A pre-treatment method for particle size analysis of fine-grained sedimentary rocks, Bohai Bay Basin, China

Abstract A new pre-treatment method is described for the disaggregation of fine-grained sedimentary rocks (FSRs). The main steps include (1) heat the samples in a muffle furnace and then put them in a beaker containing sodium sulphate solution of a certain concentration; (2) freeze the beaker containing the samples in a refrigerator; (3) take out the beaker and put it into a water-bath pan to maintain a constant temperature. Using this method, FSRs were disaggregated in Well H-1 (3756.42–3769 m) of the Dongying Depression and the particle size data were obtained to analyse sealing capacity. The result shows a close correlation between particle size distributions and capillary entry pressure, indicating that particle size distribution is one of the most important factors influencing sealing capacity. This method shows favourable performance in most of the FSRs except for rocks with greater degrees of metamorphism. The advantages of this method include the decreased use of chemical reagents with strong corrosion potential and obviation of the need to use a grinding pestle, which reduces the impact on primary particles.