Production and recovery chemistry for low-level hydrogen sulfide containing natural gas

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PRODUCTION AND RECOVERY CHEMISTRY FOR LOW-LEVEL H2S CONTAINING NATURAL GAS****Canada has significant shale gas reserves which span 7 provinces. At least two Canadian shale plays are known to be sour and can contain up to 500 ppm H2S. Before transportation to market the H2S must be reduced to less than 4 ppm for toxicity/environmental reasons and CO2 is reduced to less than 2% to maintain caloric content. Production fluids with less than 2% H2S are not suitable for conventional oxidation of H2S to recover commercial elemental sulfur; therefore, alternative chemical processes are required by Canadian producers to achieve the 4 ppm target. The overall research is focused on addressing this need by understanding these low-level H2S sources and exploring alternative oxidation processes. Specific research goals are aimed at (i) expanding kinetic models for souring of hot shale reservoirs, (ii) evaluating high-pressure catalysis in dense phase CO2, and (iii) exploring industrial sulfur chemistry in a eutectic mixture of biphenyl and diphenyl ether.****(i) Kinetic modelling for souring of hot shale reservoirs****We have previously demonstrated that non-microbial reservoir souring can occur through the degradation of fracture fluid additives (e.g., sodium dodecylsulfate). Our more recent work has focused on the rapid oxidation of native sulfides (H2S or metal sulfides) to produce elemental sulfur in the reservoir over a finite time. This elemental sulfur can then oxidize other hydrocarbons or hydraulic fluid additives to thermally generate H2S. Studies will continue in this area by focussing on gel fracture additives (versus slick water additives). This research will help producers identify when H2S will appear in the fluids and how much can be expected over the lifetime of a well.****(ii) High-pressure catalysis in dense phase CO2****Managing sources of low-level H2S production is difficult, because (a) low H2S production cannot support a flame in the conventional Claus thermal reactor and (b) the alternative low-level options rarely produce commercial quality sulfur. The catalytic direct oxidation of H2S at pressure can be completed without costly recompression of pure CO2 and provide two value-added products; namely CO2 and S8. High-pressure heterogeneous catalysis research is being applied to define the operating conditions for such a process.****(iii) Sulfur chemistry in a eutectic mixture of biphenyl and diphenyl ether (Dowtherm® A)***Hydrocarbon solvents such as PEG are used in some sulfur recovery processes; however, higher temperatures cannot be used due to reaction with elemental sulfur. For an alternative solvent, we are exploring carrying out common industrial sulfur chemistries within Dowtherm® A. ***Progress in all three of these research areas help with the safe and sustainable development of emerging low-carbon energy sources. ********