The impact of CO₂ injection on steel balls embedment in shale rock – Experimental research

One of the most important phenomenon appearing during shale rock fracturing is the interaction between the proppant and fracture wall. The proppant's role is to keep the fracture open after the fracturing fluid is released and during gas recovery. However, the stress caused by the rock mass can act on proppant grains – they can be damaged or embed into fracture wall. This phenomenon, called embedment, was tested in this study with the use of an original testing device. The impact of CO₂ injection on this phenomenon was presented. Special attention was paid to the change in properties of shale during the embedment process, i.e. saturation of rock with CO₂ rather than proppant behaviour. As a model proppant steel balls were used for the tests. The obtained results show that the average embedment depth in the case of the steel balls in the non-CO₂ environment was smaller than in the case of an average embedment depth in the case of the steel balls embedment in the CO₂ environment. A significant impact of carbon dioxide on the surface of the shale rock was observed. The shale rock lost its strength after the CO₂ interaction. Such phenomenon can be caused by the shale structure change connected with carbon dioxide sorption induced swelling.