Bound water saturation is a key parameter in reservoir evaluation and plays a significant guiding role in the formulation of oilfield development strategies. This study focuses on the G region and systematically analyzes the reservoir’s microscopic pore-throat characteristics, original oil saturation, and bound water saturation using integrated experimental methods. Specifically, high-pressure mercury intrusion (MICP) was employed to characterize the microstructure of pore-throats, while bound water saturation was determined using a combination of relative permeability tests, nuclear magnetic resonance (NMR) technology, and MICP. The results show that: 1) The main types of reservoir space in the study area are primary and secondary pores. Primary pores are predominantly residual intergranular pores, with chlorite films and authigenic clay minerals developed along pore edges. 2) When using the T2 spectral area ratio method in NMR logging to determine bound water saturation, the difficulty in accurately defining the T2 cutoff value (T2 cutoff) leads to imprecise results. Furthermore, the calculated saturation does not account for bound water present in movable water pores, resulting in systematically underestimated values. 3) The MICP method offers advantages such as fast testing speed, wide measurement range, and minimal requirements on sample size and shape. However, it also presents a discrepancy in wetting characteristics compared to actual oil-water systems. 4) Given the tight nature of the reservoir in the study area, treating the critical water saturation point as a proxy for bound water saturation may introduce certain errors. Thus, the applicability of this approach is relatively limited compared to the other two methods and should be applied with caution.
References
[1]
Chen, Y. Q., Zhang, J. C., & Chen, Q. (2016). Advances in Evaluating Reservoir Bound Water Saturation Using NMR Logging. Oil Geophysical Prospecting, 51, 582-588.
[2]
Coates, G. R., Xiao, L. Z., & Prammer, M. G. (1999). NMR Logging Principles and Applications (pp. 189-207). Halliburton Energy Services.
[3]
Liu, W., Zhou, C. C., & Chen, Q. Y. (2017). Application of Core Calibration for Determining T2 Cutoff Values in NMR Logging. Oil & Gas Geology, 38, 362-370.
[4]
Pan, B. Z., Sun, Q. H., & Liu, S. (2015). Experimental Determination of Bound Water Saturation Using Dielectric Constant Measurements. Acta Petrolei Sinica, 36, 563-570.
[5]
Su, J. L., Yang, W. G., Wang, Z. Y. et al. (2021). A Permeability Coates Model Based on Variable T2 Cutoff Values and Its Validation via Core Analysis Experiments. Natural Gas Geoscience, 32, 1120-1130.
[6]
Sui, X. J., Li, Y. P., & Wang, H. (2018). Evaluation of Bound Water Saturation in Tight Sandstone Based on Mercury Intrusion Experiments. Petroleum Geology & Engineering, 32, 89-92.
[7]
Wang, S. C., Liu, H. W., & Zhang, W. Z. (2019). Determination of Bound Water Saturation Using Variable T2 Cutoff Values in NMR Logging. Chinese Journal of Geophysics, 62, 2715-2723.
[8]
Wei, Z., Li, L., & Liu, J. (2015). Methodology for Determining T2 Cutoff Values via Core NMR Experiments. Petroleum Geology & Experiment, 37, 502-506.
[9]
Xu, P., & Zhang, C. G. (2019). Determining Bound Water Saturation in Tight Sandstone Reservoirs via Combined Rock Electrical and Mercury Intrusion Methods. Petroleum Exploration and Development, 46, 1155-1162.
[10]
Yao, H., Liu, R. B., & Li, M. X. (2020). Determination of Bound Water Saturation in Low-Permeability Sandstone Reservoirs by Relative Permeability Method. Lithologic Reservoirs, 32, 85-91.
[11]
Zhang, W. W., Huang, J. S., & Chen, G. (2014). Applicability of Mercury Intrusion Method for Determining Bound Water Saturation in Low-Permeability Reservoirs. Petroleum Geophysical Exploration, 53, 451-458.
[12]
Zhang, X. H., Yang, Z. Z., & Liu, J. (2018). Determination of Bound Water Saturation by NMR Logging Gradient Cutoff Method. Well Logging Technology, 42, 60-64.
