Heterogeneity of Fluid Distribution in Shale Based on Nuclear Magnetic Resonance Dual <i>T</i>2 Cutoff Values
Ziyun Zhang, Chuanzhi Cui, Zhongwei Wu, Ya Wang, Xia Gao, Junkang Wang
Abstract
Summary The dual-cutoff-values method has become an important method to accurately characterize pore structure. However, there is still a lack of quantitative characterization of the heterogeneity of the three fluids divided by this method. In this study, the heterogeneity of three fluids of seven shale samples was quantitatively characterized by multifractal analysis based on nuclear magnetic resonance (NMR) experiments after saturation, centrifugation, and heat treatment. The results show that the optimal centrifugal force is 862 psi, and the threshold temperatures range from 70°C to 100°C. The obtained dual cutoff values (T2c1: 1.30–1.67 ms; T2c2: 0.33–0.58 ms) divide fluids in the shale into unrecoverable fluid (T2 &lt; T2c2), capillary bound fluid (CAF) (T2c2 ≤ T2 &lt; T2c1), and movable fluid (T2 ≥ T2c1). Based on the critical pore radii (rc1 and rc2) determined by T2c1 and T2c2, the pores in the shale are further divided into corresponding fluid pore types. A novel method for obtaining fluid distribution is proposed. Based on the multifractal theory, it is found that the heterogeneity is stronger in the low-probability region and weaker in the high-probability region. The order of heterogeneity of the three fluids is movable fluid &gt; unrecoverable fluid &gt; CAF. In this study, we explore the heterogeneity of fluid distribution in shale reservoirs, expand the understanding of fluid behavior within pores, and provide a new theoretical perspective for evaluating reservoir mobility.