Unocal Grayling Platform; Cook Inlet, Alaska
As early as 1957 a Joint Venture between Atlantic Richfield, Marathon and Unocal delineated a very large, low relief anticline along the west shoreline of the Cook Inlet in Alaska and within this anticline was the vast Hemlock Conglomerate stratigraphic interval known to have numerous stacked reservoirs with good permeability and porosity. The Basin had proven source beds for hydrocarbons as the first commercial discovery of oil occured in the 1950's.
Unocal made its first discovery on its JV block in 1965 from its Grayling Platform 1-A well with an IP of 2000 BOPD of 35 API oi. The JV named its new field McArthur River Field. It lies about 60 miles SW of Anchorage. The Hemlock Unit was developed from three Platforms, the Grayling, Steelhead and Monopod. A total of 47 wells were drilled on the anticline over 15 years before the field went into a very effective pressure maintenance stage with use of water. By the year 1993 the field had produced over 321 million barrels of oil and is expected to recover 680 million barrels. It is now operated by Hilcorp and a few infill wells are still being drilled from two of the original three platforms into Hemlock and Tyonek reservoirs. The Cook Inlet has been a vital source of hydrocarbons, particularly natural gas, to Alaska, with gas now nearing 10 TCF of cumulative production.
The entire Cook Inlet and particularly this Unocal JV block had a history of shallow gas blowouts at various depths above 2,000 feet that nobody could quite seem to sort out and the JV, regardless of who was operating, was always getting its ass kicked drilling wells.
Ken Graham Photo
The Grayling Platform lost control of a development well on Memorial Day weekend in 1985 from a overpressured gas zone located several hundred feet below a protective string of casing. The BOPS were successfully closed and things seemed reasonably under control until bubbling gas could be seen coming around a support leg on the rig suggesting an underground blowout was underway. The flow actually broached the casing leg itself, on the right, and mud, water and large rocks were gettin hurled straight up the platform leg some 400 feet high hitting the water like enormous hailstones 500 feet downwind. All personal were evacuated from the rig via lifeboats, but not before shutting in, or pumping DHSV's closed, on the platforms, 14 producing wells. Boots and Coots, Inc. was on location within 2o hours.
With blowout flow confined to the rig leg, the floor, Kelly and pumps were all accessible and several attempts were made to kill the well with mud, all unsuccessfully. Relief well plans began when on day six the well bridged completely dead.
Below, a very young, David Thompson, only a year and half employed by Boots and Coots, Inc, with Boots Hansen on Unocal's, Grayling Platform, 1985. Photo by Joe Carpenter from Shellman files.
Marathon Steelhead Platform
Three years later, within sight of the Grayling Platform, Marathon's Steelhead Platform blew out on December 20, 1887, also from a shallow, overpressured gas sand. Loss of surface control occurred around the Kelly and partially closed, failed BOP actuation. Within 4 hours a large rock set the free gas on fire and the platform was engulfed, caught some diesel tanks on fire and caused extensive damage to the crew quarter module, etc. Before the platform was evacuated its only three producing wells were successfully shut in. The well in progress at the time appeared to be contributing to the uncontrolled flow but rig fuel was burning above and below decks.
Boots and Coots, Inc. including David Thompson, Joe Carpenter and Boots Hansen were are on a support vessel under the Steelhead Platform within 24 hours, once again.
A few days before the new year, 1987. Steelhead in the foreground, Grayling in the distance. back to drilling development wells after its blowout two years earlier. John Wright Photo
After day two Boots began to notice diminished flow rates and increased shale and sand unloading at the surface suggesting the well was perhaps beginning to bridge. He ordered high pressure, high volume pumps from the North Slope used to build ice roads and by day four of the event was spraying water in an effort to put the fire out. Flows continued to slow as enormous volumes of shale being blown from the well began to pile up on the rig floor. The well actually appeared to be bridging from the top down. Sea water sprayed at the fire began to freeze and all the rig fuel tanks stopped burning.
Steelhead Platform still burning after day three. Grayling in the background and Mount Redoubt Range along the Cook Inlet shore. Photo by Ken Graham.
Late on the fourth day almost the entire rig floor was covered in a thick sheet of ice and shale was being puked out of the drill pipe annulus in large volumes, covering the floor, drawworks, dog house and getting stacked almost as high as the racking board in the derrick. The fire went out and well died.
A jackup rig was towed into place and John Wright began to design and implement a relief well to intersect the interval causing the blowout. Some seven different support vessels were on standby, including the work barge, Sustina.
With the relief well soon to spud, Boots and Coots, Inc. undertook the effort of clearing shale away from the rig floor to access the drill pipe and Kelly. The water cannons and high volume pumps from the North Slope were used to wash a literal mountain of shale into the sea, from the top down, Joe and David working from dark to dark.
This was a Boots Hansen job so there was, sadly, no time for photographs and there was absolutely no staying overnight on any of the nearby work boats or other support vessels. The three of them were ferried every morning and evening into Anchorage via helicopter for fine dining and accommodations. Each day Boots gave directions and went back and forth from the Steelhead Platform to the jack up, Hawaii that John Wright was on to help orchestrate the well intersection. Within six days the entire rig floor and upper deck rig components had been washed clean enough to eat off.
The well would bubble gas occasionally around a platform leg and belch gas through the bell nipple. The boys stood by by while the drawworks, drawworks engines and pumps were pulled off the decks and replaced. Remarkably only fuel oil sheens could be seen in the water as the well made no liquid hydrocarbons whatsoever. Within 17 days the intersection was made and the well was pumped dead with sea water, mud and cement. Boots and Coots went back to Houston and Marathon rebuilt their rig. The well kicked four or five more times while washing out and top killing.
In June of 1989, just a few months after the Steelhead incident, the Unocal Monopod Platform caught fire badly burning three people. All three platforms used by the JV to develop McArthur River Field were then involved in noteworthy events. All three platforms are still used today by Hilcorp.
In early December of 1989, the same year the Steelhead blowout was intersected and killed, and the Monopod fire put three men in the hospital, the Redoubt Volcano erupted less than a hundred miles from the McArthur River Field in the Cook Inlet.
The ash cloud from this eruption lasted for several months into 1990.. So severe was this ash cloud it adversely affected military and commercial flights in and out of Anchorage for months. Several days after the eruption of Redoubt a commercial 747 jetliner lost power to four engines on takeoff from Anchorage, all clogged with ash, and had to make an emergency landing back in Anchorage.
Within 60 hours of the initial eruption the ash cloud from Redoubt reduced visibility to such a point in West Texas the the Midland Airport was closed, briefly.
Author's notes: the Ken Graham photographs are copyrighted on his website but the ones I used came directly off the internet, from public domain. I hope I got most of this post right; David and Joe both told me stories about these wells but there is now nobody left to check accuracy with. It was indeed hard to take a second to take photographs on any job Boots was involved in and a lot of major integrated companies would not allow it anyway. The Steelhead incident and subsequent rig rebuild cost $189 million dollars and I am sure there was a lot of chicken fighting between JV members,
Writing about blowouts is very difficult, they are kept secret and as much out of the press and history as possible. obviously for liability reasons. I know of a half dozen Exxon blowouts where this is not a word on any of them of public record. The best one can do is remember stories and dig from whatever sources are available. ~ Mike