Geophone array

Description

Multi-component downhole seismic array GStreamer is a cost effective solution for 3C borehole engineering and environmental surveys such as VSP and crosswell tomography.

We developed an easy-to-operate downhole tool with robust deployment and clamping system. Deployment is performed by placing multi-level 3C geophone array into the borehole without need of additional depressors. Once the borehole array is placed in the well, all units are clamped simultaneously by simply pulling the secure wire, bringing array in operational mode.

Each geophone pod housing contains 3 component sensors combined orthogonally with natural frequency of 12.5 Hz. GStreamer array configuration is quite flexible – it can be manufactured with up to 8 levels, interval between the tools is on the customer’s choice.

Combination of GStreamer array, Jack energy source and Shock borehole source provides modern acquisition setup for compressional (P) and shear (S) waves generation and registration. Registered wavefields are used to determine P- and S-wave velocity profiles which are typically used for Poisson’s ratio and other elastic modulus estimation, required for various engineering applications, such as foundation studies, soil and rock mechanics and earthquake engineering.

The geophone array can be supplied on a reel with slip ring, which allows to leave the equipment plugged into it while winding and unwinding the cable.

VSP and crosshole data processing requires efficient and sophisticated processing flow. RadExPro seismic software provides all necessary algorithms for multi-component data processing – hodogram analysis, 2C/3C component orientation, wavefield separation, velocity modelling, corridor stacking and well tie to reflection seismic data. Examples of data, acquired by GStreamer and processed in RadExPro software are shown below.

Raw VSP section, acquired by GStreamer geophone array and P-wave energy source

Vertical (Z-) component. Distance between the borehole and source (sledgehammer) is 5 m. Trace spacing is 1 m, depth range: 5–124 m.

VSP section, acquired by GStreamer geophone array and SH-wave energy source

“Right” and “left” shots were performed using SHock energy source to generate SH+ and SH- polarized seismic gathers. Rotation of the components was performed using 3C orientation routine in RadExPro software and resulted in clear SH-wave energy on X component. Subtraction of reverted polarity gathers enhanced signal-to-noise ratio with removing any residual P-wave energy. Seismic gather after such preprocessing and 3C-orientation is shown. Distance between the borehole and the source (sledgehammer, horizontal blows) is 0.6 m. The trace spacing is 1 m, the depth range: 1–120 m.

Raw VSP section, acquired by GStreamer geophone array and SH-wave energy source

Distance between the borehole and source (sledgehammer, horizontal shots) is 0.6 m. Trace spacing is 1 m, the depth range: 1–120 m. VSP section, its amplitude spectrum and extracted S-wave velocity profile are shown.

Geodevice offers equipment for borehole seismic surveys as well as acquisition, education and processing services.

Specification

Number of modules in array	1 – 8 pc
Number of channels in module	3 pc
Compensation coupled geophones	yes
Natural frequency of geophones	12.5 Hz
Maximum operating pressure	15 atm.
Interval between modules in array	1 – 10 m
Maximum diameter of module	60 mm
Borehole diameter range	70 – 150 mm
Clamping force range	1:7 – 1:11
Remote snapping of springs	yes
Operation without plummet in the well	yes
Compatible with linear seismic stations	yes

Additional Equipment

Borehole sources and energy sources

Seismographs

Reels and Synchronizes

Processing Software

RadExPro

ZondST2d — 2D seismotomography interpretation (refracted waves)

ZondST3d — 3D seismotomography interpretation (refracted waves)

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Geophone array GStreamer

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