Abstract

Hydraulic fracturing is a proven technology that is implemented through injecting highly pressurized water into tight formations. The excessive amount of water use during the process poses serious environmental problems. To address this issue, we propose and study the feasibility of a new fracturing technology utilizing air injection as an alternative fracturing fluid for tight oil and gas reservoirs. Samples from Eagle Ford and Green River formations are selected to study due to their compositional differences; carbonate rich and kerogen rich, respectively. Samples were first characterized with X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA) to determine their mineralogical and organic content. A special core holder was designed to visualize the fracture formation during experiments with X-Ray Computed Tomography (CT). CT scan results were analyzed for fracture formation and propagation during air injection. Experimental results show that the clay content and type during air injection play an important role on fracture formation. It has been found that the alterations in clays at elevated temperatures contribute to keep the formed fracture apertures open due to the cementing behavior of clays at high temperatures. Kerogen was found to also contribute to the formation of microfractures due to its thermal decomposition and the thermal expansion of formed gases at elevated temperatures. Furthermore, the decomposition of inorganic content, especially the carbonate content of shale samples, enhances the fracture formation. Hence, all clay rich, carbonate rich, and kerogen rich shale samples show a trend that favors effective fracturing with air. CT scan results also validate the formation and propagation of these effective fractures, and CT scans taken after one day of the core flooding experiments prove that the fractures remain open even without proppant addition. Because air is an abundant, cheap, and easy to handle injection fluid, it is an attractive alternative to water for fracturing. Our experimental results support the use of air as an alternative fracturing fluid in a promising, feasible, and low cost method for fracturing tight oil and gas reservoirs.

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