Experimental Study on the Synergistic Effect of «Dispersion-Chelation-Dissolution» on the Removal of Trithiane Blockages in Gas Wells

Natural gas has become an important replacement resource for conventional oil and gas resources. However, the generation of trithiane blockages during gas well development can affect the development efficiency and wellbore safety of the gas well. Unfortunately, the current research on the formation mechanism of blockages in wellbore and their removal processes is not yet complete, and cannot provide theoretical support for the removal of blockages in deep-water gas wells. In this study, based on the validation of the adaptability of the experimental system and methods, the composition of wellbore blockages during gas well development was analyzed. Then, the mechanism of dispersion chelation dissolution synergistic unblocking was explored, and the influence of factors such as wellbore temperature was studied. Research has found that blockages in the wellbore are mainly composed of calcium carbonate (accounting for up to 61.3%), and contain a certain amount of highly corrosive iron sulfide and calcium sulfate. Moreover, the dissolution rate of trithiane wellbore blockages by the unblocking system will significantly increase with the increase of temperature. However, when the wellbore temperature exceeds 140°C, the promotion effect of the increase in wellbore temperature on the accelerated dissolution rate of blockages is significantly weakened. At the same time, the dissolution rate of wellbore blockages will increase with the increase of chelating agent concentration within the low chelating agent concentration range. However, when the concentration of chelating agent is higher than 5.0 wt%, the dissolution rate of wellbore blockage will slowly decrease with the increase of chelating agent concentration. Finally, on-site application found that the wellhead pressure and gas production both returned to the level before the wellbore blockage after the removal of the trithiane blockage in the wellbore, and there were no repeated wellbore blockages in the following year.