Review of characterization methods for shale wettability: advances, applications, and future perspectives

Wettability significantly controls fluid distribution and mobility in shale reservoirs. Accurate characterization enables better reservoir management and improves shale oil recovery. This review systematically summarizes wettability characterization methods across four sample scales: core thin sections, core plugs, crushed rock samples, and digital cores. It aims to compare their advantages, limitations, and practical applicability. We analyze established techniques such as contact angle measurement and spontaneous imbibition, highlighting how integration with advanced imaging and NMR enhances their reliability. The review also examines emerging nanoscale characterization techniques (Atomic force microscopy, AFM; molecular dynamics, MD simulations) are examined to reveal the link between molecular-scale and macroscopic wettability in shale. We systematically compare the advantages and constraints of all approaches. Notably, no single method can fully capture the complex, mixed-wet behavior of shale. Our analysis considers that a multi-scale framework is essential. Such an approach combines complementary techniques and validates simulations with experimental data. This strategy improves the characterization of wettability heterogeneity and its dynamic evolution. Looking forward, we highlight the need for in-situ dynamic monitoring, integration of artificial intelligence, and standardized protocols for continental shale. These advances will support more accurate reservoir evaluation and optimized recovery strategies.