High pressure and low temperature crystallization of methane
Its chemical formula is CH4 8H2O.
Combustible ice is a clean new energy source in the future. Its main components are methane molecules and water molecules. Its formation is similar to and closely related to the formation process of submarine oil and natural gas. A large amount of organic matter buried deep in the seabed stratum is decomposed by anaerobic bacteria under anoxic environment, and finally petroleum and natural gas (LPG) are formed. Many of these natural gases are trapped by water molecules, and "combustible ice" is formed at low temperature and low pressure on the seabed. This is because natural gas has a special property that it can crystallize with water at a temperature of 2 ~ 5 degrees Celsius, and this crystallization is "combustible ice". Because the main component is methane, it is often called "methane hydrate". It will be decomposed into water and methane at normal temperature and pressure, and "combustible ice" can be regarded as highly compressed solid natural gas. The appearance of "combustible ice" looks like frost, and its molecular structure looks like a "cage" from a microscopic point of view. A cage consists of several water molecules, and each cage "closes" a gas molecule. At present, combustible ice is mainly distributed in the eastern and western Pacific Ocean and the western edge of the Atlantic Ocean, which is a new energy source with great development potential. However, due to the difficulty of mining, the combustible ice on the seabed is still well preserved in the seabed and permafrost.
The discovery of combustible ice
As early as 1778, British chemist Pudley began to study the temperature and pressure of gas hydrate. 1934, people found the phenomenon of ice-like solid blocking in oil and gas pipelines and processing equipment. These solids are either ice or what people now call combustible ice. 1965, Soviet scientists predicted that there might be natural gas hydrate on the surface of the ocean bottom. Later, people finally found a large amount of combustible ice at the bottom of the Arctic for the first time.
Formation and storage
Combustible ice is formed by ocean plate activity. When the ocean plate sinks, the older seabed crust will sink into the earth's interior, and the oil and natural gas on the seabed will rush to the surface with the edge of the plate. When exposed to cold seawater and deep sea pressure, natural gas reacts with seawater to form hydrate. Scientists estimate that the distribution of combustible ice on the seabed accounts for about 10% of the total ocean area, equivalent to 40 million square kilometers. It is by far the most valuable mineral resource on the seabed, enough for human use 1000 years.
There are three basic conditions for the formation of "combustible ice": first, the temperature should not be too high, it can be formed above zero, 0- 10℃ is appropriate, and the maximum limit is about 20℃, and then it will decompose. The second pressure should be enough, but not too great. At zero degree, it may be generated above 30 atmospheres. Third, there must be a gas source underground. Because, on land, only the permafrost in Siberia can form and maintain a stable solid state, and the sediments 300-500 meters deep in the ocean may have such low temperature and high pressure conditions. So the land-sea ratio of its distribution is 1: 100.
"Combustible ice" does not always appear in places with natural gas, because the formation of "combustible ice" is mainly due to low temperature besides pressure, so it generally appears in places with ice and soil. For a long time, some people think that there is no "combustible ice" in the low latitude of China sea area; In fact, China's East China Sea and South China Sea are ready for formation.
There is an East China Sea basin under the East China Sea, covering an area of 250,000 square kilometers. After 20 years of exploration, the basin has obtained 654.38+048.4 billion cubic meters of proven and controlled natural gas reserves. Then, the research group led by Jin Xianglong, an academician of China Academy of Engineering and a marine expert, found out the temperature and pressure range of "combustible ice" in the East China Sea according to the necessary conditions for the existence of natural gas hydrate, sketched out the distribution area of "combustible ice" according to the geothermal gradient and combined with the geological conditions in the East China Sea, calculated the thickness of its stable zone, made a preliminary evaluation of resources, and reached the conclusion of "considerable reserves". This has opened up a broader prospect for the surrounding areas to use efficient new energy in the new century.
Scientists have found that there is a solid compound on the earth that combines combustible gas with water. Because its appearance is similar to ice, it is called "combustible ice". There are two ways to form this combustible ice: one is that the cold climate causes the temperature of the seam to drop, and the high pressure of the stratum makes the hydrocarbons originally dispersed in the crust and the water in the crust form a gas-water combined seam. Second, the remains of a large number of organisms and microorganisms in the ocean are constantly deposited on the seabed and quickly decomposed into organic gases such as methane and ethane. In this way, they drill into the pores of sedimentary rocks with loose structure on the seabed and form compounds with water.
Combustible ice accumulates year after year, forming sediments that extend thousands to tens of thousands of miles. Each cubic meter contains 200 cubic meters of combustible gas, and the proven reserves are hundreds of times larger than those of coal, oil and natural gas combined. At present, the problem of developing technology has not been solved. Once a technological breakthrough is made, combustible ice will join the ranks of new energy sources in the world.
Storage capacity and prospect
1 m3 combustible ice can be converted into 164 m3 natural gas and 0.8 m3 water. Scientists estimate that the distribution of combustible ice on the seabed is about 40 million square kilometers, accounting for 10% of the total ocean area, and the reserves of combustible ice on the seabed are enough for human use 1000 years.
With the deepening of research and investigation, the number of combustible ice found in the world's oceans has gradually increased, with 57 on the seabed in 1993 and 88 on the seabed in 200 1. According to exploration estimation, the combustible ice resources of Black Ridge in the southeast coast of the United States are as high as1800 million tons, which can meet the natural gas consumption of the United States 105. The combustible ice resources in the Sea of Japan and its surrounding areas can be used by Japan for more than 0/00 years.
According to experts' estimation, the world's total oil reserves are between 270 billion tons and 650 billion tons. According to the current consumption rate, the world oil resources will be exhausted in another 50-60 years. The discovery of combustible ice has brought new hope to mankind caught in the energy crisis.
Joint inspection
On June 2 this year, 26 Chinese and German scientists boarded the German scientific research ship Susafeng from Hong Kong and began a 42-day comprehensive geological survey of the South China Sea. Through submarine TV observation and submarine TV monitoring grab sampling, giant carbonate rocks with an area of about 430 square kilometers were discovered for the first time.
Chinese and German scientists unanimously suggested that one of the most typical structures in this authigenic carbonate area be named "Jiulong Methane Reef". Among them, the word "Dragon" stands for China, and "Nine" stands for the cooperation of several research groups. Isotopic dating analysis shows that the carbonate crust in the "Jiulong methane reef" area was first formed about 45 thousand years ago and is still releasing methane gas.
Huang Yongyang, chief scientist of China and chief engineer of Guangzhou Marine Geological Survey, was very excited about this. He said that the detection evidence shows that the combustible ice reserves in the northern part of the South China Sea alone account for about half of the total onshore oil in China; In addition, the distribution area of combustible ice has been preliminarily delineated in Xisha Trough, and the estimated resource amount is 4. 1 trillion cubic meters.
China has become a pure oil importer since 1993. It is estimated that by 20 10, the net oil import will increase to about10 billion tons, and will increase to about 200 million tons in 2020. Therefore, it is of great strategic significance to understand the background of combustible ice and develop combustible ice resources for China's subsequent energy supply and sustainable economic development.
Huang Yongyang introduced that in the next decade, China will invest 8 1 100 million yuan to conduct a resource survey of this new energy source. It is expected that the properties of combustible ice will be found out around 2008, and combustible ice will be tested and mined in 20 15 years.
double-edged sword
A "double-edged sword" created by strategy and danger.
So far, at least more than 30 countries and regions in the world are conducting research, investigation and exploration of combustible ice.
1960, the first combustible ice gas reservoir was discovered in Siberia by the former Soviet Union. 1969 was put into development, producing gas 14 years, with a total gas production of 50170,000 cubic meters.
The investigation of combustible ice began in America 1969. 1998 combustible ice was included in the national long-term plan as a strategic energy source for national development, and it is planned to conduct commercial trial mining by 20 15.
Japan pays attention to combustible ice in 1992. At present, the investigation and evaluation of combustible ice in the surrounding waters have been basically completed. Seven exploratory wells have been drilled, and 12 ore concentration area has been delineated, and combustible ice samples have been successfully obtained. Its goal is to conduct commercial trial mining on 20 10.
However, mankind still faces many new problems when exploiting combustible ice buried in the deep sea. Some scholars believe that the role of methane in global warming is 10-20 times greater than that of carbon dioxide. Even the smallest damage to combustible ice deposits is enough to cause a large amount of methane gas leakage. In addition, it is very difficult to mine combustible ice on the coast of continental margin. Once a blowout accident happens, it will lead to tsunami, submarine landslide, seawater poisoning and other disasters.
It can be seen that combustible ice is not only a new energy source in the future, but also a dangerous energy source. The development and utilization of combustible ice is like a "double-edged sword", which needs to be treated with care.
"Combustible ice" is ice containing methane in the deep sea floor. It is because under the high pressure and low temperature conditions in the deep sea, water molecules are closely connected by hydrogen bonds to form a three-dimensional network, which can incorporate methane and other gas molecules decomposed by paleontological remains deposited on the seabed into the network to form hydrated methane. These hydrated methane are like light gray ice hockey, so they are called combustible ice. Once these hockey balls rise from the bottom of the sea to the surface, they will die with a bang.
Combustible ice is a potential energy source with huge reserves. According to the estimation of international geological exploration organization, the reserves of hydrated methane in the deep sea of the earth are enough to exceed 2.84× 10 2 1 m 3, which is 1000 times of conventional natural gas energy storage. And there may be1.135×10 20m3 gas under these combustible ice layers. Some experts believe that once hydrated methane is mined, it will extend the history of human fuel use for centuries.
In order to develop this new energy, with the participation of 19 countries, a joint research institute for marine geological sampling of deep strata was established, and 50 scientific and technical personnel sailed a ship equipped with advanced experimental facilities to explore the combustible ice on the seabed from the east coast of the United States. The seven-story cabin of this special ship for combustible ice exploration is equipped with advanced experimental equipment. This is the only ship in the world that can collect rock samples under the deep sea. The ship is equipped with experimental equipment, which can be used to study sedimentology, paleoanthropology, petrology, geochemistry and geophysics. This particular ship is from Texas? M is the director of the university, and he is supported by the science foundations of Britain, Germany, France, Japan, Australia and the United States and the European Joint Science Foundation.
The existence of combustible ice on the seabed is likely to make the seabed unstable, which often leads to large-scale mud flow on the seabed, causing serious damage to submarine pipelines and communication cables. What's more, if the seabed strata are broken in an earthquake, the gas generated by the decomposition of free gas and hydrated methane will be sprayed out of the sea surface, or many highly concentrated flammable bubbles will be formed on the sea surface and water surface, which will not only cause danger to passing ships, but also bring bad luck to aircraft flying at low altitude. Some scholars believe that in recent centuries, there have been many mysterious disappearances of ships and planes in the Bermuda Triangle between Florida, Bermuda and Puerto Rico, that is, the so-called Bermuda mystery may be related to this.
Because combustible ice is formed under the conditions of low temperature and high pressure in the deep sea, hydrogen bonding is a weak action, and the ice-like hydrated methane will automatically melt and decompose into gas as soon as it comes out of the water, so we don't need to bother to decompose the hydrated methane, just use special equipment to collect these gases. It is worth noting that combustible ice has a bright future as a new energy source, but methane is an efficient greenhouse gas. If the exploitation method of combustible ice is improper, the released methane will diffuse into the atmosphere, enhance the greenhouse effect of the earth, lead to the melting of permafrost and polar icebergs on the earth, and make the earth warm. To develop combustible ice safely and reasonably, environmental protection must be considered at the same time.
Development and utilization of combustible ice
Combustible ice is expected to replace coal, oil and natural gas as new energy in 2 1 century. Scientists estimate that the distribution of combustible ice on the seabed accounts for about 10% of the total ocean area, equivalent to 40 million square kilometers. It is by far the most valuable mineral resource on the seabed, enough for human use 1000 years. However, in the complicated process of exploiting combustible ice, once any mistake occurs, it will lead to serious environmental disaster and become an environmental enemy. First of all, it is very difficult to collect the gas in seawater. Combustible ice on the seabed has a large distribution area, so it is difficult to collect methane decomposed from it in a certain area. Once it leaves the seabed, it will decompose rapidly, which is prone to blowout accidents. More importantly, the greenhouse effect of methane is more serious than that of carbon dioxide 10 to 20 times. If an accident occurs due to improper treatment, the decomposed methane gas will be released into the atmosphere from seawater, which will make the global greenhouse effect more serious. In addition, seabed mining may also destroy the stable balance of the earth's crust, cause instability at the edge of the continental shelf, lead to seabed collapse, and even trigger a large-scale tsunami, with disastrous consequences. At present, there is evidence that the large-scale natural release of such gases in the past has led to a sharp change in the earth's climate to some extent. The tsunami that caused havoc in northern Europe 8000 years ago is also likely due to the massive release of this gas.
There are three main mining schemes. The first is pyrolysis. Using the characteristic of "combustible ice" being decomposed by heat, methane vapor is decomposed from solid state. But the difficulty of this method is that it is not easy to collect. The porous media on the seabed are not concentrated into "blocks" or large rocks, but distributed evenly. How to lay and collect pipelines efficiently is an urgent problem.
The second option is depressurization. Some scientists propose to bury nuclear waste underground and decompose it by nuclear radiation effect. However, they all face the same problems as pyrolysis, that is, laying pipelines and collecting pipelines efficiently.
The third scheme is "replacement method". It is proved that if CO2 is liquefied (easy to realize) and injected into the ocean surface below 1 1,500 meters (not necessarily to the seabed), CO2 hydrate will be generated, and its specific gravity is greater than that of seawater, so it will sink to the seabed. If CO2 is injected into methane hydrate reservoir on the seabed, methane molecules in methane hydrate may be "squeezed out" and replaced because CO2 is more likely to form hydrate than methane.
However, if "combustible ice" leaks during mining, a large amount of methane gas decomposes and enters the atmosphere through seawater. The greenhouse effect of methane is 2 1 times larger than that of CO2, so once this leakage is not controlled, the global greenhouse effect will increase rapidly. After the atmosphere warms, the temperature of seawater and strata will also rise, which will lead to the automatic decomposition of "combustible ice" on the seabed and lead to a vicious circle. Therefore, it is necessary to control the mining so that the released methane gas can be effectively collected.
The exploitation of submarine combustible ice involves complex technical problems, so it is still in the development stage, and it is estimated that it will take 10 to 30 years before it can be put into commercial exploitation. In fact, China, the United States, Canada, India, South Korea, Norway and Japan have started their own research projects on combustible ice. Among them, Japan has built seven exploration wells, which are expected to be put into commercial exploitation in 20 10, and the United States has also caught up in recent years, hoping to carry out commercial exploitation of seabed or permafrost in 20 15.
It can be seen that "combustible ice" brings not only new hope but also new difficulties to mankind. Only by rational and scientific development and utilization can "combustible ice" really benefit mankind.
However, due to the difficulty in developing resources, the utilization of combustible ice cannot be realized in a short time.