Citation: | CHEN Jie, HU Gaowei, BU Qingtao, WANG Xiujuan, JING Pengfei, LIU Changling, GUO Yang, WANG Zihao. Estimated gas hydrate saturation from the reservoir of clayey silt with sandy interlayers at Site U1517, Tuaheni landslide complex on the Hikurangi margin, New Zealand[J]. Marine Geology & Quaternary Geology, 2020, 40(6): 159-168. doi: 10.16562/j.cnki.0256-1492.2019111302 |
Accurate assessment of natural gas hydrate saturation and reservoir distribution in the Tuaheni landslide complex (TLC) area on the Hikurangi margin, New Zealand plays a critical role in explaining the creeping TLC phenomenon and its forming mechanisms. Gas hydrates are discovered in the interval from 104 mbsf to the BGHS at 160 mbsf based on the logging- while-drilling (LWD) and coring data from the site U1517 located on the extensional and creeping part of the TLC. Elevated P-wave velocity (>1.7 km/s), electrical resistivity (>1.5 Ω·m), and the high saturation intervals occur in 112~114 mbsf, 130~145 mbsf and 150~160 mbsf respectively. The mineral components of different well intervals are used to calculate the P-wave velocity, to estimate the gas hydrate saturation of the 104~160 mbsf interval with the simplified three-phase equation (STPE) and the biot- gassmann theory by Lee (BGTL) models, and the average saturation was 5.2% and 6.0% and the highest was 22.7% and 21.6%, respectively. Adoption of the new method made it more efficient to get BGTL model parameters. Compared with the hydrate saturation estimated by the Expedition 372 from the Archie equation was used, the average gas hydrate saturation is similar in the 104~160 mbsf interval (about 6.0%) and about 8.5% in the interval of 130~145 mbsf. In this study, two sound velocity models were used to estimate the hydrate saturation of U1517, making the results more reliable. The accurate estimation of the gas hydrate saturation and distribution at site U1517 will provide basic data for simulation of the creeping TLC phenomenon on the Hikurangi margin.
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Location map showing the Tuaheni landslide complex and U1517 Site in Hikurangi margin[36]
Well logs at Site U1517
Cross plot of formation factor versus the measured P-wave velocities at Site U1517
Simplified lithostratigraphic column with bulk powder XRD results, Site U1517
Measured and calculated baseline P-wave velocities with STPE at the Site U1517
Measured and calculated baseline resistivities and P-wave velocities at the Site U1517
Measured and predicted P-wave velocities
Measured and calculated baseline P-wave velocities with BGTL at the Site U1517
Background P-wave velocities and gas hydrate saturations at Site U1517 with BGTL
The well logs from site U1517A showing the caliper, P-wave velocity, resistivity, density and gamma ray
The gas hydrate saturation calculated by BGTL, STPE compared with the hydrate saturation calculated by the Expedition 372 scientists used the Archie equation and the chloride concentration
The measured P-wave velocity compared with the calculated results of the STPE and BGTL in water-saturated sediments (0~90 mbsf)