This mechanism is also inconsistent with the vertical projection of the reservoir and the rapid change in the anomaly with production. Water transport is frequently considered a major factor in the secondary migration process. Buoyancy of gases is the third proposed mechanism, and the mechanism favored by nearly all practitioners and researchers in surface geochemistry. Buoyancy-driven migration is due to density differences between the gaseous and liquid hydrocarbon phases. Buoyancy driven migration also applies to the density differences between the gaseous hydrocarbon and aqueous phases.
Buoyancy tends to drive small bubbles of the gaseous phase in the vertical direction.
The light hydrocarbon molecules are of a size that they can pass through the pores of a caprock, though obviously impeded, relative to more permeable formations in the sedimentary column. 1023-1041, which illustrates the buoyant transport process. The potential pressure of the gas being gradually transferred to the top of the column as the bubble rises is shown in the middle figure. When the bubble reaches the top, as shown in the right figure, the total pressure is atmospheric plus the product of fluid density times the height of the sedimentary column times the gravitational constant. The potential pressure is the pressure that would be reached if there were an absolutely leak-proof cap at the top of the system.