Characteristics and Controlling Factors of Particle Crushing in Volcaniclastic Sediments under Compaction: The Quaternary Pyroclastic Deposits of Hongtu Hill, Changbaishan Area, Northeastern China

Abstract

Recently, many scholars have conducted experimental mechanical compaction studies on sandstones, carbonates, and mudstones to visually study the mechanical compaction process and reservoir evolution of sedimentary rocks. However, experimental mechanical compaction studies on the evolution of the compaction process of pyroclastic rocks have been ignored. Volcaniclastic rock reservoirs are widely distributed across the world and strongly influenced by the crushing of pyroclastic particles. In this study, we analyzed the characteristics and controlling factors of the crushing of pyroclastic particles during compaction diagenesis from a microscopic perspective through experimental mechanical compaction. These results can provide quantitative compaction background parameters for the quantitative study of pyroclastic rock reservoir evolution. We took pyroclastic samples from Hongtu Hill in the Changbaishan area as an example, and experimental mechanical compaction experiments were conducted. Furthermore, image surface porosity and particle analysis statistical methods were used, and the variations in the effective porosity and image surface porosity under different axial stresses were studied. The results showed that, after compaction, the effective porosity did not exhibit a decreasing trend with increasing axial stress but rather a normal distribution trend that initially increased and then decreased. In the compaction experiment, the pyroclastic particle crushing process was segmented with increasing axial stress, and there was an obvious compaction band in the initial stage of the compaction, called the particle rearrangement stage (10–30 MPa). Furthermore, there were relatively non-successive compaction localization areas in the later stage of compaction, called the particle crushing stage (50–70 MPa), which was represented by vitreous basalt particles surrounded by porphyritic basalt particles. During experimental mechanical compaction, the smaller the compactness, the smaller the solidity, and the larger the slenderness of the particles, the more likely the particles were to break during compaction. Particles containing intragranular pores and vitreous basalt particles were easily crushed.