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The micro pore structure characteristics of the tight carbonate and sandstone reservoirs in Central Sichuan Basin were systematically studied, by using constant velocity mercury injection, high pressure mercury intrusion, specific surface area instrument and CT scanning, etc. the results indicate that under the same permeability, compared with the tight sandstone reservoirs, the tight carbonate reservoirs have more micron throats and less submicron throats, whose mainstream throat radii are bigger and the distribution span of throat radii are also larger. However, the number of effective throats per unit volume rock sample in the tight carbonate reservoirs is less. That is to say, tight sandstone reservoirs are characterized by "smaller in throat but larger in number", whereas tight carbonate reservoirs show "thicker in throat but fewer in number". Moreover, the specific surface, pore volume and porosity of micro-pores of tight sandstone reservoirs are larger than those of tight carbonate reservoirs, and the higher development of nano pores and throats reduces the overall percolation capacity of tight sandstone reservoirs. In tight sandstone reservoirs, micro pores are the main and better reservoir space and micro fractures are the main seepage channels. The development degree of micro pores controls the porosity of reservoirs, and the development degree of micro pores and micro fractures jointly determines the permeability of reservoirs. But for tight sandstones, micro fractures are not only the main seepage channels, but also the main reservoir space. The development degree of micron fractures dominates the reservoir permeability and porosity. What is more, there are more mobile fluids controlled by submicron pore-throats in tight sandstone reservoirs, and relatively fewer mobile fluids are governed by nano and micron pore-throats.
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