The formation of oil and gas under the sea

Subsea oil and natural gas are a pair of "twin brothers", which mostly reside in the "continental shelf" and "continental slope" under the ocean.

Tens of millions of years or even hundreds of millions of years ago, there were periods when the climate was warmer and humid than now, in the bay and estuarine areas, the seawater was full of oxygen and sunlight, coupled with a large number of nutrients and organic matter brought into the river, providing rich "food" for the growth and reproduction of organisms, so that many Marine organisms (such as fish and other plankton, mollusks) rapidly multiplied. It has been calculated that the remains of plankton in the water layer 100 meters below sea level in the world's oceans can produce 60 billion tons of organic carbon a year, which is the "raw material" for the formation of oil and gas under the sea.

However, these biological remains alone cannot form oil and gas, and certain conditions and processes are required. The ocean receives 160 4 tons of sediment each year, especially in the estuary area, which brings more sediment into the ocean each year than other areas. In this way, a large number of biological remains are buried layer by layer, year after year. If the area is sinking, the sediment and the buried remains will become thicker and thicker. The buried remains are isolated from the air, in an oxygen-deprived environment, coupled with the pressure of thick rock layers, rising temperatures, and the action of bacteria, they begin to slowly decompose, and over long geological periods, these biological remains gradually become dispersed oil and gas.

The resulting oil and gas also need to have a layer to store it and a cap layer to prevent it from escaping. Due to the pressure of the strata above, the dispersed oil droplets are squeezed into the surrounding porous rock layers. These rock layers that contain oil are called oil reservoirs. Some rock pores are very small, oil "squeezed" can not enter, can not store oil. However, because of their small pores, they are "protective shells" that do not allow oil to escape. If such layers are at the top and bottom of the reservoir, they trap the oil inside and act as a protective cap.

The oil scattered in the sandstone is not valuable to be mined, but only where the oil and gas are rich. The formation of shallow seas is often composed of sand, shale, limestone, etc., which are called sedimentary rocks. Sedimentary rocks should lie in layers on the seafloor, but changes in the earth's crust bend, skew, or break them off. Those that curve upward are called anticlines, and those that curve downward are called synclines. Some of these humps, like steamed buns, are called domes anticline. Some sedimentary rocks containing oil and gas are deformed due to great pressure, and the oil goes to the anticline, forming a rich area. Therefore, anticlinal structure is often the "warehouse" of oil storage, which is called "oil storage structure" in petroleum geology. Normally, because natural gas is the least dense, it sits at the top of the anticlinal structure, with oil in the middle and water underneath. The way to find oil and gas is to find places like this first.

It goes sideways, forming a rich area. Therefore, anticlinal structure is often the "warehouse" of oil storage, which is called "oil storage structure" in petroleum geology. Normally, because natural gas is the least dense, it sits at the top of the anticlinal structure, with oil in the middle and water underneath. The way to find oil and gas is to find places like this first.