Distribution patterns of waterflooded oil and gas distribution in carbonate reservoirs based on a triple porosity model

Weakly volatile fracture-pore type carbonate reservoirs are characterized by the presence of fractures and complex pore structures, yet the fluid distribution patterns across different pore types remain unclear. To address this, this study categorizes pores into fractures, large pores, and small pores based on observations from cast thin sections. Significant differences in the flow characteristics are found among these pore types and fractures. Building upon the flow parameter characterization methods established in previous research, this paper integrates and improves these approaches, developing a comprehensive calculation method for permeability, capillary pressure, and relative permeability applicable to different pore types. Based on this, a three-phase flow model for a fracture-large pore-small pore triple porosity system is developed, successfully simulating the migration and distribution of oil and gas under various development methods. The results indicate that during the depletion stage, the remaining oil primarily resides in small pores; after water injection, the recovery of large pores increases significantly. However, during the later stages of water injection, small pores exhibit an "oil-locking" phenomenon, while large pores show characteristics of "residual gas." A comparison of different water injection methods indicates that asynchronous injection and production can help maintain reservoir pressure stability and reduce differences in the utilization of different pore types. This study provides an important theoretical foundation for the efficient development of weakly volatile fracture-pore type carbonate reservoirs.