Speaker
Description
Tight sandstone gas reservoir is the most abundant resource among unconventional gas energy. A comprehensive investigation of the displacement patterns for the gas-displacing water process in the tight sandstone is crucial for understanding the formation mechanisms of tight sandstone gas reservoirs, predicting gas-water distribution, and adopting appropriate development strategies. In this study, the pore-scale model of the tight sandstone is reconstructed based on its micro-CT images. The gas-displacing water process under reservoir temperature and pressure conditions of 63 ℃ and 28.5 MPa is simulated using the volume of fluid (VOF) method. Based on the simulation results, the controlling effects of contact angle (θ) and capillary number (Ca) on the displacement patterns for the gas-displacing water process are analyzed and discussed. The corresponding Ca-θ phase diagram of the gas-displacing water process is established. The results show that: (1) The displacement patterns of the gas-displacing water process can be classified as: capillary fingering, viscous fingering, and capillary fingering-viscous fingering crossover. (2) The gas displacing water process under low Ca conditions follows the capillary fingering pattern, in which the gas phase is mainly distributed as a connected network throughout the pore model after displacement. In contrast, the gas displacing water process under high Ca conditions exhibits the viscous fingering pattern, characterized by the formation of numerous isolated gas bubbles after displacement, resulting in poor gas phase connectivity. Under intermediate Ca conditions, the gas-displacing water process exhibits a capillary fingering-viscous fingering crossover pattern, which demonstrates flow characteristics of both fingering patterns simultaneously. (3) Across all wettability conditions, the gas displacing water process under the capillary fingering pattern can achieve the highest gas saturation and best gas phase connectivity after gas displacement, which is most favorable for gas reservoir development.
Keywords
Tight sandstone gas, gas-water two-phase flow, displacement pattern, wettability, capillary number
| Country | China |
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