Quantitative Prediction Method of Liquid Retention Based on Nuclear Magnetic Resonance

Abstract

For tight gas reservoirs such as water-sensitive and low permeability, the incoming fluids are the most important external factors that damage oil and gas reservoirs. The liquid phase retention has become an important influence factor of production capacity. At present, the water blockage damage degree is often used to evaluate the liquid phase retention degree. Therefore, based on the study of fractal dimension by a NMR (nuclear magnetic resonance) experiment, using the existing formula of the fractal calculation of the relative permeability curve, this paper improves the relevant formula for calculating water blockage damage for NMR and studies the relative permeability curve and water blockage damage rate of tight gas reservoirs. According to the calculation results, the fractal dimension of the samples is 2.3551–2.7417, and the average value is 2.492. This shows that the micro-pore structure of core samples is relatively complex with medium heterogeneity. Through the analysis of the relative permeability curve, it can be deduced that the rocks in this block have strong hydrophilicity, and the gas–water two-phase seepages in this block strongly interfere with each other. Besides, the comparative analysis shows that the method of calculating water blockage damage rate is accurate and the average error is only 4.59%. The average damage degree of water blockage in this block is moderate water blockage damage. The results of the parametric analysis also demonstrate that irreducible water saturation and pore-throat structure relationship are the key factors governing the water blockage degree, which determines the damage degree of foreign liquid retention to reservoirs.