ĐỊA CHẤT DẦU KHÍ ( PETROLEUM GEOLOGY ) - CHƯƠNG 5 pptx

CHAPTER 05 CHAPTER 05 GENERATION AND MIGRATION GENERATION AND MIGRATION OF HYDROCARBON OF HYDROCARBON 1 1 - - GENERATION OF GENERATION OF HYDROCARBON HYDROCARBON 1.1 1.1 - - Petroleum Source Material Petroleum Source Material 1.1.1-Formation and Preservation of Organic Matter • In the nineteenth century, it was widely believed that petroleum had a magmatic origin and that it migrated from great depths along subcrustal faults. • But the overwhelming evidence now suggests that the original source material of petroleum is organic matter formed at the earth's surface. • The process begins with photosynthesis, in which plants, in the presence of sunlight, convert water and carbon dioxide into glucose, water and oxygen: 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6H 2 O + 6O 2 • Photosynthesis is part of the larger-scale carbon cycle (Fig. 01). Ordinarily, most of the organic matter produced by photosynthesis gets recycled back to the atmosphere as carbon dioxide. This can occur through plant and animal respiration, or through oxidation and bacterial decay when organisms die Fig 01-CARBON CYCLE 1.1.2 1.1.2 - - Preservation and Organic Productivity Preservation and Organic Productivity • All organic matter in the ocean is originally formed through photosynthesis. The main producers are phytoplankton, which are microscopic floating plants such as diatoms, dinoflagellates and the blue-green algae. Bottom-dwelling algae are also major contributors in shallow water, shelf environments. 1.1.3 1.1.3 - - Preservation and Organic Destruction Preservation and Organic Destruction • Areas of high productivity are not necessarily those best suited for preservation. Destruction of organic matter must also be prevented. Complete biological recycling of organic carbon is retarded by anything that limits the supply of elemental oxygen. • This occurs most favorably in either one of two settings: rapid rate of deposition; and stratified, oxygen-poor water bodies with anoxic bottoms • First, rapid deposition may be necessary to keep the organic material from being destroyed. • Preservation is also favored by density stratification, which produces oxygen-poor bottom waters. • Water stratification and oxygen depletion are well known in the modern Black Sea, • The Eocene-age lakes of Utah, Colorado and Wyoming, in which the Green River oil shale formation was deposited, have been interpreted as seasonally stratified water bodies which at a later stage become permanently stratified (Fig 02) Fig 02 • In the present-day world's oceans, there is a zone of maximum oxygen depletion at a depth of about 200 meters, with oxygen more abundant in the shallow surface waters and again at deeper levels (Figure 03) [...]... • Kerogens with 65% to 35% of oil-prone components will expel mostly condensate and wet gas With less than 35% oil-prone constituents, the kerogen will yield dry gas if dominated by vitrinite and will be non-reactive and barren if dominated by inertinite Figure 0 5- Types of petroleum generated from kerogen, based on visual analysis with reflected light microscope • The oil-prone kerogens can be divided... obliterated -Amorphous particles are not true macerals but alteration products, although the maceral term "amorphinite" has sometimes been applied to these materials 1.2-Hydrocarbons and Kerogen Type • The macerals and amorphous particles in kerogen affect its ability to generate hydrocarbons Oil-prone kerogens generally are made of more than 65% exinite and amorphous particles (Figure 0 5) • Kerogens with 65% ... a unique chemistry (Figure 0 6) • This is because kerogen composition is controlled by the types of macerals and the original biopolymers from which it was formed This chemical variability of immature kerogen types and the changes that occur as petroleum is generated are usually presented as plots of the atomic hydrogen to carbon ratio (H/C) against the oxygen to carbon ratio (O/C) This graph is often... includes all changes that occur up to the stage of petroleum generation • Freshly deposited muds are unconsolidated and may contain more than 80% water in their pores These muds compact very quickly Most of the porosity is lost in the first 50 0 meters of burial (Figure 0 4) After that, compaction to form mudstones or shales continues much more slowly Fig 04 1.1 . 5- Kerogen Components • Under the microscope,... particles derived mostly from phytoplankton, zooplankton, and higher organisms; also some macerals from these groups III Coaly Debris of continental vegetation (wood, spores, leaf cuticle wax, resin, plant tissue ) Mostly vitrinite;some exinite ( not algal ) and amorphous decomposition products IV Inert Fossil charcoal and other oxidized material of continental vegetation Mostly inertinite; some amorphous... algal kerogen (Table 1), is rich in the algal components of exinite, and is formed in either lacustrine or marine environments Type I kerogen is derived mainly from lipids and tends to produce crudes that are rich in saturated hydrocarbons Kerogen Type Origin Organic Constituents I Algal Algae of marine, lacustrine,boghead coal environments Mostly algal components: of exinite (alginite); some amorphous... affect the petroleum generation process • Of the four kerogen types, the Type I algal kerogens have the highest atomic H/C ratios during diagenesis, initially about 1. 65 Type II, III and IV start out with progressively lower H/C ratios Figure 08 • As any of these kerogens are heated, they may reach the second stage in the evolution of organic matter, the stage of catagenesis (Figure 0 8) Catagenesis... that is, graphite • Since it starts out with a lower H/C ratio (Figure 07 & Figure 0 8), Type II kerogen can generate less hydrocarbons than Type I, even though both are oilprone Similarly, Type III is less significant in the total quantity of hydrocarbons it can generate, and Type IV is almost barren 1.3-Depth, Temperature and Time in Petroleum Formation • The generation of hydrocarbons can be related... maximum and minimum generation depths • During diagenesis and at very shallow depths, only biogenic methane, or marsh gas, is generated by the action of anaerobic bacteria • 1.3-Depth, Temperature and Time in Petroleum Formation (Cont .) • At about a depth of 1 to 2 kilometers the catagenesis stage begins The early stage of catagenesis, down to a depth of about 3 kilometers, corresponds to the principle zone... atomic hydrogen to carbon ratio (H/C) against the oxygen to carbon ratio (O/C) This graph is often called a Van Krevelen diagram ( Figure 07, and Figure 0 8) Figure 06Kerogen types Figure 07 • Of particular importance is the H/C ratio, which decreases rapidly as hydrogen-rich molecules are cracked off as oil or gas • Remember that the highest possible organic H/C ratio is 4, which is found in the hydrocarbon . of more than 65% exinite and amorphous particles (Figure 0 5) . • Kerogens with 65% to 35% of oil-prone components will expel mostly condensate and wet gas. With less than 35% oil-prone constituents,. porosity is lost in the first 50 0 meters of burial (Figure 0 4). After that, compaction to form mudstones or shales continues much more slowly. Fig 04 1.1 .5 1.1 .5 - - Kerogen Components Kerogen. CHAPTER 05 CHAPTER 05 GENERATION AND MIGRATION GENERATION AND MIGRATION OF HYDROCARBON OF HYDROCARBON 1 1 - - GENERATION OF GENERATION OF HYDROCARBON HYDROCARBON 1.1 1.1 - - Petroleum Source