Researchers from Los Alamos National Laboratory developed a consistent formulation of fracture mechanics in hydraulic fracturing technology
A team of researchers from Department of Energy’s Los Alamos National Laboratory developed a computational model that can predict previously hidden fracture mechanics to potentially boost efficiencies and profits in natural gas production. Moreover, the model also accurately accounts for the known amounts of gas released during the process. Zdeněk P. Bažant, McCormick Institute Professor and Walter P. Murphy Professor of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering at Northwestern University’s McCormick School of Engineering stated that the model is more realistic than current models and software used in the industry and can help the industry to increase efficiency, decrease cost, and become more profitable.
The team took into account the closure of preexisting fractures that are caused by tectonic events in the distant past and the water seepage forces to develop a new mathematical and computational model that shows how branches form off vertical cracks during the fracking process for more natural gas release. According to classic fracture mechanics research the cracks in fracking that run vertically from the horizontal bore should have no branches. However, these cracks alone do not contribute to the quantity of gas released during the process as the gas production rate is around 10,000 times higher than calculated from the permeability measured on extracted shale cores in the laboratory. It was previously hypothesized the hydraulic cracks connect with pre-existing cracks in the shale to offer more permeability.
However, in the current research, the team found that these tectonically produced cracks that are around 100 million years old are possibility closed by the viscous flow of shale under stress. The team hypothesized that the shale layer has weak layers of micro-cracks along the now-closed cracks and these layers cause branches to form off the main crack. The team also took into account the seepage forces during diffusion of water into porous shale that was ignored by previous studies. The team developed a simulation of the process with the help of this new idea of a weak layers and calculated all the seepage forces and found that the results matched those found in reality. The research was published in the Proceedings of the National Academy of Sciences on January 11, 2019 in a paper titled ‘Branching of Hydraulic Cracks in Gas or Oil Shale with Closed Natural Fractures: How to Master Permeability.’