Relationship between Gas Hydrate Saturation and Resistivity in Sediments of the South China Sea
详细信息
- 责任者：Chen Yufeng (Key Laboratory of Renewable Energy and Gas Hydrate ; Guangzhou Institute of Energy Conversion ; CAS ; Guangzhou 510640 ; China) ; Li Dongliang
- 刊名：Acta Petrolei Sinica
- 出版年：2013
- 卷期：34(3)
- 关键词：电阻率测井 ; resistivity logging ; 天然气水合物 ; gas hydrates ; 南海 ; South China Sea
- 页码：p.507-512
- 图表：illus., 1 table, 15 refs.
- 分类号：1600
- issnNo：ISSN0253-2697
- isbnNo：CN11-2128/TE
摘要
The Archie’s formula is a fundamental equation to calculate gas hydrate saturation of sediments with downhole electric resistivity log data from gas hydrate wells.This formula is based on measurements of a large number of oil/gas-bearing cores.However,the electric resistivity of porous hydrate-bearing sediments depends on physical properties of sediments and the microscopic distribution of gas hydrate in pores,thus a certain non-Archie’s behavior in hydrate-bearing sediments may exist in these porous sediments.Therefore,an experimental calibration for the hydrate saturation calculated by electric resistivity in hydrate-bearing sediments should be conducted.So laboratory studies on properties of hydrate-bearing sediments as a function of methane saturation are very important.Herein,we conducted a series of laboratory experiments to measure electric properties of South China Sea sediments initially saturated with 3.5%salinity water and variations in electric resistivity for these sediments as gas hydrate was formed.The results show that the sediment resistivity increases with the increase of hydrate saturation during the formation of gas hydrate,especially at a low gas hydrate saturation(Sh<22%),where the electric resistivity of sediments increases dramatically with the formation of gas hydrate,rising from 1.667Ω·m to 2.661Ω·m as the gas hydrate saturation increases from 0%to 45%.Besides,the dependence of the resistivity index versus hydrate saturation for gas hydrate-bearing sediments is inconsistent with the Archie’s law,therefore,the saturation exponent(n) is not a constant but a function of hydrate saturation,i.e.it increases with the increase of water saturation(Sw),thus,it is lower than 1.938 6 when water saturation ranges between 54.8%and 78.6%but higher than 1.938 6 when water saturation exceeds 78.6%.The results are of important implication for quantitative laboratory and field calibration of geophysical measurements within gas hydrate-bearing intervals.