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 highly permeable fractures, which leads to aqueous phase trapping and reduces well productivity. In this paper, flow resistances during aqueous phase trapping are analyzed. A mathematical model of aqueous phase trapping resistances is established at the pore scale, taking into account capillary pressure, gas viscous force, and water viscous force. The factors affecting aqueous phase trapping resistances are discussed, including pore radius, throat radius, flow velocity, fracture width, etc. Results show that gas flow resistance in the matrix easily exceeds the water flow resistance in fractures. Water in fractures occupies the flow path in the formation and traps gas inside the matrix. Consequently, aqueous phase trapping occurs. The gas flow resistance is mainly affected by the throat radius because the capillary pressure accounts for more than 98% of the gas phase flow resistance. When the throat radius increases from 0.1 μm to 10 μm, the gas flow resistance decreases by 89.99%. The water flow resistance is mainly influenced by the fracture width and the flow velocity. Water flow resistance has a linear relationship with the flow velocity. The water flow resistance is also sensitive to fracture width. When the fracture width rises from 0.2 μm to 1 μm, the water flow resistance diminishes by 96%.