Petroleum Geology and Exploration

[Buela_Vigneswaran]

Petroleum Geology and Exploration

1.1 Hydrocarbon Formation and Accumulation

• Organic Matter Deposition:
  • Origin of hydrocarbons from organic material such as plankton and algae.
  • Conditions necessary for organic matter deposition (low oxygen environments, rapid sedimentation).
• Kerogen Formation:
  • Transformation of organic material into kerogen under heat and pressure.
  • Types of kerogen (Type I, II, III) and their oil or gas-generating potential.
• Thermal Maturation:
  • Process of converting kerogen into oil and gas through increased temperature and pressure over geological time.
  • Importance of the "oil window" and "gas window."

1.2 Reservoir Rock Properties

• Porosity:
  • Measurement of void space in rocks where hydrocarbons are stored.
  • Types of porosity (primary, secondary).
• Permeability:
  • Ability of a rock to transmit fluids.
  • Relationship between porosity and permeability.
• Cap Rocks and Traps:
  • Role of impermeable cap rocks (shales, salts) in trapping hydrocarbons.
  • Types of traps:
    • Structural traps: Anticlines, fault traps, salt domes.
    • Stratigraphic traps: Pinch-outs, unconformities.
    • Combination traps: Mixtures of structural and stratigraphic traps.

1.3 Basin Analysis

• Sedimentary Basins:
  • Regions where sediments accumulate, forming potential hydrocarbon reservoirs.
  • Types of basins (rift basins, foreland basins, passive margins).
• Petroleum System Elements:
  • Source rock, migration pathways, reservoir rock, cap rock, trap, and seal.
• Play Concepts:
  • Analysis of geological features likely to contain hydrocarbons.

1.4 Exploration Techniques

• Geophysical Methods:
  • Seismic Surveys:
    • Use of sound waves to map subsurface structures.
    • 2D, 3D, and 4D seismic imaging.
  • Gravity and Magnetic Surveys:
    • Identification of subsurface density variations or magnetic anomalies.
• Geochemical Methods:
  • Sampling and analysis of soil, water, or air for hydrocarbon indicators.
• Remote Sensing:
  • Satellite imagery and aerial photography to identify surface expressions of subsurface features.
• Exploratory Drilling:
  • Drill testing to confirm geological interpretations and discover hydrocarbons.

1.5 Well Logging

• Definition and Purpose:
  • Process of recording physical, chemical, and structural properties of rock layers in a borehole.
• Types of Logs:
  • Resistivity Logs: Measures electrical resistance to identify hydrocarbon zones.
  • Gamma-Ray Logs: Detects radioactive elements, useful for identifying shale.
  • Density and Neutron Logs: Provides porosity estimates.
  • Sonic Logs: Measures rock velocity for identifying formation properties.
• Integration with Seismic Data:
  • Combining seismic interpretation and log data for detailed subsurface understanding.

1.6 Hydrocarbon Migration

• Primary Migration:
  • Movement of hydrocarbons from source rock to reservoir rock.
  • Driven by buoyancy, pressure gradients, and fluid expansion.
• Secondary Migration:
  • Movement within reservoir rocks toward traps.
  • Importance of migration pathways (faults, fractures, permeable strata).

1.7 Risk Assessment in Exploration

• Geological Risk:
  • Probability of finding hydrocarbons in a specific location.
  • Factors: Seal integrity, trap effectiveness, source rock quality.
• Economic Risk:
  • Balancing exploration costs with potential production.
• Environmental Risk:
  • Evaluating impact on ecosystems during exploration.

By studying Petroleum Geology and Exploration, engineers and geologists gain the knowledge required to identify potential hydrocarbon reserves and minimize risks during exploration and development.