Petroleum knowledge

We all know the name of oil, but what exactly is oil? I am afraid that the answer is not so exact. For this issue, here may be expressed in one sentence, that is, oil is a liquid, hydrocarbon-based flammable mineral produced in underground rock.

As the name implies, oil is formed underground, how deep is it? Hundreds or even several kilometers. It has undergone an evolutionary process of millions or even hundreds of millions of years. Different generations of petroleum have different geological environments and the physical properties of the generated oil are also different. The density, viscosity, melting point, and initial boiling point of oil produced in different fields are different.

The most intuitive physical properties of crude oil are the rich colors, ranging from light to deep white, brown, dark green and black. Our common oil is generally black, and the depth of color is related to the amount of non-hydrocarbon substances contained therein. The higher the content, the darker the color.

Petroleum is a complex natural organic matter. Its main components are carbon (C) and hydrogen (H). Its carbon content is generally 80%-88%, hydrogen is 10%-14%, and it also contains a small amount of oxygen (O),* (S), nitrogen (N) and other elements. Compounds with these elements are called hydrocarbon compounds. Natural gas is also mainly composed of hydrocarbons, which come from the underground rock in the gas state. Like oil, natural gas contains mainly hydrocarbons (saturated hydrocarbons). Alkanes, which generally contain 1 to 4 carbons, are called natural gas from a gaseous state; alkanes containing 5 to 10 carbons are in a liquid state, that is, petroleum; and paraffins containing more than 17 carbons are in a solid state, such as paraffin wax and asphalt.

Oil, natural gas sources

Scientists mainly have two views on the sources of oil and natural gas (hereinafter referred to as oil and gas): one is considered to be transformed after the death of a living organism, and the theory of organic generation. The other is the theory of inorganic generation. It is believed that oil and natural gas are derived from the synthesis of inorganic materials. The basis of the organic generation doctrine is that almost all oil fields are found in sedimentary rocks, and abundant biological relics (fossils, etc.) can be found in sedimentary rocks. Through experimentation, the three major components of the organism are proteins, carbon and water. Compounds and fats can form substances similar to hydrocarbons in petroleum under certain conditions; organic substances such as heme and chlorophyll found in petroleum, the former being blood from animals and the latter from plant chlorophyll. The reason why oil is transformed from the death of a living organism is justified by the fact that there are so many reasons for it, and that the organic generation theory is accepted by most people. Now the methods and contents of oil and gas production are based on this view. Based on.

Although organic theory accounts for absolute advantages, under the premise of organic oil, there are still disputes over whether marine organisms generate oil or whether they generate oil from land-based rivers or lakes. In reality, the major oil fields in the Middle East, such as Saudi Arabia and Kuwait, are all oils produced in marine formations, and most of the oil fields in our country are produced in terrestrial formations.

As early as more than 1 billion years ago, creatures appeared on the earth. With the development of history, the number and types of organisms have become more and more, and organisms multiply and die in large numbers. One of the algae plants is under suitable conditions within 8 days. It can breed up to 1036 offspring and the weight can reach 1.4×1017 tons. A large number of organisms, mainly plankton in the oceans and lakes, after their death, part of the organic matter is oxidized into carbon dioxide to escape, and some of them are deposited as sediments and become a source of oil and gas.

Oil, gas production conditions

The basic condition for oil production is that there is a large amount of organic matter in sediments. Water is the driving force for organic matter migration. Silt and organic matter are carried by water and flow from a height to a low point. Looking for a “sedimentation site” is to find a Low-lying area. This low-lying area, according to its size, is called a basin, depression, depression, etc., but this low-lying terrain is not fixed, and continues to sink or rise with the movement of the crust in various geological and historical periods. . If it can continue to sink, keep the terrain low, you can continue to accept sediments, so that the thickness of the formation continues to increase; if the earth's crust movements increase, then the extent of low enthalpies will gradually become smaller, receiving less sediment; if you continue to rise On the surface of the water, there will be no deposition of matter, and the previously deposited organic matter will be exposed to oxygen and will be weathered and eroded away.

Although the low-lying areas continue to reduce the deposition of organic matter, it is not absolute. If the sedimentation velocity of the crust is greater than the deposition rate of sediments, the depth of the water in the depression will increase relatively, and the distance between the organic matter sinking to the bottom will become longer. Sediment is also exposed to oxygen in the water, and organic matter is oxidized. With abundant organic matter deposits, it still cannot generate oil, and it must also have factors such as anoxic environment, temperature, pressure, time, and catalyst. Anoxic environment is an environment without oxygen or oxygen. If oxygen is present, organic matter will be oxidized to carbon dioxide and water. The temperature is also an important condition for the conversion of organic matter into petroleum. A certain temperature is reached and organic matter can be converted into petroleum in large quantities. The most suitable temperature range for organic matter conversion is 60 to 210°C. Organic matter produces oil very slowly and takes millions of years. In general, the higher the temperature, the shorter the time required for organic matter to convert into oil.

The temperature of the formation is related to the depth of the formation. The deeper the formation is, the closer it is to the ground, and the higher the temperature is, the better it is for the organic matter to produce oil at a certain temperature. This can be said to be conducive to the production of oil at a certain depth. The deeper the depth of the formation, not only the temperature rise, but also the pressure increase, is also beneficial to the generation of oil. Clay minerals in bacteria and clay rocks are catalysts for accelerating the formation of oil from organic matter, and formations containing such clay minerals are also conducive to the production of petroleum.

Although natural gas, like oil, is composed mainly of hydrocarbons, its production conditions are more diversified than oil. Oil must be generated in large quantities to reach a certain depth, and natural gas can be generated from shallow to deep.

According to its production conditions, natural gas can be roughly divided into the following types: biogas-modern sedimentation sludge. Under the action of bacteria, organic matter generates natural gas with methane as the major component. For example, biogas generated in some ditch. After the oil-gas-organic matter enters into the depth of oil generation, in addition to generating large amounts of oil, natural gas is also generated. As the depth of burial increases, oil is strongly decomposed by high pressure and high temperature and generates natural gas. Coal-type gas-sedimentary rock containing coal seam is called coal-bearing stratum. Coal-type gas refers to natural gas produced by coal stratum under the action of time and temperature, and its main component is also methane. Inorganic gas - gas generated by magma and rock metamorphism, such as carbon dioxide and methane.

Sedimentary rock

The earth is an approximately elliptical spherical body with a radius of approximately 6,300 kilometers. The Earth is divided into three parts: the crust, the mantle, and the earth core. Their interfaces are different in different regions. The thickness of the crust is between 5 km and 65 km. The mantle is between the bottom of the crust and a depth of about 2,900 km. From the 2900 km up to the earth's core, it is called the core. The crust consists of three types of rocks (usually called stones), namely magmatic rocks, metamorphic rocks, and sedimentary rocks. Among them, the surface area covered by sedimentary rocks is more than 60%. The earth or gravel that we usually see is the surface weathering crust formed by the weathering of rocks. Or a newly deposited loose material. Oil is distributed in sedimentary basins. In certain geological periods, sedimentary basins receive sedimentary sediments to form thicker sedimentary rocks.

Strata Archives - Geological Age

More than 4 billion years ago, the earth's crust was formed, and sedimentary rocks formed after each period. If there is no strong tectonic movement, the first sedimentary zone is in the area below, and the later deposited layer is above it. The sedimentary rocks formed in different geological periods have different biological fossils and structural features. Based on this, the rocks that make up the crust are divided into different units, each unit corresponding to a certain geological period. Stratigraphic division is based on the "boundary" as the unit, divided into five circles according to the order from old to new: Archean, Proterozoic, Paleozoic, Mesozoic and Cenozoic.

Flowing Oil and Gas - Migration of Petroleum and Natural Gas

Oil and natural gas are fluid deposits. They differ from ordinary deposits in that they are fluid and their advanced positions are sometimes far away from their origin. The generated oil and gas flow from the generated location to the seams with cracks and fractures, and the storage and integration of dispersed oils and oils are initially concentrated, as if the streams were flowing into a large river. The power of this flow comes from the pressure of the formation, and it can also be said to come from the weight of the sediment itself. The stratum is gradually thickened during the deposition process, and the weight is gradually increased. Therefore, the pressure generated is also getting larger and larger. Oil and gas are squeezed out along with the water. After reaching the "big river", the oil and gas did not stop but continued to flow. The main driving force of this flow came from the buoyancy of the oil and gas itself. Because the density of oil and gas is smaller than that of water, when the oil and gas enter the water-bearing formation, the oil and gas flow toward high places under the influence of buoyancy. Because oil and gas are not easily soluble in water, most of them flow in water-bearing formations in the form of “oil droplets” and “bubbles”. They walk the path of bending and bending, overcoming many resistances, making difficult advances, and the speed of migration is quite slow.

Oil and gas in the underground flow space-reservoir

We often hear the saying of “oil lake” and “oil sea” and it is easy to remind people that oil is distributed underground like lakes and oceans. Some people are even worried that oil in the border oil fields of our country will flow to foreign countries. In fact, this is not the case. Then how does oil and gas exist in the earth? After oil is generated, it is stored in rocks with pores, caves and cracks. This rock, which can store liquids and allow them to flow from them, is called the reservoir. The reservoir is a rock formation with pores. The pores are invisible to human eyes. When seen under a microscope, the pore volume can also be measured experimentally. Generally, the reservoir pore volume can be 10%-35% of the rock volume. Professionals mainly use the two factors of porosity and permeability to measure the advantages and disadvantages of the reservoir. The porosity has a large value and can accommodate more oil. The high value of the permeability indicates that the pores and gaps are of the same year and the oil is easy to flow and easy to exploit.

Oil and gas underground protective layer - cap

If oil and gas moves upwards without limit, it will escape once it reaches the surface. In order for the oil and gas in the reservoir not to dissipate, a layer of tight, impervious inter-reservoir reservoirs is needed above the reservoir. This type of rock is called cap rock. The rocks that are suitable for capping are shales, mudstones, etc. Dense marl and limestone can also be used as caps. The cap layer must have a certain thickness. If it is too thin, it cannot withstand the pressure of oil and gas on it. It cannot stop the oil and gas from escaping, and does not achieve the function of a “cap”. The distribution of the cap rock must be stable, ie, the change in thickness should not be too different, but there must be no cover in some places, and no cover in some places. Otherwise, there will be "loopholes" in the top of the reservoir, and oil and gas from the "holes". "Escape away.

Oil in underground warehouse - trap

Under the ground, any geological structure that can stop oil and gas flow and store scattered "oil drops" and "bubbles" is called geological traps, or simply traps. It is like an underground oil storage that can store oil and gas. Therefore, the trap is the terminal station of oil and gas migration, and is the location of the oil and gas reservoir. Of course, there are also targets that workers have to look for. The trap is the unity of the reservoir rock and the cap rock. The reservoir rock is covered by the cap rock and the oil and gas are stored in the pores of the reservoir rock. After oil and gas enter the trap, because the density of oil, gas, and water is different, it is divided into three levels within the trap. The lightest natural gas is on top, the heavier oil is in the middle, and the heaviest water is below. So far, oil has been generated and moved into the trap, completing the entire process of oil and gas formation.