Optimization design of combined proppants for hydraulic fracturing in tight sandstone reservoirs of yanchang oilfield

The tight sandstone gas reservoirs in the Yanchang Oilfield (Ordos Basin) represent a pivotal target for efficient unconventional hydrocarbon development in China. However, high closure stress in deep formations readily induces proppant crushing, embedment, and rapid fracture conductivity decline, while single proppants fail to balance conductivity performance and material cost, severely restricting the effectiveness of reservoir stimulation. This study targets tight sandstone reservoirs in the Yanchang Oilfield. Through laboratory experiments encompassing fracture conductivity tests, full-gradation proppant sieving, and three-dimensional micro-topography characterization of rock surfaces, we systematically investigated the effects of proppant material, particle size gradation, and combination ratio on fracture conductivity, revealed the evolution mechanisms of proppant crushing, gradation reconstruction, and rock surface embedment damage, and optimized a combined proppant scheme tailored to reservoir characteristics. Experimental results demonstrate that the tight sandstone reservoirs in the study area exhibit pronounced rock mechanical heterogeneity. The same-mesh combination of 30/50 mesh ceramsite and 30/50 mesh quartz sand achieves the best comprehensive conductivity, with optimal mass ratios of 2:8 at 40 MPa and 7:3 at 80 MPa. Increasing closure stress significantly aggravates proppant crushing and plastic embedment; fine-particle pore-throat plugging and rock-wall embedment damage constitute the dominant controlling factors of fracture conductivity attenuation.