Meitan kexue jishu (Jun 2024)
Mathematical model for flow regime transition conditions of gas-liquid two-phase flow in natural gas reservoir fracture
Abstract
The flow of gas-liquid two-phase flow in reservoir fractures may exhibit various flow regimes, such as bubble flow, slug flow, and annular mist flow. Identifying the conditions for the transition between these flow regime is essential for understanding the formation mechanism of gas-liquid flow and has significant implications for the production pipeline management of natural gas Wells. Based on the flow characteristics of different flow regimes of gas-liquid two-phase flow, combined with the theory of continuous medium control and the principle of momentum conservation, transformation mathematical models between flow regimes such as bubble flow, slug flow, and annular mist flow were established. The decisive conditions and key controlling variable that govern the transitions between various flow regimes have been precisely identified. Furthermore, the precision of the mathematical model was rigorously validated through microscopic physical simulation experiments focused on gas-liquid transportation. The results indicated that, the flow state transition of gas-liquid two-phase flow in fractures was the result of the coupling effect of factors such as the physical properties of the gas/liquid phase, the pore size of the gas injection channel, the pore size of the fracture flow channel, the gas phase fluid velocity, and the liquid phase fluid velocity. The transition between bubble flow and slug flow mainly depended on the size of the initial bubble, the flow channel space, and the height of the liquid phase interface wave. The transition between slug flow and annular mist flow depended on whether the gas phase fluid can break down the liquid phase fluid and suspend it. The main control factors for the transition between different flow states were different. The pore size of the fracture system was one of the most important factors in the mutual transformation of bubble flow and slug flow, when the injection channel aperture was larger and the flow channel aperture was smaller, it was more likely to form slug flow. The mutual transformation between slug flow and annular mist flow was primarily influenced by fluid velocity and the physical properties of gas/liquid phase fluids. A higher relative velocity between the gas-liquid phases, a smaller density difference between the phases, and a lower liquid surface tension all increase the likelihood of forming annular mist flow. These research findings established a theoretical foundation for understanding the mechanism of gas-liquid two-phase flow formation in reservoir fractures and natural gas transport production.
Keywords
