Loss of Well Control Due to Leak from Seal Ring – Investigation Report

At approximately 1740 hours on February 14, 2008, a seal ring on the bottom flange below the master valve began to leak and dry gas was released into the atmosphere. Since the SCSSV was not operable and the leak was below the master valve,  it was not possible to prevent the escape of natural gas. The South Pelto No. 10 platform was evacuated shortly after the loss of well control without injury. The Well was secured on February 17, 2008.

2013.03.25 - Loss of Well Control Due to Leak from Seal Ring Figure 1

On February 13, 2008, production was performing routine scaling operations on Well No. 10 (Well), South Pelto Block 10, in an attempt to repair a leaking surface controlled subsurface safety valve (SCSSV). The Operator decided to perform an acid job to reduce the amount of scale around the SCSSV after several attempts to remove the scale with a wireline unit were not successful. Production pumped approximately 100 gallons of 1 percent hydrochloric acid (HCL) into the Well and allowed it to soak overnight. The day after the acid job Production re-entered the Well to perform more scraping.

Location of the incident

Location of the incident

On Tuesday, February 12, 2008, the parties involved in the incident began repairs on South Pelto Area Block 10, Well No. 10. The Operator was removing and replacing a ring gasket, not associated with the incident, between the crown and block valve. Prior to any operations being performed on the subject Well, a safety meeting was held and a Job Safety Analysis (JSA). During these meetings there was a discussion concerning bleeding down the downhole valve, operations involved in dissembling the tree, replacing the ring gasket, and reassembling the tree. The recommendations made within this meeting for a safe job performance were:

  1. to contain all fluids and bleed slowly
  2. lift properly to reduce back strain
  3. watch hand and foot placement to avoid pinch points
  4. maintain good communication with the crane operator
  5. inform all JSA participants they have stop work authority

After the repair was made to the tree, the SCSSV would not close. The Operator attempted to stroke the SCSSV, however, it would still not hold.

At 1430 hours, the Well was shut in. Due to inclement weather that evening, the wireline and field crew shut down operations. The previous successful SCSSV test took place on January 7, 2008. Prior to the January 2008 test, the SCSSV had no historical leakage issues reported to MMS.

The following morning, February 13, 2008, an additional JSA was held to discuss the wireline rigging up operations and the chemical injection procedures set for the day to remove scale buildup which was preventing the SCSSV to close properly. Every participant was informed of the proper personal protective equipment required for this job and of their stop work authority. During the JSA,  all representatives involved in this specific operation the location of a shower in case of contact with the acid, and it was decided to have a fresh water hose at the Well in case of emergency.

At 1100 hours on Wednesday, February 13, 2008, wireline was beginning to be rigged up and pressure was tested by Production. A restriction in the tubing was preventing them from working past 25 feet. After pulling the tool from the Well, Production reported scraping marks all around the edge of the 2-inch impression block. An undersized scratcher was then run into the hole and worked the jars. With the scratcher not being successful, Production pulled out of the hole, laid down the lubricator, and began to inject 100-gallons of 15 percent HCL into the Well overnight. The night tower monitored the chemical pump associated with the operation. Prior to this acid treatment, The Operator was not aware of any other previous acid jobs under its operation of the Well.

At 0600 hours, Thursday, February 14, 2008, following a JSA and safety meeting, the day tower resumed operations and began to rig up the wireline lubricator. Prior to running back into the hole, the day tower successfully rigged up and tested the lubricator by 0800 hours. A 1.75-inch broach, which is an outer diameter tool that allows for subsequent passage of tools and equipment of a prescribed diameter, was run into the hole by Production to approximately 300 feet without any restrictions. The 1.75-inch broach was followed with a 2.1-inch to 2.25-inch tapered broach. However, Production was unable to get past the initial restriction in the tubing.

Shortly after the restriction prevented further depth into the hole, Production ran into the hole with a 2.25-inch impression block and sat down at the location of the impression and jarred it one time. When the 2.25-inch impression block was pulled out of the hole, it was determined that there was evidence of build-up on the tubing walls.

After pulling out of the hole with the impression block, Production proceeded to run into the hole with an undersized, barbed scratcher. They were able to work it to approximately 15 feet before the tool had to be pulled out of the hole and cut down the scratcher. Production was able to cut heavy scale to approximately 300 feet, and ran up and down the tubing several times with the tool. Following the commencement of the initial scraping operation, Production ran back into the hole with a 1.85-inch paraffin knife and chipped the scale down to 300 feet. They then pulled out of the hole and began to run a 2.1-inch tapered broach. The broach was not able to get past 15 feet. It was then decided to rig up the acid pump equipment and inject additional acid into the Well to reduce the scaling.

At 1740 hours, the Well began leaking natural gas between the master valve and the adapter.

Following the blowout, approximately 35 people were evacuated to either South Pelto Block 2, Platform JA; Ship Shoal Block 91, Platform B; or a dedicated lift boat in the field. There were no reported injuries during this platform abandonment. Prior to departing to safe harbor:

  1. the field was shut in
  2. all shut down valves were closed
  3. the platform had its emergency shut down system activated

There was a dedicated field boat keeping observation on the Well following the incident, and an oil spill response organization was dispatched in the event any liquids were to begin discharging from the Well. The Operator established a Unified Command Center with the United States Coast Guard on the evening of February 14, 2008, and contacted the MMS Houma District Office with all updates.

The Operator and the Production developed a plan of action to control the Well by February 15, 2008. On February 17, 2008, the Well had been killed and secured. A back pressure valve was installed in the tree and the ring gasket was replaced. The J-3 zone, which was located at 9,963 feet – 9,978 feet true vertical depth, was squeezed with cement and successfully pressure tested. A test run on February 27, 2008, indicated the pressure on both the casing and tubing strings bled to 0 psi and had no subsequent build up. The platform returned to service. The subject tree was sent to Cameron for investigation and was received on February 22, 2008.

After the incident, the Operator conducted a formal investigation of the loss of well control. The Operator identified the causal factors as the leaking SCSSV, the leaking ring gasket, and the acid job procedure. Their findings were submitted to MMS on April 5, 2008. Further, the Operator also developed an operational procedure to ensure that pressure tests are conducted on wells prior to acid treatment operation to lower the possibility or prevent this type of incident from occurring in the future. The purpose of this pressure test will be to verify the mechanical integrity of the ring gasket and other critical wellhead components before acid is circulated into the well system.

An examination on what could have caused the incident revealed the following:

A. Mechanical/Actions:

  1. The exact condition in which the gasket was in prior to the incident is not known; however, it is known that a ring gasket downstream was replaced two days prior due to a possible corrosion failure. Pictures taken during a post-mortem inspection of the tree indicate the gasket involved in the incident was heavily corroded prior to the incident. Therefore, the amount of corrosion on the ring gasket which lead to the loss of mechanical integrity is concluded to be a cause of the incident.
  2. The performance of an acid job to reduce scale likely accelerated the loss of mechanical integrity of the ring gasket. Therefore, the performance of an acid job is concluded to be a contributing factor of the incident.
  3. If the tubing retrievable SCSSV was able to close properly, it could have prevented the loss of well control. Therefore, a leaking SCSSV is concluded to be a contributing factor to the duration of the incident.
  4. It is also possible that as the scraping operations were taking place in the Well near the ring gasket, the scratchers could have contacted the ring gasket. The manner in which that occurred could have influenced the amount of integrity loss of the ring gasket prior to the loss of well control. While it has been concluded as a very reasonable possibility, any conclusion as to the probability of such contact is made difficult by no solid data indicating this happened. This assumption was made due to an anomaly in a post-mortem picture. Therefore, the contact of the scratchers with the ring gasket is concluded to be a possible contributing factor of the incident.
2013.03.25 - Loss of Well Control Due to Leak from Seal Ring Figure 3

Ring Gasket

2013.03.25 - Loss of Well Control Due to Leak from Seal Ring Figure 4

Master Valve Ring Groove and Corrosion

2013.03.25 - Loss of Well Control Due to Leak from Seal Ring Figure 5

Tree in the Cameron Yard Post-Mortem

B. Training:

The Operators training does adequately train employees to abandon a platform if necessary. The Operator relied heavily on its emergency drill training to prepare the employees to abandon the platform in the event of an emergency. The existence of formal training and emergency drills was instrumental in the prevention or cause of any other incidents or accidents during the platform evacuation.

C. Management:

The Operator’s safety management was clearly documented in their Offshore Safety Operations Procedures (OSOP) document and implemented within the field. Also, it is concluded that the responsibilities of their representatives on the platform were performed and documented in accordance with the policies set forth within the document. It is, therefore, the conclusion of the panel that there were no failures in Apache’s safety management system that contributed to this accident.

D. Sustained Casing Pressure:

The sustained casing pressure on the production casing is concluded not to be a contributing factor to the occurrence or duration of the incident.

In summary the incident was caused by:

  1. a leaking SCSSV
  2. severely corroded ring gasket
  3. the performance of an acid job possibly accelerating the failure of the ring gasket

As a result of this incident the following recommendations have been issued:

  1. Lessees and operators should review their policies regarding the performing of acid operations especially if an SCSSV is not functioning properly.
  2. Lessees and operators should review their platform specific emergency plans to reduce further injuries or accidents when an incident occurs.
  3. Lessees and operators should be able to trace the history of ring gaskets in the field regardless of previous ownership, and/or determine the condition of said ring gaskets prior to the performance of future operations.

Source: BSEE

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