CSB: Operational lapses led to well blowout, fire
Poor barrier management combined with underbalanced operations performed without proper planning, procedures, or needed equipment caused an Oklahoma natural gas well to blow out and catch fire on Jan. 22, 2018, killing five workers in the driller’s cabin on the rig floor, a US Chemical Safety Board investigation concluded.
Failure of both the primary barrier—hydrostatic pressure produced by drilling mud—and the secondary barrier—human detection of influx and activation of the blowout preventer (BOP)—were intended to be in place to prevent a blowout at the Pryor Trust 0718 gas well No. 1H-9 in Pittsburg County, Okla., CSB said in its final investigation report on June 12.
It said that Red Mountain Energy LLC, a privately held Oklahoma City exploration company, was the leaseholder. Its Red Mountain Operating LLC division was the operator. Patterson UTI Drilling Co. was the drilling contractor.
The five workers died from thermal burn injuries and smoke and soot inhalation following the blowout about 3½ hr after drill pipe was removed from the well in a procedure known as tripping, CSB said.
“Our investigation found significant lapses in good safety practices at this site,” CSB Interim Executive Kristen Kulinowski said. “For more than 14 hr, there was a dangerous condition building at this well. The lack of effective safety management resulted in a needless catastrophe.”
Industry best practices recommend always having two protective barriers in place during drilling operations, Kulinowski said. “Our investigation found that both of those barriers failed in this instance.”
The executive summary in CSB’s final report said factors that contributed to the loss of the protective barriers included:
• Underbalanced drilling performed without the necessary planning, equipment, skills, or procedures, which effectively nullified the planned primary barrier to prevent gas influx.
• Tripping performed out of the underbalanced well, which allowed a large amount of gas to enter.
• The driller not being trained effectively in using a new electronic trip sheet, which is used to help monitor for gas influx.
• Equipment that was aligned differently than normal during the tripping operation, leading to confusion in interpreting the well data that caused rig workers to miss indications of the gas influx.
• Surface pressure that was not identified two separate times prior to opening the BOP during operations before the blowout, when there was evidently pressure at the surface of the well. This nondentification of surface pressure contributed to the gas influx not being identified.
• A weighted pill intended to overbalance the well that was apparently miscalculated. After pill placement, the well was still underbalanced.
• Both the day and night driller choosing to turn off the entire alarm system, contributing to their missing critical indications and imminent blowout. “The alarm system also was not effectively designed to alert personnel to hazardous conditions during different operating states (e.g., drilling, tripping, circulating, and surface operations) and would have sounded excessive noncritical alarms during the 14 hr leading to the blowout, which likely led to the drillers choosing to turn off the alarm system,” the investigation said.
• Not performing key flow checks to determine if the well was flowing before the incident. “Drilling rig workers performed very few of the company-required flow checks during the drilling of Well 1H-9 and the previous well. The drilling contractor did not effectively monitor the implementation rate of its flow check policy,” the investigation said.
• The drilling contractor’s not testing its drillers’ abilities in detecting indications of gas influx through, for example, simulated pit gains. “The absence of testing drillers’ influx detection skills—a safety-critical aspect of well control—might have contributed to both drillers not detecting the significant gas influx leading to the blowout,” CSB said.
• The operating company’s not specifying the barriers required during operations, or how to respond if a barrier was lost. This contributed to the performance of underbalanced operations that the drilling rig and its crew were not equipped or trained to perform, investigators said.
• The safety management system in place not being effective for managing safe rig operations. There also was no drilling-specific regulatory standard governing onshore drilling safety.
“In addition, the victims had no safe escape route from the driller’s cabin (dog house) once the drilling mud and gas ignited. The workers were effectively trapped once the fire started,” the executive summary noted.
“The [BOP] also failed to close when its activation was attempted after the fire started,” it said. “The CSB determined the BOP did not function likely because the control hoses that supplied hydraulic fluid to the BOP to function the rams had burned in the fire and leaked the hydraulic control fluid, soon depleting the accumulator stored pressure to the point the [BOP] could not be closed.”