Case History: MUD Water Well Producing Dangeous Levels of Natural Gas
I2M personnel were engaged to assess the possible causes of the decline in production of a high-capacity water well of a municipal utility district in the northern suburbs of Houston, Texas. Via an in-well video survey, an advanced stage of iron bacteria had grown up and down the slotted intakes of the well casing as incrustations along irregular sections of the casing. Also, the video showed a gaseous influx into the well originated at or near the top of the well screen from 704 to 715 feet below grade.
The produced water also contained iron-bacteria slough masses and a faint odor of hydrogen sulfide. Groundwater and air samples were taken and analyzed for hydrocarbons. Both air samples and groundwater samples contained significant volumes and concentrations of C1 through C6 (methane through the hexanes). Air samples near the upper vents of Storage Tanks exceeded the Lower Explosive Limit which represented serious explosive concerns and only required a source of spark from the electrical system within the roofs of the Tanks to ignite. I2M personnel called for a hazard alert and the MUD personnel shutdown production of the well system and vented all tanks, and an inter-connect was arranged with nearby MUDs to supply water to residents within the MUD. The well was returned to service after the safety hazard associated with the storage tanks had been eliminated by the installation of the appropriate power vents and other explosion-proof electrical system precautions.
I2M personnel made recommendations to the MUD for improved operation and maintenance procedures and for regular sampling of groundwater and air samples to monitor ongoing conditions. I2M personnel also recommended the MUD consider hydrocarbon removal after the well. A nearby MUD was located that had installed such systems, which provided impetus and justification for the MUD to install such a natural gas removal system.
Further research on the possible source of the hydrocarbons revealed that a major gas well blow-out occurred in the mid-1940s in the general area of the subject MUD well system. The near-by MUD system having a hydrocarbon recovery system is located within a few thousand feet of the site of the historical blow-out. The general consensus was that the blow-out charged the Evangeline Aquifer with large volumes of gaseous hydrocarbons that are perturbed by the high-capacity pumping of the MUD wells in the general area, impacting some MUD well systems and not others.