Kerogen-Hydraulic Fracture Fluid Interactions: Reactivity and Contaminant Release

Abstract:

The use of hydraulic fracturing of tight shales to produce oil and natural gas has grown significantly in recent years, yet it remains relatively inefficient, recovering only an estimated 5% and 25% of the oil and gas present, respectively. The need to improve efficiency and diminish environmental impact has prompted research into fundamental geochemical reactions occurring in shales. In particular, reactions between kerogen and fracture fluid components are poorly understood. Kerogen is the precursor of these hydrocarbons and contains metals in addition to organic material; it is also electron rich and therefore susceptible to oxidation and release of a variety of elements. Although some mineral phases in the shales are expected to undergo dissolution-precipitation reactions, kerogen is generally considered to be relatively unreactive [1]. Here we have investigated reactions between isolated kerogen and a hydraulic fracturing fluid typical of that used in the Marcellus shale. These experiments show that kerogen, as well as redox-sensitive minerals within shales, react with fracture fluid. In particular, kerogen exhibited more extensive release of certain metals (e.g. Al, Ba, Cu, among others) than was observed for bulk shale under the same experimental conditions. This evidence suggests that kerogen may be far more reactive to fracture fluids than previously thought. In particular, these results suggest that kerogen may significantly impact the compositions of produced waters, which have previously been attributed solely to mineral reactions. They also emphasize the need for further characterization of kerogen and its reactions with complex hydraulic fracturing fluids.

[1] Vandenbroucke and Largeau (2007) Org. Geochem.