Study and Application of Flowback Models for Proppants in Unconventional Oil and Gas Reservoirs of the Qaidam Basin

Abstract

To address the challenge of reduced flow capacity due to proppant return after fracturing in unconventional oil and gas reservoirs within the Qaidam Basin, research was conducted on the proppant return mechanism and its mathematical modeling. By analyzing the coupling effects of fluid mechanics, proppant migration, and formation stress, a multi-field coupled mathematical model for proppant recovery was established using MATLAB. This model accounts for multiple factors including fluid-borne sand transport, conditions for critical recovery rate occurrence, and dynamic variations in fracture closure stress. Using geological and engineering parameters from the target block in the Qaidam Basin, the model was solved and simulated using Well C201 as an example. This quantitatively characterized the influence of five key parameters—fluid viscosity, proppant particle size, density, sand-fluid ratio, and pumping flow rate—on proppant recovery extent. Results indicate that fluid viscosity exhibits a negative correlation with the critical flowback rate of proppant, while proppant particle size, density, and pumping flow show positive correlations. The relationship between sand-fluid ratio and critical flowback rate undergoes a phased change with increasing sand-fluid ratio: initially negative, then shifting to positive, with a critical transition threshold of 32%. Based on the model analysis results, proppant recovery prevention process parameters suitable for unconventional oil and gas reservoirs were optimized. This model can effectively guide the optimization of fracturing schemes, reduce proppant recovery rates, enhance fracture flow capacity and production, and support the efficient development of unconventional oil and gas in the Qaidam Basin.