REVERSE ENGINEERING GAS MIGRATION CONDITIONS: FORENSIC INSIGHTS AND LESSONS LEARNED FROM RESIDENTIAL WELL INVESTIGATIONS

This presentation shares instructive results from methane gas migration analyses. It demonstrates how exploratory methodologies such as manipulating pressure conditions in a residential potable well through pumping exercises were used to recreate problematic gas migration. Coupled with forensic geochemical analyses, these techniques were successfully able to identify the methane source, migration pathway, and driving mechanisms.

While a primary goal of stray-gas investigations is to determine the source of the gas, the nature and extent of impacts can be more difficult and perhaps more important to characterize. Analytical methods such as isotopic analysis may illuminate the source of the gas; however, without a site-specific understanding of the aquifer and geologic context, effectively mitigating the hazards posed by methane migration becomes problematic. Therefore, investigating parties should undertake a more comprehensive characterization whenever possible.

Case Synopsis:

A northern Pennsylvania property owner proximate to natural gas production placed an inquiry regarding unfamiliar spurting in the water spigots during recent use. As part of a stray-gas investigation, a sequence of pumping exercises was conducted while conditions in the well were monitored using an array of equipment. The exercises used in this case enabled characterization of the precise conditions under which the gas influx was occurring. A down-well camera visually confirmed that methane air bubbles were being released from one specific fracture; however, the degassing only occurred when the confining pressure was reduced to a certain critical point. Isotopic analysis determined the source of the methane, while the information gathered from these exercises provided invaluable information for effective and sustainable mitigation of the hazard.