A unified contact cementation theory for gas hydrate morphology detection and saturation estimation from elastic-wave velocities. (March 2020)

• Record Type: Journal Article
• Authors: Pan, Haojie; Li, Hongbing; Chen, Jingyi; Zhang, Yan; Cai, Shengjuan; Huang, Yucheng; Zheng, Ying; Zhao, Yi; Deng, Jian
• Is Part Of: Marine and petroleum geology. Volume 113(2020)
• Publication Date: 2020-03
• Subjects: Gas hydrate morphology -- Hydrate saturation -- Unified contact cementation theory -- Elastic-wave velocities -- Hikurangi margin; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2019.104146
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Good knowledge of hydrate morphology and accurate quantification of hydrate saturation are significant for reservoir characterization, resource exploitation and geohazards assessment. Although many of empirical or theoretical models have been developed to detect hydrate morphology and predict hydrate saturation from elastic-wave velocities, they either fail to hold true for complex morphologies or cannot provide accurate hydrate saturation estimate. In this study, we propose a unified contact cementation theory by applying the modified Hashin-Shtrikman upper and lower bounds to an extended cementation theory. By merging the cementation theory and effective medium theory, it can be used to account for four types of hydrate morphologies. Numerical modeling results provide some new insights into effects of normalized thickness of hydrate layer, friction coefficient and effective pressure on elastic-wave velocities for different morphologies, which will be helpful for analyzing the borehole stability and determining optimum production-related strategies. In addition, we propose a hydrate morphology-based inversion method by introducing the ratio of multiple hydrate morphologies from statistical analyses and apply it to the acoustic logs from the Mallik 5L-38 permafrost-related gas hydrate research well in Mackenzie Delta and other three marine wells in Nankai Trough and Hikurangi margin. The velocity-based gas hydrate saturation estimations are in good agreement with those predicted from resistivity log and Nuclear Magnetic Resonance measurement, as well as core data, confirming feasibility and applicability of our theory and inversion method, and indicating its potential in seismic characterization of gas hydrate reservoirs. Highlights: General expressions of normalized contact-cement radii for two hydrate accumulation schemes are derived. A unified contact-cementation theory is proposed to characterize four types of hydrate morphologies simultaneously. Effects of thickness of hydrate layer, friction coefficient and pressure on velocities for different morphologies are analyzed. A hydrate-morphology-based inversion method is developed to predict hydrate saturation from elastic-wave velocities. Effects of hydrate morphology and vertical resolution of logging tools on hydrate saturation estimates are investigated.