Dissolution behavior of elemental sulfur under CO2 injection conditions and its application in sulfur deposition removal in high-sulfur gas reservoirs

To address sulfur deposition in high-sulfur gas reservoirs, this study investigates the dissolution behavior of elemental sulfur in CH₄–H₂S–CO₂ systems under CO₂ injection and evaluates its desulfurization effectiveness. A CS₂ absorption–mass spectrometry method was used to quantify sulfur solubility under different temperatures, pressures, and CO₂ concentrations. Results show that solubility increases significantly with higher temperature, pressure, and CO₂ content. Four predictive models were assessed, and a high-accuracy empirical model (R² > 0.98) was developed for varying CO₂ concentrations. Coreflooding and huff-n-puff experiments demonstrated that CO₂ injection effectively reduces sulfur saturation and enhances permeability, with liquid sulfur being more easily mobilized than solid sulfur. At 130 °C, 1 HCPV (Hydrocarbon Pore Volume) injection reduced sulfur saturation by up to 1.87 % and increased permeability by 16.8 % in high-quality cores. To enhance CO₂ dissolution, high-pressure injection is recommended, with a field injection rate of 100,000–300,000  m³/day. Huff-n-puff outperformed continuous flooding not only because sufficient soaking time for sulfur dissolution, but also because the shut-in period promotes uniform gas distribution, avoiding preferential flow through dominant channels. Optimal parameters were found by evenly splitting 0.3 HCPV over three cycles for liquid sulfur and 0.4 HCPV over four cycles for solid sulfur. These findings offer theoretical and practical guidance for CO₂-based sulfur mitigation in sour gas reservoirs.