Basin characteristics

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.

Basins are divided into two types according to their genesis: one is basins formed by crustal tectonic movements, which are called tectonic basins, 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.

Characteristics of the basin

Topographic features: Basins are mostly distributed on the mountain surface, and hills, mountains and plateaus all have corresponding basins with different structures. The basin is basically a basin with a low middle and a high periphery. Compared with the outside of the basin, the terrain inside the basin is gentle, with many plains and hills, which is suitable for human habitation and agricultural production. The outside of the basin is mostly high mountains, which is suitable for developing mountain agriculture.

Climatic characteristics: According to the difference of latitude and topography in the world, the basin climate can be roughly divided into tropical rain forest basin climate, ocean basin climate, subtropical monsoon basin climate, desert basin climate and so on.

Climate of tropical rain forest basin: affected by equatorial low pressure belt, abundant rainfall and high temperature all year round. Because of being blocked by the surrounding mountains, rainwater gathers around the basin and moves into the basin, with abundant rainfall, lush plants and rich rivers. Typical example: Congo basin

Climate of marine basin: warm climate, moderate annual precipitation and developed agriculture. Typical example: Paris basin, France

Climate of subtropical monsoon basin: due to the influence of topography, cold air is blocked at the outer edge of the basin in winter, resulting in relatively higher temperature in winter than in other areas of the same latitude; In summer, due to the subtropical high pressure area, the airflow sinks and the temperature continues to be high. The airflow is blocked by high mountains and deposited in the basin, which is easy to form high temperature and sultry weather. Typical example: Sichuan basin

Climate of desert basin: Living in the deep inland, humid ocean air is blocked out of the basin, and the climate in the basin is dry with little precipitation. Typical example: Tarim basin

Characteristics of resource storage:

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.

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.