In the past decade, Hydrogen Sulfide gas has begun to appear in many Barnett Shale gas wells. As more wells are drilled and hydraulically fractured, larger populations of bacteria are introduced to the formation resulting in the current concentrations of H2S that are observed today. In addition to a lack of biocide treatments, wells are often hit by fracs from other producers in the area. As the fractures in the rock converge, new bacteria are introduced that were at first only present in a neighboring well. This idea of fracture convergence prevents treating the problem at the source, as operators cannot control well contamination caused by other companies. The rapid rate at which bacteria are growing and spreading demonstrates a clear problem. To prevent H2S concentrations from further increasing, it is critical that a sustainable field treatment program is developed and implemented.
The completed study involved an analysis of 96 wells operating under the biocide treatment method, continuous wet-gas injection method, and continuous dry-gas injection method. The study took into account gas flow rate, H2S concentration, produced water rate, and chemical usage rates. The results yielded a final $/MMCF value for each well under its respective treatment method.
The results of the study showed first that specific treatment options apply to specific circumstances. For example, the iron sponge media proved to be the most effective long term mitigation option while the scavenger chemical flow loop design provided the adequate retention time required for lower concentrations of H2S. Furthermore, there was no clear evidence that disproved the effectiveness of conventional biocide treatments. According to test results conducted before and after separation, dry gas chemical treatment proved to be more efficient than wet gas treatment.
Because H2S is not native to the Barnett Shale, many operators are only recently discovering problem wells. This report provides in detail, the pros and cons of a variety of different treatment options accompanied with field-study results. Other operators can use this information to safely develop and improve their H2S treatment programs.