Preparation and performance evaluation of thickeners for supercritical CO₂ fracturing fluid

Objective A new type of thickening agent for CO₂ fracturing fluid is prepared to address the problems of poor fracturing effect and poor sand-carrying capacity caused by the low viscosity of pure CO₂ during the fracturing process, and its performance is studied.

Method  A modified siloxane thickener DHTAF was prepared based on the silica-hydrogen addition reaction, and based on which fluorocarbon alkanes were introduced to further enhance the viscosity of the fracturing fluid system through chemical action. The synthesized thickeners were characterized by infrared and nuclear magnetic resonance; their solubility properties were observed; the viscosities of the systems were measured at different contents, temperatures and pressures; and finally, their friction and sand-carrying properties were evaluated.

Result The results showed the successful synthesis of the target thickener agent by IR and ¹H NMR analysis. The solubility properties of the synthesized thickener agent were good. The viscosity of the fracturing fluid system increased with the increase of thickener content and pressure, and decreased with the increase of temperature, and the viscosity of the fracturing fluid containing 3 wt% DHTAF thickener was up to 3.408 mPa·s at 40 ℃, 10.0 MPa. The friction coefficient decreased with the increase of pipe flow velocity and increased with the increase of thickener content; the proppant settling velocity decreased with the increase of thickener content.

Conclusion  Introducing fluorocarbon hydrocarbons onto modified siloxane molecules can further enhance the viscosity of CO₂ fracturing fluid, providing theoretical support for the future application of supercritical CO₂ fracturing technology in unconventional oil and gas resources.