The shale of the lower Silurian Longmaxi widely develops in Changning area of Sichuan basin. In order to study the micro pore structure and pore size distribution characteristics of shale reservoirs in this area. The pore structure of lower Longmaxi shale gas formation is researched by field emission scanning electron microscope (FE-SEM), high pressure Hg injection, low temperature nitrogen adsorption, low temperature carbondioxide adsorption et al. Taked the Ning 203 well for example. A set of analysis method about nanometer-micrometer all scale pore size distribution was established. The first pore size distribution was obtained by gas adsorption, and the second pore size distribution was obtained by high presser mercury injection in this method. The difference between the data of the pore size distribution obtained by the two kinds of tests was judged. According to the result of the judgment, the pore size distribution of 2nm~200nm was obtained. The pore size distribution data of the non-repeated pore size was obtained by the two methods combined. The micropores, mesopores and macropores for rock samples in proportion were calculated, so the full scale pore size distribution data of rock samples was obtained. Results show the lower part of Longmaxi shale pore structure is very complex in this area. Micropores are connected in series with mesopores and macropores. The pore throat is small, and the connectivity is poor. Mesoporous and microporous accounted for the percentage of pore volume is more than 80%. Pores of diameter above 15nm are mainly free gas, and the ones of diameter smaller than 2nm are mainly absorbed gas.
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