Porter Ranch: Lessons from past attempt to kill a well

Southern California Gas Co. says  it has finallly plugged  its badly-leaking gas well at its Aliso Canyon gas storage field near Porter Ranch. The company used a method it first tried 25 years ago on another stubborn well blowout. That experience, in a Santa Clarita Valley gas storage field called Honor Rancho, didn't go well initially.

A drill boring a relief well that was intended to pierce and plug the leaking well thousands of feet below the surface accidentally cut into the leaking well in the wrong place, two SoCalGas engineers wrote  in the Oil & Gas Journal in 1992. A similar mishap came within two feet of happening to the Aliso Canyon relief well in late December, public records say.

SoCalGas has been very careful in its recent Porter Ranch updates not to specify when the relief well at Aliso Canyon would intercept the leaking well, other than to state it could be by the end of February. Despite that care, representatives of agencies and officials who were getting closed-door briefings have repeatedly said for the past week that the meet-up could happen at any time. Thursday afternoon, the first step to permanently shutting the leak, was accomplished with the intersection of the two wells.

A call to SoCalGas asking if that long-ago mishap had made them wary in sharing information about the progress of this latest well-plugging effort was not immediately returned. It's unclear how many times SoCalGas has responded to a leaking well by drilling a relief well.

The Aliso Canyon and Honor Rancho well failures are similar in a few respects. At Honor Rancho, a well called WEZU 30 developed a leak, and repeated efforts to plug it failed. The leak  was bad enough that it threatened the integrity of the entire gas field. A leaking gas well in a pressurized gas field is like an leaky balloon, over time the gas flows out and the pressure in the balloon falls low enough that the exit of gas stops. It's unclear how much gas was lost from the Honor Rancho field during the months it took to seal the leak.

Like the 1953-vintage leaking well at Aliso Canyon, WEZU 30 began as an oil well in 1961 and was later converted to gas storage.

At both Porter Ranch and at Honor Rancho, engineers used the same method to identify the point at which the relief well should cut into the leaking well, using a tool called a magnetic ranging device. As a relief well is dug, the pipes carrying the drill bit are removed and a tool is lowered down the relief well. The tool creates a magnetic field to detect the location of the leaking well.

The idea is to dig the relief well far enough down to bore into the leaking well at a point where fluids, drilling mud and concrete can be pumped down into the relief well to plug the leaking well. But it's difficult to know where the wells are underground. WEZU 30 had been directionally drilled, meaning it didn't go straight down into the earth.

At one point the rescue well unintentionally broke through the leaking well 9,860 feet below the surface when the readings from the magnetic tool told them they should be about four feet away from the well.

That required more repairs and a lengthier process to plug the well. Eventually the wells intersected at the correct point and the well was returned to service. WEZU 30 remains an active gas storage well today, according to records of the state Division of Oil, Gas and Geothermal Resources.

The public record filed with state oil and gas regulators by SoCalGas about the digging of its relief well shows that the same thing nearly happened at Aliso Canyon. The magnetic well-finding tool was sent down the relief well when it was about 3,806 feet deep, and it showed that the hole had bored to within two feet of the leaking well. That put the new well in peril of prematurely piercing the leaking well many thousands of feet above the target, which was the base of the well. The relief well was plugged back about 200 feet and drilling resumed in a different direction. The incident was first reported by L.A. Weekly.