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A Novel Model for Estimating Saturation Exponent from Nuclear Magnetic Resonance Logs in Tight Sands
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 77th EAGE Conference and Exhibition 2015, Jun 2015, Volume 2015, p.1 - 5
Abstract
A significant percentage of the world’s hydrocarbon reservoirs are contained in tight sands. It is difficult to obtain precise saturation exponent by using the cross plot of resistivity index vs.water saturation (I-Sw) to calculate hydrocarbon saturation in tight sands. The saturation exponent is not a constant due to complicate pore structure, which is a difficulty in hydrocarbon saturation calculation. Based on laboratory resistivity, nuclear magnetic resonance (NMR) and mercury injection capillary pressure (MICP) measurements from 20 core samples in Yanchang Formation, Member 8 (Chang 8) reservoir, Ordos basin, we found that T2LM, sorting coefficient and porosity are the main three factors to determine pore structure and saturation exponent. We propose a novel model which take all three factors into consideration, where porosity and T2LM could be calculated by NMR logs directly,besides, sorting coefficient is calculated by using uniformity of T2 spectrum. The absolute error and relative error between predicted saturation exponents by using proposed model and the experimental results are 0.16 and 4.25% respectively, which confirmed the credibility of proposed model.