The Damage Appraisal on Elemental Sulfur Deposition in High Sulfur Content Gas Reservoirs

Abstract

Abstract Research on the elemental sulfur deposition belongs to one of the most important tasks in the development of high sulfur content gas reservoirs. In order to evaluate the formation damage from elemental sulfur deposition in the developing process of the sour gas reservoir accurately, experimental procedures are devised to establish measurement method for determining elemental sulfur deposition by purchasing corresponding experimental accessories. The quantitative research on the elemental sulfur deposition is carried out for the first time at home and abroad. Natural carbonate cores and over-saturated natural sour gas are adopted to observe sulfur precipitation and plugging in the sulfur precipitation damage experiments, which is conducted under the condition of pressure and temperature close to actual reservoir as much as possible. Results illustrate that the sulfur deposition in core has little effect on the porosity with pressure decreased, but great impacts on the permeability. The damage factor of permeability increases with rising initial pressure, and temperature has rarely influence on the sulfur deposition with the same initial pressure. Furthermore, the declining permeability of core results in increasing the damage to the permeability, which means sulfur deposition will cause more harm in low permeability formation. Therefore, it is essential to lay full emphasis on the sulfur deposition during the development of sour gas reservoirs. The reasonable and efficient development strategy can be achieved by alleviating the elemental sulfur deposition as far as possible. With the expanding energy contradiction between the supply and demand in the world, the development of high sulfur content gas reservoirs has caught more and more attention in public. However, the dissolution and deposition of elemental sulfur will take place during the developing process of sour gas reservoirs, compared with sweet gas reservoirs. The elemental sulfur solubility in sour gas decreases with the descent of formation pressure, the elemental sulfur will precipitate once the sulfur content exceeds its solubility. The precipitated sulfur will block the formation pore and reduce its permeability, which leads to lower the capacity of gas well seriously and even brings great detriment to the normal production and management of gas well. So far elemental sulfur deposition researches are mainly concentrated on oil reservoirs, papers about sulfur deposition experiment in sour gas reservoirs has not been published yet. Consequently, experimental procedures are devised to establish measurement method for determining elemental sulfur deposition by purchasing corresponding experimental accessories. Experiment of elemental sulfur precipitation in core is carried out for the first time at home and abroad, which lays the foundation for the further research on the safe and reasonable development of high sulfur content gas reservoir.