What is downhole seismic survey?
This method is commonly used to determine compressional and shear wave velocity versus depth. In a downhole seismic survey, a seismic source is placed on the surface near a borehole, and two tri-axial geophones are placed at selected depths in the borehole. …
What is cross hole seismic test?
Cross-Hole testing consists of measuring the travel time of compression (P) and shear (S) seismic waves between several boreholes. It enables us to determine, depending of the depth, their seismic velocities, Vp and Vs, as well as geodynamic parameters (Young’s modulus E, shear modulus G, and Poisson’s ratio n).
What is down hole testing?
Downhole seismic test is an in-situ test and determine the velocity of primary (P) and secondary (S) seismic waves to provide the elastic soil parameters. The P and S waves velocities are used in geotechnical foundation analysis, static and dynamic soil analysis, liquefaction assessment and etc.
What is MASW Geophysics?
Multichannel Analysis of Surface Waves (MASW) is a geophysical method that uses surface wave (Rayleigh wave) propagation to profile the subsurface. Surveys can be designed to provide high resolution near surface results, or to profile up to 60 meters depth.
How many survey holes does the cross-hole test require?
The CS is a cross-hole test that requires at least two boreholes, while DS testing requires only one.
Which parameter is measured in cross-hole seismic studies?
Description. Crosshole (or “crosswell”) seismic measures the velocity of seismic waves between boreholes.
What is down hole seismic geophysical test?
Downhole seismic testing is one field test that is commonly used to determine compression-wave (P) and shear- wave (S) velocity profiles in geotechnical earthquake engineering investigations. An improved downhole test that can be used for wave velocity profiling to depths of 300 to 600 m or more is presented.
What does MASW measure?
MASW is a seismic method that measures the shear-wave velocity distribution, thereby can be used to measure the arrangement of overburden and bedrock. It analyzes the dispersion of surface waves (usually the fundamental-mode Rayleigh waves).
What is multichannel analysis of surface waves MASW?
The Multi-channel Analysis of Surface Waves (MASW) is a seismic method used to evaluate the shear-wave velocities of subsurface materials through the analysis of the dispersion properties of Rayleigh surface waves (“ground roll”). The data are collected on the surface without the need of borehole.
What are seismic reflection and seismic refraction tests?
Seismic reflection and refraction is the principal seismic method by which the petroleum industry explores hydrocarbon-trapping structures in sedimentary basins.
What causes seismic refraction?
Refraction is (1) the deflection, or bending, of the ray path of a seismic wave caused by its passage from one material to another having different elastic properties.
How is a downhole used for seismic testing?
It is similar in several respects to the Crosshole Seismic Test Method (Test Methods D 4428/D 4428M). A seismic source is used to generate a seismic wave train at the ground surface offset horizontally from the top of a cased borehole. Downhole receivers are used to detect the arrival of the seismic wave train.
What’s the difference between a Crosshole survey and a downhole survey?
Crosshole Survey – The difference between this survey and the Downhole one is that in the Crosshole approach there are two boreholes. A downhole seismometer is in one of the holes and the shear wave source in the other. This approach is a little more definitive for acquiring information on discrete layers.
How is seismic velocity measured in a borehole?
This technique measures vertical changes in seismic velocity by placing a source at the top of a borehole and measuring travel-times at multiple intervals in the borehole, usually with a 3-component geophone. Common applications include:
Are there any benefits to using a downhole?
Benefits/Limitations 1 Although similar to crosshole in that a borehole is used, in this case the source stays on the surface. This means that… 2 Unlike refraction, downhole looks at direct raypaths, and as a result does not require increasing velocity with depth. More