Coupled Lab-Scale and Numerical Analysis of Proppant Transport in Unconventional Reservoir

Abstract Constant-proppant-concentration fracturing offers an efficient solution for China's unconventional resources, addressing excessive fluid consumption and inconsistent placement in conventional stepwise designs. Validation via geo-engineering integrated software and fractal-based rough fracture modeling demonstrates superior proppant transport for 20/40, 40/70, and 70/140 mesh sands: conventional methods form near-wellbore dunes with sparse distal coverage, while constant concentration achieves uniform distribution along fracture length, enhancing toe-end concentration, effective fracture support, and hydrocarbon mobility. This technique optimizes placement profiles and stimulation economics. Proppant distribution within fractures is a crucial factor in enhancing the production from fracturing. Currently, most studies on the transport and settling behavior of proppants in fractures are based on the models of smooth, straight fracture. There is rarely research considering the effects of fracture tortuosity and roughness on proppant movement and settling. To further reveal the trends of proppant transport and setting in tortuous and rough fractures, physical experiments were conducted to observe proppant behavior in smooth and flat fractures firstly. Based on this, established tortuous and rough fracture models to explore proppant movement and settling patterns. Results indicate that larger proppant particle sizes are more conducive to settling within smooth plate fractures, and medium-to-large particle proppants are more likely to accumulate near the branch fracture entrances. For smooth-plate fractures, the increased the injection rates will allow proppants to penetration deeper into both main and branch fractures. For tortuous rough fractures, larger proppants are more impacted by fracture structure, often accumulating in the middle sections and causing blockage; however, increased injection speeds can effectively mitigate these blockages. These findings reveal the influence of various operational factors on proppant transport and settling, offering theoretical guidance for optimizing hydraulic fracturing techniques.