Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

Abstract

[1] Gas hydrate saturations were estimated using five different methods in silt and silty clay foraminiferous sediments from drill hole SH2 in the South China Sea. Gas hydrate saturations derived from observed pore water chloride values in core samples range from 10 to 45% of the pore space at 190-221 m below seafloor (mbsf). Gas hydrate saturations estimated from resistivity (R t ) using wireline logging results are similar and range from 10 to 40.5% in the pore space. Gas hydrate saturations were also estimated by P wave velocity obtained during wireline logging by using a simplified three-phase equation (STPE) and effective medium theory (EMT) models. Gas hydrate saturations obtained from the STPE velocity model (41.0% maximum) are slightly higher than those calculated with the EMT velocity model (38.5% maximum). Methane analysis from a 69 cm long depressurized core from the hydrate-bearing sediment zone indicates that gas hydrate saturation is about 27.08% of the pore space at 197.5 mbsf. Results from the five methods show similar values and nearly identical trends in gas hydrate saturations above the base of the gas hydrate stability zone at depths of 190 to 221 mbsf. Gas hydrate occurs within units of clayey slit and silt containing abundant calcareous nannofossils and foraminifer, which increase the porosities of the fine-grained sediments and provide space for enhanced gas hydrate formation. In addition, gas chimneys, faults, and fractures identified from three-dimensional (3-D) and high-resolution two-dimensional (2-D) seismic data provide pathways for fluids migrating into the gas hydrate stability zone which transport methane for the formation of gas hydrate. Sedimentation and local canyon migration may contribute to higher gas hydrate saturations near the base of the stability zone.

Architecture, evolution history and controlling factors of the Baiyun submarine canyon system from the middle Miocene to Quaternary in the Pearl River Mouth Basin, northern South China Sea

“…During the recent years, in the northern continental margin of the South China Sea, scientists found abundant gas hydrate accumulations, especially in the Shenhu area (close to the current study area) (Zhang et al, 2002;Wang et al, 2011;Wu et al, 2007;Lin et al, 2009). Sun et al (2012) identified two types of tectonically and stratigraphically controlled fluid flow related systems in the deep-water area of the Baiyun Sag adjacent to our current study area.…”

Recurrent slope failure and submarine channel incision as key factors controlling reservoir potential in the South China Sea (Qiongdongnan Basin, South Hainan Island)

“…Such a character contrasts with areas of the South China Sea (e.g. Wang et al, 2011;Wang et al, 2014), including around the Dongsha Uplift, in which gas hydrates were systematically observed in near-seafloor sediment Wu et al, 2005).…”

Gas hydrate saturation from seismic data constrained by log data in the Krishna-Godavari Basin

“…Acoustic impedance computed from seismic data can be used to estimate gas hydrate saturations (Lu and McMechan 2002;Dai et al 2008;Wang et al 2011;Riedel and Shankar 2012) using various post-stack impedance inversion methods of seismic data. In this paper the model-based inversion of Russell and Hampson (1991) was used as implemented in the Hampson Russell STRATA software package.…”