Influence of Hydraulic Fracturing on Leaky Abandoned Wells

The association between hydrocarbon-rich reservoirs and organic-rich source rocks means unconventional oil and gas plays usually occur in mature sedimentary basins – where large-scale conventional development has already occurred. Abandoned wells in proximity to hydraulic fracturing could be influenced by increased fluid pressures and corresponding newly generated fractures that directly connect to an abandoned well or to existing fractures connected with an abandoned well. If contaminants migrate to a pathway hydraulically connected to an abandoned well, upward leakage may occur. Potential effects of hydraulic fracturing on upward flow through a leaky abandoned well were investigated using numerical modeling. Several factors that affect flow to leaky wells were considered; proximity of a leaky well to hydraulic fracturing, flowback, production, and leaky-well abandonment methods. The numerical model used historical records and available industry data for the Eagle Ford Shale play in south Texas. Numerical simulations indicate upward contaminant migration could occur through leaky converted wells if certain spatial and hydraulic conditions exist. Flow was constrained to the stimulated reservoir volume of the shale. Magnitudes of upward flow through leaky converted wells increased with proximity to hydraulic fracturing, but decreased when flowback and production occurred. Fluxes ranged from approximately 0.086 to 0.006 m³ d⁻¹ for hydraulic fracturing scenarios. Detection of contaminants in shallow aquifers is challenging, and upward fluxes through leaky abandoned wells could be unrelated to hydraulic fracturing. The results also underscore the need to evaluate historical activities.