|Table of Contents|

Interpretation of zero-offset VSP profiles from the pilot hole of Chinese continental scietific drilling(PDF)

《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]

Issue:
2004年第01期
Page:
55-60
Research Field:
Publishing date:

Info

Title:
Interpretation of zero-offset VSP profiles from the pilot hole of Chinese continental scietific drilling
Author(s):
JIANG Xiu-dao1; ZHU Guang-ming2; ZHU Long-sheng2; ZHANG Wen-bo2; LI Gui-hua2
1 .School of Earth Sciences and Resources Management , Chang'an University , Xi'an 710054, China ; 2.School of Geological Engineering and Surveying Engineering , Chang'an University , Xi'an 710054 , China
Keywords:
CCSD; zero-offset VSP observation; seismic velocity ; horizon calibrating ; cause of seismic reflections
PACS:
P631.43
DOI:
-
Abstract:
A zero-offset VSP observation was carried out with a 6-level 3-component geophone at the pilot hole of Chinese Continental Scientific Drilling CCSD).The results of data processing show that the seismic velocities of the ultrahigh pressure metamorphic rocks in the hole area range mainly from 4500 to 7000m/ s, being apparently higher than that of common sedimentary rocks and not varying obviously with their seated depth .Sonic velocities are systematically slightly lower than the VSP interval velocities partly because of the effect of drilling damage around the hole .Seismic velocities of rocks are related evidently to their densities and lithologies.The eclogites are much higher in density and velocity than gneisses;plagioclase amphibolites vary in velocities and densities in a large range between eclogite and gneisses because they are retrograded from the eclogite and their lithology and physical properties vary synchronously with the degree of retrogressive metamorphism ;and velocity and density of ultramafic rock are lowered apparently due to fractures in it .Since large impedance contrasts exist between eclogite and other rocks, it is effective that the VSP profiles are used to calibrate geological horizons of seismic reflections.With regard to the origin of seismic reflections, compositional contrasts, ductile shear zones and fractures are considered as the main cause on the basis of integrated study of the features of seismic waves including PP reflections , PS converted reflections and tubewaves), distribution of velocities and densities and the caliper conditions, but some other elements involved need to be studied in detail.

References:

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Last Update: 2004-03-20