Simulation Study of Well Deliverability Reduction Due to Sulphur Deposition in Naturally Fractured Carbonate Reservoir

Abstract

The sour gas reservoir of interest is the fractured oolitic dolomite formation, containing dry gas with high H2S and CO2. Elemental sulphur (S8) dissolved in sour gas may precipitate in both the near-wellbore reservoir region, tubing and surface facilities, along with the pressure and temperature decreasing in the flow process. The precipitate may form gas flow restrictions.The gas reservoir has been producing for 4 years, sulphur deposition issue in the tubing or reservoir has been observed by production performance so far. Frequent change of separator filters occurred due to filter blockage, and lab test confirmed elemental sulphur solids which were collected from the filter cartridge operating with lower pressure and temperature conditions than in the tubing. Although the issue hasn’t posted a significant threat to production but increased the filter changing frequency, which expose the operations team to H2S risks and higher operational cost.Elemental sulphur deposition in pipelines and surface facilities can be visually monitored, however, presently there is no mature algorithm to simulate the deposition in reservoir. Very few studies about the deposition impact focused on the methods that can be applied to reservoir simulation. Roberts et al. [1] has published a relatively robust method, which productivity index change depends on independent variables, e.g. simulation time, sulphur solubility, porosity etc. Reservoir simulation SME added a Python control script to the simulator to facilitate productivity index reduction along with reservoir depletion. Applying the empirical methods to reservoir simulator helps analyse the significance of solid deposition impact, which can improve production forecast at various deposition rates. The sulphur saturation level in sour gas in the reservoir condition was estimated based on the monitoring of deposition volume in surface facilities.The study has added more insight of S8 precipitation and deposition, and supported develop mitigation plans, production optimization, and future optimization for the surface process technology, which can be utilized to mitigate S8 deposition in future development of other sour gas fields.KeywordsSour gasHydrogen sulphide (H2S)Elemental sulphur (S8) DepositionSulphur SolubilitySulphur saturation levelReservoir simulationWell production optimizationMitigation methods