Equivalent Capillary-Based Liquid Phase Invasion Model for Low Permeability Gas Reservoirs

The goal of this study was to avoid formation damage by finding a better way to map the flow of fluids through pore networks in tight sandstones. In order to investigate the flow mechanism of liquid phase invasion in low permeability gas reservoirs from the microscopic scale, a pore network model of tight sandstone was established by using laser etching technology. In that way, the microscopic visualization flow experiment of liquid phase invasion was carried out, and the dynamic aqueous phase distribution in the pore network during the process and fluid flow back was analyzed. The liquid phase invasion microscopic flow model for low permeability gas reservoirs was established based on equivalent capillary beam, and the model was verified by aqueous phase self-absorption invasion experiment in tight sandstone. Experimental results showed that the rule of aqueous phase invasion in the pore network is similar to that of capillary force invasion. The liquid phase mainly flows through larger pores initially, and then advances through the throats communicating with the pores gradually; It is difficult for the aqueous phase in the smaller throat to flow back, which can hinder the flow of gas phase. The research suggested that viscous drag plays a dominant role in the invasion of aqueous phase in tight sandstone; the liquid phase can still invade the core under negative pressure difference. Further, the denser the rock, the greater the maximum invasion depth of aqueous phase would be. The established liquid phase invasion model will provide a theoretical reference in studying liquid phase invasion damage and protection mechanism of low permeability gas reservoirs.