PORE STRUCTURE CHARACTERIZATION OF THE NIUTITANG SHALE IN CHONGQING AREA, CHINA

In this study, we picked 45 samples with different depth (larger than 400 m) from the Niutitang Formation in Chongqing area, South China. The mineral compositions and the geochemical properties (maturity) of these shale samples were characterized by using the X-Ray diffraction and Rock eval, respectively. Then, the properties of these samples (the porosity and the permeability) were measured and the pore size distributions were derived using the mercury intrusion data. The results showed that quartz and clay minerals (most illite) are the two major mineral compositions. The total carbon content (TOC) of the Niutitang shale samples from the studied well is no more than 1% and the maturity value of these shale samples is very high, indicating that the organic matter now is in the gas production window. The ink-bottle shape and slit shape pores are widely spread in these shale samples. No correlations can be found between porosity and permeability values. The fractal dimension D-f1 shows that the burial depth does not have big influence on the pore size distributions of shale samples but the fractal dimension D-f2 indicates that the burial depth could affect the heterogeneity of pore geometry. The methane adsorption capacity value of Niutitang shale samples is around 1.14-2.6 m(3)/t, which is close to the value of Longmaxi shale.