A basin, as its name implies, is like a big basin on the ground. Therefore, people call the basin-like terrain with high periphery (mountains or plateaus) and low middle (plains or hills) a basin. The largest basin on earth is in the middle of East Africa, called Congo Basin or Zaire Basin, with an area of about 1/3 of Canada. This is an important agricultural area in Africa, and there are rich mineral resources on the edge of the basin.
Basin type
There are two main types of basins. One is the basin formed by crustal tectonic movement, called tectonic basin, such as Turpan basin and Jianghan plain basin in Xinjiang, China. The other is a basin formed by glacier, flowing water, wind and karst erosion, which is called erosion basin, such as Jinghong Basin in Xishuangbanna, China, which is mainly formed by the erosion and expansion of Lancang River and its tributaries.
Formation of basin
The basin was mainly formed by crustal movement. Under the action of crustal movement, underground strata are squeezed or stretched and become bent or fractured, which will cause some rocks to rise and some to fall. If the descending part is surrounded by the ascending part, the prototype of the basin is formed.
Many basins were submerged by seawater or lake water after their formation, such as Sichuan basin, Tarim basin and Junggar basin. Later, with the continuous uplift of the earth's crust and sediment deposition, the seas and lakes in the basin slowly retreated and dried up, leaving only some rivers or streams. However, in the oceans, lakes and rivers that once existed, a large number of creatures that once lived were buried by soil after death, which will become the material basis for the formation of oil and coal, which is also an important reason why scientists are very concerned about basin research. Most of the rock deposits in the basin are relatively complete and continuous, and the animals and plants living there are easy to be preserved as fossils after death, so the basin is also a good place for paleontologists to look for fossils.
There are also some basins, mainly formed by external forces on the surface, such as wind and rain. Rivers erode and cut along the weak points of surface rocks, forming valley basins of different sizes. In the vast arid areas of northwest China, the wind is particularly strong, which blows away the sand and gravel on the surface and forms a dish-shaped wind erosion basin. Some basins in Gansu, Inner Mongolia and Xinjiang were formed in this way.
In addition, in some areas where limestone is developed underground, groundwater flowing all the year round will dissolve the rocks there, make the rocks on the surface collapse, and also form basins, which geologists call karst basins. There are many such basins in Yunnan-Guizhou Plateau and Guangxi, southwest of China.
Under the strong compression or extension, the basement of some large basins will fracture, forming some "fault basins", which are common in areas with strong crustal activity such as Bohai Bay in North China and Hengduan Mountain in Southwest China.
The development of sedimentary basins is often influenced by crustal tectonic activities, which can be recorded by the sediments continuously accepted by the basin. Through the geological and geochemical study of these sediments, people can describe and inverse the historical process of earth evolution in these areas, such as climate change, sea level change, exchange of greenhouse gases with the atmosphere, and topographic changes determined by tectonic activities.
The formation and accumulation of oil and natural gas are also closely related to tectonic movement. Oil and gas usually form and exist in sedimentary rocks, and relatively independent adjacent sedimentary rocks are often called "oil-bearing basins" by oil and gas prospectors. The formation and distribution of this petroliferous basin is the inevitable product of tectonic movement. Mr. Huang, a late geologist in China, pointed out long ago: "A prerequisite for oil exploration is to divide structures according to geological structural characteristics, and then discuss oil generation, oil storage and oil and gas potential according to structural units." As a part of fluids in the earth's crust, the formation, migration and preservation of oil and natural gas are controlled by the development and change of geological bodies. The deeper the basic sciences such as geotectonics and structural geology understand the composition and evolution of geological bodies, the easier it is to grasp the particularity of oil and gas geology.
Characteristics of the basin
First, there are many vertical oil-bearing strata in the basin, and the reservoir is buried deeply. From Archaean, Middle-Upper Proterozoic, Paleozoic, Mesozoic to Cenozoic, 19 sets of oil-bearing strata have been found in Liaohe Basin, with the buried depth of 550 ~ 4050 meters, which is a typical small and fat compound oil and gas area.
Secondly, the basin has experienced multi-stage tectonic movement, developed faults and complicated structures. According to the existing data, there are 8 first-class faults, 20 second-class faults, more than 400 third-class faults and 1200 fourth-class faults on the land of the basin alone, forming 7 first-class structural units, 35 second-class structural units, 83 third-class structural units and more than 800 fourth-class fault blocks with three convexities and four depressions, which are typical complex fault block reservoirs.
Third, there are many types of reservoirs, great changes in physical properties and serious heterogeneity. Reservoir lithology is mainly composed of all kinds of sandstone deposited normally, and there are also special lithologic reservoirs such as volcanic rocks, carbonate rocks and metamorphic rocks. There are various types of reservoir space, and the porosity of the reservoir is between 3% and 35%. Due to factors such as sedimentation, the reservoir heterogeneity is serious.
Fourthly, affected by multi-stage structure, multi-deposition and multi-reservoir lithology, Liaohe Basin has various reservoir types, different oil and gas enrichment degrees and great depth changes. According to the origin of traps, they can be divided into three types: structural, lithologic and stratigraphic reservoirs, and then subdivided into 18, and can be divided into 9 types according to the distribution characteristics of oil, gas and water. The original oil saturation is 47% to 75%, and the oil abundance of proven reservoirs ranges from less than 6.5438 million tons to tens of millions of tons per square kilometer.
Fifth, there are many kinds of oil products, and the physical properties of crude oil change greatly. There are condensate oil, dilute oil, ordinary heavy oil, super heavy oil, super heavy oil and high pour point oil. After more than 30 years of development, Liaohe Basin has become the largest production base of heavy oil and high pour point oil in China.
Sixth, heavy oil is generally buried deeply. The ultra-deep reserves from 1300m to 1880m account for 42.2% of the produced reserves of heavy oil, and the deep reserves from 900m to 1300m account for 291million tons of the produced reserves of heavy oil, accounting for 36.7% of the produced reserves.
river basin development
China's oil resources are concentrated in Bohai Bay, Songliao, Tarim, Ordos, Junggar, Pearl River Mouth, Qaidam and great basin on the East China Sea shelf, with recoverable resources of 1.72 billion tons, accounting for 81.3% of the whole country. Natural gas resources are concentrated in Tarim, Sichuan, Ordos, East China Sea Shelf, Qaidam, Songliao, Yinggehai, Qiongdongnan and great basin in Bohai Bay, and the recoverable resources are 18.4 trillion cubic meters, accounting for 83.64% of the whole country.
Since the early 1950s, China has explored oil and gas in 82 major large and medium-sized sedimentary basins, and discovered more than 500 oil fields. The following are the main oil-producing areas on land in China.
Daqing Oilfield:
Located in the west of Heilongjiang Province, in the middle of Songnen Plain, in Harbin and Qiqihar. The oilfield is 0/40km long from north to south and 70km wide from east to west, with a total area of 5,470 square kilometers. 1960 In March, the CPC Central Committee approved to launch an oil battle, and in June, 45438+0963, the production capacity was 6 million tons, and the crude oil produced in that year was 4.39 million tons, which played a decisive role in realizing China's oil self-sufficiency. 1976, the crude oil output exceeded 50 million tons, making it the largest oil field in China. At present, the output of crude oil in Daqing Oilfield has remained above 50 million tons by adopting new technologies and new processes.
Shengli Oilfield:
The Yellow River Delta, located on the Bohai Sea in northern Shandong Province, is mainly distributed in 8 cities and 28 counties (districts) including Dongying, Binzhou, Dezhou, Jinan, Weifang, Zibo, Liaocheng and Yantai. The main mining area is about 4.4 square kilometers, which is the second largest oil field in China.
Liaohe Oilfield:
Mainly distributed in the middle and upper reaches of Liaohe Plain, eastern Inner Mongolia and Liaodong Bay beach area. Twenty-six oil fields have been developed and constructed, and nine production bases have been built, including Xinglongtai, Shuguang, Huanxiling, Jinzhou, Goldman Sachs, Shenyang, Ciyutuo, Lengjia and Horqin, covering 32 counties (banners) in Liaoning Province and the Inner Mongolia Autonomous Region 13 cities, with a total area of 654.38 million square kilometers and the output ranking third in the country.
Karamay Oilfield:
Located in Karamay, Xinjiang. In the past 40 years, the 19 oil and gas fields have been discovered in Junggar basin and Tarim basin, mainly in Karamay, and the 15 oil and gas fields have been developed to produce 7.92 million tons of crude oil (6.031889 million tons of thin oil and 0/889 million tons of heavy oil). Since 1900, the onshore crude oil production has been increased.
Sichuan Oilfield:
Located in Sichuan Basin with a history of 60 years, 12 oil fields have been discovered. There are four gas zones in the basin: south, southwest, northwest and east. At present, natural gas production accounts for nearly half of the country, making it the largest gas field in China.
North China Oilfield:
Renqiu City is located in the central plain of Hebei Province, including oil and gas producing areas in Beijing, Hebei, Shanxi and Mongolia. During the period of 1975, Renqiu Oilfield, the largest carbonate buried hill oilfield in China, was discovered in Ren4, an exploratory well in Jizhong Plain, and a high-yield industrial oil flow with a daily output of 1000 tons was ejected. 1978, the crude oil output reached17.23 million tons, which made an important contribution to the breakthrough of the national crude oil output in that year. Until 1986, the annual output of crude oil remained at 100000 tons10 year. At present, the output of crude oil is about 4 million tons.
Dagang Oilfield:
Located in Dagang District, Tianjin, it has a vast exploration area, including Dagang Exploration Area and Xinjiang Yurdusi Basin, with a total exploration area of 34,629 square kilometers, including Dagang Exploration Area 18628 square kilometers. At present, Dagang exploration area has completed and put into operation 15 oil and gas fields and 24 development zones, forming an annual production capacity of 4.3 million tons of crude oil and 380 million cubic meters of natural gas. At present, hundreds of millions of tons of oil-bearing structures, such as Qianmiqiao, have been discovered, which has opened up new oil and gas areas for increasing reserves and production in old oilfields.
Zhongyuan Oilfield:
Located in Puyang, Henan Province, found in 1975. After 20 years of exploration, development and construction, 455 million tons of petroleum geological reserves, 39.57 billion cubic meters of natural gas geological reserves, 77.23 million tons of crude oil and 0/3.38 billion cubic meters of natural gas have been proved. Now it is one of the important oil and gas production bases in eastern China.
Jilin Oilfield:
Located in Fuyu area of Jilin Province, it has carried out oil and gas exploration and development in great basin, Jilin Province, and successively discovered and proved 18 oil fields, among which Fuyu and Xinmin oil fields are large oil fields with reserves exceeding 100 million tons, and the oil field output reaches more than 3.5 million tons/year, forming a super-large enterprise production scale with a crude oil processing capacity of 700,000 tons.
Henan Oilfield:
The mining area is located in Nanyang Basin in the southwest of Henan Province, spanning Nanyang, Zhumadian and Pingdingshan, and distributed in 8 counties such as Xinye and Tanghe. A total of four oil fields/kloc-0 have been discovered, with proven petroleum geological reserves of 65,438+700 million tons and oil-bearing area of 1 17.9 square kilometers.
Changqing Oilfield:
The exploration area is mainly in the Shaanxi-Gansu-Ningxia Basin, with a total exploration area of about 370,000 square kilometers. The exploration, development and construction of oil and gas started at 1970, and 22 oil and gas fields were discovered successively, including 19 oilfield, with a cumulative proven oil and gas geological reserve of 5418.88 million tons (including proven natural gas reserves of 233.008 billion cubic meters). At present, it has become the main natural gas producing area in China and the main natural gas transportation base in Beijing.
Jianghan Oilfield:
It is an important comprehensive oil base in central and southern China. The oilfields are mainly distributed in seven cities and counties, including Qianjiang and Jingsha in Hubei Province, Shouguang and Guangrao in Shandong Province, and Hengyang in Hunan Province. Twenty-four oil and gas fields have been discovered successively, with proven oil-bearing area of 139.6 square kilometers and gas-bearing area of 710.04 square kilometers. The cumulative production of crude oil is 210/87,300 tons and natural gas is 954 million cubic meters.
Jiangsu Oilfield:
The oil areas are mainly distributed in eight counties and cities such as Yangzhou, Yancheng, Huaiyin and Zhenjiang in Jiangsu, and 22 oil and gas fields have been put into development. At present, the main target of exploration is Dongtai sag in Subei basin.
Qinghai Oilfield:
Qaidam basin in the northwest of Qinghai province. The basin area is about 250,000 square kilometers, the sedimentary area is 6.5438+0.2 million square kilometers, and the oil and gas prospect in Mesozoic and Cenozoic sedimentary areas is about 96,000 square kilometers. At present, 16 oil fields and 6 gas fields have been proved.
Tarim oilfield:
Located in Tarim basin in southern Xinjiang. East-west length 1400 km, north-south width of 520 km, with a total area of 560,000 square kilometers. It is the largest inland basin in China. In the middle is the Taklimakan Desert, known as the "Sea of Death". 1988 After the high-yield oil gas flow was ejected from Lunnan 2 well, after 7 years of exploration, 9 large and medium-sized oil and gas fields and 26 oil-bearing structures have been proved, with a cumulative proven oil and gas geological reserve of 378 million tons and an annual output of 5 million tons of crude oil. Resource guarantee of 65.438+100,000 tons of condensate gas and 2.5 billion cubic meters of natural gas.
Tuha Oilfield:
Located in Turpan-Hami basin of Xinjiang, responsible for oil exploration in Turpan-Hami basin. The basin is 600 km long from east to west and 130 km wide from north to south, with an area of about 5. 30 thousand square kilometers. 199 1 February, the oil exploration and development campaign in Turpan-Hami was in full swing. By the end of 1995, * * discovered 14 oil and gas fields and 6 oil-bearing structures in Shanshan and Wenjisang, with proven oil-bearing area of 178. 1 square kilometer, with accumulated proven petroleum geological reserves of 208 million tons and natural gas reserves of 73/kloc-0.
Yumen Oilfield:
Located in Yumen City, Gansu Province, with a total area of 1 14.37 square kilometers. The oilfield was put into development in 1939, and the crude oil produced in 1959 reached 1402900 tons, accounting for 50.9% of the national crude oil production in that year. 600,000 tons in 1970s and 10 in 1980s were achieved. Known as the cradle of China's oil industry.
In addition to land oil resources, China is also rich in marine oil and gas resources. A series of sedimentary basins with a total area of nearly one million square kilometers have developed in the offshore of China, which has rich oil and gas prospects. From north to south, these sedimentary basins include Bohai Basin, North Yellow Sea Basin, South Yellow Sea Basin, East China Sea Basin, Okinawa Trough Basin, Taixi Basin, Southwest Taiwan Province Basin, Taidong Basin, Pearl River Mouth Basin, Beibu Gulf Basin, Yinggehai-Qiongdongnan Basin and South China Sea Basin.
Representative region
Major basins in China
There are five famous basins in China, namely, Sichuan, Tarim, Turpan, Junggar and Qaidam, covering an area of over 654.38 million square kilometers. Tarim Basin, Junggar Basin, Qaidam Basin and Sichuan Basin are also called "China Four great basin".
Tarim Basin
Tarim Basin, located in the south of Xinjiang, is the largest basin in China. "Tarim Basin" is a Chinese translation of Uygur language, which means "great basin without reins". The basin starts from Pamir Plateau in the west and reaches the junction of Gansu and Xinjiang in the east. It is about 1.600 km long from east to west and 600 km wide from north to south, covering an area of about 530,000 square kilometers, with an average elevation of about 1.000 m, accounting for about half of the total area of Xinjiang. It is 2.6 times larger than Sichuan Basin, 1.4 times larger than Junggar Basin in northern Xinjiang and 10 times larger than Turpan Basin, making it the largest inland basin in China.
Tarim basin is located in the hinterland of Eurasia, and the surrounding mountains are all at an altitude of 4000 ~ 6000 meters. It is far from the sea, with dry climate and little rain, large temperature difference between day and night, and great seasonal changes. It is a typical continental desert climate. It's cold in winter and hot in summer. 1 Monthly average temperature-10℃, and July average temperature is 25℃. The temperature difference between winter and summer in the same place can reach 50℃-60℃, and the temperature difference between day and night can reach 15℃-20℃. Whenever it is cold at the turn of spring, summer, autumn and winter, I often wear cotton-padded clothes; The temperature is very high at noon, and it is still hot in light clothes. So people use "wearing fur coats in the morning, tulle in the afternoon and eating watermelons by the fire" to describe the climate characteristics here. Rainfall in most areas of the basin is less than 50 mm, and in the east it is only about 10 mm, and in some places it doesn't even drop all year round.
Gobi desert, alluvial fan plain and sand dune area appear in turn from the edge of the basin to the center, and the whole basin is in a ring structure. Alluvial plains formed by rivers in the surrounding mountains are usually oases. The oases are Kashgar, Dongsha, Hotan, Aksu and Kuqa. Oasis agriculture is developed, canals are vertical and horizontal, fields and buildings are connected, trees are shaded, and wheat, corn, rice, cotton and fruits are abundant. This is an important grain, long-staple cotton and silk producing area in China. The central part of the basin is the largest Taklimakan desert in China, with an area of about 334,000 square kilometers, which is also a world-famous desert. Because of the large desert area and extreme water shortage, few people in the old society could enter the central area of the desert, so this big desert was named "Taklimakan", which means Uygur, because it was impossible to get in and out. There is a famous wandering lake in the east of the basin-Lop Nur. There are also many inland rivers, the water source is not from rain, but mainly from melting snow in the mountains.
The people living in Tarim Basin are mainly Uighurs. In the old society, due to various reasons such as inconvenient transportation, it was naturally closed and few people came. After liberation, with the progress of society and the development of science, the communication between people has been accelerated, and the number of people coming here is increasing day by day. In particular, the people's government has sent scientific investigation teams here many times to inspect natural conditions and resources, and found that there are not only rich mineral resources, but also a variety of non-ferrous metals and oil, as well as a large number of salt mines. With the development of China's construction, these precious resources will be rationally developed and utilized.
Junggar Basin
Junggar basin is located at the northern foot of Tianshan Mountain, between Tianshan Mountain and Altai Mountain. Surrounded by mountains on three sides, the northwest, northeast and south are triangles with different sides, covering an area of about 380,000 square kilometers. It is the second great basin in China. The topography of the basin is slightly inclined from east to west, and the elevation of the eastern end can reach 1000 meters, while the lake depression in the west has dropped to 200-400 meters, and the water level of Ebinur Lake is only 189 meters, which is the lowest place in the basin.
The topographic structure of Junggar basin is similar to that of Tarim basin, but there are many gaps in the surrounding mountains, so the shape of the basin is not as complete as that of Tarim basin. The east and west ends of the basin are relatively developed, which has become the channel for China to Central Asia. The average elevation of the basin is about 500 meters, and the terrain gradually increases eastward, which is connected with the Inner Mongolia Plateau. The scenery inside the basin is very complicated, including grasslands, deserts, salt lakes and swamps. Among them, the desert is limited to the central and eastern part, that is, the east of Manas River, which is collectively called Gurbantunggut Desert. The climate here is dry, and the sand dunes are relatively small and low in height. There is more precipitation in the west of Manas River, mostly in grassland and swamp areas. There are mountains as high as 2000 meters in the west of the basin, but there are several gaps. The northwest wind blows into the basin, and the climate is cold in winter.
Junggar basin is rich in oil, coal and various metal deposits. Karamay in the west of the basin is one of the larger oil fields in China. The northern area of Altai Mountain has been famous for its rich gold since ancient times. There are few oases in Junggar basin, mainly distributed in the northern Tianshan Mountains. There are basically no oases in the eastern margin of the basin, because there are no tall mountains to provide water for the development of oases.
Qaidam Basin
Qaidam basin is a giant basin with the deepest subsidence in Qinghai-Tibet Plateau, which is slightly equilateral triangle. Located between Altun Mountain, Qilian Mountain and Kunlun Mountain in Qinghai Province, it is 800 kilometers long from east to west and 350 kilometers wide from north to south, covering an area of about 220,000 square kilometers. It consists of many small mountain basins. The basin is high in the west and low in the east, with an altitude of 2,500-3,000 meters, which is 2-3 times higher than that of the Tarim Basin, and is a plateau basin. From the edge of the basin to the center, there are Gobi, hills, plains and lakes in turn.
"Qaidam" means "Yanze" in Mongolian. 230 million years ago, it was a big lake. Later, the western part of the basin rose and the lake gradually narrowed, leaving more than 5,000 salt lakes. Chaerhan Salt Lake, located in the center of the basin, is the largest salt lake in China, with an area of about 1.600 square kilometers and a salt storage capacity of 25 billion tons, which can be eaten by people all over the country for 8,000 years. A large area of hard and deep salt cover is formed on the surface of salt lake, and the thickest part reaches 15 meters. There are 3 1 km highways running through the north and south of the basin and built on the salt cover of Chaerhan Salt Lake. Many houses here are also built with salt blocks. There are also colorful salt crystals in the basin, among which crystal salt blocks can be carved into various works of art. Qaidam is not only a world of salt, but also rich in oil, asbestos and various metal deposits, and was once known as the "cornucopia". Nowadays, this "cornucopia" that has been sleeping for thousands of years is being built into one of the important industrial bases in the northwest of China, and its eastern and southeastern parts have become newly reclaimed agricultural areas.
Sichuan Basin
The natural scenery of Sichuan Basin is quite different from the three great basin mentioned above. The rivers here are surging all the year round. The dense forests and green fields set off the purple soil, and the red and green set each other off, making this basin, which is known as the "land of abundance", particularly enchanting.
Sichuan Basin is a hilly basin with an area of about 200,000 square kilometers, which is not only complete in shape, but also a standard structural basin. Surrounded by Qionglai Mountain, Longmen Mountain, Daba Mountain, Wushan Mountain and Dalou Mountain, the altitude is1000 ~ 3000m. Rich in purple sand shale, it is called "purple basin" and "red basin". About 654.38+35 million years ago, Sichuan Basin was still an inland lake. Later, due to crustal movement, the surrounding area rose to a mountainous area, and Wushan on the eastern edge was low. The lake overflowed from Wushan, and the bottom of the lake gradually dried up and became a basin. Under the action of horizontal crustal movement, all the mountains in the basin are arranged in southwest-northeast direction, with the highest terrain in eastern Sichuan, and Huaying Mountain, the highest peak, is about 1800 meters above sea level, which is the highest point in the basin. The hills in the middle of the basin are gently undulating, accounting for almost half of the basin, forming a hilly basin.
Chengdu Plain, located in the west of the basin, is a fan-shaped alluvial plain formed by continuous crustal subsidence and long-term accumulation of sediment carried by rivers. Rivers and canals crisscross the plain, which is convenient for irrigation. This is the essence of Sichuan Basin. More than 2,200 years ago, the ancient working people in China built the famous Dujiangyan water conservancy project in Chengdu Plain and the upper reaches of Minjiang River for flood control and irrigation.
Dujiangyan is a levee built near guanxian in the center of Minjiang River, which divides Minjiang River into Neijiang River and Waijiang River. The weir tip at the front end of Dujiangyan resembles a fish mouth, which is called Du Jiang fish mouth. The outer river rolls down and flows into the Yangtze River. The water from Neijiang passes through the artificially cut headland and is introduced into Chengdu Plain through the channel. This water intake is called "Baojingkou", and the stone pile isolated from the shore after being cut is called "Staying Pile". In order to control irrigation water, a sand-flying weir was built between the inner and outer rivers in the lower reaches of Dujiangyan, so that all the water in Neijiang flows into the river when it is flat, and the excess water can be discharged into the outer river over the sand-flying weir when it is flooded. After the completion of this project, millions of acres of farmland were irrigated, which effectively promoted the agricultural production in Chengdu Plain. Working people also carved Shui Ge on the stone wall of the bottle mouth, observed the change of water level, and accumulated a lot of valuable experience in water conservancy projects.
Except alluvial soil in Chengdu Plain, the vast hilly areas in Sichuan Basin are covered with purple soil. This kind of soil is weathered from purple sand shale and contains mineral nutrients such as phosphorus and potassium needed by plants. This is one of the most fertile soils in southern China. However, due to loose soil, abundant precipitation and hilly terrain, soil erosion is easy to occur in places lacking vegetation protection. For a long time, people in Sichuan have built many terraces to conserve water and soil.
Sichuan basin has experienced a history from continental basin to sea basin, from sea basin to lake basin, and then from lake basin to continental basin, and rich minerals such as coal, iron, salt, natural gas and oil have been deposited. Coupled with the warm and humid climate and intensive fertile soil in the basin, the Sichuan Basin, known as the "Land of Abundance", is not only an important high-yield area of rice, wheat and corn in China, but also rich in sugarcane. After the founding of New China, heavy industries such as steel, machine building, chemical industry and many light industries also developed rapidly. Today, Sichuan Basin is being built into an important modern industrial and agricultural production base in China.