Down Hole Sulphur Removal and Recovery
Authors: Maktouf Soufiene , Lallemand Francois , Weiss Claire , Petrinec Bryan , Seeger David 
Published: March 2015

Total and Crysta Tech are developing a regenerable solvent based process to prevent the formation of sulphur deposition during production in natural gas well bores or even in the surface circuits and facilities. While producing gas from certain formations, solid sulphur has been observed to deposit on the well tubing which causes gas production to diminish and ultimately stop. Such scenarios can result in production time losses ranging from one day for batch treatment to three days for coiled tubing cleaning. In cases of severe plugging, one to two weeks could be required for a work-over. Deposited sulphur is corrosive with condensed aqueous brine phase and could have devastating effects. In addition, if not removed from the process gas stream, the elemental sulphur can also interact with the chemicals that are employed in the process treatment pants (such as amine used for gas sweetening, or Triethylene glycol (TEG) used for gas dehydration, etc.) Most of existing technologies require producers to either shut-in gas production while injecting disposable solvents to clear blocked well bores, or inject non-regenerable solvents on a continuous basis.

Down hole Sulphur Removal (DSR) is a regenerable process where solvent is continuously injected in the well to prevent the formation of solid sulphur deposits. The solvent dissolves the sulphur down hole and the sulphur rich solvent is separated from the gas in surface equipment. The separated sulphur rich solvent is regenerated and elemental sulphur is recovered by crystallization and filtration. The regenerated solvent is pumped back down into the well to dissolve additional sulphur and then can be re-utilised in subsequent cycles of the process. Unlike existing once-through technologies, DSR is designed for centralized treatment of a gas field and high sulphur throughput.

For large gas producing fields, the required amounts of sulphur solvent may be large enough in volume to be economically significant and environmentally impactful. For these reasons, it is of great importance to ensure that an efficient and reliable solvent regeneration process is always available and running such that regenerated solvent will be re-circulated continuously into the well with reduced operating expenditures.

Various solvents have been evaluated for use as the sulphur solvent for the DSR process. Solvent testing has been primarily conducted at the Gas Technology Institute in Chicago, Illinois. A dedicated screening program has been specifically designed to select the most cost effective physical solvent for this application. Sulphur solvents may be classified as either physical (such as hydrocarbons) or chemical (such as amine based formulations), whereby a chemical reaction occurs between the sulphur and the solvent. The solvents have been tested for various parameters necessary for use in the DSR process such as: sulphur solubility at well bottom and top-side conditions, solvent vapour loss, solvent separation and degradation, temperature and pressure effects, sulphur quality and reaction with H2S. Pilot scale crystallization and filtration studies have also been performed.

Total is currently pursuing a pilot scale demonstration of the DSR technology. This single well application will prove the process over long term operation and will be used to develop commercial scale-up and economic data. The preliminary design and process package of the pilot unit are underway. The final detailed design, installation and start-up will be scheduled and completed soon after a well site candidate is identified and confirmed for the pilot demonstration and once all the site specific data are integrated into the final design.

A regenerable DSR process is expected to be the only cost effective method to produce natural gas from wells that would experience solid sulphur deposition of approximately greater than 1.5 tons per day.