Study On Sulfur Deposition Model And Capacity Prediction Of Horizontal Wells In High-sulfur Gas Reservoirs

In the development of high sulfur gas reservoir, a reduction in pressure and temperature leads to elemental sulfur precipitation and liquid deposition from the gas at relative high temperature, resulting in changes in the physical properties of gas reservoir parameters, such as porosity and permeability, and ultimately affecting the productivity of the gas reservoir.Currently, few study focus on correlational research on sulfur deposition of horizontal wells in high sulfur gas reservoir, and research on the productivity prediction in consideration of liquid sulfur deposition and stress sensitivity is rare. So it is likely that there is a calculation bias in the prediction of horizontal well productivity in high sulfur gas reservoir. Based on the study of mechanism of sulfur solubility and physical parameters and the improvement of solubility model, in combination of percolation mechanism experiments, a modified sulfur saturation prediction model was established, this modified model accorded with horizontal seepage mechanism and took the effect of stress sensitivity and the variation in gas properties and sulfur solubility changing with pressure into consideration, and influence factors are analyzed. And then, for the situation of sulfur in liquid precipitation at relative high temperature in high sulfur gas reservoir, according to the experimental data and the sulfur deposition model, a gas and liquid sulfur mathematical model are established, and the influence of liquid sulfur deposition and stress sensitivity on gas well productivity is studied through the case. Following conclusions are deduced:(1) Rock stress sensitivity experiments are conducted on the core from a specific high sour gas well. The experimental results show that the stress sensitivity of matrix core is medium, and the stress sensitivity of fracture is strong. The damage degree of crack cores is always higher than that of matrix in experimental process.(2) The gas-liquid phase relative permeability curve was measured. High critical flow saturation of liquid sulfur and narrow two phase seepage zone refer that the flow capacity of liquid sulfur is limited. And then the relative permeability curve, considering the effect of stress sensitivity, was measured. With the increase of stress sensitivity, the relative permeability of gas and liquid phase both reduce, and isotonic point moves left and down.(3) Microscopic percolation mechanism experiments was conducted to study the formation and distribution characteristics of sulfur deposition in the process of gas-liquid sulfur seepage. It was founded that elemental sulfur deposition tends to form in the crack under the condition of fracture and matrix, with a result of non-uniform distribution.(4) Sulfur deposition will increase with the increase of production, therefore, it is important to note the reasonable production of horizontal well at the beginning of the exploitation of high sulfur gas reservoir, at the same time it is also a must to pay attention to the reasonable control and adjustion of the gas well production in the process of gas well production. Reservoir rock stress sensitivity has great influence on sulfur deposition, and it was found that strong stress sensitivity will accelerate sulfur deposition when the stress sensitivity is taken into account in the prediction model.(5) Sulfur deposition of planar radial flow stage nearly vertical seepage area of horizontal well is dominating. And attention should be paid to sulfur deposition on both ends of horizontal well in far well part. Compared with vertical Wells, factors affecting sulfur deposition of horizontal well include well length and reservoir heterogeneity. In the same condition of production, the speed of sulfur deposition will slow down with the increase of horizontal section length and reservoir heterogeneity.(6) According to numerical simulation for gas and liquid sulfur percolation at high temperature in high sulfur gas reservoir, liquid sulfur deposition and the stress sensitivity will cause the decrease of gas well stable production time and decline of total production, and the influence of liquid sulfur deposition is greater than other factors on gas well productivity.