Pore-scale Analysis of Aqueous Phase Trapping Resistance in Carbonate Gas Reservoirs

Abstract

In carbonate gas reservoirs, water in aquifers can flow into reservoirs through high-permeable fractures, which leads to aqueous phase trapping and reduces well productivity. To investigate the mechanism of aqueous phase trapping, this paper established a mathematical model of aqueous phase trapping resistance at the pore scale, which takes capillary pressure, gas viscous force and water viscous force into account. The model was used to analyze the aqueous phase trapping resistance in a carbonate gas reservoir of the Sichuan Basin. Results show that gas flow resistance in matrix easily exceeds the water flow resistance in fracture. Water in fracture occupies the flow path in the formation and locks gas inside matrix. Consequently, aqueous phase trapping occurs. The aqueous phase trapping resistance is influenced by a series of factors i.e. pore radius, throat radius, flow velocity, fracture width, etc. The gas flow resistance is mainly affected by throat radius, because the capillary pressure accounts for more than 98% of the gas phase flow resistance. When the throat radius increases from 0.1μm to 10μm, the gas flow resistance decreases by 89.99%. The water flow resistance is mainly influenced by fracture width and flow velocity. The water flow resistance has a linear relationship with the flow velocity. Water flow resistance is also sensitive to fracture width. When the fracture width rises from 0.2μm to 1μm, the water flow resistance diminishes by 96.00%.