The major driving forces for hydrocarbon accumulation in subtle sand lens reservoirs includes differential capillary pressure on sand-shale boundary

diffusive force triggered by differential hydrocarbon concentration between source beds and sandbodies

and volume expansion caused by kerogen generating hydrocarbons;while the dominant forces that prevent hydrocarbons from pooling include capillary pressure the hydrocarbons faced when entering sandstones and resistance occurred when displacing water in sandstones.For hydrocarbons to accumulate in sandstones

the driving forces must be stronger than the resistances.Apart form that

the porosity and permeability of sandbodies and the hydrocarbon saturation of sourrouding rocks also control the accumulation of hydrocarbons in sandstones.The critical geologic condition for the hydrocarbons generated by the surrounding source rocks entering sandbodies is that hydrocarbon saturation of the surrounding source rocks exceeds 5%-10%

and while that for the hydrocarbons to accumulate in the sandbodies is that the porosity and permeability of sandstones are higher than 5%-10% and 1×10

-3

-2×10

-3

μm

2

respectively.The accumulation of hydrocarbons in sand lens reservoirs can be divided into three stages.The first is preparation stage when no large quantity of hydrocarbons are generated by the source rocks and the strong capillary pressure in the micro pores of these rocks prevents the migration of dispersed oil drops.The second is migration and pooling stage when large amount of hydrocarbons are generated and accumulate in the reservoirs with the differential capillary pressure between the surrounding rocks and sandstones as the main driving force.The third is preservation stage when the hydrocarbon no longer generated in large amount and the differential capillary pressure between the surrounding rocks and sandstones is weaker than the resistant forces.The reservoiring dynamics and controls on hydrocarbon accumulation can be used to predict the hydrocarbon abundance and changing patterns.