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Evaluation of gas hydrate-bearing sediments below the conventional bottom-simulating reflection on the northern slope of the South China Sea

Liang Jinqiang, Zijian Zhang, Su Pibo, Sha Zhibin and Yang Shengxiong
Evaluation of gas hydrate-bearing sediments below the conventional bottom-simulating reflection on the northern slope of the South China Sea
Interpretation (Tulsa) (May 2017) 5 (3): SM61-SM74

Abstract

The continuous bottom-simulating reflection (BSR) is commonly considered to mark the base of gas hydrate stability zone. Below this depth, gas hydrate gives away to free gas or water filling with pore spaces of sediments. We integrated and analyzed seismic data collected in 2008, and logging-while-drilling (LWD) data and coring results acquired by the Fugro Voyager in 2015 in the Shenhu area on the northern slope of the South China Sea. Based on seismic and well-log correlation, a BSR with typical characteristics of gas hydrates and free gas was identified at 237 m, below the mudline (BML). However, LWD data reveal a 63 m thick hydrate layer from 205 to 268 m BML. Increases in resistivity and velocity at 262 m BML indicate that gas hydrate is likely presented below the BSR. The observed pore-water freshening with depth and infrared image of core samples are consistent with geophysical interpretation. Seismic and well interpretations reveal continuous, discontinuous, and pluming BSRs in the Shenhu area. The continuous BSR indicates the base of the methane gas hydrate stability zone, and structure II gas hydrate is likely presented below the BSR. Deep thermogenic fluid locally entrapped within shallow-buried sediments may reinforce gas-hydrate accumulations near the discontinuous and pluming BSRs. We conclude that seismic responses of structure II gas hydrate can be distinct from structure I gas hydrate. Understanding the seismic characterizations of structures I and II will help in the evaluation of gas-hydrate reservoirs and inferring the presence of deep thermogenic reservoirs.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 5
Serial Issue: 3
Title: Evaluation of gas hydrate-bearing sediments below the conventional bottom-simulating reflection on the northern slope of the South China Sea
Affiliation: Guangzhou Marine Geologic Survey, China
Pages: SM61-SM74
Published: 201705
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
Accession Number: 2017-085803
Categories: Economic geology, geology of energy sourcesApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
N00°00'00" - N25°00'00", E99°10'00" - E122°00'00"
Secondary Affiliation: Fugro, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201745
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