Enhancing complexity of the created fracture geometry is the primary challenge for hydraulic fracturing treatment design in shale formations because of their stress anisotropy. Therefore, near-wellbore diversion is required to evenly stimulate all perforated clusters while far-field diversion inside the created fracture induces additional branch fracturing by overcoming the stresses holding the natural fractures closed. Solid particles with different shapes and sizes are widely used as diverting agents during fracture treatments. The recommended particles should temporarily bridge inside the fracture to create a low- permeability pack that increases the pressure within the fracture and enables redirection of next-stage fluid to understimulated intervals.
The objective of this study is to experimentally investigate and optimize parameters affecting the selection of solid particles as diversion agents such as material chemistry, particle size, particle shape, particle size distribution, particle loading, carrier fluid type, and carrier fluid viscosity. Three tests were performed in this study: Bridging tests to determine the optimized particle size and loading as function of fracture width (0.04 to 0.2 in.); pack permeability tests to optimize the particle size distribution and shape needed to minimize fracture conductivity and build the needed pressure; and dynamic dissolution tests to determine the time need to completely dissolve the particles as function of temperature, rate, particle size, and produced fluid.
The results of this paper can help in understanding the diversion parameters required to effectively enhance the complexity of the fracturing geometry. For far-field diversion applications (targeting fracture widths of 0.04 to 0.08 in.), larger particles are not required, as the fracture width is small. However, very tight particle pack permeability is needed. For near-wellbore and perforation diversion (targeting fracture widths of 0.2 in. and higher), only larger particles can bridge the wider fractures. Therefore, a wider (in this case tri-modal) particle size distribution is required: coarse particles to bridge the fracture along with a bi-modal distribution of medium and small particles to minimize the particle pack permeability and achieve the diversion. A diverter pack with bi-modal size distribution and higher concentration of small particles reduces particle pack permeability more than a tri-modal size distribution with more medium-size particles. Diverter A and B tested in this study were able to bridge inside the fracture, reducing its conductivity by converting the open width into a porous medium with a tight permeability for both applications: far-field and near-wellbore. Diverter A (NW) is more efficient and effective than commodity benzoic acid flakes for a simulated near-wellbore application with a fracture width of 0.2 in. The diverter pack dissolved more slowly in slickwater fluid than in DI water, probably more due to the slickwater's polymer content than its minimal increase in viscosity.