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Methane, CH4 is a more powerful greenhouse gas than CO2 but its concentration is much less. It is produced by anaerobic bacteria. These occur in bogs and rice paddies, but also in the intestines of ruminant animals (cattle) and termites. Before oxygen appeared in Earth’s atmosphere methane may have been the most important greenhouse gas. The dominant sites of production of methane are low-latitude wetlands, but with warming of the Earth, increasing amounts of methane are being released from Arctic bogs. Methane can combine with water to form an ice, termed a clathrate. These ices form under the pressure of a few hundred meters of seawater at temperatures well above the freezing point of the water itself. Clathrates cement sediment grains together, acting in some areas to stabilize continental slopes. Warming of the ocean may decompose clathrates releasing methane into the seawater or atmosphere and resulting in tsunami-producing slope failure on the continental margins. Nitrous Oxide, N2O, is another powerful greenhouse gas released into the atmosphere from decaying vegetation. Since the middle of the last century, it has been artificially produced for munitions and then fertilizer but through overuse it has become an anthropogenic pollutant. It is becoming the most effective destroyer of ozone in the twenty-first century.
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In 1981 we were getting the results of the engineering studies we had commissioned from Santa Fe International. I recount some of the conclusions here because they are relevant even today in the light of the recent BP Deepwater Horizon disaster in the Gulf of Mexico. The first major disaster in offshore drilling occurred on June 3, 1979 , in the Gulf of Mexico’s Campeche Bay, about 100 k 62m ( mi) northwest of Ciudad del Carmen, Mexico. Ixtoc I was an exploratory oil well being drilled by the SEDCO’s semi-submersible drilling rig 135 -F in waters 50 m160 ( ft) deep. The well was equipped with blow-out prevention devices, but they were not activated until the well was no longer controllable. In Intermezzo XIX I explained how drilling at sea works, with a riser to enclose the drill string and permit return circulation of the fluids in the well. The connection at the sea floor is a complicated affair. There must be a solid base for the riser, and this is where the well must be shut off should anything go wrong. The shut off is accomplished by squeezing the riser and drill pipe closed. That requires a lot of force and is done by hydraulic rams, usually powered by explosive charges. What can go wrong? Gas is generated by the decomposition of organic matter in the sediment. If it is produced in large amounts its pressure can exceed the lithostatic pressure, the weight of the rock above it. It can’t escape because the rock is glued together by mineral cements. If there is ‘over pressured gas’ in the pore space of the sediment it can escape into the drilling mud. This makes the mud lighter, and the weight of the mud column decreases so that more gas flows in, and before you know it gassy drilling mud is coming up the annulus between the drill pipe and hole wall. The more gas gets into the well the faster the process goes. This is what caused ‘gushers’ back in the early days of petroleum exploration. Downhole sensors can detect the changes in weight of the drilling mud column. The sensors are monitored on board the drillship, and if they show that something is happening the blowout preventers must be fired off. That means a loss of many millions of dollars; the well is lost. The problem is that the deeper the hole beneath the vessel, the smaller the danger signal from the sensors. It is my understanding that at Ixtoc, the crew on the ship needed permission from Petroleos Mexicanos Headquarters in Mexico City to approve firing the blowout preventers. It came much too late. Here is the problem. The person monitoring the sensors guages on the drillship has a very boring job. But it is a huge responsibility. That person will probably want to see a very clear signal before pressing the button. After all, by pressing it they are costing the company many millions of dollars. And, if the blowout preventer works as it should, one will never really know whether a blowout was about to happen. That employee will surely be blamed for over-reacting. We had long discussions at Santa Fe in Houston about this problem. It was thought that the monitors would need to attend a special school for training. I do not know whether such a school was ever established. Exactly this sequence of events, with the delays in decisions, appear to have happened to the Deepwater Horizon on April 20, 2010 . Only this time there was a further complication. Already days earlier bits of the rubber sealing rings of the blowout preventers had been seen in the returning drilling mud. Even if the blowout preventers had been fired off in time, the sealing of the hole would not have occurred. Incidentally, the Deepwater Horizon, being operated for British petroleum, belonged to Transocean, which is the amalgam of Global Marine, SEDCO, and Santa fe International. Another aspect of the engineering was to ensure that the operations could be carried out even if there were to be a hurricane. This would mean that the drill ship should be able to disengage from the drill string and riser, but leave them held up by floats at a safe depth below the surface. The ship would be moved to calmer waters and return later when conditions permitted. We had to plan for a 100 -year storm. Our meeting to discuss this was held in late September, 1979 , after a series of very heavy rain in Houston. Someone remarked,”We’re supposed to plan for a once in a hundred years storm. I think we’ve already had three of those this year in Houston.” The engineering studies indicated that the proposed Ocean Margin Drilling Program (OMD) might be ahead of its time. The final meeting of industry, NSF, and JOI to decide on the future of the OMD took place in early October, 1981 on Catalina Island, California. Transport to island was by yachts or other vessels belonging to several of the companies. On the way out to the island, my confidantes in industry told me what was going to happen. They would no longer be able to support the program. There were two reasons; (1) first, they felt it would infringe on their competitive interests in economic exploration of the margin; (2) second, they had discovered that the composition of the US Congress changes every two years and they believed it was risky to suppose that the US Congress could guarantee it would honor a ten year commitment of support as they were being asked to do. Then, as we approached the island, the Director of NSF, John Slaughter, took me aside. The Reagan administration had decided that the OMD program was really a means of subsidizing the US petroleum industry and could no longer support the program. It was a wonderfully harmonious meeting. After flowery introductions of all involved, the head of Exxon Production Research Corporation, speaking for the industry participants said “We can’t support it” and John Slaughter said “Neither can we.” We had a lot to drink and a great time celebrating the demise of this ill-formulated venture. Although I could not show it, I was delighted. It meant that our international program might have a future. The Catalina conference lasted for a couple more days, where we simply enjoyed each others company as we listened to technical reports and discussed matters over excellent food and wines. But on the side I learned a lot, in strict confidence. In fact, industrial wells had already been drilled at the most prospective sites off the US East Coast. They had not found any petroleum but had encountered very highly overpressured gas, levels so extreme that drilling operations had been forced to cease. In fact, the proposed OMD drilling would not have been possible. Offshore gas production was not economical because of the cost of pipelines and other infrastructure required to bring it onshore. The OMD was finished. Now it was essential to go back to our international partners to explore a future program of ocean drilling to carry on the DSDP tradition. A revolution had been brewing in the academic science community for months. With the proponents of OMD in the OSTP gone as the new administration took over, the time for action had arrived. Since the beginning of he year JOIDES had begun to make preparations made for a challenge to the proposed OMD. The Catalina meeting had avoided a confrontation. For the US community I was the villain in the OMD affair so I was careful to be a very inconspicuous observer at the conferences to organize the new program. A new program for Scientific Ocean Drilling beyond 1983 was prepared at a conference held in Austin, Texas in mid November, 1981. Some members of Congress had been following the whole affair, and NSF selected me to testify before the House’s Committee on Science and Technology. It was like walking a tightrope to explain how all this had worked out without offending anyone. But the science community and NSF had a very supportive Chairman, Don Fuqua of Florida. If I recall correctly my exchanges were primarily with member George Brown of California who made sure that the right ammunition for a special appropriation for NSF was in the record. A young Al Gore was a member of the Committee. My father had testified before Congress several times, and he called to congratulate me on having survived the experience.
- Other Greenhouse Gases
William W. Hay
- Springer Berlin Heidelberg
- Chapter 21