REPORT - PTIL Shallow gas project rev 4 Konvertert/Helse, miljø og... · Petroleum Safety Authority Norway (PSA) Page: 5 Rev: 4 Shallow gas events 1984 – 2006 in the Norwegian

Petroleum Safety Authority Norway (PSA)

Customer: PSA Report, rev. 4, date 20.02.2007 Prepared by: Tor Austlid

Verified by: Jan Ledsaak

Approved by: Egil Tjelta

SHALLOW GAS PROJECT Shallow gas events 1984 – 2006

in the Norwegian Sector Search of shallow gas events in data from PSA’s Database.

Report by AGR-Triangle

Petroleum Safety Authority Norway (PSA) Page: 2 Rev: 4 Shallow gas events 1984 – 2006 in the Norwegian Sector Date: 20.02.07

CONTENTS

1 INTRODUCTION......................................................................................................................3

2 SUMMARY.................................................................................................................................5

3 DATA RECEIVED FROM PSA...............................................................................................7

4 DEFINITION OF SHALLOW GAS EVENTS .......................................................................9

5 STAGE 1 - SUMMARY OF SEARCH METHOD ...............................................................10 5.1 SEARCH METHODS...............................................................................................................10

5.1.1 Search – additional comments ...................................................................................11

6 STAGE 2 – DETAILED CHECK OF DAILY DRILLING REPORTS .............................13 6.1 DETAILED CHECK OF DAILY DRILLING REPORTS ................................................................13

6.1.1 Additional comment - Daily Drilling Reports ............................................................14

7 RESULTS – SHALLOW GAS EVENTS...............................................................................15

8 STATISTICS ............................................................................................................................30

APPENDIX 1 – OLD PSA SEARCH FOR SHALLOW GAS EVENTS....................................36

APPENDIX 2 – DAILY DRILLING REPORTS FOR THE WELLS WHERE SHALLOW GAS EVENTS HAVE OCCURRED..................................................................39


1 INTRODUCTION

The Shallow Gas Project by PSA has been aimed at identifying the shallow gas events that have taken place in wells drilled on the Norwegian Continental Shelf in the time period from 1984 to 2006. This has been done by extensive searching in the PSA database to identify the wells where shallow gas events have occurred, and then to find the detailed story of each of these shallow gas events from the Daily Drilling Reports from these wells. There may be wells where shallow gas events have occurred which have not been found due to incomplete data base files, reporting or format, such that they have not been identified by the search words used. A description of the data material that was used for the search is found in Section 2. The project was done in two stages: Stage 1:

A first time very wide data search was done by PSA in their data base for Daily Drilling Reports (using the search words shallow, flowing, gain, kick, shutin, dynamic, gas, kill, diverter) to encompass all wells where a shallow gas even might possibly have occurred. This first search resulted in 5 big data files (totaling 116 527 Daily Drilling Reports lines from 3330 different wells) which constituted the base data for the detailed search to identify the wells where shallow gas events had occurred. The detailed search of the base data resulted in 33 wells being identified as wells where shallow gas events had taken place.

Stage 2:

The base data used in Stage 1 did not contain all the Daily Drilling Report lines for the 33 identified wells, but only those report lines that were picked out by the original search words. In order to verify that shallow gas events had taken place in these wells and to find the detailed story of each of these events, it was necessary to access the full PSA data base for Daily Drilling Reports and read through the reports for each of the 33 wells. This was done by working for some time in the PSA main office building which made it possible to access the full Daily Drilling Report database. Some years back PSA had done an earlier search for shallow gas events. From this old search there existed a list containing 41 well numbers. By checking these well numbers against the list of 33 wells identified to have had shallow gas events in Stage 1, it was found that 19 wells from the old PSA search were not included in this list. In order to also check these wells, the Daily Drilling Reports for the 19 wells were accessed and read through. The result was that of these remaining 19 wells, 11 of them were found to be shallow gas events (the remaining 8 were not shallow gas events). The 11 wells were added to the 33 wells identified as shallow gas events from Stage 1, giving a total of 44 identified wells where shallow gas events had taken place.

A Summary is given in Section 2.


More detailed descriptions of Stage 1 and 2 are found in the Sections 5 and 6. The results from the search are found in Section 7. Statistical plot of the findings are shown in Section 8.

It should be emphasized that also shallow water influxes contributes as drilling hazards, but these incidents are not covered in this project.


2 SUMMARY

A total of 44 wells with shallow gas events have been identified in the period 1984-2006. Of these wells, 8 were production wells and 36 were exploration/ appraisal wells. Of the 36 exploration/ appraisal wells, 3 were of the classification “shallow wells” which are wells drilled only to a limited depth below seabed to investigate shallow formations. Fig. 2-1 below shows the yearly distribution of the 44 wells with shallow gas events. As it can be seen, the figure indicates an increased trend of wells with shallow gas events in the period 1984-1993 and a declining trend in the period 1997-2006. The average % of wells with shallow gas events for all drilled wells in the period is approx 2%. For all exploration/appraisal wells the average is 5.56 %. Note: All the statistical plots are shown in Section 8.


Fig. 2-1 Number of wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where shallow gas events have occurred in the time period from 1984 to 2006.

Number of wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where SHALLOW GAS EVENTS have occurred in the period 1985 - 2006

1

4

0

3 3

1

6

3

2

5

0 0 0

6

3

0

1

2

0

1

0

1

2

0

1

2

3

4

5

6

7

Wel

ls w

ith S

hallo

w g

as e

vent

s

Wells with shallow gas events

4 per. Mov. Avg. (Wells with shallow gas events)

Wells with shallow gas events 1 4 0 3 3 1 6 3 2 5 0 0 0 6 3 0 1 2 0 1 0 1 2

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

NOTE:The average curve values represent the average for the 4 preceding years


3 DATA RECEIVED FROM PSA

As the basis for the search of shallow gas events, the following data were received from PSA:

1) The Excel file DDRS fritekstsøk på shallow.xls was first received on 26 October 2006. The

file was the result from a PSA search using the key word “shallow”. This file contained 4741 Daily Drilling Report lines.

2) It was decided by PSA to extend the base data for the search to ensure that (in principle) all reported shallow gas events were encompassed by the base data. Four new data files were therefore received from PSA on 30 October 2006:

Borerapporter_shallow_flowing_gain_kick_shutin_dynamic.xls Borerapporter_gas.xls Borerapporter_kill.xls Borerapporter_diverter.xls

Total data files received with base data for the search:

Table 3-1 The data files representing the BASE DATA

Data files Daily Drilling Report lines (excel rows)

Search words used for selection

Short name for file in this report

DDRS fritekstsøk på shallow.xls 4 741 shallow file 0

Borerapporter_shallow_flowing _gain_kick_shutin_dynamic.xls

28 244

shallow flowing gain kick shutin dynamic

file 1

Borerapporter_gas.xls 23 533 gas file 2 Borerapporter_kill.xls 27 772 kill file 3 Borerapporter_diverter.xls 32 237 diverter file 4

SUM Daily Drilling Report lines 116 527

The data files 0, 1, 2, 3 and 4 constituted the base data for the detailed search to identify the wells where shallow gas events had taken place. The base data represented a varying number of Daily Drilling Report lines from 3330 different wells.


3) Four Excel file showing some shallow gas event statistics from earlier searches done by PSA were received on 27 October 2006. These files were:

Table 3-2 Data files related to old PSA search for shallow gas events

Data files Comments

1984_1997_shallow kicks.xls This file provided a table with 41 well numbers of wells where an earlier PSA data search had found shallow gas events to have occurred. (This table is shown in Appendix 1).

It should be noted that some of the well numbers in this table had been repeated two or three times, such that the actual number of different wells listed in the table was only 34 wells.

1985_1996_shallow kicks.xls



These files only listed the number of shallow gas events for various years, but did not provide well numbers that would have made it possible to identify in which wells these shallow gas events should have occurred. These files could therefore not provide any useful information for the new data search.

4) One Excel file was received 15 January 2007 containing the official/latest listing of well

numbers for the wells drilled in the period 1984 – 2006. The listing contained well numbers for 719 exploration wells and 2558 production wells, total 3277 wells. These well numbers, however, also included side-tracks which have well numbers that are different from the “mainbore” wells they were drilled in. Shallow gas events, per definition, occur only prior to installing the HP BOP (prior to installing the surface casing). Side-tracks, on the other hand, are drilled after the HP BOP has been installed. When comparing the number of wells with shallow gas event to the total number of wells drilled, it would be incorrect to include the side-tracks in the comparison number of wells drilled – this comparison number of wells drilled should only contain the “mainbore” wells drilled. From the total number of 3277 wells, the side-tracks were therefore extracted. It was found that of the 3277 well numbers, 2171 of them represented mainbore wells and 1106 represented side-tracks. Of the 2171 mainbore wells, 647 were exploration/ appraisal wells. The rest (1524 wells) were production wells. Additional comments: The base data, ref. Table 3-1, contain 3330 different well numbers for the period 1984 – 2006. The official NPD list of all wells drilled in the same period contains 3277 well numbers (including side-tracks). The reason for the difference between the numbers is, by information from PSA, that the base data includes “fictive well” which are actually well interventions in already drilled wells.


4 DEFINITION OF SHALLOW GAS EVENTS

The main definition used in this search for what should be called a “Shallow gas event” is that the gas event took place BEFORE the high pressure BOP was installed on the well.

A well is not regarded to have has a shallow gas event unless shallow gas has actually been observed to come from the well, either at seabed or surface. (For some wells it has been reported that a (possible) shallow gas sands has been seen on MWD, but without any observations of shallow gas prior to installing the HP BOP. These wells are not regarded to have had shallow gas events).

The PSA system for reporting shallow gas events is in theory such that if more than one formation containing shallow gas is drilled through before the HP BOP is installed on a well that is being drilled, and these formations show signs at seabed/surface of flowing gas, then signs of gas from each of these formation shall be counted as separate shallow gas events.

In practice, however, it is difficult to determine/verify if observations of shallow gas while drilling a well prior to installing the HP BOP comes from more than one formation.

This is the case for the 44 wells that have been identified to have had shallow gas events in this report. From the Daily Drilling Reports for these 44 wells it has not been possible to determine or verify whether the shallow gas observations have been caused by having drilled through one or more shallow gas formation. The various shallow gas observations for each well has therefore been counted as one (main) shallow gas event, totaling 44 shallow gas events.


5 STAGE 1 - SUMMARY OF SEARCH METHOD

The base data searched through in Stage 1 consisted of the data from the files 0, 1, 2, 3, 4 (ref. Table 3-1).

In Stage 1 the base data were searched to identify the wells where shallow gas events had taken place.

5.1 Search methods File 0 (”DDRS fritekstsøk på shallow.xls”) was checked first since it arrived first.

To find the wells where shallow gas events had occurred, the search was done in steps:

1. Find all wells where shallow gas events possibly had taken place.

To do this, various search macros were run to search for a number of key words. Fig. 5-1 shows a typical example of key word search.

Report lines not mentioning anything related to gas events were removed. A list of the remaining wells were then made.

Having arrived at this list of possible wells, this well list was moved into a new file and all available program lists for these wells were imported into the file.

2. Find all wells where shallow gas events had taken place.

Step a: The report lines for all the wells on the “possible“ list were red through quickly in order to remove those wells from the list where shallow gas events had obviously not occurred, or had obviously occurred after the HP BOP had been installed on the well. These wells and their report lines were removed. Step b: For the remaining wells on the “refined possible” list a detailed read-through of the report lines was done to identify those wells where a shallow gas even had taken place before the HP BOP had been installed on the well.

When the data files 1, 2, 3 and 4 arrived, each of these files were first separately “filtered down” to 5000 – 6000 report lines by using macros to search for key words (and combination of key word) in order to eliminate report lines where possible shallow gas events were not mentioned. The remaining report lines from each file were then put together in a new file. When the same report line for the same well occurred more than once, the excess line(s) were removed.


The search process then continued as described above for file 0. Arriving at the “refined possible” list for the files 1, 2, 3 & 4, the “certain” + “possible” shallow gas events found in file 0 were added to the list. All available report lines for the wells on the list were then imported into a new file, and the last detailed read-through was done in order to arrive at the final list of wells, derived from all the data files, where shallow gas events were found to have taken place. The total number of wells where shallow gas events had occurred was found to be 33.

5.1.1 Search – additional comments

About key words and miss-spellings When doing the searches for key words, it was found necessary to also search for possible different ways the key words could be written or miss-spelled.

Examples: shutin, shut in, shut-in, shutin, shut - in, shut -in. exercise, exersice About the old PSA search In the old PSA search for shallow gas events 34 different wells had been listed (file “1984_1997_shallow kicks.xls”). By comparing the list of these 34 wells with the list of 33 wells identified to have had shallow gas events in the Stage 1 search of the base data it was found that 15 of the old PSA search wells were included in the 33 wells. This meant that 19 of the old PSA search wells were not included in the new list of 33 wells identified to have had shallow gas events. In order to check this more in detail the following was done: a) The list of 34 wells from the old PSA search was compared with the list of all the 3330 wells

contained in the base data. It was found that all the old PSA search wells, except one, were represented with one or more program lines in the base data. The one well not included in the PSA base data was the “West Vanguard well” 6407/6-2, ref. Section 6.1.

b) The program lines in the base data for the 19 old PSA search wells not having been identified as

shallow gas events were then read through, but none of the relatively few program lines contained in the base data for these wells indicated that shallow gas events had occurred. It was decided to double-check on these wells in Stage 2 by reading through their full Daily Drilling Reports (ref. Section 6).


Fig. 5-1 Example: Text (report lines) with typical key word findings.

text shallow_gas shallow kick drill drill drilled exersice simulat meeting no_indication flow check sonar install_diverter gas flowing gain hydraulic kill bubble Kill & chokeKILL/CHOKE VALVES TO 2.07 MPa/58.60 MPa 5/10 MIN AND ANN kill24.13 MPA 5/10 MIN.CONT PRESS TEST BOP'S AND KILL/CHOKE. NO PROBLEMS. SET W killINSTALL DIVERTER. install diverterCONTINUE MAKE UP DIVERTER.FUNCTION TEST DIVERTER SYSTEM.HELD PREJOB MEETING WITH CREW CONCERNING SHALLOW GAS ALERTNESS. shallow gas shallow meeting gasP/U 12 JNTS 6.625"" DP. INSTALL DIVERTER BAG. install diverterHELD SAFETY MEETING WITH CREW DUE TO POTENTIAL OF SHALLOW GAS. shallow gas shallow meeting gasFLOWCHECK 6 BBL INCREASE, WELL STABLE. CIRC BTM UP TO CHECK FOR GAS, flow check gasNEGATIVE. LOCATED PROBLEM TO THE DESILTER-PUMP, TRANSFERRING MUD TO THEACTIVE SYSTEM.RIG UP AND COLD CUT 30"" CSG. MADE 2 CUTS. FIRST 7.5"" ABOVE LOAD RING,SECOND 3' ABOVE FIRST CUT (RIGHT BELOW DIVERTER RISER).L/D DIVERTER.RISER CONNECTION BELOW DIVERTER HOUSING LEAKING. RETRIEVE L/P RISER.CLEAN CONNECTION, CHANGE SEAL AND USE SILICONE ON CONNECTION. REINSTALLRISER.OPEN BOP, JETWASH WELLHEAD, BOP & RISER, FLOWCHECK F/ 15 MIN, GAIN 2.5 flow check gainBBL.WASH WELLHEAD W/ ABB WASHING TOOL. WELL FLOWING W/10 BPH. flowingDUMMY RUN W/PACK OFF RUNNING TOOL T/CHECK CORRECT LANDING. WELL FLOWING flowingW/10 BPH.OPEN WELL, RIH & ATTEMPT T/SET PACK OFF, NO GO, PACK OFF LEFT IN HOLE.,WELL FLOWING W/80 BPH. flowingRIH & SCREW INTO PACK OFF & POOH W/PACK OFF. PACK OFF O.K. WELL FLOWING flowingW/25 BPH.RIH & SET PACK OFF. WELL STOPPED FLOWING, POOH. TOTAL GAIN SINCE BULL flowing gainHEADING : 140 BBL.CONT CIRC BTM UP AND TREAT MUD. MAX GAS 2,9% ON BTM UP. gasCIRC 15 MINS AND CONT TO PUMP OUT OF HOLE. DEPTH AT REPORT TIME 3700'.LOST 10 BBL ABOVE CALCULATED. NO GAS. gasFLOWCHECK PRIOR TO PULL BHA THROUGH BOP. WELL FLOWING W/6 BBLS/HR. (4 flow check flowingBBLS GAIN) SHUT WELL IN ON ANNULAR. SICP INCREASED TO 50 PSI IN 20 MIN. gainBLED OFF WELL AND MONITOR WELL. WELL FLOWING 5.1 BBL/HR. ( GAIN 1.8 flowing gainBBLS) SHUT WELL IN ON ANNULARCONT PUMP OOH TO 11550'. MAX GAS ON BOTTOMS UP: 1% gasM/U STINGER FOR STORM VALVE AND RIH.PERFORM KICK DRILL. kick drill drillCIRC HOLE CLEAN. NO GAS. gasPUMP 50 BBLS HI-VIS MUD & CIRC BTTMS UP. MAX GAS BTTMS U gas(13.78%)R/U CMT HEAD. CIRC BTTMS UP.14 UNITS GAS ON BTTMS UP gasPULLED 2 STDS DP & CIRC BTTMS UP. 7 UNITS GAS ON BTTMS U gasCIRC BOTTOMS UP. MAX GAS 11 UNITS. gasRAN BOP AND RISER. NIPPLED UP DIVERTER AND KILL CHOKE LI killTESTED BOP, ACOUSTIC SYSTEM AND CASING. FUNCTION TESTEDALL TESTS WERE OK. SET SEAT PROTECTOR.FUNCTION TESTED DIVERTER SYSTEM, PRESSURE TESTED SAME TOBOP test. Pressure test well head connector and kill lin kill689b.Continue BOP test to 35/146b.Run riser/LMRP. Continue to run LMRP.Pick up slip joint,supportring,kill and choke lines.Land MLRP,pull test 20t kill kill and chokePressure test choke line. Flush lines,test kill and chok kill


6 STAGE 2 – DETAILED CHECK OF DAILY DRILLING REPORTS

In Stage 2 the Daily Drilling Reports for the 33 wells identified to have had shallow gas events were red through. In addition the 19 wells from the old PSA search that had not been identified to have had shallow gas event were read through to check if shallow gas events had actually taken place in these wells.

6.1 Detailed check of Daily Drilling Reports The base data used in Stage 1 did not include all the Daily Drilling Report lines for the wells represented, but only those report lines that were picked out by the original PSA search words when compiling the base data. In order to verify that shallow gas events had taken place in the 33 wells identified to have had shallow gas events, and to find the detailed story of each of these events, it was necessary to access the full PSA data base for Daily Drilling Reports and read through the reports for each of the 33 wells. This was done by working for some time in the PSA main office building which made it possible to access the full Daily Drilling Report database. First, by reading through the full suit of Daily Drilling Reports for the 33 wells identified to have had shallow gas events from the search in Stage 1, it was verified that shallow gas events had taken place in these wells, and the detailed story for each of the wells with regard to the shallow gas events were written down. Next, the full suit of Daily Drilling Reports for the 19 wells from the old PSA search that had not been identified to have had shallow gas event were read through to check if shallow gas events had actually taken place in these wells. I was found that shallow gas events had taken place in 11 of these wells, while for the remaining 8 wells shallow gas event could not be found to have occurred. Ref. Table A1-2 in Appendix 1. For the 11 wells now having been identified from the old PSA search to have had shallow gas events the detailed story of the event for each of the 11 well was written down. (One of these wells was not included in the base data. This was the well 6407/6-2, where the most severe shallow gas event that has happened in the Norwegian Sector took place. The reason it was not included in the base data was that the Daily Drilling Reports for this well ends before the shallow gas event took place. This well was drilled in 1985 with the semi-submersible rig West Vanguard). Including well 6407/6-2, a total of 3331 different well numbers have been included in the search for wells where shallow gas events have occurred. The 11 wells from the old PSA search found to have had shallow gas events were added to the 33 wells identified as shallow gas events from Stage 1, giving a total of 44 identified wells where shallow gas events had taken place. A chronological list of the 44 wells with the detailed story of the shallow gas event that had happened in each of them were prepared and is found in Section 7, Table 7-1.


6.1.1 Additional comment - Daily Drilling Reports When reading through the Daily Drilling Reports in the PSA data base it was found that many of the reports for older wells were missing words from the end of report lines. This was, according to information from PSA, due to a change of the data base system some years back. Despite the missing words, the basic detailed story of the shallow gas events having taken place could be understood, even though some minor details in some cases were unclear. The Daily Drilling Reports for the 44 wells, from starting the wells and until the shallow gas events had ended (usually when the HP BOP was installed on the well) were extracted from the PSA data base and have been added to this report as a separate appendix – ref. APPENDIX 2 (volume 2).


7 RESULTS – SHALLOW GAS EVENTS

A total of 3331 different well numbers have been included in the search for wells where shallow gas events have occurred. This also includes the wells in the old PSA search. These well numbers represent both drilled (mainbore) wells, side-tracks and well interventions. The actual number of drilled wells when side-tracks and well interventions are excluded is 2171 wells (647 of these wells are exploration/ appraisal wells and the rest, 1524 wells, are production wells. These wells have all been drilled on the Norwegian Continental Shelf in the time period from 1984 to 2006. Shallow gas events were found to have taken place in 44 wells. The full suit of Daily Drilling Reports for these 44 wells were accessed in the PSA data base and read through. This was done both to verify that shallow gas event actually had taken place in these wells, and to find out what the detailed story of the shallow gas events was for each of the 44 wells. In Table 7-1 below, the 44 wells where shallow gas events took place are listed chronologically, with a description of the shallow gas events. Table 7-1 Wells where shallow gas events have occurred on the Norwegian Continental

Shelf (NCS) in the time period from 1984 to 2006. Ref. no. Operator Well no. YEAR Description of shallow gas events 1 HYDRO 16/4-1 1984 Rig: Treasure Seeker

30” casing set at 206 m. Drilled 17 ½” hole to 494 m. Well started flowing. Closed diverter. Well blew out through (?) (Parts of the report text are missing. It is probable that the gas came up the annulus and dispersed into the sea above seabed. The flow seems to have lasted approx. 30 minutes, then the flow died out by itself. It is unclear whether the pumps were on or off during the flow. Subsequent flow checks showed no flow).

2 SAGA 6507/11-3 1985 Rig: Treasure Saga

30” casing set at 414 m. Installed seabed diverter and riser. Drilled 17 ½” hole to 868 m. Closed annular and opened dump valve on seabed diverter – found that well was flowing. Underreamed 17 ½” hole from 30” shoe down to 473 m. Made flow check and found that well was flowing. Circulated bottoms up and found well static. Raised mud weight from 1.15 sg to 1.18 sg. Underreamed hole down to 868 m. Filled hole up to seabed with 1.38 sg mud. Flow checked via dump valve on Seabed Diverter and found well slightly flowing. Pumped 10 bbls extra of 1.38 sg mud into the hole. Flow check – no flow. Pulled to seabed and displaced riser with seawater – well static. Opened dump valve – well flowing. Displaced riser to 1.13 sg mud – well static. Ran in hole to 868 m. Pumped 226 m3 with returns to seabed. Flow checked at dump valve – slight flow. Filled up riser with seawater – slight flow. Pumped 24 m3 1.50 sg mud – well static. Pooh to 200 m – slight flow. Filled up riser – well static. Unlatched SBD – well static. (No more flow observed 20” casing & HP BOP was run).


Ref. no. Operator Well no. YEAR Description of shallow gas events 3 STATOIL 6506/12-4 1985 Rig: Dyvi Stena

30” casing set at 354 m. Ran riser and installed diverter. Drilled 12 ¼” pilot hole to 680 m. Observed gain in active pit – well was flowing. Close diverter and diverted gas to port side while pumping 1.06 sg mud. (Report text for 1.5 days is here missing. What seems to have taken place during this time is that heavier mud was circulated around – resulting in (at least) partial lost circulation). Then - 1.5 days after initially observing the well was flowing - 1.12 sg mud was circulated around and the subsequent flow check is reported as OK (no reference to well flowing after this time).

4 STATOIL 6407/6-2

1985 Rig: West Vanguard

(This is the most severe shallow gas event that has happened in the Norwegian part of the North Sea. The Daily Drilling Reports from these well stops before the shallow gas event occurred. The summary of events given below was found on internet).

Date when shallow gas event happened:

06 October 1985

Summary According to Norwegian Petroleum Directorate records, well 6407/6-2 was drilled to a TD of 504m MDRT. At or about this depth, a shallow gas pocket was encountered in the Pliocene sediments whilst drilling, at around 0900 in the morning. The well blew out and, with no BOP yet installed, the diverter was unable to contain the flow of gas. The liberated gas then exploded and engulfed the rig in a fireball. The one fatality is assumed to have resulted from this explosion, although reports indicate the victim's remains were never found. The rig's deck structure, two of its legs and the engine room were damaged in the blast, resulting in the rig listing by 10 degrees. The rest of the crew were able to evacuate the rig in a matter of minutes using the fore lifeboats.

After the accident, the rig was towed to Freifjorden near Kristiansund, Norway and investigated by Norwegian police and SINTEF (a Norwegian industrial research institute). The investigation revealed the formation of a gas 'cloud' on the cellar deck level due to a leak between the riser and the slip joint. The gas then migrated into the shaker house via a poorly closed valve and travelled through an exhaust pipe, across the upper deck and into other rooms via air ducts before igniting. To quote the SINTEF report: 'Doors and hatches in and around the drilling module on the upper deck were knocked open in a pattern that gave indications of the course of explosions.'


Ref. no. Operator Well no. YEAR Description of shallow gas events 5 STATOIL 34/10-A-2 H

1985 Rig: Deepsea Bergen (production well)

30” casing set at 229 m. 26” hole was drilled to 994 m. The 20” casing was run and cemented. It was then observed that gas bubbles were coming out of the cement ports in the 30” casing. The gas flow gradually increased. (Parts of the report text are missing, and it is unclear what happened next – it seems that the well was temporarily plugged. Work on the well was resumed 6 months later (in 1996). The HP BOP was then installed on the well. The 20” casing was perforated from 335 m to 336 m with 12 SPF, and 64 m3 of gas tight cement slurry was pumped into the annulus. At a flow check afterwards no gas was observed).

6 PHILLIPS 2/7-20 1987 Rig: Dyvi Stena

With the 30” casing set at 172 m, a 12 ¼” pilot hole was drilled to 608 m. While making a wiper trip a small amount of gas/bubbles (?) was observed coming from the 30” wellhead. When running back to bottom the drill string got stuck. A day went by to free the stuck pipe, which was finally cut and retrieved. While pulling the cut string, it was observed a slight flow from the well and some gas coming out of the drill string being pulled. The kelly was picked up and the hole was circulated with seawater. When subsequently shutting down the pumps and observing the well it is reported to be OK (no reference to well flowing after this time).

7 STATOIL 6201/11-1 1987 Rig: Deepsea Bergen

30” casing set at 474 m. Drilled 12 ¼” hole to 930 m – bubbles were observed. Pulled out to 589 m and circulated with seawater. Increased flow was observed. Pumped 20 m3 of 1.15 sg mud and observed reduced flow. Pumped 65 m3 of 1.20 sg mud and still observed bubbles. Pulled out while filling well with 1.30 sg mud every stand. Ran logs. Pumped 62 m3 of 1.30 sg mud – observed well dead. Ran in hole with cement stinger and set a cement plug and pulled out with cement stinger. Ran in hole with 12 ¼” drilling assembly and tagged TOC at 719 m. Set a new cement plug and pulled out. Tagged the new cement plug at 551 m. Displaced the hole to seawater – well static. Drilled cement plug with 12 ¼” assembly to 650 m. Pulled out and ran back in with 26” drilling assembly. Opened hole to 26” down to 646 m. Installed 20” casing and HP BOP.


30” casing set at 327 m. Seabed diverter (SBD) and riser were installed. Drilled 17 1/2” pilot hole to 861 m. Opened hole to 26” down to 861 m. Opened dump valve on SBD and flow checked well – found well to be flowing. Circulated well with 1.20 sg mud – well stable. Pulled riser and SBD. Installed 20” casing and HP BOP.


Ref. no. Operator Well no. YEAR Description of shallow gas events 9 AMOCO 2/8-12 1988 Rig: Dyvi Stena

30” casing set at 185 m. While drilling below 30” shoe at 935 m, gas was observed coming out of the annulus (at seabed). Circulated 10 ppg mud and the amount of gas bubbles starting to decrease. Two hours later the gas rate was observed to be increasing. Built additional kill mud and circulated. Gas rate was decreasing. With hole displaced to 11.5 ppg mud only occasional gas bubbles came out of the well at seabed. Displaced 60 bbls mud down the drill pipe. Both drill pipe and well observed to be static. (No reference to well flowing after this time).


30” casing set at 218 m. Installed seabed diverter (SBD). Drilled 17 ½” pilot hole to 922 m. Displaced the hole to 1.20 sg and pulled out to 30” shoe. Closed annular on SBD and opened dump valve. When doing a flow check the well was first static, but then some flow was observed. Ran the bit to bottom and circulated bottoms up. Flow checked well – static. (No reference to well flowing after this time).

11 HYDRO

6407/7-3 1988 Rig: Polar Pioneer

30” casing set at 440 m. Drilled 17 1/2” hole to 891 m – observed gas bubbles coming from well. Pumped seawater/mud – observed minor amount of gas bubbles. Pulled out of hole. Set a cement plug from 890 m to 860 m. Set a new cement plug up to 832 m. The plug was tagged at 829 m. 1.80 sg kill mud was pumped. A cement plug was set up to 792 m. After the cement had set the well was displaced to 1.80 sg kill mud from 630 m. A new cement plug was set – tagged at 524 m. The hole was displaced to seawater – no flow observed from well. The hole was opened to 26” and the 20” casing and HP BOP were installed.

12 PHILLIPS 2/7-21 S 1989 Rig: Ross Isle

30” casing set at 173 m (through subsea template). Drilled 9 7/8” pilot hole to 764 m. While running single shot survey some gas was observed coming out from the 30” wellhead. The well was displaced with 11 ppg kill mud. Indication of shallow gas (bubbles) was observed. Continued drilling pilot hole to 1068 m. Pumped 50 bbls hi-vis pill around – well static. While the pilot hole was opened up to 26”, flow checks were frequently made (well found to be static).

13 BP 2/7-22 1990 Rig: Ross Isle

Drilled 9 7/8” pilot hole from seabed to 1100 m. Small amount of gas observed by ROV. Pumped hi-vis pills and then displaced the hole to 1.20 sg mud. (From here on, no gas was observed to escape from the well).


Ref. no. Operator Well no. YEAR Description of shallow gas events 14 PHILLIPS 2/7-23 S 1990 Rig: West Delta

30” casing set at 174 m (through subsea template). Drilled 26” hole to 292 m. Then continued drilling 12 ¼” hole to 657 m. Gas bubbles were observed by ROV camera to come out from the well. Circulated seawater and gas decreased to zero. Drilled to 664 m. Gas bubbles started to come out at the 30” wellhead – gradually increasing. Hi-vis mud pills and 11 ppg kill mud was pumped around to clean the hole, and a good amount of gas was seen at seabed. Continued to circulate seawater and hi-vis mud pills, and the gas decreased. Reamed the hole, then continued drilling to 749 m and lost returns. Pumped hi-vis pills around and pulled out to 607 m. The drill pipe started flowing and the top drive was connected. Pumped hi-vis pills and displaced well to seawater. Started to pull out of hole. Drill pipe started flowing at 259 m. Circulated seawater. Back-reamed to 30” shoe and circulated – had returns inside 30”. Ran in hole and drilled to 1076 m. Started pulling out of hole. Stopped at 550 m and circulated due to back-flow in drill pipe. (The hole was opened to 26” before running 20” casing. No more references to well/pipe flowing after this time).

15 SAGA 6406/11-1 S 1990 Rig: Treasure Saga

30” casing set at 454 m. Installed Seabed Diverter and riser. Drilled 17 ½” hole to 1215 m. Under-reamed hole to 26”. Continued drilling 17 ½” hole to 1218 m. Flow checked well on SBD – no flow (mud weight in well was 1.16 sg). Displaced riser to seawater and pulled up with SBD. Observed a few gas bubbles coming from the well. Re-landed SBD on wellhead. Ran in hole with drill string and displaced the riser with 1.18 sg mud. (From here on, no gas was observed).

16 PHILLIPS 2/7-25 S 1990 Rig: West Delta

30” casing set at 208 m (through subsea template). Drill 26” hole to 290 m. Continued drilling 12 ¼” hole to 713 m. A high gas escape from well was detected by ROV, but the gas flow decreased to zero. Ran single shot survey at 712 m. Gas flow started. Pull out with single shot, large amounts of gas escaped from the well. Pumped 11 ppg mud and displaced with 215 bbls seawater. Back-reamed to 636 m. Circulated with seawater – gas flow to zero. Drilled to 780 m – sweeping hole and observing well. Pulled out to 506 m – gas started to escape from well. Ran in hole to bottom. Circulated and swept hole with hi-vis mud, small amounts of gas escaping well – gradually decreasing to zero. Opened hole to 26” down to 496 m. Large amount of gas escaping from well. Circulate and sweep hole – gas gradually decreased to zero. Opened hole to 26” down to 776 m. Displaced open hole to hi-vis mud prior to running 20” casing. A slight flow of mud was observed. Circulated seawater – observed increasing gas flow from well, thereafter the gas flow started to decrease. Pulled out to 107 m and observed well – well stable. (20” casing was then installed).


Ref. no. Operator Well no. YEAR Description of shallow gas events 17 HYDRO

30/6-23

1990 Rig: Transocean-8

30” casing set at 261 m. Drilled 17 1/2” hole to 601 m and pulled out for wiper trip – flow was coming up the drill pipe. Connected the top drive and circulated 70 m3 of 1.20 sg mud – well static. Ran in hole to 601 m and circulated 100 m3 with 1.20 mud. Pulled out to below seabed – observed gas bubbles from the well. Pumped 5 m3 mud to displace bubbles – well static, pulled out of hole. Ran in with cement stinger and displaced well to 1.20 sg mud. Set cement plug up to 350 m. Displaced well over plug to 1.20 sg mud – well static. Set a new cement plug up to 300 m and displaced well from 300 m and up with 1.20 sg mud and pulled out of hole – well static. Ran in with 17 ½” drilling assembly and drilled cement down to 378 m. Pulled out of hole - well static. The hole was opened up to 26” down to 377 m. The 20” casing and HP BOP were installed.

18 HYDRO

6407/7-5 1990 Rig: Transocean-8

30” casing set at 435 m. Drilled 8 1/2” pilot hole to 650 m – observed minor amount of gas bubbles coming from well. While observing, the amount of bubbles decreased. Ran in hole and pumped one circulation with 1.20 sg mud. Flow checked well for 1 hour – well static. Displaced well to 1.20 sg mud. Pulled out of hole. (No further references are made to bubbles/ shallow gas. 13 3/8” casing and HP BOP were installed).

19 BP 2/1-10 1991 Rig: Ross Isle

A 9 7/8” pilot hole was drilled from seabed. At 881 m the bit was picked off bottom due to indications of gas registered by the ROV. When observing by ROV for 10 minutes, a very small amount of gas was seen. The drilling of the pilot hole then continued. (From here on, no more references to gas are made).

20 STATOIL 6507/8-5 1991 Rig: Ross Rig

30” casing set at 417 m. Drill 9 7/8” pilot hole. While drilling at 854 m, the well was observed to be flowing. Pumped (kill) mud and killed the well. Flow check by ROV showed no flow. (From here on, no gas was observed).

21 MOBIL 35/11-5 1991 Rig: Sovereign Explorer

The first attempt to drill this well was given up due to first going stuck in the pilot hole and then loosing part of the BHA in the side-tracked pilot hole. The well was re-spudded and the 30” casing was set at 446 m. The well was then drilled to 856 m., Spotted 50 m3 (kill) mud across the Utsira sand from 771 – 855 m. At this point it is reported that the well appeared to be flowing. The drilling of the hole continued. (From here on, no more references to gas are made).


Ref. no. Operator Well no. YEAR Description of shallow gas events

22 HYDRO 7316/5-1 1992 Rig: Polar Pioneer

30” casing set at 560 m (seabed at 473 m). An 8 ½” pilot hole was drilled to 662 m. Gas bubbles at the wellhead was then observed. The hole was displaced to 1.60 sg mud – gas bubbles were still observed. The pilot hole was drilled to 906 m (had drilling break at 897 m). On flow check, gas bubbles were still observed. What followed now was repeated attempts to stop the gas by circulating/displacing the well with various mud weights:

1.20 sg mud – still observing gas bubbles.

Seawater – gas gradually reduced and then the well seemed stable, then mud returns were observed.

1.50 sg mud – flow gradually reduced and well stable after circulation 25 m3.

A 75 m cement plug was set on bottom of the pilot hole. Pulled out to 800 m. After 4 hours gas bubbles were observed again – stopped after circulating 26 m3 mud. When running in hole to check the cement plug it was tagged at 901 m (should have been 831 m). A flow check showed no flow. Ran logs. Circulated bottoms up afterwards and observed gas. Then a flow check was made and showed the well to be stable. Set a 25 m3 LCM pill at 878 m, and then a balanced cement plug. When afterwards checked, the TOC was tagged at 841 m, dressed off plug to 845 m. Flow checks showed no gas. Ran logs. Ran in hole with cement stinger on drill pipe to top of plug. Was unable to set cement plug. When pulling out it was found that drill pipe had broken off 102 m from the bottom of the stinger. Ran in hole with 8 ½” BHA to 785 m. Strong flow was observed coming from the well. Pumped 70 m3 of 1.30 sg mud. Drilled out previous cement plug from 785 m to 811 m using 1.30 sg mud. Displaced hole to seawater. Observed some flow from the well, then flow increased to strong flow of fluid with some gas. Pumped 100 m3 of 1.30 sg mud – the flow decreased. The well started flowing again 3 hrs later. Pumped 50 m3 with 1.30 sg mud and 33 m3 with 1.50 sg mud – well static. Pumped down a 13 m3 heavy barite plug. Pulled out to 640 m, then ran back in to tag barite plug – no sign of barite plug. Pumped another barite plug. Pulled up and waited for barite to settle. No indication of barite plug when attempting to tag it. Pumped new barite plug and pulled out to 660 m. No indication of barite plug when attempting to tag it. Displaced hole to 1.41 sg mud. Small amount of gas observed. Displaced hole to more times with 1.41 sg mud. Set new cement plug – well static. Tagged TOC at 772 m. Set hi-vis pill – observed some bubbles while circulating. Set new cement plug. From 650 m circulated bottoms up with 1.41 sg mud. Set new cement plug. TOC was later tagged at 610 m. Set new cement plug, tagged TOC later at 514 m ….(approx. 12 days had gone since the pilot hole first reached 906 m).

The well was abandoned, and then re-drilled from a location 51 m away from the abandoned well. The shallow gas problems experienced in the abandoned well was not encountered in the new well.


Ref. no. Operator Well no. YEAR Description of shallow gas events 23 SHELL 1/6-6 1992 Rig: Dyvi Stena

Drilled 9 7/8” pilot hole from seabed to 1205 m. Opened pilot hole to 36” down to 180 m. Installed 30” casing. Opened pilot hole below 30” shoe to 26” down to 910 m – observation by ROV showed bubbles coming from the well. Pumped seawater at 4600 LPM. Gas flow from well was steadily reduced. Pumped 235 m3 of 1.30 sg kill mud and 110 m3 of 1.40 sg mud – bubbles still flowing from well. Continued pumping a total of 157 m3 of 1.20 sg mud – well observed to be stable. Pulled out of hole. Ran in hole with mule shoe to 1036 m and circulated around 1.30 sg kill mud. Frequent gas bubbles were observed. Set cement plug from 1205 m to 1100 m. Pulled out and changed to 26” drilling assembly. Opened pilot hole to 26” from 910 m to 914 m - some gas bubbles were observed coming from the wellhead, then the gas bubbles stopped. Opened pilot hole to 26” down to 1127 m and circulated hole with mud – well static. Made wiper trip to 30” shoe. Ran in hole to 276 m - gas bubbles coming from wellhead were observed. Ran in hole to 1127 m – gas bubbles coming from wellhead. Pumped 15 m3 hi-vis pill, followed by LCM oil, 80 m3 seawater and 105 m3 of kill mud – bubbles still coming from well. Pulled out of hole. Ran and cemented 20” casing. Installed the HP BOP.

24 SAGA 34/7-I-1 H 1993 Rig: Scarabeo 5 (production well)

Drilled 9 7/8” pilot hole from seabed (at 250 m) to 335 m. The well was then observed to flow. The well was displaced to 1.20 sg mud (which seems to have stopped the flow). And the pilot hole was drilled to 339 m. The hole was then step-wise displaced to seawater. When flow checked, it was observed that the well started flow. The hole was displaced to 1.45 sg kill mud, but flow from the hole started again. A balanced cement plug was set in bottom of the pilot hole. Top of the cement plug was tagged at 314 m and drilled out down to 327 m. A flow check was made (apparently showing no flow). The pilot hole was opened up to 36” down to 327 m and displaced to 1.20 sg mud. 30” casing was installed with shoe at 327 m, and cement and shoe was drilled out. A 17 ½” hole was then drilled down to 1154 m. The hole was under-reamed to 26” down to 1147 m. A flow check showed no flow. The 18 5/8” casing was run and cemented. Before landing the HP BOP on the wellhead a constant gas flow from the well was observed by ROV. Installed the BOP on the well. With the shear rams closed, the kill & choke line were flushed and the choke line opened to the trip tank. Monitoring of the trip tank showed no flow. The BOP test tool was run and the well flow checked – no flow.

25 STATOIL 9/2-4 S 1993 Rig: Deepsea Bergen

30” casing set at 179 m. Drilled 9 7/8” pilot hole to 231 m. When circulating bottoms up, indications of shallow gas was seen on the ROV sonar. Continued to drill the pilot hole down to 645 m. (No more references to shallow gas are made).


Ref. no. Operator Well no. YEAR Description of shallow gas events 26 AGIP 2/5-10 1993 Rig: Polar Pioneer

30” casing set at 185 m. Drilled 8 ½” pilot hole to 815 m. The hole was circulated with seawater and hi-vis sweeps. A flow check showed the well to be static. 1.5 hours later it was observed by ROV that the well started to flow. Ran in hole with drill string to 582 m and reamed down to 591 m. Observed that the flow from the well was significantly reduced. The flow from the well, described as cloudy turbulence at the wellhead, was observed to start increasing with time. After pumping 51 m3 of 1.40 sg kill mud a rapid decrease on gas activity was seen. After pumping 65 m3 kill mud the well was observed to be static. A cement plug was set from 600 m to 520 m. A new cement plug was set with top of the plug tagged at 465 m. After pumping out of the hole, gas was observed bubbling at the wellhead. With 8 ½” bit the cement was drilled out down to 600 m. The hole was displaced to 1.20 sg mud. The well was observed to be static. A new cement plug was set with top tagged at 528 m. The pilot hole was opened up to 26” down to 520 m, and 20” casing and HP BOP was installed without having observed more gas.

27 AMOCO 2/11-9

1993 Rig: Mærsk Gallant

30” conductor installed with shoe at 194 m. Install diverter. Drilled out inside conductor. Drilled 12 ¼” pilot hole to 365 m. (Parts of the report text are missing, but what seems to have happened at this point is that bubbles were observed coming out at seabed on the outside of the conductor. Drilling was stopped while investigating these bobbles. Then drilling operations continued, and 20” casing and BOP were installed. There are no further references to bubbles/ gas).

28 HYDRO

6305/12-2

1993 Rig: Deepsea Bergen

30” casing set at 222 m. Drilled 17 1/2” hole to 437 m – observed gas with ROV. Circulated seawater at max. rate – gas decreased after approx. 20 m3 had been pumped. Pumped 134.7 m3 of 1.50 sg kill mud – gas flow stopped. Ran in hole with cement stinger and set cement plug from 437 m to 390 m. Pulled out of hole with stinger and ran in with 17 ½” drilling assembly. Tagged TOC at 391 m and drilled cement to 402 m. Pumped around in steps four volumes of hi-vis mud, each volume 15 m3. Then pumped 40 m3 of seawater. Gas bubbles stopped after 10 minutes. (The 20” casing and HP BOP were then installed).


Ref. no. Operator Well no. YEAR Description of shallow gas events 29 BP 2/1-11 1997 Rig: Mærsk Jutlander

30” casing set at 188 m. Drilled 26” hole to 724 m. Observed gas flow at wellhead. Gas could also be seen bubbling in the sea below the moonpool. Circulated with seawater keeping the hole full. Flow at wellhead appeared to be decreasing. Pumped 1409 bbls 1.26 sg kill mud. Only a small flow of bubbles was observed at the wellhead. Pumped out of hole and changed to 12 ¼” drilling assembly, at this point no flow was observed. Drilled 12 1/4” hole from 726 m to 731 m. Flow was observed at wellhead. Displaced well to 1.26 sg kill mud – observed well static. Drilled to 802 m – the well started to flow with large quantities of gas, with gas coming out of the sea below the moonpool. Pumped 1440 bbls of 1.26 sg kill mud – the well continued flowing for 15 minutes after finishing the pumping, then the well became static. Drilled to 900 m and observed small quantities of gas coming from the wellhead then the flow stopped. Drilled to 1121 m. The well started to flow with large quantities of gas - gas was bubbling out of the sea below the moonpool. Displaced well with 1.26 sg kill mud, but well continued to flow. Continued to pump around kill mud – flow from well appeared to be stopping. A flow check showed the well to be static. The hole was displaced to seawater and drilling continued to 1156 m. Displaced the well to 1.26 sg kill mud – observed the well starting to flow. Continued pumping kill mud – the well continued flowing for 30 minutes after the pumping stopped. Pumped out of hole and flow checked the well – no flow. Ran in hole with 26” drilling assembly and opened up the 12 ¼” hole to 26” from 720 m to 726 m. Displaced well to seawater and observed gas at wellhead. Continued to pump seawater and gas flow stopped. Opened hole to 830 m and circulated around with seawater. Pumped kill mud – flow stopped after 600 bbls were pumped. Opened hole to 935 m – well started to flow significant amounts of gas. Pumped 1230 bbls 1.26 sg kill mud – well observed to be static. Opened hole to 997 m. Well started to flow gas, but the flow died out quickly. Opened hole to 26” down to 1038 m. Some initial gas returns were observed. Opened hole to 1158 m. When drilling the last 3 m of hole the well started to flow. Pumped a 42 bbls mica pill and displaced the hole with 1.26 sg kill mud. Continued pumping kill mud and the well stopped flowing. Made wiper trip. When running back in the well started to flow. Pumped 40 bbls mica and displaced well to 1.26 sg kill mud. Initially some flow was observed, but the well went static. Pumped out of well –well static. (20” casing and hp BOP was installed. The time from first observing the first gas flow and until ready to install the 20” casing was approx. 6 days).

30 BP

Amoco 2/8-F-7 1997 Rig: Valhall DP (production well)

20” casing set at 379 m. 21 ¼” LP BOP installed on LP riser/ surface wellhead. With 16” steerable assembly it was drilled down from the 20” shoe to 385 m. When flow checking the well it was observed to flow. The well was shut in on pipe rams and circulated with 1.50 sg mud through the choke and degasser. On flow check the well was static. Opened pipe rams and circulated bottoms up – when flow checking the well a small flow of 2 – 3 bbls/hr was seen. The 16” hole was drilled to 1475 m. The well was during the drilling flowing with approx.2 - 3 bbls/hr. After circulating and doing wiper trips, the flow was down to 1.2 bbls/hr. The mud weight was raised to 1.57 sg, and the well was observed to be static. 13 3/8” casing and HP BOP was installed.


Ref. no. Operator Well no. YEAR Description of shallow gas events 31 STATOIL 31/6-A-18 1997 Rig: Troll A (production well)

The conductor was installed at 477 m. A 17 ½” hole was then drilled down to 656 m where the well had a gain of 800 liter. The well was flow checked for 10 minutes, and drilling of the 17 ½” hole then continued down to section TD at 1139 m without experiencing any further gain. (14” casing and HP BOP was installed).

32 SAGA 34/7-26 S 1997 Rig: Scarabeo 5

Drilled 9 7/8” pilot hole from seabed (through subsea template). Drilled to 363 m. On the MWD logs a shallow gas sand was seen at 355 m. The well started to flow gas and mud. Displaced the hole with 1.20 sg kill mud. A flow check showed the well to be flowing. The hole was displaced to 1.25 sg mud weight. Observations showed the well to be static. (From here on, no more flow was observed).

33 STATOIL 6507/11-5 S 1997 Rig: Deepsea Trym

30” casing set at 347 m. Drilled 9 7/8” pilot hole to 489 m. MWD indicated shallow gas zone from 483.5 m to 485 m. Gas bubbles at the wellhead were observed by ROV. 10 m3 of 1.30 sg mud was pumped – gas bubbles were again observed after 45 minutes. Circulated bottoms up with 1.30 sg mud – no gas observed. Displaced well back to seawater – gas bubbles were observed at wellhead. Pumped bottoms up with seawater – well static. Drilled pilot hole to 516 m – gas bubbles escaping from wellhead were observed. Circulated bottoms up – no gas observed. Drilled pilot hole to 530 m. Displaced well to seawater – gas bubbles observed at seabed. Pumped 40 m3 of seawater – gas bubbles still observed at wellhead. Again pumped 40 m3 of seawater – well observed to be static. Drilled pilot hole to 582 m. MWD indicated shallow gas. Circulated bottoms up – well started offloading. Pumped 16 m3 of 1.30 sg mud and 40 m3 of 1.60 sg mud. The well was confirmed killed after observation of well. (No gas flow/bubbles were observed from here on).


Ref. no. Operator Well no. YEAR Description of shallow gas events 34 AMOCO 2/8-17

1997 Rig: Transocean Nordic

Drilled 9 7/8” pilot hole from seabed (at 110 m) to 249 m. Pulled out of hole due to not being able to rotate string. It was found that the string had twisted off, leaving a 29.48 m fish in hole. The fishing operations to retrieve the fish took approx. 3 days. Ran in hole with 9 7/8” drilling assembly. Drilled to 250 m and displaced hole to 10.5 ppg mud. Pulled out of hole and ran in with 36” hole opener assembly. Opened pilot hole to 36” down to 250 m. Continue drilling 24”/36” hole to 304 m. 30” conductor was installed with shoe at 300 m. Drilled 9 7/8” pilot hole to 555 m (possible gas bearing sand from 534 m to 536 m). Drilled pilot hole to 1023 m (possible hydrocarbon bearing sand from 1015 to 1018 m). Well started flowing with 6 bbls flow in 8 minutes at the trip tank. Closed diverter and starting pumping mud to kill the well. The gas came to surface and the diverter unloaded. Pumped 10 ppg kill mud at a slow rate. When the mud was at surface, a flow check showed that the well was static. Circulated bottoms up – had static loss of 5 bbls in 30 minutes. (Drilling operations continued, but no more gains are reported).

35 STATOIL 34/10-U-12 1998 Rig: Transocean Wildcat

Drilled 9 7/8” pilot hole from seabed (160 m) to 360 m. Displaced well to seawater – the well started flowing after 13 minutes. Killed well by pumping 1.15 sg mud. Pulled out of hole and ran in with 3.5” open ended pipe to TD. Pumped 1.15 sg mud, observed gas bubbles at bottoms up. Filled hole with 14.9 m3 cement.


Drilled 9 7/8” pilot hole from seabed (160 m) to 360 m. Displaced well to seawater – started flowing after 7 minutes. Killed well by pumping 1.15 sg mud. Pulled out to 170 m – flow checked well and found rate of bubbles from well increasing. Ran in hole to 360 m. Displaced well to 1.20 sg mud. Pulled out of hole and ran in with 3.5” open ended pipe to TD. Pumped 1.15 sg mud. Filled hole with 14.9 m3 cement.


Drilled 9 7/8” pilot hole from seabed (160 m) to 375 m. Displaced well to seawater – started flowing after 7 minutes. Killed well by pumping 1.15 sg mud. The hole was filled hole with 14.9 m3 cement.


Ref. no. Operator Well no. YEAR Description of shallow gas events 38 STATOIL 6506/11-E-3 H 2000 Rig: Transocean Winner (production well)

30” casing set at 395 m. Drilled 9 7/8” pilot hole to 650 m. Had indication of shallow gas on ROV sonar and camera – observed well flowing. Pumped seawater at 4800 LPM – reduced pump rate to 3200 LPM and observed well starting to flow after ½ bottoms up. Pumping seawater at 4800 LPM. Observed flow from well decreasing gradually while decreasing flow rate step-wise. Circulated bottoms up and flow checked for 30 minutes – well static. (No more gas was observed from here on).

39 ESSO 16/7-A-1 H 2001 Rig: Byford Dolphin (production well)

30” casing set at 166 m. Drilled 9 7/8” pilot hole to 674 m. Stopped drilling due to indications of gas bubbles on ROV sonar. Visually verified gas bubbles by ROV camera. Pumped 52 m3 of 1.760 sg kill mud. Observed well static. (No more gas was observed from here on).

40 STATOIL 6407/2-Z-3 2001 Rig: Transocean Winner (production well)

30” casing set at 331 m. Drilled 9 7/8” pilot hole to 813 m. Opened pilot hole to 26” down to 688 m. Had signs that well was flowing slightly. Displaced hole with 40 m3 with 1.30 sg mud and 120 m3 with 1.60 sg mud. (No more gas was observed from here on).

41 HYDRO 35/8-5 S 2003 Rig: Deepsea Delta

30” casing set at 458 m. Drilled 12 1/4” pilot hole to 683 m. A flow check showed that the well was flowing. Displaced well with 1.30 sg mud – no flow observed. Pulled out of hole and ran in with open ended pipe. Set cement plug on bottom of the 12 1/4” hole – no flow observed. Ran in hole with 12 ¼” drilling assembly and tagged TOC at 596 m. Drilled soft cement to 598 m. Observed well flowing. Circulated bottoms up with seawater – no reduction in flow observed. Drilled hard cement down to 680 m and displaced hole to 1.30 sg mud. Pulled out of hole and ran back to 679 m with open ended pipe. Displaced well to 1.15 sg mud – well stable. Set a 12.9 m3 cement plug. Ran in hole with 12 ¼” drilling assembly and tagged TOC at 675 m. Flow checked well – still flowing. Displaced well with 1.30 sg mud and flow checked well – well static. Pulled out of hole and ran in with open ended pipe to 674 m. Ran in with open ended pipe and set a 15.2 m3 cement plug, then pulled back to surface. Ran in hole with 12 ¼” assembly. Tagged TOC at 658 m. The well was observed to be stable. Displaced well to 1.30 sg mud and pulled out of hole. Set a 11.8 m3 cement plug and pulled out of hole. Ran in hole with 12 ¼” assembly and tagged TOC at 571 m. Flow checked well – stable. Displaced well to 1.30 sg mud and pulled out. Ran in hole with open ended pipe and set 7.6 m3 cement plug. Pulled out and ran back in with 12 ¼” drilling assembly. Tagged TOC at 513 m and drilled to 558 m. Displaced well to seawater – flow check showed well stable. Pulled out of hole and ran in with 26” drilling assembly. Opened pilot hole to 26” down to 555 m. Flow check showed well stable – the time from first observing the well flowing and until now was approx. 6 days. (No more shallow gas was observed from here on).


Ref. no. Operator Well no. YEAR Description of shallow gas events 42 STATOIL 6302/6-1 2005 Rig: Eirik Raude

Seabed was tagged at 1284 m. 30” casing set at 1363 m. Drilled 26” hole to 2121 m (section TD). Pumped 15 m3 hi-vis pill and flow checked with ROV – well flowed. Pumped 75 m3 1.40 sg mud followed by 500 m3 of 1.35 sg mud. Flow checked well – well stable. Pulled out with 26” assembly – observed well flowing by ROV. Ran in hole with open ended pipe to 1438 m. Observed the well to be static while the pipe was static. Pulled out to 1361 m – observed well flowing. Ran in hole to bottom (2121 m) – observed well to be seeping. Pumped 457 m3 of 1.45 sg kill mud – flow check with ROV showed well stable. Pulled out of hole with open ended pipe. Made wiper trip to TD with 26” drilling assembly – well observed to be stable. Ran 20” casing and hung off in 36” wellhead. When attempting to cement the casing, the cement equipment malfunctioned and the attempt to cement was aborted. Repair of cementing equipment commenced. While waiting on repair of equipment, flow from the well was observed by ROV. 150 m3 of 1.45 sg mud was pumped, but well still flowed. While repair work on the cementing equipment continued, the well was observed to be flowing with a steady rate. As the repair of the cementing equipment ended (had taken 1.5 days), observations by ROV showed only minor flow from the well. Displaced well to 1.45 sg mud – observed well to be stable. Problems with foaming cement slurry caused the next attempt to cement the casing to be aborted. Waiting on new mud from onshore and continued repairs of cementing equipment caused the delay of the cementing of the 20” casing for another 2 days. After displacing the cement it is reported that a “minor cloud” from cement return holes below the wellhead could be seen. This flow from the cement return holes continued – resulting in the decision to re-spud the well. Re-spudded well (6302/6-1): For the re-spudded well the 20” casing and HP BOP were installed without observing any signs of shallow gas.

43 HYDRO 35/11-B-21 H 2006 Rig: Bideford Dolphin (production well)

30” casing set at 467 m (subsea template well). Drilled 12 1/4” pilot hole to 558 m (a sand interval from 536 m to 539 m was drilled through). Observed by ROV that the well was flowing slightly. Pumped a total of 14 m3 of 1.30 hi-vis mud. A 30 minutes flow check showed the well to be flowing 2 – 2.5 times the rate observed with seawater in the well. Displaced the well to 1.30 sg hi-vis mud – the well was then observed to be static. Displaced the well to 1.50 sg Glydrill mud – the well was observed to be static. Pulled out with drilling assembly and ran into the well with drill pipe and cement stinger to 557 m. Set a 10.7 m3 cement plug at bottom of the hole. Pulled out with cement stinger. Ran in hole with 26” drilling assembly. Tagged TOC at 464 m. Drilled cement down to 493 m. Displaced the well to 1.50 Glymud. Pulled out with 26” assembly. (No more flow from the well was observed. The 20” casing and HP BOP were installed).


Ref. no. Operator Well no. YEAR Description of shallow gas events 44 TALISMAN 7/8-5 S 2006 Rig: Mærsk Giant

30” conductor installed with shoe at 210 m. Drilled 17 1/2” hole to 750 m. Observed gains of 4.6m3 at surface. The diverter bag was closed and returns were diverted overboard – observed mud and gas go out the diverter lines. Seawater was continually pumped down the well, and normal returns at surface continued after approximately 10 minutes. After having pumped 30 m3 of seawater, pumping continued with 1.20 sg kill mud. Opened the diverter bag and continued to pump 1.20 kill mud until returns of 1.20 mud came back on surface. Stopped pumping and observed well – well static. Starting pumping 1.20 mud and increased pump rate in stages to 3000 LPM. At this stage the formation was observed to break down causing losses of 6 – 13 m3 while circulating. (From this point on, no more gain from the well was observed).


8 STATISTICS

The official NPD list of wells drilled in the period 1984 – 2006 contains 3277 well numbers, of which 1106 are side-tracks. When extracting the sidetracks, this gives a total of 2171 “mainbore” wells drilled in the period (ref. Section 3, point 4). Of these 2171 mainbore wells, 647 are exploration/ appraisal wells and 1524 are production wells. Table 8-1 below shows the number of wells with shallow gas events and mainbore wells (side-tracks excluded) drilled each year in the period, and the percentage of wells that had shallow gas events. Fig. 8-1, 8-2 show graphical representations for all the wells and shallow gas events. Fig. 8-3 and 8-4 show graphical representations for the exploration/appraisal wells and the related shallow gas events.


Table 8-1 Number of wells with shallow gas events and mainbore wells (side-tracks excluded) drilled on the Norwegian Continental Shelf (NCS) in the time period from 1984 to 2006.

ALL WELLS

EXPLORATION/ APPRAISAL WELLS

SHALLOW GAS EVENTS

SHALLOW GAS EVENTS

SHALLOW GAS EVENTS

SHALLOW GAS EVENTS

Year

Wells with shallow gas

events

ALL WELLS (number of wells drilled excluding

side-tracks)

% of ALL WELLS

(number of wells drilled excluding

side-tracks)

EXPLORATION/ APPRAISAL

WELLS with shallow gas events

EXPLORATION/ APPRAISAL

WELLS (number of wells drilled excluding

side-tracks)

% of EXPLORATION/

APPRAISAL WELLS

(number of wells drilled excluding

side-tracks)

1984 1 77 1.30 % 1 46 2.17 %

1985 4 97 4.12 % 3 50 6.00 %

1986 0 69 0.00 % 0 34 0.00 %

1987 3 71 4.23 % 3 35 8.57 %

1988 3 72 4.17 % 3 26 11.54 %

1989 1 73 1.37 % 1 26 3.85 %

1990 6 77 7.79 % 6 34 17.65 %

1991 3 96 3.13 % 3 44 6.82 %

1992 2 102 1.96 % 2 37 5.41 %

1993 5 101 4.95 % 4 26 15.38 %

1994 0 97 0.00 % 0 19 0.00 %

1995 0 105 0.00 % 0 32 0.00 %

1996 0 119 0.00 % 0 28 0.00 %

1997 6 123 4.88 % 4 41 9.76 %

1998 3 111 2.70 % 3 21 14.29 %

1999 0 113 0.00 % 0 18 0.00 %

2000 1 131 0.76 % 0 22 0.00 %

2001 2 125 1.60 % 0 29 0.00 %

2002 0 91 0.00 % 0 13 0.00 %

2003 1 87 1.15 % 1 18 5.56 %

2004 0 79 0.00 % 0 13 0.00 %

2005 1 71 1.41 % 1 12 8.33 %

2006 2 84 2.38 % 1 23 4.35 %

Sum 44 wells

with shallow gas events

2171 wells Average 2.03 %

36 Exploration/ Appraisal wells

with shallow gas events

647 Exploration/ Appraisal

wells

Average 5.56 %


Fig. 8-1 Number of wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where shallow gas events have occurred in the time period from 1984 to 2006.

Number of wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where SHALLOW GAS EVENTS have occurred in the period 1985 - 2006

1

4

0

3 3

1

6

3

2

5

0 0 0

6

3

0

1

2

0

1

0

1

2

0

1

2

3

4

5

6

7

Wel

ls w

ith S

hallo

w g

as e

vent

s

Wells with shallow gas events

4 per. Mov. Avg. (Wells with shallow gas events)

Wells with shallow gas events 1 4 0 3 3 1 6 3 2 5 0 0 0 6 3 0 1 2 0 1 0 1 2

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006



Fig. 8-2 % Wells with shallow gas events out of the total mainbore wells (sidetracks excluded) drilled on the Norwegian Continental Shelf in the time period from 1984 to 2006.

% Wells with SHALLOW GAS EVENTS out of the total number of mainbore wells (sidetracks excluded) drilled on the Norwegian Continental Shelf in the time period

from 1984 to 2006

1.30 %

4.12 % 4.23 % 4.17 %

7.79 %

1.37 %

3.13 %

1.96 %

4.95 % 4.88 %

2.70 %

0.76 %

1.60 %

1.15 %1.41 %

2.38 %

0 %0 %0 %0 %0 %0 %0 %0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

% (W

ells

with

Sha

llow

gas

eve

nts

of to

tal d

rille

d m

ainb

ore

wel

ls)

% Wells with shallow gas events

4 per. Mov. Avg. (% Wells with shallow gas events)

% Wells with shallow gas events 1.30 4.12 0.00 4.23 4.17 1.37 7.79 3.13 1.96 4.95 0.00 0.00 0.00 4.88 2.70 0.00 0.76 1.60 0.00 1.15 0.00 1.41 2.38

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006



Fig. 8-3 Exploration/ appraisal wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where shallow gas events occurred in the time period from 1984 to 2006.

Number of exploration/ appraisal wells (sidetracks excluded) drilled on the Norwegian Continental Shelf where SHALLOW GAS EVENTS occurred in the time period from 1984 to 2006

1

3

0

3 3

1

6

3

2

4

0 0 0

4

3

0 0 0 0

1 1 1

00

1

2

3

4

5

6

7

Wel

ls w

ith S

hallo

w g

as e

vent

s

Exploration wells with shallow gas events

4 per. Mov. Avg. (Exploration wells with shallow gasevents)

Exploration wells with shallow gas events 1 3 0 3 3 1 6 3 2 4 0 0 0 4 3 0 0 0 0 1 0 1 1

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006



Fig. 8-4 % Exploration/ appraisal wells with shallow gas events out of the total number of these type wells drilled (sidetracks excluded) on the Norwegian Continental Shelf in the time period from 1984 to 2006.

% Exploration/ appraisal wells with SHALLOW GAS EVENTS out of the total number of these type wells (sidetracks excluded) drilled on

the Norwegian Continental Shelf in the time period from 1984 to 2006

0 0 0 0 0 0 0

4.35 %

8.33 %

5.56 %

00

14.29 %

9.76 %

15.38 %

5.41 %

6.82 %

3.85 %

17.65 %

11.54 %

8.57 %

6.00 %

2.17 %

0.00 %

2.00 %

4.00 %

6.00 %

8.00 %

10.00 %

12.00 %

14.00 %

16.00 %

18.00 %

20.00 %

% (W

ells

with

Sha

llow

gas

eve

nts

of to

tal d

rille

d m

ainb

ore

wel

ls)

% Exploration wells with shallow gas events

4 per. Mov. Avg. (% Exploration wells with shallow gasevents)

% Exploration wells with shallow gas events 2.17 % 6.00 % 0.00 % 8.57 % 11.54 % 3.85 % 17.65 % 6.82 % 5.41 % 15.38 % 0.00 % 0.00 % 0.00 % 9.76 % 14.29 % 0.00 % 0.00 % 0.00 % 0.00 % 5.56 % 0.00 % 8.33 % 4.35 %

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006



APPENDIX 1 – Old PSA search for shallow gas events Table A1-1 shows the well numbers from old PSA search where shallow gas events had been found to have occurred. (The list represents 34 different wells since some of the well numbers have been repeated). The shaded (blue) lines in the table shows the well numbers that were identified as shallow gas events in the new search of base data in Stage 1. In this search 15 of the total of 34 different wells in Table A1-1 were identified as shallow gas events. (Ref. also Table A1-2 for further comments on those wells not identified in the search in Stage 1).

Table A1-1 List of well numbers from old PSA search for shallow gas events


Table A1-2 shows those well numbers from Table A1-1 that were not identified as shallow gas events in the search in Stage 1 (Table A1-2 represents 19 different wells since one well no. is repeated twice). In Stage 2 the full suite of Daily Drilling Reports for these 19 wells were accessed and read through. It was found that in 11 of these wells shallow gas events had occurred, ref Table A1-3. For the remaining 8 wells shallow gas events could not be identified from the Daily Drilling Reports to have taken place (ref. Comments in Table A1-2).

Table A1-2 List of well numbers from old PSA search that were not identified as shallow gas event in the search in Stage 1. 11 of these wells were identified as shallow gas events in Stage 2.


Table A1-3 shows those the 11 wells from Table A1-1 that were identified as shallow gas events in Stage 2, by reading through the full suite of Daily Drilling Reports for the wells. Additional comment: By checking the report lines for these wells contained in the base data, it was found that the relatively few report lines from these wells in the base data did not identify shallow gas event to have occurred. In Stage 2 it was seen from the Daily Drilling Reports for these wells that the wording used to report the shallow gas evens were such that the pertinent report lines had not been picked up by the search words used by PSA when assembling the base data.

Table A1-3 List of well numbers from old PSA search identified in Stage 2 as shallow gas events


APPENDIX 2 – DAILY DRILLING REPORTS for the wells where shallow gas events have occurred.

For Appendix 2 ref. Volume 2 of this report (SHALLOW GAS PROJECT).

Documents

REPORT - PTIL Shallow gas project rev 4 Konvertert/Helse, miljø og... · Petroleum Safety Authority Norway (PSA) Page: 5 Rev: 4 Shallow gas events 1984 – 2006 in the Norwegian