated regularly. The data are mainly from Texas, as well as Louisiana. This database contains almost all blowouts in Texas and. Partial trends were extracted from the updated database in a previous paper 5, including blowout depth, blowout causes, operation in progress and etc. Present paper is a follow up of a recent paper, which focuses on what happened after the blowouts were underway. The updated database contains 112 blowout events from the period between 196 and 1996, geographically distributed as follows: 826 in Texas, and 187 in the Outer Continental Shelf (). The remaining 11 from Louisiana, Mississippi and Alabama are incomplete and not included in this paper. Five agencies contributed the blowout data: State Oil and Gas Board of Alabama, Louisiana Office of Concervation, Mississippi State Oil and Gas Board, Texas Railroad Commission (RRC) and Minerals Management Service (MMS.). This article analyses the following aspects: blowing fluid type, mode of control, blowout duration, pollution, fire and explosion, and fatalities. No systematic method to report blowout existed before 1973. Although it has been mandatory to report the events in United States since 1973, a more detailed and standard reporting is needed, and a blowout report form is recommended. Blowing Fluid Type The blowing fluids are categorized into 11 groups as shown in Table 1. Shallow gas is defined as gas which comes from depths shallower than 2 ft or for wells with the last casing set at only 2 ft. There are 22 wells (2.7%) and 6 wells (3.2%) where fluid type are missing in Texas and respectively. Pure gas blowouts account for 76.4% in, including 57.7% gas and 18.7% shallow gas. Flow of liquids occur in 1.6 % blowouts, and 9.6% events compound to a mixture of Gas and liquids. In Texas, the blowout occurrences caused by pure gas (as well as shallow gas), liquids, and mixtures of gas and liquids are 5.3%, 8% and 39%, respectively. Obviously, gas is by far the most dangerous kick medium. It is noted that 89.3% and 86% of the blowouts contain gas in some forms in Texas and. Figure 1 shows the clear difference in fluid types between and Texas. It is apparent that there are more dangerous gas blowouts in than in Texas. Especially in exist 35 (18.7%) shallow gas events, but only 2 wells (.2%) in Texas. It is only in that oil blowouts (9 wells, 4.8%) and condensate blowouts (7 wells, 3.7%) were reported. In Texas occurrences are characterized by 198 wells (24%) blowing
2 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 mixtures of gas and water, as well as 3.6% mud. This difference is real, but partly caused by an imprecise reporting form. Mode of Control Blowout control methods are divided into 8 categories: Collapse of open hole wellbore (Bridging), Closing the blowout preventer (BOP), Pumping Cement slurry (Cement), Capping, Depletion of small reservoirs, Install equipment, Pumping Mud, and Drilling Relief wells. Figure 2 and 3 give the modes of control in and Texas respectively. Figure 4 compares the two areas. In, bridging is the most common control of blowouts with 39.6%. Killing with weighted mud ranks second with 19%. In Texas, mud is the favorite method, accounting for 41% of total killing events, while bridging ranges second with 19%. 11% of Blowouts were killed by means of cement in both areas. Other modes of control such as BOP, depletion, install equipment and relief well, have almost same importance in and Texas. Duration Blowout duration has a wide range from. to 18 hours (about one and half years) according to the database. Figure 5 shows the proportion of blowouts vs duration. In, 12% more occurrences (15%-3%) than in Texas ceased in less than one hour, which means that significantly more blowouts were controlled quicker in. A little bit more blowouts lasted in 1-24 hours in Texas than in. Only about 4% of blowouts continued blowing in more than one month in both areas. A cumulative percentage of blowouts vs duration is shown in Figure 6. Suffice it to say that the majority of the events were of short duration. 52.4 % and 44.9 % of the occurrences were controlled in one day or less in and in Texas respectively, which demonstrated that duration in was obviously shorter than in Texas. About 8% of blowouts stopped blowing in one week or less. In other words, only 2 % of blowouts continued blowing after one week. Some record about formations in which blowouts occurred. It is, however, only in Texas where enough records are available to extract trends statistically (see Table 2). In Texas, 189 blowout events took place reportedly in sand, 8 in lime and 11 in other rocks. The further studies are made in sand and lime. Table 3 and Figure 7 give the duration distribution in different rocks. Totally 51.1% of events ceased in less than 24 hours in sand, but only 43% in lime. Table 4 and 5 and Figure 8 show the relationship between duration and depth in two rocks. In sand, average duration of blowouts increases with depth. In shallow formation (< 1 ft), the average duration is 58 hours. The average duration is 519.6 hours for each blowout when the depth is over 1 ft. By comparison, the correlation in lime is not as clear as in sand. A partial reason may be the relative shortage of data in lime. In the column of < 1 ft, there was only one record with a blowout of 3 hours. Blowouts happening in the depth from 1-25 ft lasted in average 19.5 hours. At the average depth of 467 ft, the average blowing period was 114.9 hours. When the depth was over 1 ft, the duration was 83 hours without counting the longest duration of 18 hours. Pollution Blowout pollution is divided in 4 levels according to the spills: Enormous (>1 bbls), Large ( 1 bbls), medial ( 1 bbls) and Small ( 1 bbls). Statistics are shown in Table 6. Pollution Rate is defined as number of pollution cases in 1 blowouts. It is clearly shown that 17.6% pollution rate is highest in, while only 7.5% in Texas. As regard to the pollution size, most cases (24 of 33 in, 44 of 62 in Texas, and 9 of 14 in Louisiana) are among the small size. Only in we found cases (2) of enormous size in which spills are over 1 bbls. It is concluded that blowouts in have a higher risk of polluting the environment than in Texas. Besides oil, hydrogen sulfide (H 2 S) is dangerous as an air pollutant. So far, there have been only 9 cases of blowouts in Texas that contained reportedly H 2 S. The concentration of H 2 S ranged from 3 PPM to 12, PPM. The data are not enough to obtain trends. More attention should be paid to H 2 S pollution. According to data available, pollution rates are low and pollution sizes are small in all three investigated areas. The same conclusion as Kato 1 can be reached that a low probability exists for a blowout resulting in pollution. Fire and Explosion In some cases, blowout may cause fire and explosions, especially in gas blowouts. Table 7 gives the number of blowouts with fire or explosion in 3 areas. In the last column is the term, Fire Rate, which is defined as number of fire and explosion in each 1 blowouts (usually explosion incurs fire). Fire rate in was 6.95%, which is twice as high as in Texas or in Louisiana. The main reason may be much higher percentage of gas (including shallow gas) blowouts as mentioned in Table 1. As the fire is dangerous to personnel and equipment, it is predicted that blowouts in is much easier to cause loss of life than in Texas and in Louisiana, which has been demonstrated by the past casualties shown in Table 8. Fatalities Table 8 gives the data about deaths associated with blowout disasters. In, 65 people died from 11 blowout events. It was gas blowouts that caused 6 fatalities. Oil rushing out from wellbore caused 4 persons to die. Therefore, gas blowing was extremely dangerous in and contingency planning should be improved. In Texas, 14 casualties resulted from 9 blowouts. 4 people unfortunately died of blowing gas, while 1 deaths were from the mixture of gas and oil / gas and water. Number of fatalities in was more than triple compared to Texas although the total number of blowouts
SPE 53974 KILLING METHODS AND CONSEQUENCES OF 112 GUL COAST BLOWOUTS DURING 196-1996 3 was less than one forth of the number of blowouts in Texas. The observed trend that blowout events in was much likely to cause casualties than in Texas is partly explained through the higher fire rate (especially explosion) in. Figure 9 compares the number of death during different decades. 34 people died of blowouts in the 196's. The fatalities decreased to 14 in the 197 s. The number of deaths increased again during 198-1989 because the number of wells drilled were at a peak. A decreasing trend in fatalities is seen over the 36 year s period. This trend we believe is caused by ever improving alertness precautions. May this trend continue! Blowout reporting Today, all blowouts (and kicks) are reported to official agencies, e.g., The Railroad Commission (RRC) in Texas. But the different reporting forms are designed to meet special needs. The RRC puts their emphasis on safety and surface pollution. No reporting form is designed to really find the detailed reasons behind the accidents. Useful information was lost forever, although it could have been included in the reporting form with no much extra effort. Therefore a worldwide acceptable Blowout Reporting Form is suggested, as shown in the Appendix. Its main objective is to save valuable information for future investigation. Conclusion Following conclusions can be drawn from this analysis: 1. Two thirds of fluids rushing out of well were pure gas in ; by contrast, about 5% of the blowout were gas in Texas, while 39% were a mixture of gas and liquids. 2. The dominating method of controlling blowouts was bridging (39.6%), while weighted mud and cement slurries accounted totally for 29% of killing events; In Texas, weighted fluids have been the prior method to control blowouts (4%); Bridging and cement rank the second and the third with 16% and 1.6% respectively. 3. About one half of all blowouts ceased in less than one day while only 2% of all blowouts continued blowing for more than one week. The duration in sand is a little bit longer than in lime. Duration of blowouts seem to increase with drilled depth. 4. A low probability exists for pollution resulting from blowout; Pollution rate and fire rate in were significantly higher than in Texas. Although casualties are decreasing and fire rate is low, an ever improving contingency planning should be worked out to further reduce the probability and to guarantee personnel safety. 5. A Blowout Reporting Form is suggested. GOW GW OW No ShG = gas plus oil plus water = gas plus water = oil plus water = outer continental shelf = number = shallow gas Acknowledgments The authors wish to thank Belinda Wolf at the Texas Railroad Commission for granting us access to all the compiled files of blowouts in Texas. Thanks are also given to following agencies: State Oil and Gas Board of Alabama, Louisiana Office of Concervation, Mississippi State Oil and Gas Board, Texas Railroad Commission (RRC) and Minerals Management Service (MMS) (). References 1. Kato S. and Adams N.J., Quantitative Assessment of Blowout Data as It Relate to Pollution Potential, paper SPE 23289 presented at the First International Conference on Health, Safety and Environment, The Hague, The Netherlands, November 1-14,1991. 2. Adam N.J. and Kuhlman L.G., What Can Go Wrong and How To Deal With It: One Company s Experiences, paper OTC 799 presented at the 25th Annual OTC, Houston, Texas, May 3-6, 1993. 3. Danenberger E.P., Outer Continental Shelf Drilling Blowouts, 1971-1991, paper OTC 7248 presented at the 25th 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 Gulf Coast Blowouts, In Situ, 14(2)(199)21-228. 5. Skalle P. and Podio A.L., Trends Extracted from 12 Gulf Coast Blowouts During 196-1996, paper SPE 39354 presented at the IADC/SPE Drilling Conference, Dallas, USA, March 3-6,1998. Nomenclature Subscript AV = average BO = blowout BOP = blowout Preventer COND = condensate DURA = duration
4 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 Table 1. Number of Blowouts With Different Blowing Fluids FLUID TYPE TEXAS % % GAS 414 5.1 18 57.7 SHALLOW GAS 2.2 35 18.7 GAS+OIL 76 9.2 14 7.5 GAS+WATER 198 24. 4 2.1 GAS+COND 19 2.4 GAS+OIL+WATER 28 3.4 COND 7 3.7 OIL 9 4.8 OIL+WATER 6.7 WATER 31 3.7 3 1.6 MUD 3 3.6 1.5 MISSING DATA 22 2.7 6 3.2 TOTAL 826 1 187 1 Table 2. Number of Blowouts in Rocks ROCK TYPE SAND LIME TEXAS 189 8 1 LOUISIANA 7 Table 3. Duration Distribution in Rocks in Texas DURATION - 1 hr 1-24 hr 1-2 days 2-3 days 3-7 days 7-3days >3 days No.of BO in Sand 5 89 32 15 15 15 9 % 2.7 48.4 17.4 8.2 8.2 8.2 4.8 No.of BO in Lime 2 32 18 7 8 7 3 % 2.5 4.5 22.8 8.9 1.1 8.9 3.8 Table 4. Duration vs Depth in Sand in Texas DEPTH kft < 1 hr 1.-2.5 2.5-5. 5.-1 > 1 No. of BO 9 29 54 54 24 AV DEPTH ft 549 1784 368 711 124 AV DURA hr 58 12 82.6 238.6 519.6 Table 5. Duration vs Depth in Lime in Texas DEPTH kft < 1 hr 1.-2.5 2.5-5. 5.-1 > 1 No. of BO 1 7 23 23 22 AV DEPTH ft 316 1754 467 754 1212 AV DURA hr 3 19.5 114.9 52 83 Consequences of Blowout Events Table 6. No. of Blowouts with Pollution Size POLLUTION SIZE ENORMOUS (>1bbls) LARGE ( 1bbls) MEDIAL ( 1bbls) SMALL ( 1bbls) TOTAL CASES POLLUTION RATE % TEXAS 5 13 44 62 7.5 2 4 3 24 33 17.6 LOUISIANA 5 9 14 14.5 Pollution Rate = Number of pollution cases / Number of blowouts 1 (%)
SPE 53974 KILLING METHODS AND CONSEQUENCES OF 112 GUL COAST BLOWOUTS DURING 196-1996 5 Table 7. Number of Blowouts with Fire and Explosion LOCATION FIRE EXPLOSION FIRE RATE % TEXAS 21 6 3.27 4 9 6.95 LOUISIANA 2 1 3.15 Fire Rate = Number of fire and explosion/number of blowouts 1 (%) Table 8. Fatalities Caused by Blowing Fluids BLOWING FLUIDS TEXAS No. of Disasters Fatalities No. of Disasters Fatalities GAS 9 6 4 4 GAS+OIL 1 1 3 7 GAS+WATER 2 3 OIL 1 4 TOTAL 11 65 9 14
6 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 BLOWOUT % 6 5 4 3 2 1 Texas Gas ShG G+Cond Oil FLUID TYPE Figure1 Blowing Fluids in Texas and Mud 41% missing Relief well 5% 3% Install equipment 6% Bridging 16% BOP 9% cement 11% Capping Depletion 5% 4% Figure 2 Kill Methods Applied to Texas Relief well missing Mud 19 % 5 % 3 % Bridging 39 % Install equipment 5 % Depletioncement 9 % 11 % BOP 9 % Figure 3 Kill Methods Applied to
SPE 53974 KILLING METHODS AND CONSEQUENCES OF 112 GUL COAST BLOWOUTS DURING 196-1996 7 missing Relief well Mud Install equipment Depletion Capping Texas cement BOP Bridging 5 1 15 2 25 3 35 4 45 PERCENTAGE OF K ILL METHODS Figure 4 Comparison of Kill Methods Between Texas and 45 PERCENTAGE 4 35 3 25 2 15 Texas 1 5-1 hr 1-3 days 1week- 1month miss data DURATION Figure 5 Blowout Duration
8 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 CUMULATIVE PERCENTAG 1 9 8 7 6 5 4 3 2 1 Texas 1 hr. 3 days 1 DURATION month Figure 6 Blowout Duration 6 PERCENTAGE % 5 4 3 2 Lime Sand 1-1 hr 1-2 days 3-7 days over 3days DURATION Figure 7 Duration in Sand and Lime In Texas
SPE 53974 KILLING METHODS AND CONSEQUENCES OF 112 GUL COAST BLOWOUTS DURING 196-1996 9 6 AVERAGE DURATION 5 4 3 2 1 lime sand 5 1 15 AVERAGE DEPTH Figure 8 Duration vs Depth No. of Fatalities per 1 wells drilled 3 2,5 2 1,5 1,5 196 s 197 s 198 s 199 s YEAR Figure 9 Fatalities vs Decades
1 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 Appendix: BLOWOUT REPORT FORM: PAGE 1: Before blowout REPORT DATE NAME OF REPORTER TEL. No. Date of Blowout e-mail: RIG TYPE Land rig Drilling ship Semisub Juckup +? WELL LOCATION 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 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 DETAILED DESCRIPTION OF OPERATION IN PROGRESS SURFACE EQUIPMENT OF INTEREST Work Over O Pull tubing O Pull/Drill out well plugs O Install BOP O Other O Runing tubing REASONS FOR KICK (PRIMARY BARRIER) O Swabbing OGeopressure OLow mud weight OGas cut mud O Fmtn Breakdown OOther X-mas tree BOP EXPLAIN IN DETAIL:
SPE 53974 KILLING METHODS AND CONSEQUENCES OF 112 GUL COAST BLOWOUTS DURING 196-1996 11 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? 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: 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