Natural gas hydrate is a white solid substance, which looks like ice and has strong combustion ability, so it can be used as a superior energy source. Mainly composed of water molecules and hydrocarbon gas molecules (mainly methane), it is also called methane hydrate. Natural gas hydrate is a white solid crystalline substance formed by the interaction between gas or volatile liquid and water under certain conditions (suitable temperature, pressure, gas saturation, water salinity, PH value, etc.). ). Once the temperature increases or the pressure decreases, methane gas will escape and solid hydrate will tend to collapse. (1 m3 combustible ice can release 164 m3 natural gas and 0.8 m3 fresh water at normal temperature and pressure), so solid natural gas hydrate is often distributed in seabed sediments or cold permafrost with a water depth of more than 300 meters. Seabed gas hydrate depends on the pressure of extremely thick water layer to maintain its solid state, and its distribution can range from seabed to seabed 1000 meters, and it is difficult to exist in deeper places due to the increase of ground temperature.
In terms of physical properties, the density of natural gas hydrate is close to and slightly lower than that of ice, and the shear coefficient, electrolytic constant and thermal conductivity are all lower than that of ice. The acoustic wave propagation velocity of natural gas hydrate is obviously higher than that of gas-bearing sediments and saturated water sediments, and the neutron porosity is lower than that of saturated water sediments. These differences are the theoretical basis for geophysical exploration to identify natural gas hydrate. In addition, the capillary pore pressure of natural gas hydrate is high.
Combustion equation of combustible ice
CH4 8H2O+2O2 = = CO2+10H2O (the reaction condition is "ignition") [Edit this paragraph] The cause of combustible ice is that natural gas molecules (alkanes) are wrapped in water molecules and crystallized at low temperature and low pressure on the seabed. There are three basic conditions for the formation of combustible ice: temperature, pressure and raw materials. First of all, combustible ice can be generated above 0℃, but it will decompose above 20℃. However, the seabed temperature is generally kept at about 2~4℃; Secondly, at 0℃, combustible ice can be generated at only 30 atmospheres, while in the depths of the ocean, 30 atmospheres is easy to ensure. The greater the air pressure, the less likely the hydrate is to decompose. Finally, the organic matter on the seabed is deposited, and the rich carbon can generate sufficient gas source after biotransformation. Submarine stratum is a porous medium. Under the conditions of temperature, pressure and gas source, combustible ice crystals will be generated in the cracks of the medium. [Edit this paragraph] The resources of combustible ice. Most natural gas hydrates in the world are distributed in the ocean. It is estimated that the natural gas hydrate resources in the ocean are more than 100 times of those on land. According to the most conservative statistics, the total methane stored in natural gas hydrate in the world is about 65.438+0.8 billion cubic meters (18000× 10× 02m3), which is about 1. 1 trillion tons (1/kloc-).
Combustible ice is called "2 1 century energy" or "future new energy" by western scholars. Up to now, the proven reserves of "combustible ice" in marine and terrestrial strata around the world are more than twice the reserves of traditional fossil energy (coal, oil, natural gas, oil shale, etc.) around the world. ), in which the reserves of combustible ice on the seabed are enough for human use 1000 years. [Edit this paragraph] The disadvantages of combustible ice natural gas hydrate not only bring new energy prospects to human beings, but also bring severe challenges to human living environment. The greenhouse effect of methane in natural gas hydrate is 20 times that of CO2, and the abnormal climate and sea level rise caused by greenhouse effect are threatening human survival. The total amount of methane in the global submarine gas hydrate is about 3000 times that in the earth's atmosphere. If methane in submarine gas hydrate escapes into the atmosphere carelessly, the consequences will be unimaginable. Moreover, once the conditions change, methane gas will be released from hydrate, which will also change the physical properties of sediments, greatly reduce the engineering mechanical properties of seabed sediments, soften the seabed, cause large-scale submarine landslides, and destroy submarine engineering facilities, such as submarine power transmission or communication cables and offshore oil drilling platforms. Hard-won combustible ice is a solid compound composed of natural gas and water, and its shape is similar to that of ice. Because it contains a lot of combustible gases such as methane, it is extremely flammable. Under the same conditions, the energy produced by the combustion of combustible ice is dozens of times that of coal, oil and natural gas, and no residue and waste gas are produced after combustion, thus avoiding the pollution problem that people have the most headache. Scientists call combustible ice "the energy of the future" if they get the treasure.
Combustible ice is a hard-won treasure, and its birth must meet at least three conditions: First, the temperature should not be too high. When the temperature is higher than 20℃, it will "disappear", so the temperature of the seabed is most suitable for the formation of combustible ice; The second is that the pressure should be large enough. The deeper the seabed, the greater the pressure and the more stable the combustible ice. Third, there must be a methane gas source, and the sediments of the seabed paleontological corpses will be decomposed by bacteria to produce methane. Therefore, combustible ice is distributed in all the oceans in the world. [Edit this paragraph] Combustible ice reserves and hydrate reserves
Researchers have realized that natural gas hydrate exists widely all over the world. About 27% of the earth's land is a potential area where natural gas hydrate can be formed, and about 90% of the world's marine waters are also such potential areas. Natural gas hydrate is mainly found in the permafrost region of the Arctic and in the seabed, continental slope, land-based and trench all over the world. Due to the different standards adopted, the estimated values of world natural gas hydrate reserves by different institutions vary greatly. According to the estimation of potential natural gas combination (PGC, 198 1), the natural gas hydrate resources in permafrost regions are1.4×13 ~ 3.4×1016m3, including the total marine natural gas hydrate. But most people think that the carbon stored in steam hydrate is at least 1× 1.0 1.3t, which is about twice the total carbon content of all fossil fuels (including coal, oil and natural gas). Because of the impermeability of natural gas hydrate, it can often be used as a sealing layer for free natural gas below it. Therefore, with the increase of the amount of free gas in the lower layer of steam hydrate, this estimate may be larger. If these predictions can be proved to be true, natural gas hydrate will become a rich and important energy source in the future.
From the chemical structure, natural gas hydrate is composed of water molecules in a cage-like polyhedron frame, and the cage-like frame contains methane-based gas molecules. Different temperature and pressure conditions have different polyhedral frames.
In terms of physical properties, the density of natural gas hydrate is close to and slightly lower than that of ice, and the shear coefficient, electrolytic constant and thermal conductivity are all lower than that of ice. The acoustic wave propagation velocity of natural gas hydrate is obviously higher than that of gas-bearing sediments and saturated water sediments, and the neutron porosity is lower than that of saturated water sediments. These differences are the theoretical basis for geophysical exploration to identify natural gas hydrate. In addition, the capillary pore pressure of natural gas hydrate is high.
The proven reserves alone are hundreds of times larger than the total oil reserves on the earth. All this ice is hidden in the seabed 450 meters deep all over the world. The surface looks like dry ice, but it can actually burn. There are 2,700 square meters of hydrate on the southeast coast of the United States, which contains enough combustible ice to supply the United States for more than 70 years. Its reserves are estimated to be 2.6 times that of conventional reserves. If fully developed and utilized, it can be used for about 100 years. The results of large-scale geophysical exploration carried out by China Geo University (Wuhan) and the Fifth Geophysical Brigade of Central South Petroleum Bureau in Qiangtang Basin of northern Tibet Plateau show that Tibet may become the second strategic replacement area of petroleum resources in China in 2 1 century after Tarim Basin.
Tentative idea of exploiting combustible ice [1]
Because combustible ice is unstable at normal temperature and pressure, the methods of exploiting combustible ice are as follows: ① pyrolysis. ② hypotensive method. ③ Carbon dioxide replacement method. [Edit this paragraph] There are as many global distribution areas as 1 16. According to experts' prediction, the conventional oil and natural gas resources in the world are consumed greatly, and it is expected that they will be exhausted after forty or fifty years. People are worried about the energy crisis, and combustible ice is like a treasure given to mankind by heaven. It accumulates year after year, forming thousands or even tens of thousands of miles of sediments. The proven combustible ice reserves alone are several times more than the total reserves of coal, oil and natural gas in the world.
The evaluation results of scientists show that the distribution area of combustible ice in the seabed area alone is 40 million square kilometers, accounting for 1/4 of the total ocean area of the earth. At present, there are as many combustible ice distribution areas as 1 16 in the world, and its seam thickness and scale are incomparable to those of conventional natural gas fields. Scientists estimate that the reserves of combustible ice on the seabed are at least enough for human use 1000 years. [Edit this paragraph] Improper use will lead to disaster. Natural combustible ice is solid and will not be ejected like oil exploitation. If it is carried out from the bottom of the sea piece by piece, methane will completely evaporate during the transportation from the bottom of the sea to the surface of the sea, which will also cause great harm to the atmosphere. In order to obtain this clean energy, many countries in the world are studying the exploitation methods of natural combustible ice. Scientists believe that once the mining technology makes a breakthrough, combustible ice will immediately become the main energy source in 2 1 century.
On the contrary, if mining is improper, the consequences will be absolutely disastrous. In terms of global warming, the role of methane is 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, thus causing a strong greenhouse effect. 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. Therefore, the development and utilization of combustible ice is like a double-edged sword, which needs to be treated with care. [Edit this paragraph] Countries all over the world are competing to develop combustible ice 1960. The former Soviet Union discovered combustible ice in Siberia and put it into development on 1969. The investigation of combustible ice began in the United States in 1969, and 1998 was included in the national long-term plan as a strategic energy source for national development; Japan began to pay attention to combustible ice from 1992, and has basically completed the investigation and evaluation of combustible ice in the surrounding waters. But Germany was the first country to dig out combustible ice.
Since 2000, the research and exploration of combustible ice has entered a peak period, and at least 30 countries and regions in the world have participated in it. Among them, the plan of the United States is the most perfect-the President's Science and Technology Committee recommended the research and development of combustible ice, and many people in the Senate and House of Representatives also proposed bills to support the research and development of combustible ice. At present, the annual financial allocation for combustible ice research in the United States amounts to tens of millions of dollars.
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 special-purpose ship is led by an M University in Texas, and it is financially assisted by science foundations in Britain, Germany, France, Japan, Australia and the United States and the European Joint Science Foundation. [Editor's paragraph] The distribution of combustible ice in the world. As an important follow-up energy source in 2 1 century, submarine natural gas hydrate and its disaster impact on human living environment and submarine engineering facilities are increasingly concerned by scientists and governments all over the world. The Deep-sea Drilling Program (DSDP) which started in 1960s and the Ocean Drilling Program (ODP) which followed have carried out a lot of deep-sea drilling and marine geological geophysical exploration in various oceans and seas around the world, and directly or indirectly discovered natural gas hydrate in many seabed areas. Up to now, the main distribution areas of submarine gas hydrate in the world are the Gulf of Mexico, the Caribbean Sea, the eastern continental margin of South America, the western continental margin of Africa and the Black Plateau on the east coast of the United States, as well as the Bering Sea, the Sea of Okhotsk, the Kuril Islands Trench, the Okinawa Trough, the Sea of Japan, the Shikoku Trough, the South China Sea Trough, the Sulawesi Sea and the northern waters of New Zealand in the western Pacific Ocean. Central American Trough, California Offshore Trough and Peru Trough in the Eastern Pacific Ocean, Gulf of Oman in the Indian Ocean, Ross Sea and Weddell Sea in the Antarctic, Barents Sea and Beaufort Sea in the Arctic, and Black Sea and Caspian Sea in the mainland.
Therefore, since the 1980s, developed countries such as the United States, Britain, Germany, Canada and Japan have invested heavily in the investigation, research and evaluation of natural gas hydrates at home and abroad, while countries such as the United States, Japan, Canada and India have formulated national plans for the exploration and development of natural gas hydrates. Japan and India, in particular, are in a leading position in the exploration and development of natural gas hydrates.
In September, 2009, the geological department of China announced that a new energy source named combustible ice (also known as natural gas hydrate) has been discovered on the Qinghai-Tibet Plateau, and it is expected to be put into use in about ten years. This is the first time that China has discovered combustible ice on land, making China the third country to discover combustible ice on land through national planned drilling after Canada and the United States. According to a rough estimate, the prospective resources are at least 35 billion tons of oil equivalent.
[Edit this paragraph] The situation of combustible ice in China As the largest developing maritime power in the world, China's energy shortage is very prominent. At present, there is a big gap between supply and demand of oil and gas resources in China. 1993 China has changed from an oil and gas exporter to a net importer. 1999 imported more than 40 million tons of oil, and nearly 70 million tons in 2000. It is estimated that the 20 10 oil gap will reach 200 million tons. Therefore, it is urgent to develop new energy sources to meet the rapid development of China's economy. Submarine natural gas hydrate resources are abundant, and the upstream exploration and production technology can learn from conventional oil and gas, and the downstream natural gas transportation and use are very mature. Therefore, strengthening the investigation and evaluation of natural gas hydrate is an important measure to implement the sustainable development strategy determined by the CPC Central Committee and the State Council, and it is also an important way to develop new energy in 2 1 century, improve energy structure, enhance comprehensive national strength and international competitiveness, and ensure economic security.
Some progress has been made in the research and exploration of submarine gas hydrate in China. The geophysical marker BSR of natural gas hydrate has been found in the Xisha Trough in the South China Sea, indicating that natural gas hydrate resources are also distributed in the China sea area, which is worthy of further study. At the same time, Qingdao Institute of Marine Geology has established a natural gas hydrate laboratory with independent intellectual property rights and successfully ignited natural gas hydrate. [Edit this paragraph] China found combustible ice on the seabed. On April 14, 2005, China held a ceremony in Beijing to collect the first batch of natural gas hydrate carbonate samples found in geological museum, China.
It is announced that China has discovered the world's largest "cold spring" carbonate rock distribution area for the first time, which is regarded as important evidence of the existence of "combustible ice" or natural gas hydrate, covering an area of about 430 square kilometers.
This distribution area was first discovered by the "Susafeng" scientific research ship in the investigation of natural gas hydrate in the South China Sea jointly conducted by China and Germany on the northern slope of the South China Sea. The formation of cold spring carbonate rocks is considered to be related to the submarine gas hydrate system and the activities of chemical biological communities living near the cold spring vents. During this investigation, a large number of authigenic carbonate rocks were discovered in the waters east of dongsha islands on the northern slope of the South China Sea, with water depths ranging from 550m to 650m and 750m to 800m respectively. It is found by TV observation and TV grab sampling that a large number of authigenic carbonate rocks, such as tubular, chimney-shaped, doughnut-shaped, plate-shaped and massive, are produced on the seabed, either lying alone on the seabed or suddenly protruding from the sediments. The bipedal shells from the vents are scattered in dots, and the huge carbonate structure stands on the seabed, similar to the "chemical reef" found in the marginal sea of Costa Rica and the offshore of Oregon, USA, but on a larger scale.
"Combustible ice" is a white or light gray solid crystalline substance with an ice-like appearance, which is composed of natural gas and water molecules. Because its composition is 80% ~ 99.9% methane, the formation and distribution of these carbonate rocks record the types, properties, sources, intensity changes of methane-rich fluids and their relationship with possible hydrate systems on the seabed.
Chinese and German scientists unanimously suggested that the most typical structures in authigenic carbonate area should be named "Jiulong Methane Reef" with China, Hong Kong and Jiu, which are closest to the work area, where "Dragon" stands for China and "Jiu" stands for the cooperation of several research groups. [Editor's Note] According to the strategic plan, the commercialization development route of combustible ice in China will be in the investigation stage from 2006 to 2020, the trial production stage will be in 2020-2030, and the combustible ice in China will enter the commercial production stage from 2030 to 2050. [Edit this paragraph] Japan's risky exploitation of combustible ice may lead to the collapse of the trench. Nowadays, Japan, forced by development needs and eager to change the situation of energy dependence on others, has turned its attention to the sleeping "energy crystal" on the seabed-natural gas hydrate, also known as "combustible ice". (It is a crystalline substance produced by mixing water and natural gas at medium, high pressure and low temperature. It looks like ice and snow, and it can burn when it is ignited. Hundreds of millions of tons of combustible ice are waiting to be used 3,000 feet under the calm Pacific Ocean near Japan. Japan believes that if these resources can be used by Japan, it will greatly improve its dependence on energy imports from the Middle East and Indonesia. According to preliminary estimation, these "combustible ice cubes" can be used in Japan for 14 years. But while developing these unknown resources, there is a key problem that must be dealt with: environmental protection.
Japan and Canada cooperate to exploit "combustible ice"
30 miles from the coast of Honshu Island, scientists discovered a trench with amazing reserves: the methane in the trench is crystal, about 500 meters thick, and the total amount is 40 trillion cubic meters. Although this reserve is not comparable to Saudi Arabia or Russia's oil resources, it is enough for Japan to use for some time. Japanese scientists are very excited about this result, and they say they will come up with appropriate plans to exploit these forgotten resources as soon as possible.
Compared with Japan, Canada with vast marine resources can be said to be a step ahead in this regard. They usually use the method of "depressurization" to exploit this frozen resource, that is, first make many deep holes in the ice layer, and then use a large number of pumps to reduce the heavy pressure brought by drilling, so that useful methane gas can be separated from seawater and slowly float to a depth convenient for human extraction. Scientists from Japan and Canada decided to cooperate and use this most effective method to develop the resources in the waters near Honshu Island.
The Japanese government quickly agreed to this mining method. The first exercise was completed in April this year, and the rest of the tests will be completed in early 2008.
The mining industry faces many unknown threats.
In addition to huge energy, there are many invisible dangers beckoning to Japan. For example, in the third step of the "depressurization" method, depressurization makes a large amount of methane gas slowly float on the sea surface, and what impact these greenhouse gases will have on the global temperature is still unknown. The Japanese government also said that they have always attached great importance to environmental protection and will never sacrifice the environment for energy. They have arranged many preliminary tests just in case.
This is still a concern after successful mining, and there are still many unknown threats in the mining process. Scientists warned the Japanese government to be alert to the collapse of the submarine trench during mining. What is happening under the seemingly calm ocean has not been fully understood. If the target trench collapses or debris flow-like disasters are caused inadvertently during mining, it will not only bring huge human and financial losses to the mining country, but also make the world worry about leaking a lot of greenhouse gases from it.
In addition, large-scale drilling and installation of various equipment on the seabed will undoubtedly keep fish away from the coast, and the income of fishermen who depend on the sea for a living will naturally be greatly affected. Japanese fishermen expressed such concerns.