ORIGIN AND PROPERTIES OF HYDROCARBON (cơ sở KHOA học địa CHẤT dầu KHÍ SLIDE TIẾNG ANH)

CHAPTER 1: ORIGIN & PROPERTIES OF HYDROCARBON THE ORIGIN OF PETROLEUM HYDROCARBON REQUIREMENTS FOR PETROLEUM ACCUMULATION PETROLEUM CHEMISTRY PHYSICAL and CHEMICAL PROPERTIES OF CRUDE OIL CLASSIFICATION and OCCURRENCES OF CRUDE OIL ALTERATION OF CRUDE OIL GAS PROPERTIES and CLASSIFICATION THE ORIGIN OF PETROLEUM HYDROCARBON • THEORIES OF INORGANIC ORIGIN – Hypothesis of Dimitri Mendeleev – Hypothesis of Sokolof • THEORY OF ORGANIC ORIGIN • Analogy with organic matter • Biomarker • The present of porphyrins • The polarization of ray-light • Evidence of carbon isotopes Requirements for Petroleum Accumulation The task of finding a petroleum field is not a simple one • First, there must be a rock containing original organic matter-a source rock Usually this is a mudrock or shale, which is a very common rock type and makes up about 80% of the world's sedimentary rock volume However, even an average shale contains only about 1% to 2% organic matter, and this number can vary widely Many shales have very low organic content and make poor source rocks • Then, the source rock must be buried deeply so that temperature and time can cause the organic matter to mature into petroleum This usually requires deposition into sedimentary basins, depressed areas thickly filled by sediments Our search for petroleum is further limited, since over half of the world's continental areas and adjacent marine shelves have sediment covers either too thin or absent Requirements for Petroleum Accumulation (cont) • Even where the organic matter can become mature, not all of it becomes petroleum In a typical example (Figure 01 ) a normal marine shale with only 1% original organic matter will have less than a third of it converted to the hydrocarbon molecules that make up oil and natural gas (Waples, 1981) The rest remains behind as an insoluble organic residue Figure 01 Requirements for Petroleum Accumulation (cont) • Five factors, therefore, are the critical risks to petroleum accumulation (Figure 02): (1) a mature source rock, (2) a migration path connecting source rock to reservoir rock, (3) a reservoir rock that is both porous and permeable, (4) a trap, and (5) an impermeable seal • If any one of these factors is missing or inadequate, the prospect will be dry and the exploration efort will be unrewarded Not surprisingly then, less than half of the world's explored sedimentary basins have proved productive, (Huf, 1980) and typically only a fraction of 1% of the petroleum basin's area, and at most 5% to 10%, is actually prospective (Weeks, 1975) Figure 02: Five factors for petroleum accumulation PETROLEUM CHEMISTRY • Strictly speaking, hydrocarbons are compounds that contain only two elements, hydrogen and carbon Consequently, petroleum is quite simple in its elemental composition It contains relatively few impurities, mainly atoms of nitrogen, sulfur, and oxygen PETROLEUM CHEMISTRY • Table 1, shows the average composition of petroleum in all three of its natural states of matter, as natural gas, liquid crude oil and solid or semi-solid asphalt HYDROCARBON GASES Defined based on their occurrence: • Free gas is a hydrocarbon gas that exists in the gaseous phase in a reservoir and remains in the gaseous phase when produced • Dissolved gas is defined as natural gas in solution in crude oil in a reservoir The reduction in pressure when oil is produced from a reservoir often results in dissolved gas being emitted from oil as free gas • Associated gas is natural gas which occurs as a gas cap which overlies and is in contact with crude oil within a reservoir Nonassociated gas is natural gas in reservoirs that not contain crude oil (Figure 13) Figure 13 Liquified Gases • Some hydrocarbons in the gaseous phase in the reservoir become liquid at the surface, and some liquid hydrocarbons become gases at the surface, as temperatures and pressures change LIQUIFIED GASES • NGL, natural gas liquids, are hydrocarbon liquids separated from the produced gas stream Condensates are an important type of natural gas liquid • LPG, liquified petroleum gas, is comprised of heavier hydrocarbon gases, usually propane and butane, stored under pressure in a liquid form • LNG, liquified natural gas, is natural gas, commonly methane, which is compressed into liquid for storage and transportation Gas Hydrates • Gas hydrates are an unusual form of subsurface hydrocarbon gas in which ice lattices, called clathrates (Figure 14), physically trap gas molecules in cagelike structures without the aid of direct chemical bonds Hydrates look like wet snow Figure 14: Gas hydrates form • There are two gas sites within the hydrate structure - a smaller one that can only contain methane, and a larger site that can also hold hydrogen sulfide, carbon dioxide, and the larger hydrocarbon molecules of ethane, propane and butane • The composition of the gases in gas hydrates indicates that their origin is probably biogenic and shallow, rather than deep, much like the origin of marsh gas Gas hydrates are formed as subsurface pressure increases and temperature decreases They are stable only within a specific temperature range, which depends greatly on both the pressure and the composition of the hydrate gas mixture (Figure 15) Most hydrates are found only beneath strata colder than 5°C Figure 15: HGs are stable only within a specific temperature range, which depends greatly on both the pressure and the composition of the hydrate gas mixture • Consequently, gas hydrates occur in shallow arctic sediments and in deep oceanic deposits They have been documented in arctic permafrost in Alaska and Siberia • An example of deep ocean hydrates can be seen on the Blake Plateau of the east coast of the United States, in water depths of about four kilometers (Figure 16) Figure 16 • The prominent reflector on a seismic line across the Blake Plateau indicates the base of a gas hydrate deposit (Figure 17) This has been confirmed by drilling activity Notice how this reflector can be recognized It runs parallel to the sea floor topography and cuts across reflectors caused by stratigraphic layering • Areas of the arctic and of the ocean floors appear to contain vast reserves of hydrocarbon gas locked up in clathrate deposits When all of the ice cages are filled, hydrates are able to hold six times as much gas as an open free-gas-filled pore system Figure 17 • Unfortunately, gas hydrates present considerable production problems, which have yet to be overcome These are due, in part, to the low permeability of the reservoir and, in part, to chemical problems and energy requirements concerning the release of gas from the crystals • Gas hydrate deposits may be of indirect economic significance, perhaps acting as barriers to gas migration Because of their low permeability, the hydrates would prevent the upward migration of conventional hydrocarbons that are present below the reflector Natural Gas Liquid (NGL) Classified into: INORGANIC ORIGIN Inert Gases Helium Argon Krypton Radon Nitrogen Also Carbon dioxide, Hydrogen sulfide ORGANIC ORIGIN Hydrocarbon Gases Methane (dry) Ethane (wet) Propane Butane ... ALTERATION OF CRUDE OIL GAS PROPERTIES and CLASSIFICATION THE ORIGIN OF PETROLEUM HYDROCARBON • THEORIES OF INORGANIC ORIGIN – Hypothesis of Dimitri Mendeleev – Hypothesis of Sokolof • THEORY OF ORGANIC...1 THE ORIGIN OF PETROLEUM HYDROCARBON REQUIREMENTS FOR PETROLEUM ACCUMULATION PETROLEUM CHEMISTRY PHYSICAL and CHEMICAL PROPERTIES OF CRUDE OIL CLASSIFICATION and OCCURRENCES OF CRUDE OIL... oil and tar as a result of bacterial action and of flushing by fresh meteoric waters of surface origin • This oil falls into one of two classes (aromatic-asphaltic or aromaticnaphthenic), both of