Research on pore characteristics of shale reservoirs in Well Wuxi 2 based on AFM

Shale reservoir pores are the basis for shale gas occurrence and seepage, but it is difficult to combine quantitative pore information and shale surface morphology in its research, and the existing pore qualitative and quantitative research methods have their own limits. In order to study the pore characteristics of shale reservoirs and combine the quantitative information of the pores with the surface morphology of the shale, the shale samples were scanned using atomic force microscopy (AFM), and the AFM data was analyzed using two softwares, NanoScope Analysis and Gwyddion. The pore characteristics of the Longmaxi shale in Wuxi No.2 Well were studied, and some of the results were compared with those obtained by the low-temperature N2 adsorption experiment. The root-mean-square roughness of Longmaxi shale in Wuxi No.2 Well is from 1.7 to 13.6 nm, the average roughness is from 1.3 to 10.7 nm, the correlation coefficient of TOC and root-mean-square roughness is 0.811 2, and the correlation coefficient between TOC and average roughness is 0.900 8, the shale roughness is controlled by microscopic components, especially organic components; the shale pores are mostly slit-type pores, and wedge-shaped pores, and the main pore sections are located at 4-6 nm and 14-50 nm, The average pore diameter fluctuates in the range of 3.9-6.6 nm, and mesopores account for more than 70%; the aspect ratio of the pore section is in the range of 1.5-3.1. The pore morphology, the proportion of pores in each pore size range of the IUPAC classification standard, the average pore diameter obtained by atomic force microscopy and the results obtained by the low-temperature N2 adsorption experiment are similar; the main pore sections obtained by AFM of part of samples are different from the results obtained by low-temperature N2 adsorption experiments. The comparison of the results of AFM and low-temperature N2 adsorption experiments shows that AFM has insufficient ability to qualitatively characterize the pores with complex structures inside, but the qualitative measurement results of pores are intuitiver than the results of low-temperature N2 adsorption experiments. It is suitable for qualitatively and quantitatively characterize pore characteristics of the pores whose aperture is in the range of 2-50 nm, and can obtain some important parameters not obtained by traditional experimental methods, is a potentially important characterization method.