Revealing fluid dynamics in unconventional reservoir rocks: A novel approach of T₁-T₂ analysis

Fluid distribution and migration characteristics hold significant importance in evaluating the quality of reservoir rocks. Two-dimensional nuclear magnetic resonance (2D NMR) measurements have been widely applied to identify specific hydrocarbon contents within rocks. However, due to the complexity of the pore and fluid system, thistechnique was not fully exploited and was limited by existing data processing methods. In this study, a novel centroid method was developed to enhance the quantification of 2D NMR data for fluids in reservoir rocks. This method calculates the centroid of the 2D NMR map, which correlates with the average pore size derived from the imbibition process. To validate its effectiveness, the method was applied to analyze the T₁ (longitudinal relaxation time) – T₂ (transverse relaxation time) relationships taken during imbibition processes in three different reservoir rocks. Results demonstrate that the position of centroid can be used to analyze the dominant type of water in pores involved in the imbibition process. Besides, this method can also successfully assess state changes for different water types inside samples by tracking centroids’ movements and fluctuations in centroid T₁/T₂ ratios, as well as utilizing the 2D NMR map’s signal partitioning capacity. Compared to other approaches, it elucidates the distribution and migration characteristics of water in different types of pores and provides significant advantages in the quantitative processing and comparative analyses of 2D NMR data across various water-bearing conditions. Furthermore, it also demonstrates significant potential for investigating interactions and dynamics of multiphase fluids in unconventional reservoirs.