Research On Experiment And Modeling Of Formation Damage Caused By Sulfur Deposition Of Gas Reservoirs With High H₂S Content

Gas reservoirs with high H2S content are an important part of unconventional gas reservoirs, which are widely distributed in Sichuan-Chongqing region in Sichuan basin. During the course of production of gas reservoirs with high H2S content, formation pressure falls continually, which leads to decline of solubility of sulfur particles in gas phase, and sulfur particles will precipitate from gas phase, forming solid sulfur at appropriate temperature, and deposit at pore space and throat, sequentially resulting in formation porosity and permeability reduction and gas deliverability decrease.According to characteristics of complex flow through porous media in gas reservoirs with high H2S content, breaking through classical filtration theory, based on sulfur deposition causing formation damage experiment to build a mathematical model for describing transportation and precipitation of sulfur particles in gas reservoirs with high H2S content, a new gas-liquid-solid coupled mathematical model in gas reservoirs with high H2S content accounting for sulfur deposition has been proposed and production mechanism study was made, which could give directions in theory for allocation of production rate of gas well, forecasting of dynamic index, working out ODP and productivity construction.The main contents of the works are as follows:(1) Combining with experimental and theoretical research, we independently developed sulfur deposition experimental procedure and experimental device, and built the country's only laboratory to assess sulfur deposition. Physical simulation was used to test characteristic parameters of H2S-CO2-H2O-solid sulfur-gas phase coexisting system in the porous medium. Laboratory equipment developed by ourselves was applied, and confirmed that elemental sulfur indeed deposited in the formation. Sulfur deposition are in connection with the temperature, the pressure, gas flow rate, gas composition, the H2S content, the pore structure and other factors.(2) Base on thermodynamics and dynamics, a sulfur deposition prediction model was established to indentify sulfur precipitation and deposition, giving directions in theory to precisely predict and prevent sulfur deposition.(3) The mechanism of sulfur deposition was studied in Puguang gas field, combining with Puguang gas field development plan, gas reservoir engineering, and mechanics of flow through porous media to predict the starting time of sulfur deposition in Puguang gas field.(4) The non-equilibrium phase transition theory was introduced into the research of sulfur deposition in the formation, to describe the different radial distribution of sulfur deposition during different development phases of the development process in the Puguang gas field, and on the basis to further predict the impact of sulfur deposition in the different time on gas wells.(5) The sediment transport model and gas-liquid-solid coupling integrated model in porous media were established in gas reservoirs with high H2S content, and high sulfur gas reservoir simulation software was developed to adapt to the development of sour gas reservoirs. The software was used to design development program and forecast development index, providing an important theoretical basis for the efficient development, for making reasonable working system parameters, for stable gas production, and for gas production to succeed in Puguang gas field.