Open AccessEstimation of Gas Hydrate Saturation Using Constrained Sparse Spike Inversion: Case Study from the Northern South China Sea
Author(s) -
Xiujuan Wang,
Shiguo Wu,
N. Xu,
Guangxue Zhang
Publication year - 2006
Publication title -
terrestrial, atmospheric and oceanic sciences/terrestrial, atmospheric, and oceanic sciences
Language(s) - English
Resource type - Journals
eISSN - 2223-8964
pISSN - 1017-0839
DOI - 10.3319/tao.2006.17.4.799(gh
Subject(s) - inversion (geology) , geology , saturation (graph theory) , clathrate hydrate , china , china sea , hydrate , mineralogy , oceanography , geomorphology , mathematics , geography , chemistry , organic chemistry , archaeology , combinatorics , structural basin
Bottom-simulating reflectors (BSRs) were observed beneath the seafloor in the northern continental margin of the South China Sea (SCS). Acoustic impedance profile was derived by Constrained Sparse Spike Inversion (CSSI) method to provide information on rock properties and to estimate gas hydrate or free gas saturations in the sediments where BSRs are present. In general, gas hydrate-bearing sediments have positive impedance anomalies and free gas-bearing sediments have negative impedance anomalies. Based on well log data and Archie's equation, gas hydrate saturation can be estimated. But in regions where well log data is not available, a quantitative estimate of gas hydrate or free gas saturation is inferred by fitting the theoretical acoustic impedance to sediment impedance obtained by CSSI. Our study suggests that gas hydrate saturation in the Taixinan Basin is about 10 - 20% of the pore space, with the highest value of 50%, and free gas saturation below BSR is about 2 - 3% of the pore space, that can rise to 8 - 10% at a topographic high. The free gas is non-continuous and has low content in the southeastern slope of the Dongsha Islands. Moreover, BSR in the northern continental margin of the SCS is related to the presence of free gas. BSR is strong where free gas occurs