By Seth Richardson
The media has been generally remiss in describing to us how the disaster in the Gulf of Mexico happened, and everybody’s too busy pointing fingers and talking about the impending damage from the oil to take the time to do so, so I’m going to have to give it a shot myself.
After consulting with some experts, here’s a layman’s explanation of how deep-sea oil drilling works and what likely happened beneath the Deepwater Horizon.
First, some basics on oil drilling. Take a soda straw and and the ink reservoir and tip from a Bic ballpoint pen. Now insert the ink pen into the soda straw. Now jam the whole thing into the dirt, and twist and push the ballpoint parts downward. That’s pretty much how an oil drilling rig works. The ink reservoir tube is the “drill stem,” the ballpoint tip is the “tool” or “drill bit,” and the soda straw is the “casing.”
As the well is drilled, drilling mud, a chemical concoction used to lubricate the drill bit and carry the rock chips the bit creates, is pumped down through the center of the drill stem, and it flows back up out of the hole along the outside of the drill stem. As the hole gets deeper, the casing is slipped down into the hole with the drill bit and drill stem inside the casing. Sections of casing are added to this stack as the hole is drilled.
At the top of the stack of casing, which does not extend to the bottom of the hole where the oil is, is a “blowout preventer,” or BOP. This is a complex device that has at least four different ways of sealing the well casing and preventing oil from flowing up the casing uncontrolled. It has a hydraulic ram that can crush both the casing and the drill stem shut, another hydraulic ram with a shear plug that can punch a hole through both the casing and the stem, creating a horizontal plug in the well, an “annular plug” which can seal the casing but not the drill stem, and a pair of fittings at the very bottom of the BOP called the “kill” and “choke” ports, through which high pressure fluid can be pumped to create pressure in the casing to keep oil from flowing up the pipe.
As the well is drilled, and the casing is rammed into the hole, there is space between the rock wall of the hole the tool is boring and the 1/2 inch thick wall of the casing pipe. This is the space that is cemented in order to seal the space around the casing and the borehole. This must be done to prevent the high-pressure oil from flowing up the outside of the casing, where it cannot be controlled or captured.
Once the casing is cemented properly, there is a strong seal around the casing that will withstand the upwards pressure of the oil.
During drilling, the upwards pressure of the oil is balanced by the weight and pressure of the drilling mud being pumped down the drill stem, so the oil cannot flow upwards. This pressure is kept on until the well is cemented and the cement has hardened. Then the pressure can be let off, and the valves on the BOP closed to cap the well, and the whole system is sufficient to withstand the pressure of the oil.
What seems to have happened here is a failure in the cementing process, likely caused by the nature of deep-water drilling. At the depths involved, methane gas is a frozen liquid, not a gas. The pressure turns it into a liquid, and the temperature turns it into an icy slush or solid.
As the well is drilled, it may pass through layers of frozen liquid, which so long as it stays frozen, is not a problem. But the cementing process generates heat. Cement, as it hardens, chemically changes into concrete, and in the process, it heats up.
To cement the well, the cement is pumped down the drill stem, from which the tool has been removed. The cement flows out the end of the drill stem and is forced under pressure back upwards towards the surface along the outside of the casing pipe. Normally, a calculated amount of cement is injected into the well as engineers observe the pressure, and when completed, the cement has formed a strong seal around the casing pipe for hundreds or thousands of feet upwards from the bottom of the casing, sealing the bore hole and setting the casing in place.
In this case, however, it appears that there were fissures in the rock strata filled with methane ice, and when the cement hit a fissure or pocket, the heat of the cement curing melted the methane ice. When melted, the ice becomes gas, and the pressure rises dramatically, which can, if the pressure outside the casing and inside the casing are not carefully kept in balance, rupture the casing somewhere above the bottom of the casing, driving methane gas into the casing on the outside of the drill stem. This gas begins to flow upwards and at the same time, the cement, which is supposed to flow up the outside of the casing and fill the space between the casing and the bore hole, can flow into the fissure that contained the methane ice, which means that the desired seal around the outside of the casing cannot be guaranteed.
The methane gas flowed up the casing to the drill rig, a mile above, expanding all the way as the pressure dropped, and exploded. The rig sank, and the riser pipe, which is similar to the casing but is attached to the top of the BOP, fell to the side, kinking and cracking.
Three of the four safety systems in the BOP, the shear ram, the blind ram and the annular valve all failed or worked only partially for some unknown reason, so the flow of oil was not cut off at the BOP as intended, and is now flowing through the casing, drill stem and riser. The drill stem has been capped where it protrudes from the riser pipe, but the broken riser pipe end, with the drill stem inside it, is leaking, as is a crack near the BOP where the riser and drill stem folded over as it sank to the bottom.
The problem BP engineers are facing now is that they are not certain of the strength of the cementing, and if they plug the well, they don’t know if the pressure from the oil will cause the cement to fail and allow the oil to flow up the outside of the casing rather than the inside, which would make the leak completely uncontrollable.
At the moment, the oil is coming up the casing into the riser, where hopefully it can be captured and pumped to the surface, which is preferable to blowing out the cement and ending up with a massive, uncontrolled release of oil.
So, BP is reluctant to try to plug the well, lest the cement fail, and, according to my sources, are pinning their hopes on the lateral well they are drilling in hopes of intercepting the well bore so they can pump the whole well bore full of cement to plug it. The problem is that it’s going to take a long time to drill the intercept well, and in the past, such attempts have rarely hit the 12 inch wide borehole from four miles away on the first try. The last time this was attempted, in Ixtoc, Mexico, it took six attempts to hit the bore. If it takes two months per attempt, it could be a year before they manage to shut the well down that way.
But, BP may be preparing to try a “junk shot,” which is injecting bits of rubber and other debris through the kill and choke lines to clog up the annular valve at the top of the BOP and stop the flow of oil that way, even though they risk blowing out the cement, which could lead to an even greater and faster release of oil that would be completely uncontrollable, and likely cannot be contained and pumped away by dropping a structure over the BOP.
Why it happened will take months to determine, but I hope I’ve given you a better idea of how it happened, and what the risks are.