Report Investigation of gas blowout on Snorre A - Well Integrity ...

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The detailed plans were completed by the drilling supervisor and toolpusher on the 25th and 26th <strong>of</strong> November respectively. At the same time, risk assessments in connection with taking the scab-liner through the BOP were removed from the detailed plan. 10 On 25 November 2004, the land organization conducted risk analyses (HAZOPs), for two sub-operations in the program. HAZOP No. 1: dealt with ”Drop <strong>of</strong> 5 ½” tubing with 4” straddle”. The document was approved and signed by the SNA RESU manager when it was completed. HAZOP No. 2: dealt with "Perforation and pulling <strong>of</strong> scab-liner”. The document was not signed/approved by the SNA RESU manager. On 25 November 2004, the tubing with straddle was unscrewed from the work string. The pipe sections were run into the well and dropped. The scab-liner was punctured on 27 November 2004. The crew waited for an hour and observed the well for <strong>gas</strong>. The liner hanger at the top <strong>of</strong> the scab-liner was then cut and pulled. The crew then started to pull the scab-liner itself out <strong>of</strong> the fastening point in the bottom (PBR). An expected ”U-tube” effect, due to the fact that the brine behind the scab-liner was heavier than the drilling mud, was not observed. According to the detailed program, this effect should have resulted in a pressure increase <strong>of</strong> 32 bar in the mud system. However, the anticipated pressure change was not recorded. During the pulling operation, the crew stopped at regular intervals and observed the well for volume changes. It later proved that the casing spear that fastened the drill string/work string to the scab-liner either had no seal, or the seal was defective. Therefore, observation <strong>of</strong> a "u-tube" effect was not possible. In the same evening, swabbing was noted for the first time 11 . In the first part <strong>of</strong> a pulling operation, swabbing is not regarded as abnormal. At this point in time, approx. 2 m 3 <strong>of</strong> reservoir fluid 12 was swabbed when pulling the 2nd and 3rd stand. 13 As compensatory measures for the observed swabbing, the drilling report describes that they "pull the scab-liner slowly and make regular observations”. On 28 November 2004 during the period from 0000 - 0215 hours, the drilling crew pulled a single, but swabbing continued. The drilling supervisor - night elected to stop and discuss the situation with the toolpusher and drilling supervisor - day. Another attempt was then made to circulate the well down through the scab-liner and up the annulus on the outside. Low circulation pressure and rapid return <strong>of</strong> drilling fluid to the surface was observed. This was 10 Ref. document list Items 38 and 55. E-mail correspondence between the program engineer and the drilling supervisor dated 23 November 2004. 11 Swabbing is an undesirable piston effect that can occur during pulling <strong>of</strong> pipe strings. 12 2 m 3 <strong>gas</strong> under reservoir conditions is equivalent to about 20 m 3 on the seabed and 200 m 3 at atmospheric pressure. 13 One drill pipe / a ”single”= approx. 9 m . One stand = approx. 27 m = 3 drill pipes/”single” 16
another sign that the casing spear did not have the necessary seals, or that the seals were defective, i.e. the circulation went through the casing spear and not through the scab-liner. They observed that the well took mud, i.e. that the volume balance in the well seemed satisfactory and just as much mud went into the well as came out. During further pulling <strong>of</strong> the scab-liner they were repeated forced, for various reasons, to use overpull. This means that the traction used was greater than the weight <strong>of</strong> the scab-liner. At 0500 hours, the top <strong>of</strong> the scab-liner was under the BOP. Before the drilling crew pulled this through the BOP, they stopped and observed to check for changes in the well volume (flowcheck). The well did not exhibit any changes in volume. The scab-liner was pulled on through the BOP and blocked the cut and hold function. At 0700-0715 hours on 28 November 2004, the crew changed from night to day shift. During the period 0800 – 1530 hours, the day shift continued to pull the scab-liner. Swabbing with altogether approx. 4 m 3 volume increase was observed, and mud loss equivalent to 31 m 3 was also observed. During this period, the operation was observed for flowcheck for both brief and longer periods. Again, the well was regarded as being stable, and the drilling crew continued to pull the scab-liner after each flowcheck. During the course <strong>of</strong> the day, the drilling supervisor maintained continuous contact with the OIM and the drilling operations supervisor on duty on land, in order to inform them about developments in the well. 3.3 Third part: the well control situation develops At 1530 hours on the same day, the annular preventer <strong>of</strong> the BOP stack was closed, for the first time, due to influx. This type <strong>of</strong> valve was the only one <strong>of</strong> three types <strong>of</strong> safety valves that could be utilized in the BOP. A Kelly cock was installed and the top drive was screwed in. After a brief period <strong>of</strong> pressure increase, the well started to lose pressure. At about 1630 hours, the annular preventer was opened again, to pump mud to <strong>of</strong>fset for the mud loss. A total <strong>of</strong> about 25 m 3 <strong>of</strong> drilling mud was pumped into the work string and annulus. Attempts were made to circulate the well, but no mud was returned. Up until 1800 hours, the well was observed and an additional loss totaling 13 m 3 was ascertained and noted in the drilling report. The increasing problems with well P-31A throughout the afternoon were the topic <strong>of</strong> discussion at the regular platform management meeting at 1700 hours. The planned emergency preparedness drill was cancelled because <strong>of</strong> the situation. At about 1800 hours, after an attempt was made to reverse-circulate the well (down the annulus and up the work string), a backflow <strong>of</strong> well liquids was observed, which developed in an undesirable manner. Once again, the annulus safety value was closed in the BOP. The instability in the well proved to be on the rise, with a strong pressure increase to approx. 130 bar in the course <strong>of</strong> 2 hours. 17
Page 1 and 2: Report Inv
Page 3 and 4: SUMMARY On 28 November 2004, an unc
Page 5 and 6: TABLE OF CONTENTS 1 INTRODUCTION ..
Page 7 and 8: 1 INTRODUCTION In connection with a
Page 9 and 10: 2 STATUS PRIOR TO THE INCIDENT 2.1
Page 11 and 12: shut-in, well barriers were establi
Page 13 and 14: In a preparatory meeting for RTD on
Page 15: ams, i.e. the holding function in t
Page 19 and 20: Figure 3. Timeline for gas<
Page 21 and 22: On SNA, personnel were aware at an
Page 23 and 24: The log shows confirmation that the
Page 25 and 26: • Non-conformities. In this categ
Page 27 and 28: • The Activity Regulations, Secti
Page 29 and 30: Requirement: • The Facilities Reg
Page 31 and 32: Statoil could not document that an
Page 33 and 34: The status of the
Page 35 and 36: to provide for barrier integrity as
Page 37 and 38: information regarding the incident.
Page 39 and 40: descriptions are no longer used, bu
Page 41 and 42: 6.3 Participation in meetings The s
Page 43 and 44: The reason that the Pressure Alarm
Page 45 and 46: 7.4 Effect of redu
Page 47 and 48: clay. The foundations and the facil
Page 49 and 50: MTO Man - Technology - Organization
Page 51 and 52: Appendix 2 Overview of</str
Page 53: Appendix 3 Interview subjects (Exem

Report Investigation of gas blowout on Snorre A - Well Integrity ...

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