Multifactor Coupled Evaluation Model of Fracability Based on a Combinatorial Weighting Method: A Case Study of the Low-Permeability Sandstone Reservoirs of Yanchang Formation, Southwestern Ordos Basin, China

The accurate evaluation of the fracability of low-permeability rocks is crucial for designing and optimizing hydraulic fracturing strategies in low-permeability reservoirs. In this study, fracability was defined as a property that measures the ability of low-permeability sandstones to form complicated fractures through hydraulic fracturing. Therefore, we investigated the influence of mechanical characteristics, physical properties, and geological conditions on the breakdown pressure and fracture morphology in low-permeability sandstones. To address the limitations of existing fracability evaluation models, a combinatorial weighting method (CWM) combining subjective and objective weighting methods was proposed. Based on this weighting method, we established a multifactor coupled evaluation model (MCEM) for evaluating the fracability of low-permeability sandstones and introduced a new fracability index to quantify the results derived from this model. The effectiveness of the evaluation model was validated through comparative analysis with existing fracability evaluation models. Using this evaluation method, we evaluated the fracability of Yanchang Formation’s low-permeability sandstone reservoirs in the southwestern Ordos Basin to identify the best candidates. The evaluation results were consistent with the daily oil production from the field reservoirs. The multifactor coupled evaluation model based on the combinatorial weighting method (MCEM–CWM) comprehensively considers the effects of physical, mechanical, and geological factors on fracability, and combines the subjective and objective weighting methods to overcome the shortcomings of the single weighting method of existing fracability evaluation models. The study provides a novel approach for designing and optimizing hydraulic fracturing stimulation strategies in low-permeability reservoirs.