MR41C-2646
A Geochemical Framework for Evaluating Shale-Hydraulic Fracture Fluid Interactions

Thursday, 17 December 2015
Poster Hall (Moscone South)
Anna L Harrison1, Adam D Jew2, Megan Kathleen Dustin2, Claresta M Joe-Wong3, Dana Thomas4, Katharine Maher2, Gordon E Brown2 and John Bargar5, (1)Stanford University, Geological Sciences, Stanford, CA, United States, (2)Stanford University, Stanford, CA, United States, (3)Stanford University, Department of Geological Sciences, Stanford, CA, United States, (4)Stanford Earth Sciences, Stanford, CA, United States, (5)Stanford University, Los Altos Hills, CA, United States
Abstract:
The development of shale oil and gas reservoirs has increased dramatically due to the application of hydraulic fracturing techniques. Fracture fluids contain dissolved oxygen and numerous chemical additives [1] that are out of equilibrium with the reducing conditions in shale reservoirs and could react extensively with shale minerals and alter porosity. Yet, the complex dissolution-precipitation reactions in shales along with the poorly constrained characteristics of many fracture fluid additives hinder predictive modeling based on established reaction kinetics and thermodynamic constants [2]. Here, we are developing a reaction framework to better predict reaction progress and porosity evolution upon exposure of shales to hydraulic fracturing fluids. To this end, the reactive transport model CrunchFlow [3] was applied to the results of batch reactor experiments containing shales of different mineralogical and organic compositions exposed to simulated fracturing fluid. Despite relatively good agreement between modeled and experimental data for pH and aqueous Ca concentrations, which are strongly governed by carbonate dissolution, the model is presently unable to reproduce observed trends in aqueous Fe concentration. This is largely attributable to the dearth of thermodynamic data for certain fracture fluid components and the complex interactions between multiple Fe-bearing mineral phases. Experimental results revealed that the presence of organic fracture fluid components strongly influenced the precipitation of Fe-bearing phases, which are speculated to coat fracture fluid polymers that formed in the reactors. The incorporation of these effects in our reactive transport model will permit improved prediction of reservoir permeability evolution and metal release during hydraulic fracturing operations.

[1] Stringfellow et al. (2014) J. Hazard. Mater. [2] Carroll et al. (2013) Environ. Sci. Technol. [3] Steefel and Maher (2009) Rev. Mineral. Geochem.

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