Experimental Study on the Influence of Fracturing Fluid on the Wettability of Medium and High Rank Coal

The coal’s wettability is a key factor of fluid migration and pressure drop transfer in the reservoir. The Large-scale hydraulic fracturing is the core technology of efficient development of coalbed methane. In order to provide an important basis for the betterment of coal reservoir fracturing technology, an experiment was conducted on the influence of fracturing fluid with different concentrations of KCL and CSG on the wettability of the medium and high rank coal. Firstly, different concentrations of KCL solution and CSG solution are prepared. Next, the medium and high rank coal samples are soaked in different types and concentrations of fracturing fluids. Finally, we measure their contact angles respectively after 24 h and analyze the influence of the liquids on the wettability of the medium and high rank coal. The results show that the medium and high rank coal are both hydrophilic, and the high rank coal is more hydrophilic than the medium rank coal. The influence of ash content on the wettability of coal is more significant than the coal rank. The change of KCL solution concentration has a slight impact on the wettability of the medium and high rank coal. The change of CSG solution concentration has the opposite effect. The wettability of the medium and high rank coal increases sharply and then decreases slowly with the increase of CSG solution concentration. Therefore, it is possible to further improve the fluid migration rate and pressure drop transfer efficiency in coal reservoir and upgrade the fracturing effect through reasonable optimization of fracturing fluid type and concentration.