Landtech always uses state of the art instrumentation that is particularly adjusted to Passive Seismic Tomography surveys (PST). The standard off-the-shelf seismographs, which are used by the Academic community and by some of our competitors, are not suitable for high resolution passive seismic tomography investigations due to their low sensitivity and low S/N ratio of the recorded seismic signals.
We possess the largest portable microearthquake network in the world. Since we are directly involved in the specification and design our seismic instrumentation, we can mobilise large networks worldwide and can operate in parallel many passive networks in various countries.
Below we present some of our seismological instruments particularly designed for passive seismic.
The seismic digitizers we use typically have 3 input channels, and capability for connection to a wide range of sensors. The digitizer is based on a powerful, wide dynamic range delta-sigma analog-to-digital converter, with very low noise characteristics and excellent power supply rejection. The sampling rate can be set to 40, 50, 60, 100, 125, 150, 200, 250, 300, 400 and 500 samples per second.
Optional, sampling rates of 1, 2, 5, 10, 20, 25 and 600, 700, 750,1000 samples per second can be supported. Data are stored in a Compact Flash type storage unit. Maximum acceptable storage unit is 2 GB, enough to store approximately 26 days data of 3 channels @ 100 samples per second. Compact Flash card units larger than 2GB can be optionally used to increase the recording period.
The power consumption is extremely low, allowing the recorder to operate connected to a typical 12V/55Ah battery without the need of recharging for long time periods. Communication plug-in allows the instrument to be connected to any Seiscomp PC. Seiscomp server collects data from the remote stations.The LCD display, displays the State-of-Health, time date and other information related to the instrument’s operation. Software tools have also been developed to support both field and base station operation. The recorder is intended for installation in harsh environments and is supplied with a portable waterproof plastic case, manufactured of HPX high-performance resin, with easy press & pull latches and durable soft-grip handle with easy access to all user features.
The Passive Seismic sensor (seismometer)
Landtech uses three-component velocity equivalent output seismic sensors. The design is based on the force-balance principle, thus using three simple geophone elements with natural frequency 4.5Hz the bandwidth of frequencies is extended from 90Hz, down to 0.2Hz.
The default length of the cable between the sensor and the electronics box is approximately 20 meters but it can be extended up to100 meters.
The geophones are housed in the same enclosure producing a solid waterproof sensor suitable for installation into boreholes where the noise is much less than the surface. The geophones are placed in order and are orientated following the 3-axes principle. A dot mark, incised on the plastic cover of the case, indicates the direction of each axis. Optionally, surface mount installation is available.
The sensor is totally controlled by an advanced signal conditioner circuit which supplies current to the geophones forcing them to a constant vibration at different frequencies. The signal conditioner circuit is fully protected against over voltage, opposite power supply polarity and lightning inductive currents. When inactive, it enters the “power-off” mode in order to reduce power consumption of the system.
This (3-component) seismometer is specifically designed for passive seismic surveys with a flat response towards the higher frequencies (encountered in this kind of seismic data). It uses sensitive electromagnetic sensors and no phase distorting digital filtering and amplification modules (DSP’s). The sensor is usually lowered to a depth of a few meters (in case of noisy areas) and is water proof.
LandTech’s real time telemetry station
Landtech has also developed a telemetry version of its digitizer. This unit is used in remote places where the accessibility is difficult. In this case data are sent to the collection centre via telemetry while the station is powered via solar panels. In addition to GSM telemetry the data can be sent via FM or Satellite telemetry as well.
LandTech’s seismic station consists of a combination between LandTechs digitizer, 3channels 24 bit digitizer, and an ARM embedded PC running Embedded Linux. The open source Seiscomp/Seedlink software has been compiled for the ARM-Linux operating system, and has been installed to the flash memory of the PC. The implication of the ARM based embedded PC enables the system to operate with considerably low energy consumption, running on a simple 12V55Ah DC battery for a long time. The SR-24 digitizer has 3 input channels, and capability for connection to a wide range of sensors. The digitizer is based on a powerful, wide dynamic range delta-sigma analog-to -digital converter, with very low noise characteristics and excellent power supply rejection. The sampling rate can be set to 1, 5, 25, 40, 50, 60, 100, 125, 200, 250, 300, 400 and 500 samples per second. The embedded PC provides an ethernet port. Configuration, as well as communication with the unit, is achieved through the ethernet port. Real-time telemetry can be achieved by connecting the instrument with any communication device like GSM modem, satellite modem UHF wide spectrum modem, wireless ethernet bridges… and many more. The station communicates with any seedlink server implementing a reliable real-time seismic station.
The LT FS ultra-sensitive sensor
The Landtech FS sensor is the only surface sensor in the market which can record microseismic events (even negative magnitudes!) from many kilometres down even microseisms generated during hydraulic fracking of a reservoir.
The sensor body has been designed in order to house twin or quad geophone strings for each axis. The orientation follows the 3-axis principle. This sensor has an external diameter of 50mm allowing it to be installed into small and shallow boreholes, hence reducing the cost of installation.
The sensor houses OMNI-2400 geophones. Using single geophone element per axis, the electronic noise floor becomes a limiting factor for this type of acquisition. Increasing the gain and minimizing the noise floor of the sensor give us the ability to record even smaller events.
Efforts were concentrated on minimising the electronic noise floor, increasing the down hole gain, and increasing the sensor sensitivity. This target has been achieved by adding more geophones (1-4) to the down hole sensor connected in series. Four different sensors have been manufactured.
The signal conditioner circuit is fully protected against over voltage, opposite power supply polarity and lightning inductive currents. When inactive, it enters the “power-off” mode in order to reduce power consumption of the system.
Landtech introduces the “state of the art” 32-bit resolution seismic digitizer, based on it’s latest technology. It has three analogue channels, with extremely high resolution, especially in higher sampling rates from 250 to 1000 samples per second (sps). The effective resolution is 23.6 bits when the data rate is 250 sps, giving a dynamic range greater of 136db to the instrument. Power consumption is extremely low, only 0.7W, allowing it to operate for long period, powered from a small 7.2Ah Lead-Acid battery. CoRE32 format data files are recorded directly to the FAT32 removable compact flash card. Timing is performed using a very accurate DPLL unit getting synchronized from a GPS receiver. The drift is extremely low (4*10-9sec) when GPS is off, and it can be periodically on and synchronize the DPLL. The digitizer provides also real-time data streaming in parallel with the local (CF) data storage, trough the serial port, or Ethernet port, or wi-fi spot. The digitizer is ideal for micro-cracking monitoring, hydraulic fracking monitoring, micro-seismic monitoring and other applications that high resolution and high dynamic range is required.
|Raw Data Plot|
|Signal Spectrum||Signal Histogram|
|Wi-Fly technology – Real-time data transmission|
|Station connections in chains – manual addressing mode|
|Ability for repeater usage if not clear line of sight|
|Error correction transmission algorithm|
|Satellite transmission of the network data in near real time|
This the latest development of Landtech Geophysics in the field of real-time reservoir monitoring. Instead of collecting all the waveforms from all deployed seismographs of the deployed surface network to a central processing unit, each 32-bit seismograph has an embedded PC with auto-picking algorithms and we send via VHF to the central processing unit only the arrival times of the seismic phases.