Hydrocarbon Migration Pathways: A Comprehensive Overview

 Hydrocarbon migration, a critical process in petroleum systems, encompasses the movement of generated hydrocarbons from source rocks to accumulation sites. This process is conventionally divided into three stages: primary, secondary, and tertiary migration.

1. Primary Migration

  • Movement of hydrocarbons from the source rock into carrier beds or fractures.
  • Driven by expulsion mechanisms such as pressure buildup, hydrocarbon buoyancy, and diffusion.
  • Occurs through micropores, organic matter networks, or natural fractures.

2. Secondary Migration

  • Transport of hydrocarbons through carrier beds (e.g., porous sandstones, carbonates) toward a trap.
  • Governed by buoyancy forces, capillary pressure, and hydrodynamic flow.
  • Pathways include interconnected pores, fractures, and fault systems.

3. Tertiary Migration (Remigration)

  • Movement of hydrocarbons from an existing reservoir due to tectonic disturbances, fault reactivation, or changes in pressure conditions.
  • Can lead to oil seepages at the surface or secondary trapping in new reservoirs.

Key Factors Controlling Migration Pathways

Permeability and Porosity of Carrier Beds

High-permeability formations (e.g., well-sorted sandstones) facilitate efficient migration.

Low-permeability rocks (e.g., shales) act as barriers, redirecting flow.

Buoyancy and Capillary Forces

Hydrocarbons move upward due to density differences with water.

Capillary forces control migration through small pores and fractures.

Faults and Fracture Networks

Can serve as conduits or barriers to migration, depending on sealing properties.

Fault reactivation can cause remigration or leakage.

Structural and Stratigraphic Features

Anticlines, unconformities, and channel systems influence migration routes.

Shale drapes and cemented layers can block or divert flow.

Hydrodynamic Flow

Regional groundwater movement can alter migration directions, leading to tilted oil-water contacts.

Identifying Migration Pathways in Exploration

Geochemical Analysis: Oil-to-source correlation using biomarkers and isotopes.

Seismic Interpretation: Mapping faults, unconformities, and carrier beds.

Reservoir Pressure Data: Understanding fluid movement through pressure gradients.

Surface Seeps and Anomalies: Indicating active migration.




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