A fracability evaluation method for low-permeability sandstone-hosted uranium deposits and its application

Poor injectability and limited recoverability remain key technical challenges restricting the efficient exploitation of low-permeability sandstone-hosted uranium deposits. Hydraulic micro-fracturing is an effective approach for improving permeability, and fracability evaluation provides a critical basis for selecting favorable ore-bearing intervals for fracturing. Existing methods focusing on brittleness and fracture toughness neglect energy mechanisms and fracture network complexity. This study proposes a novel comprehensive fracability evaluation method based on the entire fracturing process, which is divided into fracture initiation, fracture opening, and fracture propagation stages, with rock strength, fracture-opening capacity, and fracture-propagation capacity as core indicators. Complete stress–strain curves are obtained from triaxial compression tests. The post-peak stress-drop complementary angle is used to characterize fracture extension capability and is combined with compressive strength to construct strain energy density. Fracture parameters are extracted from post-fracturing optical scanning images, and the areal fracture ratio and dip-angle dispersion are used to characterize fracture complexity. The fracability index is expressed as fracture complexity divided by strain energy density. Applied to six core samples from Inner Mongolia uranium deposits, results show negative correlation between fracture complexity/fracability index and grain size. Fine sandstone has the highest fracability index, while very coarse sandstone/conglomerate has the lowest. Among the six specimens tested, Sample No. 2 exhibited high peak differential stress followed by a pronounced post-peak stress drop. It had the lowest value of the proposed strain energy density parameter, the highest calculated fracability index, and the largest permeability increase following triaxial compression failure, with post-test permeability approximately 144 times its initial value. These results support a comparative assessment under the tested laboratory conditions, while their applicability to hydraulic stimulation requires further validation.This method integrates fracturing energy and fracture complexity, offering a theoretical basis for selecting favorable ore-bearing intervals for fracturing in low-permeability sandstone-hosted uranium deposits.