Risk Assessment of Liquid Waste Disposal by Deep Well Injection

Hydrocarbon development is experiencing significant growth due to development of unconventional hydrocarbon resources. Hydraulic fracturing of shale gas formations is the focus of much of this development. Recent analyses recognize that the greatest threat posed by these activities is wastewater disposal. The most common disposal practice in Texas is by deep-well injection. Successful disposal is achieved when the wastewater is safely injected in the targeted horizon without loss of waste into non-targeted horizons and that the injected fluids remain in the targeted horizon after injection. Failure in disposal can occur when liquid wastes escape the targeted deep horizon and migrate into freshwater aquifers or to the surface. Threats to successful disposal of the liquid wastes are encountered when the targeted disposal horizons are former oil and gas formations into which previous exploration and production wells had been drilled, but not properly abandoned. This risk of inadvertent release of hydraulic fracturing wastewater can be mitigated by: (i) avoiding injecting wastewater into depleted oil and gas formations, (ii) expanding the area of inspection to identify improperly abandoned wells, and (iii) developing a comprehensive database of all cases of “breakout” to allow comprehensive assessment of the risk posed by inadvertent wastewater releases.