Prediction Of Sulfur Deposition In High Sulfur - Bearing Fractured Gas Reservoirs And Its Effect On Capacity

In the development process of high sulfur fractured gas reservoir, a reduction in pressure and temperature leads to elemental sulfur precipitation and deposition from the gas, resulting in changes in the physical properties of gas reservoir parameters, such as porosity, permeability and other parameters, changes in these physical parameters affect the gas flow in turn, and ultimately affect the recovery efficiency of the gas reservoir.Currently, few study focus on prediction of high sulfur fractured gas reservoir sulfur deposition, and sulfur deposition prediction model is not perfect, unreasonable assumptions of most prediction models do not reflect the change of actual formation condition. In order to accurately predict the effect of sulfur deposition of high sulfur fractured gas reservoir on formation and gas productivity, based on the research on sulfur deposition mechanism, a modified sulfur saturation prediction model was established, this modified model based on non-Darcy flow took the effect of stress sensitivity and the variation in gas properties and sulfur solubility changing with pressure into consideration. For high sulfur fractured gas reservoirs, considering the dual media seepage law, a sulfur deposition prediction model was established based on the cubic law, and analyzed the impact of fracture parameters and production parameters on sulfur deposition. For high formation temperature, elemental sulfur precipitate in liquid form in the formation, a gas-liquid sulfur flow mathematical model was established, and the effect of liquid sulfur on gas well productivity was studied by numerical simulation. By establishment of the above model and example analysis, the prediction model of sulfur deposition was perfected, and obtained the following conclusions:(1) Comparison of different models shows that Robert’s model underestimates the rate of sulfur deposition. The modified model, considering the non-Darcy flow, stress sensitivity and parameters changing with the drop of pressure, is more accurate and practical in predicting sulfur deposition.(2) Reservoir compaction is a common phenomenon which should be considered in sulfur deposition prediction, as it leads to a faster rate of deposited sulfur and relatively shorter time of sulfur plugging.(3) The effect of variation in the gas properties on sulfur deposition can be directly attributed to the influence of pressure change; thus, parameters in the model should be calculated according to the corresponding pressures. When the reservoir formation was worse, sulfur plugging is more likely to happen, and the time of occurrence is sooner.(4) The damaged radial distance caused by sulfur deposition will increase with increasing gas production rate and production time. The formula of gas well production which under the condition of sulfur deposition was established, as sulfur saturation increases the gas production rate will dramatically decrease.(5) As to the high sulfur fractured gas reservoir, the larger fracture aperture or higher fracture height or smaller contact area of fracture surface will lead to a slower deposition of sulfur. (6) In case of liquid sulfur, when sulfur precipitate as liquid phase, the time of stable production will be shorted, and the final total production will decline. The worse the liquid sulfur flow ability, the greater the impact on well productivity.