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Properties of Petroleum and Natural Gas Petroleum and hydrocarbon natural gas are mobile, combustible and non-renewable mineral resources stored underground. They are important categories of fossil fuels in nature. Petroleum and hydrocarbon natural gas are complex natural mixtures composed of various hydrocarbons. The main elements of its composition are carbon and hydrogen, also commonly known as hydrocarbon minerals. Petroleum is a liquid, flammable mixture of hydrocarbons. Natural petroleum formed underground and stored in various pores and cracks in rocks is also called crude oil. ； The flammable liquid extracted from coal or oil shale is called artificial petroleum. Natural gas, in a broad sense, refers to various natural gases formed in the atmosphere and the earth's crust, including nitrogen, carbon dioxide, hydrogen sulfide, hydrocarbon gas and helium. This chapter is devoted to hydrocarbon gases. Hydrocarbon gas, also known as hydrocarbon gas. Since the proportion of other gas reservoirs discovered today is small, people often use the term "natural gas" to describe hydrocarbon natural gas. Petroleum and natural gas are the main energy sources and important chemical raw materials in the world today. Its products are widely used in various fields of human social activities and deeply penetrate into all aspects of people's lives, almost everywhere. In the 20th century, because oil "played a profound impact on the world economy, major changes in oil prices could stimulate economic growth or promote inflation and cause recession." "Oil as a commodity is closely related to * * strategy, global * * and strength" (Daniel Yergin, 1991). Therefore, the various forms of competition and war that have occurred in the world (such as the war in the Middle East in 1973 and the war in the Gulf region in 1991) fully reflect the leading role and extremely important position that oil plays in today's world. The 20th century is often described as the "century of oil." China was the first in the world to discover and utilize natural gas * * , and was also the first to discover and utilize oil in the world. * * one. Due to the long-term rule of feudal society, especially the confinement of the semi-feudal and semi-colonial system in the past 100 years, especially the shackles of imperialist aggression and the "China is poor in oil" advocated to invade the Chinese market, China's oil industry has * * Lagging behind world development trends and competing with world industry * * In comparison, the gap is huge and the lag behind is obvious. In 1949, with the founding of the People's Republic of China, the petroleum industry entered a new period of development. In the early days of the founding of the People's Republic of China, * * We attach great importance to the development of the energy industry and establish specialized agencies for unified planning. Attaching importance to the application of existing petroleum geological theories, with special emphasis on the application of the evaluation made by Chinese geologists based on China's geological reality, we organized a large-scale petroleum geological survey practice, accumulated data, deepened our understanding, pointed out key points, and mainly relied on our own strength to discover and build a large-scale oil field - Daqing Oilfield - in the shortest time and fastest speed. This is undoubtedly the "blood" of great vitality for New China, which is facing hundreds of wastes and industries waiting to be developed and developing its economy, and has greatly supported the recovery and development of all walks of life. Premier Zhou Enlai announced at the first session of the Second National People's Congress in December 1963: The oil China needs can now be basically self-sufficient. The era when the Chinese people used "foreign oil" is about to be gone forever. The discovery and development of Daqing Oilfield, as a glorious milestone in the development of China's petroleum industry, not only heralded the huge potential of China's petroleum resources, but also more effectively promoted the process of petroleum exploration and development. For decades, my country’s petroleum industry has been dominated by the Party and * * Under the care and leadership of relevant ministries and commissions and local * * With the support of the Ministry of Finance and the joint efforts of the petroleum and geological departments and the Chinese Academy of Sciences, batches of oil and gas fields were discovered and production and development bases were built one after another, becoming * * key industries that have played and will continue to play a huge role in the construction of the national economy. Petroleum can be divided into natural petroleum and man-made petroleum. This section mainly briefly describes the properties of natural petroleum extracted from the ground, that is, crude oil. Natural gas refers specifically to flammable hydrocarbon gases. (1) Chemical composition of petroleum There are many kinds of hydrocarbons in nature, hundreds of which are known. However, among the hydrocarbons that make up petroleum, from the perspective of their influence on petroleum properties and the breadth of their existence, the structures of the three series of alkanes (family), cycloalkanes (family), and aromatic (family) are the most important and common. Paraffin (family) hydrocarbons can be divided into two categories: saturated hydrocarbons and unsaturated hydrocarbons according to the characteristics of their molecular structures. Judging from the average composition of petroleum with dissolved natural gas, paraffins account for 53%, naphthenic hydrocarbons account for 31%, and aromatic hydrocarbons account for 16%. Alkanes, with the molecular structural formula CnN2n+2, are a type of saturated and stable hydrocarbon compounds composed of carbon atoms combined with hydrogen atoms in a single bond chain. Those without branches are called normal alkanes, which are named methane, ethane...octane, etc. according to the increase in the number of carbon atoms. ； Those with more than ten carbon atoms are directly represented by numbers, such as n-undecane, n-dodecane...n-triacontane, etc. Now take methane, ethane, and n-undecane as examples to illustrate their molecular structures.: When straight-chain alkanes have branched chains, they are called isoparaffins. For example, the molecular structure of isopentane is n-alkane and iso-alkane. Due to the different arrangement forms, the properties of the compounds are also quite different. Taking octane (C8H18) as an example, normal octane is prone to knocking when burned, while iso-octane is relatively stable when burned. At room temperature, methane, ethane, propane, and butane are gases ； Pentane to pentadecane are liquid ； Above hexadecane, it is solid. Naphthenic hydrocarbons, the molecular formula is CnH2n. Carbon atoms are connected in a ring with single bonds and combined with surrounding hydrogen atoms. The number of hydrogen atoms is reduced compared to alkanes. But it is still a saturated and stable compound, such as cyclohexane, whose molecular structure is: Cyclohexane and cyclopentane are the main naphthenes in petroleum. The chemical properties of cycloalkanes and alkanes are relatively close, but the physical properties reflected in the petroleum they form are different. Petroleum oils with a high proportion of naphthenes tend to be denser and have higher melting and boiling points than oils with a high proportion of alkanes. Aromatic hydrocarbons, also called benzene hydrocarbons, have a general molecular formula of CnH2n. The carbon atoms are cyclically bonded to hydrogen atoms with single and double bonds. Benzene (C6H6) is the simplest and typical representative. Its molecular structure is such that most of these hydrocarbons have an aromatic smell. In petroleum, it is often concentrated in heavy distillates. Alkanes, cycloalkanes, and aromatic hydrocarbons are relatively stable saturated hydrocarbons. However, among chain alkane compounds, there are unsaturated hydrocarbon compounds. The carbon atoms of this type of compound are linked to hydrogen atoms in a chain with double bonds. Those lacking two hydrogen atoms are called alkenes, and their general molecular formula is CnH2n. For example, ethylene (C2H4) has a molecular structure in which the carbon atoms are still arranged in a chain but connected by three bonds. It is called an alkyne, and its general molecular formula is CnHn. For example, acetylene (C2H2) has a molecular structure of: HCCH. This type of unsaturated hydrocarbons are chemically unstable. When it is relatively pure, it ignites and burns calmly, but once it is mixed with air, it is prone to violent explosions. In petroleum, carbon and hydrogen are the main constituent elements. Carbon generally accounts for 84% to 88%, hydrogen accounts for 12% to 14%, and the atomic ratio is between 5.7 and 8.5. Other elements, such as oxygen, nitrogen, and sulfur, account for about 1%, rarely reaching 2% to 3%. There are also trace elements and minerals such as phosphorus and vanadium. These elements exist in heavy components either in free form or in the form of compounds. (2) Physical properties of petroleum The physical properties of petroleum vary significantly depending on its chemical composition. Different properties of petroleum have a greater impact on development, gathering, transportation, storage, and processing, so their economic evaluations are also different. 1) The color of oil is closely related to the amount of gum and asphaltene contained in the crude oil. Dark crude oil has high density and high viscosity. Crude oil with obvious liquid properties is mostly light-colored or even colorless. ； stick * * Strong crude oil is mostly dark in color, ranging from dark brown, dark green to black. The crude oil in Yumen, Daqing and other oil fields in my country is mostly dark brown. ； Crude oil from Karamay Oilfield in Xinjiang is dark brown ； The crude oil in Qaidam Basin in Qinghai is mostly light yellow in color ； The condensate oil produced by some condensate gas fields in Sichuan, Tarim, East China Sea and other basins ranges from light yellow to colorless. 2) The odor of petroleum is caused by different volatile components contained in crude oil. Crude oil with a high content of aromatic components has an ether odor. Crude oil with higher sulfide content emits a strong and pungent odor. Due to the high sulfur content, the processing of this type of crude oil requires the addition of special processing equipment and the investment of more funds. The sulfur content of my country's major oil fields is much lower than the sulfur content of crude oil in the Middle East (higher than 2%). The sulfur content of Daqing Oilfield crude oil is less than 1‰, and the sulfur content of Shengli Oilfield crude oil is no more than 1%. 3) The density of oil refers to the mass per unit volume of degassed crude oil under standard ground conditions. Expressed in tons per cubic meter (t/m3) or grams per cubic centimeter (g/cm3). The relative density of oil (previously expressed in terms of specific gravity in literature) is the ratio of the density of crude oil at 15.5°C or 20°C to the density of water at 4°C. API degree is commonly used internationally as a standard for determining oil prices. The correlation between API degree and relative density is:: API degree (15.5℃) = (141.5/relative density)-131.5. The higher the API degree, the lower the relative density. The API degree of water is 10. Density is related to the chemical composition of petroleum and the amount of impurities it contains. High content of gum and asphaltene, high density, dark color ； Low molecular weight hydrocarbons have high content and low density. There are great differences in the density of crude oil produced in different regions and different formations. Crude oil can be divided into four categories according to its density: light crude oil (density <0.87g/cm3), medium crude oil (≥0.87~0.92g/cm3), heavy crude oil (≥0.92~1.0g/cm3), and extra-heavy crude oil (≥1.0g/cm3). The density of crude oil produced in my country also varies greatly. The crude oil produced in Daqing (mostly around 0.8601g/cm3), Changqing (0.8437g/cm3), Qinghai Gaskule (0.8388g/cm3) and other regions is mostly light crude oil; Shengli (mostly around 0.8873g/cm3), Liaohe (0.8 The crude oil produced in areas such as Shengligudao (0.9472g/cm3), Dagang Yangsanmu (0.9492g/cm3), Liaohe Gaosheng (0.9609g/cm3), and Xinjiang Wuerhe (0.9609g/cm3) is heavy crude oil. 4) The viscosity of petroleum refers to the friction force moving between liquid particles, expressed in m Pa·s. The viscosity determines the flow performance of oil underground and in pipelines. It is generally closely related to changes in the chemical composition of crude oil, temperature and pressure. Generally, when crude oil contains a lot of alkanes, is light in color, has a high temperature, and has a large amount of gas solubility, the viscosity becomes smaller. As the pressure increases, the viscosity also increases. The viscosity of underground crude oil is smaller than that of crude oil on the ground. According to the viscosity, crude oil is divided into four categories: conventional oil (<100mPa·s), heavy oil (≥100~<10 000mPa·s), extra heavy oil (≥10 000~50 000mPa·s) and super heavy oil or asphalt (>50 000mPa·s). Since measuring absolute viscosity is complicated, Engler viscometer is commonly used to measure relative viscosity in research. Relative viscosity refers to the ratio of the absolute viscosity of a liquid to the absolute viscosity of water under the same temperature conditions. The viscosity of crude oil in my country varies widely. The viscosity of Daqing Cretaceous crude oil (50℃) is 19~22mPa·s, the viscosity of Renqiu Sinian subcontinental crude oil (50℃) is 53~84mPa·s, and the viscosity of Shengli Gudao crude oil (50℃) is 103~6451mPa·s. 5) Fluorescence reaction of petroleum. Petroleum is stimulated to emit light under ultraviolet light irradiation, and this fluorescence reaction characteristic of disappearing immediately after irradiation is generally used in field work as an important indicator to determine whether rocks contain petroleum. Based on the different luminous colors and distribution, the displayed petroleum components and their percentages can be roughly estimated. Generally, oil is sky blue, gum is yellow-green, and asphaltene is tan. 6) Optical rotation of petroleum Petroleum has the property of rotating the polarized plane to the right under polarized light. The degree of deflection is generally less than 1°. Optical rotation is a property unique to organic matter and disappears when heated to 300°C. Therefore, when studying the formation of petroleum, this optical activity and the presence of pigments found in petroleum (changed from animal and plant pigments such as chlorophyll or heme, and destroyed when the temperature exceeds 200°C) are often used as the basis for the organic origin of petroleum. 7) Solubility of petroleum Petroleum is insoluble in water, but soluble in organic solvents, such as benzene, essence, ether, chloroform, carbon sulfide, carbon tetrachloride, etc., and can also be partially dissolved in alcohol. Crude oil can also dissolve gaseous hydrocarbons and solid hydrocarbons as well as grease-resin, sulfur and iodine, etc. 8) The freezing point and wax content of petroleum. The freezing point refers to the temperature at which crude oil changes from a flowing liquid state to an immobile solid state. This is a very important indicator when considering storage and transportation conditions at different temperatures, especially in low-temperature areas. According to the freezing point, petroleum can be divided into three categories: high pouring oil (≥40℃), conventional oil (≥-10~<40℃), and low pouring oil (<-10℃). The freezing point of crude oil produced in most oil fields in my country is between 15 and 30°C. Petroleum wax content refers to the percentage of paraffin in crude oil. Paraffin is soluble in petroleum at its melting point temperature (37-76°C). Once the temperature is lower than the melting point, paraffin crystals appear in the crude oil. The wax content of crude oil produced in major oil fields in my country is relatively high, ranging from 20% to 30%. The content of Daqing Sartu Oilfield is mostly 22.6% to 24.1%, Henan Weigan Oilfield is 42% to 52%, Jianghan Wangchang Oilfield is 2.8% to 11.4%, and Karamay Oilfield is only about 7%. Crude oil with a high wax content also has a high freezing point. 9) Combustion characteristics of petroleum The flammability degree of petroleum and refined oil varies with temperature, which is reflected in the differences in flash point, ignition point and auto-ignition point. “"Flash point" refers to the temperature when oil is heated in a container and a fire occurs at the mouth of the container, but then goes out. “"Ignition point" refers to the temperature that continues to rise when heated, and not only flash fire occurs but also causes combustion when exposed to fire. “"Autoignition point" refers to the temperature at which crude oil has reached a very high temperature when heated, and will spontaneously ignite even if it is not exposed to fire. Petroleum is a mixture of hydrocarbon compounds with different boiling points. Unlike water (boiling point is 100°C), it has no fixed boiling point. The flash point varies depending on the proportion of compounds with different boiling points. The higher the boiling point, the higher the flash point. For example, among petroleum products, the flash point of kerosene is above 40°C, diesel is between 50 and 65°C, heavy oil is between 80 and 120°C, and lubricating oil should reach about 300°C. On the contrary, the auto-ignition point of refined oil products with high boiling points decreases. For example, the auto-ignition point of gasoline is 415-530°C, the auto-ignition point of cracked residual oil is about 270°C, and the auto-ignition point of petroleum asphalt is reduced to 230-240°C. As a mixture, petroleum has a flash point between -20 and 100°C, and an autoignition point between 380 and 530°C. 10) Fractional composition of petroleum Since petroleum is a mixture of hydrocarbon compounds with different boiling points, different petroleum products can be obtained by controlling different temperatures. As the temperature increases, first the light components are distilled off, then the heavier hydrocarbon fractions, and finally the gum and asphaltene residues remain. Through practical measurements, the initial boiling point of my country's crude oil is between 70 and 100°C. In a process, the distillation sequence of products is roughly: Below 95℃ is petroleum ether, between 40℃ and 180℃ is aviation gasoline, around 205℃ is automobile gasoline, between 120℃ and 240℃ is heavy gasoline, and between 200℃ and 315℃ is kerosene. ； 270~300℃ is lubricating oil, 190~350℃ is diesel oil, and above 350℃ is residue (residual oil). (3) Chemical composition of natural gas The natural gas referred to in this section refers to hydrocarbon gas. In the earth's crust, natural gas can be classified into four types: free state, dissolved state (dissolved in crude oil and water), adsorbed state and solid gas hydrate. According to the distribution characteristics, it can be divided into two categories: aggregation type and dispersed type. Gas reservoir gas, gas cap gas, condensate gas, and oil-soluble gas belong to the accumulation type, also known as conventional natural gas ； Water-soluble gas, coalbed methane, and solid gas hydrate are dispersed types, also known as unconventional natural gas. From the perspective of their relationship with oil reservoirs, gas cap gas, oil-soluble gas, and gas reservoir gas between or above oil reservoirs that are genetically associated with the oil-forming process are all classified as associated gas. ； Gas reservoir gas that has no obvious connection with oil or contains only a very small amount of crude oil is called non-associated gas. In my country, conventional natural gas storage forms are common, including gas layer gas, dissolved gas, water-soluble gas, and condensate gas. Generally speaking, "gas reservoir gas" means that natural gas is stored in the reservoir in the free gas phase under original reservoir conditions. “"Dissolved gas" refers to the natural gas stored in the crude oil in the reservoir in a dissolved state under the original reservoir conditions. “"Water-soluble gas" refers to natural gas dissolved in the edge water or bottom water of the reservoir under original reservoir conditions. “"Condensate gas" means that under original formation conditions, natural gas exists in a free phase, but when the formation pressure drops below the dew point pressure, reverse condensation occurs. Unconventional natural gas types are still potential areas in our country. However, coalbed methane, also known as coal mine gas, has great potential according to the research and predictions that have been carried out. Since the 1990s, my country has started work to varying degrees and has become an area of exploration and development. Hydrocarbon natural gas is mainly methane (CH4) gas, and contains a small total amount of heavy hydrocarbon (C2-C5) gas in varying amounts. Among the non-hydrocarbon gases, nitrogen (N2), carbon dioxide (CO2), and hydrogen sulfide (H2S) are more common. In addition, natural gas also contains trace to trace amounts of inert gases such as carbon monoxide (CO), sulfur dioxide (SO2), hydrogen (H2), mercury (Hg), helium (He), neon (Ne), argon (Ar), xenon (Xe), and radon (Rn). The elemental composition of hydrocarbon natural gas is similar to that of petroleum, with carbon accounting for 65% to 80%, hydrogen accounting for 12% to 20%, and the H/C atomic ratio between 4 and 5. Generally, methane accounts for more than 85% of the total, ethane and propane are more common, accounting for about 2% to 12%, and butane and above are smaller. According to the content of heavy hydrocarbons (above C2) in natural gas, natural gas is divided into dry gas (lean gas) and wet gas (rich gas). The heavy hydrocarbon content higher than or equal to 5% is classified as wet gas, and the heavy hydrocarbon content lower than 5% is classified as dry gas. Most of the natural gas produced in the Sichuan Basin is dry gas, and its methane content often exceeds 95%. Moisture often coexists with crude oil and is often called associated gas. The ethane, propane, and butane in the wet gas can become liquid after being pressurized, so they are also called liquefied petroleum gas. The composition of natural gas varies in different regions and often varies from place to place. Even in the same oil and gas field or different layers within an oil and gas field, the composition also changes, and some even vary greatly. (4) Physical properties of natural gas Natural gas is a colorless and odorless gas. When hydrogen sulfide is mixed with natural gas, a strong pungent odor will appear. Its important physical properties also include: 1) Density The density of natural gas refers to the weight of unit volume of gas, expressed in kg/m3. Natural gas is a multi-component mixture, and the densities of each component are also different. Under ground standard conditions, the density of natural gas mixtures is generally 0.7-0.75kg/m3, and the density increases as the heavy hydrocarbon content increases. The density of associated gas in some oil fields can reach 1.5kg/m3. Density increases as pressure increases and decreases as temperature increases. The relative density of natural gas refers to the ratio of the density of natural gas to the density of air under the same temperature and pressure (such as 15.6°C, 101 325Pa or 20°C, 101 325Pa). Natural gas mixtures are generally between 0.56 and 1.0. 2) Viscosity of natural gas Viscosity refers to the frictional resistance of particle migration within gas molecules. It is an important parameter for studying gas migration and evaluating mining and gathering and transportation conditions. It is commonly expressed as dynamic viscosity (absolute viscosity), and the unit is mPa·s. Kinematic viscosity can also be used, that is, the ratio of dynamic viscosity to density, expressed in mm2/s. The viscosity is related to the chemical composition and its environment. Under standard conditions, as the molecular weight increases, the viscosity becomes smaller, and as the temperature increases, the viscosity increases. Under higher pressure conditions, viscosity increases as pressure increases. 3) Natural gas compressibility and solubility Natural gas is compressible. The same volume of natural gas has different densities and weights on the ground and underground. Natural gas has the ability to dissolve in two different liquids: water and petroleum, but it is easily miscible with petroleum but not with water. For example, the solubility coefficient of methane in crude oil is 0.3, while the solubility coefficient in water is only 0.033. The difference between the two can be an order of magnitude. The main factor affecting the solubility of natural gas is pressure, while the effect of temperature on the solubility of natural gas is more complex. (5) Calorific value of oil and natural gas Calorific value refers to the heat generated when burning unit weight of fuel. It is an important indicator for evaluating fuel quality. The unit is expressed in MJ/kg. The average low calorific value is 41.87MJ/kg for oil, 38.97MJ/kg for natural gas, and 20.93MJ/kg for raw coal. Internationally, it is mostly measured based on the basic calorific value (standard coal equivalent) of standard fuel application of 29.27MJ/kg. The standard fuel coefficients for oil and natural gas are 1.4286 and 1.33 respectively. (6) Differences between petroleum and natural gas Petroleum and natural gas have commonalities and affinities as well as characteristics and differences in terms of elemental composition, structural form, raw materials and timing of generation. In terms of chemical composition characteristics, natural gas has a small molecular weight (less than 20), a simple structure, a high H/C atomic ratio (4 to 5), and significant fractionation of carbon isotopes. Petroleum has a large molecular weight (75-275), a complex structure, a relatively low H/C atomic ratio (1.4-2.2), and the fractionation effect of carbon isotopes is weaker than that of natural gas. In terms of physical properties, natural gas is basically a single gas phase containing only a very small amount of liquid hydrocarbons and water. ； Petroleum can contain a mixture of three phases: gas, liquid, and solid, characterized by the liquid phase. Natural gas is much less dense than oil and is easy to compress and expand. Under standard conditions, the viscosity of natural gas is only n×10-2~10-3mPa·s, while the viscosity of oil is n~n×10-3mPa·s, which is several orders of magnitude different. The diffusion capacity and solubility of natural gas in water are greater than that of oil. In terms of the conditions for generation, natural gas is broader than oil. Natural gas is formed from both organic matter and plutonic inorganic matter. ； The sedimentary environment is mainly lacustrine and swamp type. ； The biogas parent material is mainly humic kerogen (type III), and the temperature range generated is wide. Biogas begins to be generated at shallow low temperatures. ； In the range of medium depth (most temperatures are between 65 and 90°C), the thermal degradation of organic matter occurs and a large amount of petroleum is generated during the "liquid window" stage, which can also be accompanied by the formation of petroleum. ； Under deep high temperature conditions, the cracking of organic matter mainly produces natural gas. Natural gas also has wider requirements for reservoirs than oil. Generally, the porosity of rocks is 10% to 15% and the permeability is 1×10-3 to 5×10-3 μm2, and reservoirs can be formed. Due to the active nature of natural gas, the requirements for caprock are much stricter than those for oil. Therefore, natural gas is distributed in a wider area than oil, and its output types and storage forms are also more diverse than oil. There are conventional natural gas reservoirs similar to oil accumulation forms, such as structural, stratigraphic, lithological gas reservoirs, etc., as well as unconventional natural gas reservoirs such as coalbed methane, water-sealed gas, gas-water compounds, tight sandstone, and shale gas. Coalbed methane reservoirs, in which coal seams are both gas source rocks and reservoirs, have become a very realistic type. “About 90% of the world's proven natural gas reserves are not associated with oil, but appear in the form of pure gas reservoirs or condensate gas reservoirs, forming gas-bearing belts or gas-bearing areas. This shows that although natural gas geology and petroleum geology have some similarities and close connections, natural gas has its own geological laws for the occurrence, development and formation of mineral deposits" (Bauts, 1988). Due to some characteristics of natural gas, the theoretical research, resource evaluation, exploration technology methods and mining methods are also different from those of oil. It is necessary to develop some targeted working methods and technology series to adapt to the needs of the future expansion of natural gas resource development.