Adsorption behavior and mechanism analysis of siloxane thickener for CO2 fracturing fluid on shallow shale soil

Reducing the adsorption of CO 2 thickeners in soil particles of shallow shale is a pathway to protect the shale environment and water cycle. In this work, we first synthesized a siloxane-based thickener named AOB based on ring-opening polymerization and hydrosilylation reaction and discussed the influence of geological factors (including contents, pressure, temperature and shear rate) on the adsorption capacity of this thickener. The soil surface adsorption behavior of AOB was characterized by a self-assembled high-pressure soil adsorption device and the adsorption capacity was analyzed by Attenuated Total Reflectance Infrared Spectroscopy (ATR-FTIR). The results showed that AOB molecule belongs to the monolayer adsorption type on the soil surface by measuring the contents. Moreover, an inverse relationship was showed between pressure and adsorption capacity for AOB, while the significantly proportional relationship was presented for temperature and shear rate, respectively. It is found that the combined force formed by soil repulsion (originated from aromatic groups in AOB) and grid drag weakens the adsorption of AOB on the soil surface, resulting in a much lower adsorption capacity than the commercial PDMS. This work not only paves a new avenue for synthesizing siloxane-based polymer as CO 2 thickener, but also provides an efficient measure to reduce the adsorption of thickener on the shallow soil.