Sensitivity analysis and optimization of operational parameters during CO2 huff and puff in the shale oil reservoir: A case study

Abstract

To investigate the comprehensive impact of operational parameters on the performance of CO₂ huff and puff (CO₂-HNP) in shale oil reservoirs, the workflows of parameter sensitivity analysis and optimization were proposed. Firstly, three objective functions reflecting the different aspects of CO₂-HNP's performance were proposed and simulation schemes were designed using Latin hypercube sampling method. Subsequently, sensitivity analysis was conducted using Sobol method for each objective function. Finally, the operational parameters were optimized for each objective function using the particle swarm optimization algorithm. Moreover, a field case of CO₂-HNP was presented. The results demonstrate that: 1) The CO₂-HNP timing and CO₂ injection amount have the greatest influence on the oil recovery degree. The CO₂ injection amount has the greatest influence on the CO₂ storage ratio. Moreover, the CO₂-HNP timing and the soaking time have significant influence on the composite indicator of the oil recovery degree and CO₂ storage ratio. There exist certain interactions among these operational parameters. 2) Early CO₂-HNP timing, large CO₂ injection amount, long soaking time, and high injection rate are conducive to enhancing the oil recovery degree. While late CO₂-HNP timing, small CO₂ injection amount, long soaking time, and medium injection rate are conducive to increasing the CO₂ storage ratio. 3) Early CO₂-HNP timing, large CO₂ injection amount, long soaking time, and medium CO₂ injection rate are conducive to achieving an optimal equilibrium between the oil recovery and CO₂ storage ratio. 4) Compared with the field data, the cumulative oil production is increased by 1520t under the global optimal parameter combination, showing a significantly enhanced development effect.