Case Study: Produced Water and New Catalyst Offer Low-Cost Route to H2S Treatment

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Investment research firm TSCS reports that 60 to 65% of the highest-quality acreage in the Permian Basin, the most productive US shale basin, has already been drilled.

The firm also estimates that only 3 to 4 years of Tier 1 premium inventory remains at the current drilling rate. This is driving industry-wide strategy shifts as companies move to lower tier and speculative acreage to maintain production.

Although these reserves are accessible, they pose challenges, including lower rock quality, higher temperatures, increased associated gas, and greater water production per barrel, all of which substantially increase production costs.

Hydraulic fracturing in the Permian requires approximately 15 to 20 million gal of water per well. With the region experiencing severe drought conditions and aquifer levels at historic lows, operators face mounting water costs that do not appear in headline production figures.

Some operators report water costs exceeding $5/bbl, a 300% increase from 2019 levels. Recycling infrastructure cannot keep pace with demand, and freshwater sourcing faces increasing regulatory scrutiny.

Despite these challenges, environmental efforts are focused on reducing flaring and the rate of water injection into saltwater disposal wells. While these are reasonable and important environmental goals that should be viewed positively, they add complexity to the already emerging challenges of secondary acreage.

In this context, Merichem Technologies developed a new technology, Ecotreat, and chemistries for gas desulfurization, using produced water as a solvent for gas conditioning. The solvent-based technology involves a modular treatment process that uses a proprietary catalyst designed to safely and sustainably remove hydrogen sulfide (H2S) from sour gas streams using either produced water or an alkaline water as the treating media.

The solvent-based technology underwent a successful month-long field trial in the Permian to demonstrate whether it could achieve sustained removal of H2S without producing solid waste.

The Technological Solution

The solvent-based technology covered in this case study employs a proprietary water-soluble catalyst that forms covalent bonds with H2S, resulting in an irreversible reaction unless further chemicals are added.

Changes in pH or temperature do not release H2S. Each catalyst molecule can react with H2S multiple times, achieving similar efficiency to existing liquid scavengers. The reaction continues until the catalyst is fully spent. Unlike triazine (i.e., a scavenger chemical) derivatives, full consumption of the catalyst does not harm the product or produce amorphous dithiazine. The catalyst bond remains stable under low-grade heat and pH changes.

The catalyst can be regenerated in air under ambient conditions. When exposed to oxygen, it rapidly oxidizes H2S to thiosulfate anions and releases the catalyst from the bond. Thiosulfate anions are highly soluble in water and acidic, so the solution must contain sufficient cations; carbonate salts are particularly effective.

Produced water, such as that from the Permian, where it is generated at multiple times the rate of oil, is a brine rich in salts which contain sodium, calcium, and potassium. Its high salinity, typically above 3.5%, provides strong buffering capacity due to sufficient alkalinity present in the water, making it suitable for this reaction. The cationic strength effectively buffers the thiosulfate ions formed. Small volumes of water can absorb at least 5% of their weight in sulfur and can then be diluted into the main produced water stream, resulting in a minimal increase, often less than 1%, in total sulfur-oxoanion content.