A New Method for Determining Tight Sandstone Permeability Based on the Characteristic Parameters of the NMR T2 Distribution

Abstract

This paper proposes a new method to determine the permeability of tight sandstone using characteristic parameters of the nuclear magnetic resonance (NMR) transverse relaxation time (T₂) distribution. First, the Swanson parameters (T_s) and Capillary–Parachor parameters (T_cp) are calculated as the percolation characteristic parameters (T_c) of NMR T₂ distribution. The logarithmic mean (T_lm), arithmetic mean (T_am), and harmonic mean (T_hm) are calculated as the pore structure characteristic parameters (T_m) of NMR T₂ distribution. T_x, the transverse relaxation time when the value of Y-axis is x% in the normalized accumulated T₂ distribution curve accumulated from long relaxation time part to short relaxation time part, is selected as a characteristic parameter of pore size distribution. Second, different T_c, T_m, T_x, and NMR porosity (T_por) values are selected to establish single-, double-, three-, and four- parameter models for estimating permeability. An analysis of the relationships between calculated permeabilities of different models and measured permeability in tight sandstone rocks indicated that the four-parameter model based on T_cp, T₄₀, T_am, and T_por was the best model. Moreover, this model was superior to the calibrated Timur model and the calibrated SDR model for calculating permeability in tight sandstone reservoirs.