TY - JOUR T1 - Detection of free gas and gas hydrate based on 3D seismic data and cone penetration testing: An example from the Nigerian Continental Slope A1 - Sultan,Nabil A1 - Voisset,Michel A1 - Marsset,Tania A1 - Vernant,Antoine-Mathieu A1 - Cauquil,E A1 - Colliat,J A1 - Curinier,V AD - IFREMER, Dept Geosci Marines, F-29280 Plouzane, France. AD - UR - https://archimer.ifremer.fr/doc/00000/2610/ DO - 10.1016/j.margeo.2007.02.012 KW - Piezocone KW - Niger delta KW - Gas hydrate KW - Free gas KW - Effective medium theory N2 - We present a new method to characterize free gas, gas hydrates and carbonate concretions occurrence which are considered as high-risk factors for sub-sea developments in the Niger delta. This method is based on the combination of 3D seismic data to the geotechnical site characterizations using piezocone CPTU tests (Cone Penetration Test with additional measurement of the pore water pressure). A special processing of the 3D seismic data has enabled the determination of the interval compressional velocity. Using the effective-medium theory, velocity anomalies (negative and positive) within the first 15 m were translated in gas hydrate and free gas distribution. The calibration of the P wave velocity anomalies was done thanks to in-situ geotechnical testing carried out during two oceanographic surveys (2003 and 2004). Comparison between in-situ testing, recovered cores and the prediction of the gas and the gas hydrate distribution based on the compressional wave velocity have shown that 3D seismic data is a valuable tool to identify heterogeneous areas but the use of the piezoeone was essential to discriminate between gas hydrate occurrences and carbonate concretions' presence. Furthermore, in-situ compressional wave velocity (V-p) measurements have clearly demonstrated what it was suspected from the 3D seismic data, the co-existence in the study area between gas hydrate and free gas. (c) 2007 Elsevier B.V. All rights reserved. Y1 - 2007/06 PB - Elsevier JF - Marine Geology SN - 0025-3227 VL - 240 IS - 1-4 SP - 235 EP - 255 ID - 2610 ER -