It moved until encountering impermeable layers, such as shale or salt domes, which acted as caps. The Biological Origins of Crude Oil The story of crude oil begins in warm, shallow seas that once covered vast regions of the planet.
Crude Oil Formation and Migration Pathways to Reservoirs
Migration and Trapping Once formed, the crude oil was less dense than the surrounding rock and began to migrate upward through porous geological formations. The organic deposits from the Cretaceous period, roughly 145 to 66 million years ago, account for a significant portion of today’s reserves.
Reservoir Rocks and Caprocks The porous rock that held the oil, such as sandstone or limestone, is called the reservoir rock. Above it, a dense, non-porous caprock, like shale or salt, prevented further upward movement.
Crude Oil Migration Pathways and Trapping Mechanisms
Tiny organisms such as algae and zooplankton thrived in these nutrient-rich waters. Catagenesis: The Oil Window As burial continued and temperatures rose further, kerogen underwent thermal cracking in a phase called catagenesis.
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