The influence of diagenetic evolution on rock physical properties of sandy conglomerate of Baikouquan formation

The existing researches on seismic rock physical properties of reservoir rock do not consider the influence of geological process, which leads to the lack of geological significance in rock physical research and restricts the effect of reservoir prediction by seismic methods. Based on the measurement of rock physical properties of the sandy conglomerate samples of Baikouquan formation in Mahu depression, combined with the analysis of petrological characteristics and the division of sedimentary environment, the variation of rock physical characteristics is analyzed in the framework of sedimentary environment and diagenesis process. The results show that the mineral composition of the primary sediment of different microfacies affects the later diagenetic process, and the different diagenetic process forms different rock microstructure characteristics. The braided channel and debris flow microfacies samples in delta plain have high content of plastic components, which have been compacted tightly in the stage of mechanical compaction. The diagenesis is mainly characterized by the continuous coat of fresh water illuviation clay and pyroclastic altered clay in the early diagenetic stage, with the plastic clay as the load-bearing frame. The contents of rigid granite debris, quartz and feldspar in the samples of delta front bar and underwater distributary channel are relatively high, resulting the relatively weak mechanical compaction, high primary intergranular pores and well developed dissolution pores; the diagenesis is characterized by the transformation from siliceous cement of samples of front bar microfacies to siliceous and clay cement of underwater distributary channel microfacies, with the rigid quartz or quartz and clay as the loadbearing frame. The sample of elastic flow of deltaic front shows fast accumulation with calcareous basement cement, with calcareous cement as the load-bearing frame. The load-bearing frame determined by the micro contact characteristics (cementation characteristics) of glutenite particles controls the variation of rock physical properties, which shows that the same microfacies sample with the similar mechanical characteristics of particle boundary has the consistent relationship of velocity versus density, V-P versus V-S and velocity versus porosity, which also results in the apparent variation of V-P/V-S ratio and resistivity of different microfacies samples The V-P/Vs ratio and resistivity can be used as sensitive rock physical parameters for evaluation of Baikouquan formation reservoir. The research results can provide a basis for logging interpretation and "sweet spot" seismic prediction of conglomerate reservoirs, and can be used as an example to form a new method to study the evolution of rock physical characteristics in geological process.