Experimental Investigation of Particulate Diverter Used to Enhance Fracture Complexity
Authors: Gomaa Ahmed M. , Nino-Penaloza Andrea , Castillo Dorianne , McCartney Elizabeth , Mayor John 
Published: January 2016

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 temporary low-permeability pack that increases the pressure within the fracture and enables redirection of next-stage fluid to under-stimulated 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 dissolution tests under static and dynamic conditions to determine the time need to dissolve the particles as function of temperature, rate, particle size, carrier and produced fluid.

At both static and dynamic conditions, the tested solid diverters will dissolve in an aqueous solution with temperature and time. However, temperature has a more significant effect than time on the dissolution rate. For Diverter A, Increasing the water salinity reduced the dissolution of Diverter A. However, water salinity did not affect dissolution until a certain amount of solid was dissolved into solution. Dissolution was increased by reducing the particle size (and therefore increasing particle surface area). Live and spent HCl acid dissolve significantly less Diverter A than Deionized water (DI water) or Potassium chloride (KCl) solution.

For Diverter B (10/30), DI water dissolved 0.06 ppg (14.2% dissolution) of Diverter B after 24 hrs. However, increasing the temperature to 225 and 250 °F, increased the dissolution to 28.7%, and 95.7%, respectively. Finally, at 300°F, 100% dissolution was noted for Diverter B after 8 hrs. Diverter B dissolves in 3 wt% KCl solution very similarly to dissolution in DI water. This gives indication that above 225°F, the dissolution of Diverter B is independent of water salinity. Hydrochloric acid (HCl acid) significantly increases the dissolution of Divert B (10/30) and (20/70), taking only 4 hrs for completely dissolution (100%). Also, the dissolution rate in live 15wt% of HCl was independent of particle size.

The ratio between the fracture width and the average particle size needed to bridge was found to be 2.4. Diverters A and B tested in this study were able to bridge inside a fracture, reducing its conductivity by converting the open width into a porous medium with a tight permeability for both applications: far-field (FF) and near-wellbore (NW). Diverter A (NW) is more efficient and effective than commodity field grade 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.