Overview of issues related to mixing CO₂ and proppant in the method of gas extraction from shale rocks.
Tadeusz Niezgoda, Danuta Miedzińska, Sebastian Stanisławek, Michał Kwietniewski
Vol. 33, no. 2 (2016), s. 307-312, 
To increase the efficiency of fracturing process, proppant materials are added to fracking fluid. This admixture allows to keep developed fracks, that tend to lock, opened. The aim of this overview is to present methods of carbon dioxide and proppant mixing. The most often applied methods are as follows: special medium admixing, direct proppant with CO₂ mixing. Liquid CO₂ and proppant blenders are currently commercially used, but are not very popular.