Diagenesis of the Cretaceous glutenite and its control on the reservoir porosity in the Fangzheng depression, Northeast China

The reservoir of glutenite has obvious anisotropy characteristics, so diagenesis has a significant impact on its physical property of the reservoir. In view of unclear control factors for densification of the Cretaceous glutenite reservoir in the Fangzheng depression, the diagenesis type of glutenite reservoir and its impact on the physical property of reservoir in the research area were studied by core analysis, electronic probe analysis, scanning electron microscope (SEM) analysis, X-ray energy spectrum analysis, and X-ray diffraction (XRD) analysis. The results showed that there are four types of diagenesis, compaction, dissolution, cementation, and metasomatism. The glutenite reservoir experienced a relatively strong mechanical compaction, which seriously damaged the original pores of the reservoir, with a decrease of 15.97%. This is the most important cause of the densification of the Cretaceous glutenite reservoir. Due to the injection of other hydrocarbon fluids, a large amount of organic acid entered the reservoir through residual pores and fractures, which promoted the dissolution of minerals such as potassium feldspar, formed secondary pore zone, improved the glutenite reservoir performance, and increased the porosity by 6.79%. The primary and secondary pores are filled by cementation with a porosity reduction of 6.53%, which is another key factor for reservoir densification. Through the analysis of the physical property of glutenite reservoir, it is believed that the high-quality Cretaceous reservoir in the Fangzheng depression is mainly developed in the subaqueous distributary channel in frontal fan delta near the oil-source fault. The frontal fan has a high primary porosity and is the material basis for the formation of the reservoir.