Tinsukia: The expert committee, formed by National Green Tribunal (NGT) to analyse the Baghjan fire, stated that there was a “flaw in operation plan” on part of public sector giant Oil India Limited (OIL) that led to blowout in Assam’s Tinsukia district causing extensive damage to environment, flora, fauna and local residents.
The committee, headed by former judge of Gauhati High Court Justice Brojendra Prasad Katakey, was constituted on the directions of the principal bench of NGT on June 24.
In the 407-page preliminary report, signed by member secretary of Central Pollution Control Board (CPCB) Prashant Gargava, the expert committee has held OIL accountable for the blowout on more than one count, exposing a series of lapses between between May 18 and May 27 – the day blowout occurred.
The report has been accessed by this correspondent.
Cause of the Accident
The report reads ad verbatim: After going through the replies received from OIL to the queries raised by the committee and having reviewed the DPR from 20.05.2020 – 27.05.2020, prima facie, the Committee could identify, pending further investigation, the following probable causes of the accident i.e. blowout of Well Baghjan-5.
(i) There was a flaw in the operational plan.
The decision to place a Cement Plug at a depth of 1000 Mtr in an inclined portion of the well (26 to 27degree as a secondary safety barrier itself was flawed. The cement plug should have been placed as near to the perforated Zone and in this case near to the Packer i.e. about 100 Mtr above packer by placing a 100 Mtr Sand plug above Packer to protect Packer from cement cutting falling during cement drilling.
(ii) Planned not to tag and test the Cement Plug was another flaw in the planning of Cement Plug job.
It was planned to place 100 Mtr Plug but cement slurry surfaced during reverse circulation at a depth of 655 Mtr i.e. after pulled out of D/P by about 340 Mtr. Probaby nobody read the cement plug job execution report of 27.05.2020. In such a situation, Plug should not only have been tagged and tested but also negatively tested to check its integrity of purpose as safety barrier before nipple down of BOP. This was a mandatory requirement as per the Standard Operating Procedure.
(iii) Moreover, when the cement slurry starts to set, slurry loses water and static gel develops.
At this time, cement column would behave like water column and reduced Hydrostatic Head. Secondly, in static condition of gas well i.e. WOC time when well fluid was static, gas bubble enters slowly from the perforated zone and gas bubbles percolated up, and expanded and burst at surface. This process continued in static condition of well at a faster rate being well fluid was brine. Same phenomenon would have been little slow in case of viscous fluid like mud.
But in the process, Sp gravity of fluid in the well was reduced slowly. In this well as cement plug was placed much above the perforated zone i.e. nearly 2700 Mtr. As a result, gas bubbles diluted a long column of brine solution in the well and so there was reduction of Hydrostatic Head of brine solution which was just above formation pressure of the perforated gas zone.
The combination of gas bubble phenomenon and reduction of head due to long contaminated cement plug resulted reduction of Hydrostatic head in the well after 13-14 Hours of WOC and well became active. And as there was no tested secondary safety barrier in the well after removal of BOP, well slowly started flowing and within one and half hour or so final blowout of the Well Baghjan-5 took place. This is therefore, a reason to place cement Plug near to the perforated Gas Zone to work as secondary safety barrier.
(iv) Against one of the queries raised by the Committee as to why it was not planned to set retrievable Bridge Plug (RBG) as a safety barrier in place of Cement Plug, OIL replied that use of Retrievable Bridge Plug is not in practice in OIL.
The Committee found this to be surprising. SLB logging contract with OIL is in place, only needed a provision in contract to use Retrievable Bridge Plug as and when required basis. Such standard provisions in ONGC contract with SLB are there with well logging contract to utilize such services as and when required. Moreover, ONGC departmental Production Team also does this type of job departmentally. Setting of Retrievable Bridge Plug to isolate the Gas zone would had been more convenient and also time saving.
(v) In the plan of cement plug job, it was mentioned WOC as 48 Hours. But in actual D/P were pulled out of casing after 12 hours of WOC and BOP was removed from well head after 15 Hours of WOC. This was a gross violation of written instructions of WOC of 48 Hours in the Plan. It is very hard to believe that Contractor Driller would act on his own to remove BOP after 15 hours of WOC against a written instruction of WOC of 48 hours unless Driller gets some instruction in writing or telephonically from someone from OIL.
From above discussions, it seems that planning group and execution team of OIL did not take the Cement Plug Job very seriously though it was placed as a secondary safety barrier before nipple down of BOP.
“Probably, the planning group relied mostly on primary safety barrier i.e. hydrostatic head of well fluid which was sufficient to stop any activity and cement plug was just an additional barrier, even though it failed would not matter. Therefore, it was first decided by planning group to place the plug at a shallower depth inside the casing, testing of the plug to check its integrity was not planned considering it was not necessary,” the report read.
It mentioned that while execution of cement plug job also nobody bothered to watch how it was placed, cement slurry channelled and rose higher than planned, and cement slurry design for this plug job was also faulty. Only cement additive Retarder was used to give longer IST without control of water loss from cement slurry after placement. Vital parameter of compressive strength was also not measured at BHCT (Bottom Hole Circulating Temperature) of 46 degree centigrade at plug depth of 1000 MT. So plug strength was not known.
According to the report, the probable reasons of the blowout include – deficiency in understanding of the gravity of a critical operation like removal of BOP without having a confirmed and tested secondary safety barrier, deficiency in proper planning of critical operations and a clear mismatch between planning and its execution at site and deviations from the Standard Operating Procedure (SOP) and serious deficiencies of proper level of supervision of critical operation at well site both from the contractor as well as from OIL.
Wildlife Institute of India, meanwhile, had submitted it report on the Baghjan blowout pointing out that the blowout has caused extensive damaged to the biodiversity of the region.
The “blowout” occurred at the gas well number 5 at Baghjan oilfield while work over operations was operations was going on to produce gas from new sand (oil and gas bearing reservoir) at a depth of 3,729 metres, leaving natural gas and condensate oil gush to hundred feet of in the air and spill all around. The well caught fire on June 9 and continues to rage.
According to latest reports, the efforts to place the Blow Out Preventer (BOP) in order to cap the well on Friday failed following which operations were suspended for the day.