Objective Multi-layer commingled production is a common method for enhancing production efficiency in oil and gas reservoirs with varying physical characteristics. In gas reservoir-type gas storages with highly developed fractures, fluids exhibit complex seepage patterns, leading to unclear mechanisms of commingled production. Most existing research on multi-layer commingled production in gas reservoirs has been conducted from a macro perspective. Therefore, conducting flow simulations at the pore scale to investigate the development mechanisms and influencing factors of multi-layer commingled production is of significant practical importance for designing gas storage development plans.
Methods Based on images obtained from CT scanning and microscopic pore-throat structures, a two-dimensional geometric model of fracture-pore double-layer commingled production was developed. The finite element method (FEM) was then employed to solve the two-phase flow numerical model based on the Navier-Stokes equations (N-S equations), allowing for the exploration of dynamic fluid migration patterns in both gas and water phases during multi-layer commingled production. The effects of double-layer commingled production in gas reservoir-type storages with varying interlayer heterogeneity were evaluated at the pore scale.
Results When interlayer heterogeneity is weak, gas-water interface migration is relatively uniform, and pressure distribution remains stable, indicating enhanced balance in reservoir development and improved capacity in stabilized production. Conversely, when interlayer heterogeneity is strong, fluids tend to flow along the layer with higher permeability, increasing the likelihood of crossflow and negatively impacting development effectiveness. During double-layer commingled production, the output difference between the layers gradually narrows and stabilizes, although it remains influenced by heterogeneity. In cases of weak heterogeneity, the output of the fracture-pore layer and the pore layer tends to balance in the later stage of production, resulting in more uniform fluid flow. The difference in production pressure affects gas well output; specifically, as the pressure gradient increases, the proportion of gas output from the pore layer with lower permeability rises, leading to a trend toward overall balance. Therefore, it is recommended to control the rate of reservoir pressure reduction during the initial stage of production and to appropriately pressurize or supplement reservoir energy in the later stage. These measures can enhance the utilization of the low-permeability pore layer while reasonably managing the pressure gradient to avoid stress sensitivity that may negatively affect production capacity.
Conclusion The research results highlight the significance of rational output allocation in development plans to fully leverage the advantages of different layers with substantial variations in physical properties within actual gas reservoir-type storages. Additionally, strong interlayer heterogeneity resulting from the development of large-scale fractures is identified as a critical factor influencing the effectiveness of commingled production, necessitating the accurate identification of these heterogeneities and the formulation of reasonable plans in engineering design. In multi-layer commingled production, adjusting production pressure differences can optimize the interlayer development balance during the production process, thereby improving the overall recovery ratio.
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