How relief wells can make a blowout worse
Actuarial data reveal BP's blowout in the Gulf of Mexico belies industry norms
Aerial view of the Deepwater Horizon spill
While politicians and environmentalists race to deplore BP’s tragedy in the Gulf of Mexico, the expert authorities that police offshore drilling are receiving reality checks. Just as in medicine a cure can be worse than the disease, in industry the most attractive-looking remedy for an accident can backfire.
A second or “relief” well can make a blowout worse and other ways to tame the runaway should be tried first, the Texas dean of oil- and gas-field disaster-fighting firms has told the National Energy Board (NEB). Houston-based Wild Well Control Inc., a veteran of 35 years in its dramatic specialty, delivered the warning to Canada’s safety review of proposed Arctic deepwater drilling shortly before BP’s disaster. The NEB expanded the study, which began as an exchange of technical papers among specialists, into a wider inquiry to take into account lessons learned from the BP case and hear public submissions.
“Drilling the relief well could be more risky than drilling the original well,” Wild Well says in a 22-page paper. Just for starters, the second hole is bound to take more time because it has to be “directional” or pierce the geology at an angle from an entry point some distance away from the first one.
A relief well poses greater difficulties than the technical challenge of achieving the hair-line accuracy required to intersect with the first hole, the Texas firm warns. The second well can run afoul of spreading leaks from the blowout that “charge” surrounding geological zones with high-pressure gas or oil, and potentially encounter entirely new and unexpected deposits.
“The relief well might become an additional or independent exploration well [into a fresh gas- or oil-saturated rock fault] with the same, differing or more problematic issues than the designated exploration well – therefore, essentially doubling the risks for well-control issues,” Wild Well warns.
The blowout-tamers describe an array of potential actions, ranging from cutting off flows with special hole-plugging substances or equipment to installing a second blowout preventer (BOP) device on top of the original one if it fails.
The primary means of controlling wells – including relief ones – is blowout prevention, by management of the gas-and-oilfield drilling fluids known in the industry as “mud.” The materials, used in a wide range of types and mixtures, simultaneously lubricate rotating equipment as it penetrates rock and counter underground pressures with their weight. Mud forms a tall, continuous column of liquid in the drill pipe and hole.
Transocean Offshore Deepwater Drilling Inc., owner of the lost Gulf of Mexico rig and potential contractor for new exploration planned in Canadian waters of the Beaufort Sea, likewise emphasizes blowout prevention with the use of suitably dense drilling fluids and BOP equipment made strong enough for the well and its natural environment. If the systems fail, restoring control requires industrial counterparts to firemen, paramedics and emergency-room physicians.
In a 12-page paper filed with the NEB, Transocean highlights the role of specialists like Wild Well. “In the extremely rare case where the normal well control procedures and existing blowout prevention equipment and back-up blowout prevention equipment fail to contain the well, the specific conditions of the resultant blowout will determine which method of intervention will be attempted. These activities are normally through the direction of third parties who specialize in this type of operation.”
Det Norske Veritas, a Norwegian risk-management foundation with global operations, underlines the rarity of offshore drilling mishaps in a lengthy review of Beaufort Sea conditions that was commissioned by the partners in proposed Arctic deepwater exploration, Imperial Oil Ltd. and ExxonMobil.
Using statistical techniques akin to the actuarial calculations of insurance firms, the risk specialists calculated the odds of losing control of offshore wells for even a moment as one incident for every 500 drilled. The estimate includes all types of mishaps ranging from well hiccups known in the industry as “kicks” to serious environmental events caused by failures of equipment and control procedures.
In a global review of performance by BOPs since 1980, including their record in the Gulf of Mexico and the North Sea, Det Norske rated the probability of a failure as 0.68-1.0 per cent depending on the design of the equipment. Chances of an outright blowout and leak due to catastrophic failure of all safety, prevention and control procedures and hardware are much slimmer.
“No evidence was found of any relief wells ever being required for deepwater drilling operations using a drillship,” Det Norske says. “The study concluded with an estimated likelihood of uncontrolled flow after using all available options on the drillship to be once for every 100,000 wells drilled, or once in every 10,000 years based on 10 wells drilled per year in the Beaufort Sea.”
A previously approved, deepwater exploration well in the Orphan Basin offshore of Newfoundland and Labrador was allowed to go ahead after the Gulf of Mexico accident by the Canada-Newfoundland Offshore Petroleum Board (CNOPB), a joint agency of the federal and provincial governments. A 244-page “strategic environmental assessment” by the authorities in St. John’s parallels the Det Norske findings. The BP mishap was out of character.
“The industry of exploring, developing and producing offshore oil and gas has a relatively good record compared with other industries that have potential for discharging petroleum into the marine environment,” the CNOPB document says. “The spill record is particularly good for the U.S. Outer Continental Shelf where 28,000 wells were drilled and over 10 billion barrels were produced from 1972 to 2000. During that time only 10 blowouts occurred that involved any discharge of oil or condensate. The total oil discharged in the 10 events was only 751 barrels.” That compares with flow-rate estimates that range from 21,500 to 60,000 barrels per day at the site of the BP spill.
Before issuing permits for deep drilling in the Beaufort, NEB chairman Gaetan Caron said, “We need to learn from what happened in the Gulf. The information taken from this unfortunate situation will enhance our safety and environmental oversight.”
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