(546q) Enhancing Fracture Aperture and Evolution of New Fractures in Utica Shale By Subcritical Water Treatment

In the U.S. unconventional shale is one of the major resources for natural gas production. The demand for natural gas is growing rapidly. So far hydraulic fracturing is the most productive way for shale gas extraction. Hydrocarbon recovery from shale reservoirs is still very low. According to the U.S. Energy Information Administration (EIA) only 10-30 % of the hydrocarbon is recoverable from unconventional shales with the current hydraulic fracturing practice. Low porosity (<5 %) and low permeability (2-50 nD) of shale rock are primarily responsible for the low hydrocarbon recovery.

Shale permeability enhancement is an indispensable to improve the hydrocarbon recovery by fracking. Fracture aperture and fracture branches have a good influence to enhance the shale permeability thus to improve overall hydrocarbon recovery. Within the current scope of hydraulic fracturing more than 90% water is used as fracturing fluid within a temperature range of 55-95°C. Water with a temperature below 100°C and water within a temperature range 100-374°C are very different in physical and chemical properties. Thermodynamic properties (e.g. density, ionic product and dielectric constant) of subcritical water (100-374°C) changes significantly which makes it more reactive. And it is likely to react with the shale structure.

In this study, Utica shale samples were treated in subcritical water to observe the changes in fracture aperture and creation of new fracture or fracture branches. Fracture aperture of the treated shale was changed significantly. Along with the changes in fracture aperture, creation of new fractures and fracture branches were also observed. Treatment was run for three different temperatures 200°C, 250°C, and 300°C. Digital microscope and micro computerized tomography (CT-scan) images were used to measure the fracture aperture. Micro CT-scan images were analyzed with Avizo 3D image analysis software. Effective permeability was calculated for both raw and treated shale sample with the help of Avizo 9.3.