INFLUENCE OF HYDRAULIC FRACTURING ON LEAKY ABANDONED WELLS

Many unconventional plays occur in mature sedimentary basins – where conventional development has already occurred on a large scale. Abandoned wells in proximity to modern hydraulic fracturing operations could be influenced by increased fluid pressures and corresponding generation of fractures. Hydraulically generated fractures could directly connect to the abandoned well or propagate into natural fractures connected with an abandoned well. If contaminants migrate to a pathway hydraulically connected to an abandoned well, upward leakage may occur.

This study applies numerical modeling to investigate potential effects of hydraulic fracturing on upward flow through different types of leaky abandoned wells. Several factors were considered, such as proximity to hydraulic fracturing, flowback and production, and leaky-well abandonment scenarios. The numerical model is based on the Eagle Ford Shale play in south Texas; modeled scenarios used industry data specific to the play and historical records for nearby abandoned wells.

Numerical simulations revealed that upward flow through leaky wells occurs under certain spatial and hydraulic conditions. Flow was constrained to the stimulated reservoir volume (SRV) of the target shale. Within the SRV, magnitudes of upward flow in leaky abandoned wells increased with proximity to hydraulic fracturing, but decreased with additions of flowback and production at the horizontal well. Rates of flux are small, and ranged from approximately 0.086 to 0.006 m³ d^-1 for hydraulic fracturing scenarios. Small upward fluxes and the potential for natural leakage, unrelated to modern hydraulic fracturing operations, complicate chemical detection and definitive identification of leakage sources. The results of this study underscore the importance of historical oil and gas activities in a sedimentary basin when evaluating potential flow pathways.