Abstract:

With extensive distribution, low permeability reservoirs have large resource quantity. They have particular accumulation characteristics: (1)With fine and poor sorted grains, high content of cementing material, feldspar and cuttings, low permeability reservoirs are characterized by low compositional maturity, low textural maturity, low porosity and permeability. The types of pore structure are small pore-subtle throat and micro pore-micro throat. Fractures of the reservoir are relatively developed.(2).Not only abnormal pressure but also subnormal pressure can exist in the low permeability reservoirs.(3)With poor oil(gas)-water differentiation, the relationship between oil(gas) and water in low permeability reservoirs is complicate and usually inverted.(4)The effect of buoyancy on hydrocarbon migration in low permeability sandstone is very limited. The main driving force of hydrocarbon migration is abnormal pressure. The hydrocarbon migration is characterized by Non-Darcy flow. The fracture, higher permeability sand and local unconformity are main carriers. The distance of hydrocarbon migration is not far and there is less parallel migration.(5) Oil(gas) saturation of low permeability sand reservoir is always less than 60%. The oil(gas) saturation-porosity relationship and oilgas) saturationpermeability relationship are very complex. Reserves abundance is low and mainly accumulates in lithologic traps and lithostructural traps. Because the reservoirs are hardly controlled by structures, oilgas) always widely distributes. Oil and gas exploration of low permeability sandstone area should break the traditional thought that oil and gas are always accumulate in structural high. The declination area of structural slope and syncline are usually the favorable areas. The rich “sweet points” are also important in low permeability sand reservoir exploration.

Key words: low permeability sandstone, hydrocarbon migration and accumulation, exploration inspiration