PRODUCTIVITY LOSS IN GAS WELLS DUE TO SALT DEPOSITION

Production of gas can result in drying of the near wellbore region due to gas expansion which causes evaporation and hence salt deposition. The deposition of salt usually leads to a reduction in porosity and permeability of the rock in the near wellbore which then leads to reduction in well productivity. The main objective of this study is to understand the role of capillary effects on the salt deposition process and well productivity reduction. We develop and solve the dimensionless conservation equations for solid salt saturation using numerical methods under radial flow conditions. The results of the calculations show that when the capillary effects are strong, the salt accumulates near the wellbore which leads to plugging and hence higher skin values. The salt saturation continues to evolve until a limiting value, in the rock pores, is reached. Higher values of the limiting saturation leads to a greater reduction in permeability and hence results in a larger skin value for the gas well. The flow efficiency of a gas well, calculated as a dimensionless ratio of the flow with and without skin, decreases continually with time eventually approaching a constant value. In a simulation for dimensional case we find that the largest increase in skin factor and corresponding decrease in flow efficiency occurs in approximately the first 50 days after which the changes are slower. Using the model developed in this study the decline of gas well productivity due salt deposition can be predicted and hence accurate timing of the well operations such as water wash can be made. Also, the modeling study can be used to select remediation strategies such as wettability alteration to reduce capillarity or application of inhibitors which can reduce the limiting salt saturation by preventing growth salt crystals within the reservoir rock.