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Requirements for an Oil Field

Requirements for an Oil Field. Source rock Reservoir rock Cap rock Timing of migration Temperature. Geochemical Exploration Questions. Are source rocks present? (Requires minimum amt. of organic C) Are they oil or gas prone? (Type of OM) Are they thermally mature?

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Requirements for an Oil Field

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  1. Requirements for an Oil Field Source rock Reservoir rock Cap rock Timing of migration Temperature

  2. Geochemical Exploration Questions Are source rocks present? • (Requires minimum amt. of organic C) Are they oil or gas prone? • (Type of OM) Are they thermally mature? • (Are source rocks in the oil window?)

  3. Characteristics of a Good Oil Source Rock High organic carbon (TOC) High Hydrogen Index (HI) Vitrinite reflectance (indication of maturity) between 0.5 - 1.4 Ro

  4. Oxidation of Organic Matter • Oxic conditions CH2O + O2 ===> CO2 + H2O (Limiting condition: O2 > OM) • Anoxic conditions 2CH2O + H2SO4= ===> 2CO2 + 2H2O + H2S (Limiting condition: OM > O2) Anoxia: O2 demand > O2Supply

  5. Preservation of OM • High productivity (high nutrient supply) • Moderate sedimentation rate • Low oxygen supply

  6. Factors Leading to Low OM • Low productivity • Low or high sedimentation rate • Low OM supply from land • High water depth OM decreases Onshore ------------------------------> Offshore

  7. Composition of Organic MatterCommon Analytical Methods Used • Elemental Analyses (C, H, O, N, S) • Isotopes • Gas Chromatography (GC) • GC combined with Mass Spectrometry (GC/MS) • Rock-Eval pyrolysis (Hydrogen Index and Oxygen Index)

  8. Types of POM in Sediments • Structured • Spores and pollen • Cellular plant tissues (leaves, stems, roots) • Amorphous • Algal debris • Decayed higher plants (marine or terrestrial) • Charcoal (carbonized wood) • Recycled kerogen

  9. Sources of n-Alkanes in Sediments • Organisms in the water column • Phytoplankton and zooplankton • Organisms on/in the sediment • Bacteria, sea grasses, invertebrates • Terrestrial runoff • Fossil fuel

  10. HC Generation 1-Source Rocks • Deposited in environments conducive to preservation of abundant sedimentary OM • OM (kerogen) releases hydrocarbons • Marine kerogen tends to generate oil; terrestrial kerogen tends to generate gas • Methane forms at high (thermogenic) and low (<50 oC) temperatures (biogenic)

  11. HC Generation 2-Temperature Effects • Thermal alteration of kerogen requires minimum of 50-60 oC • Oil generation is a time- AND temperature-dependent process • Quantity generated increases linearly with time, geometrically with temperature • At high T, wet or dry gas is more stable than liquid HC • Laboratory experiments at high T reproduce general aspects of HC generation

  12. Importance of Hydrogen • Generation of HC (alkanes) requires hydrogen • Kerogen is the source of H • With increasing maturity: • Kerogen loses hydrogen • H/C of kerogen decreases Immature oil-prone kerogen will have a relatively high H/C

  13. Petroleum Generation • A temperature-dependent chemical process that occurs in sedimentary basins as a natural consequence of thermal alteration of OM deposited with the sediments. • The sedimentary OM is of biogenic origin. • The extent of the reaction (i.e., amount of oil generated is a function of the T at which the reaction occurs and the duration of the reaction.

  14. Map of Proved Oil Reserves in 2006

  15. U.S. Oil Peak

  16. World Oil Prospects

  17. World Oil Peaking is Going to Happen • World production of conventional oil will reach a maximum and decline thereafter. • Many forecasters project peaking within a decade; others say it will occur later. • Prediction is difficult because of geological complexities. • Peaking will happen, but the timing is uncertain.

  18. Oil Peaking Presents a Unique Challenge • The world has never faced a problem like this. • Previous energy transitions (wood to coal and coal to oil) were gradual and evolutionary. • Without massive mitigation (i.e., alternatives) more than a decade early, the problem will be pervasive and will not be temporary. • Oil peaking will be abrupt and revolutionary.

  19. The Coming World Oil Crisis World oil peaking is going to happen Oil peaking could cost our economy dearly It presents a unique challenge The problem is liquid fuels Mitigation will require substantial time (~20 yrs) Both supply (alternate fuels) and demand (get rid of gas guzzlers) require attention It is a matter of risk management Government intervention will be required Economic upheaval is not inevitable

  20. Oil Consumption Per Capita

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