The objective of this study is to introduce a technique of far-field diversion using a mixture of soluble solid particles and an engineered proppant that can ensure that the temporarily bridged fractures re-open and remain propped for hydrocarbon flow after the soluble material has fully dissolved. Far-field diversion is required inside the fracture network to increase complexity by creating additional branch fractures through overcoming stresses holding the natural fractures closed. Usually, diverter particles temporarily bridge inside the fracture to create a low-permeability zone that increases the net pressure within the fracture and enables redirection of the next fluid stage to previously unstimulated intervals. However, if the diversion does not include proppant, the created fracture may close after particle dissolution.
Two tests were performed in this study: solid bridging test to describe the bridging capabilities of solid particulate diverters as a function of fracture width (0.04 to 0.08 in.); and conductivity reduction tests to determine the reduction in the flow rate due to the particle pack permeability. Two types of particle diverters (Diverter A and B) were tested. Diverter A is typically used for low- to medium-temperature applications (less than 225°F) and Diverter B for high-temperature applications (greater than 225°F). The two diverters have nearly the same particle size and distribution, the only difference being a difference in particle shape.
Modeling performed before the experimental work indicated that a proppant size of 50 mesh or higher minimized the far-field segregation between the proppant and 20 mesh soluble particles under all modeled conditions. Modeling also showed that reducing the proppant size to a larger mesh number improved proppant placement in the far-field area with good vertical coverage. Based on this information, the diverter particles for the tests were selected to be in the medium-size range (10 to 50 mesh) while the proppant particles were selected to be in the fine size range (70 to 140 mesh). At a low injection rate, slickwater fluid (2 cP) may not have adequate transport characteristics to place soluble diverter particles for far-field application. Modeling indicated that a carrier fluid with viscosity of 10 cP could carry the soluble diverter at least 130 ft from the wellbore.
Experimental data, using the CFD recommended sizes of proppant-diverter mixture, confirmed that a loading of 0.5 ppga of Diverter A was needed to bridge and plug the 0.04-in. slot width, while only 0.25 ppga of Diverter B was needed to plug the same width. The spherical shape of Diverter B helps to bridge inside that fracture more than the flake shape of Diverter A. Finally, both diverters significantly reduced the conductivity of the test slot discs.