For several years, Landtech has been involved in surface micro-seismic monitoring and hydraulic fracturing monitoring applications. Our approach to microseismic monitoring services is to keep the cost to you at a minimum by avoiding expensive borehole sensors and using surface monitoring devices. All of which have been specifically designed for this type of application.

There are many benefits to our method of surface monitoring:

Benefits

  • Use of miniature digitizer/recorder units measuring just 168 x 106 x 68mm.
  • Units can be easily buried into the ground, meaning they will be hidden from view.
  • Our units have an extremely low power consumption of just 0.7W. They can be run for 6 days with a 9Ah battery.
  • 3/6 channels compact digitizer/recorder units.
  • Ultra high 23.6bit (>139dB) resolution at 250sps. Up to 32bit at lower sample rates.
  • Custom embedded FAT32 file system.
  • Data recorded to a microSD card for easy data retrieval.
  • DPLL with ultra low drift (less than 17usec between one hour GPS cycles) synchronised by GPS.
  • Full sensor/digitizer test functions.
  • Units allow for both Serial and Ethernet communication.
  • Real time Telemetry operation.
  • Seiscomp/SEEDlink and Earthworm ready.
  • On site data processing and automatic P arrival time.
  • P arrival time transmission over VHF, UHF, WiFi, GSM to the central processing PC.
  • MS Windows custom acquisition software available.
  • Units are fully waterproof and can operate under a wide range of temperatures.
  • Units come supplied with plug bayonet connectors making them quick and safe to use.
  • Units can be used with a variety of different software applications including: DataViewer; DataMonitor; DataConverter; and Firmware Update.
  • Double or quad geophone sensor for higher sensitivity and lower noise.
  • Small sensor diameter, with smart and efficient clamping.
  • Real time data transmission and processing (where possible.)
  • Near real time data processing.
  • Quick and easy seismic network installation with reliable recording equipment.

 

 Landtech’s Microseismic Sensor

Figure 1: The C400 borehole micro-seismicity monitoring sensor

Our S-400 seismic sensor design is based on our favorite S-100 three-axis seismic sensor, mainly used in Passive Seismic Tomography applications. The new S-400 seismic sensor has specially designed to be installed into small diameter boreholes in oil and gas fields. This keeps installation costs low. The sensor can be placed at a depth of up to 200m. However, we usually suggest it is installed at a depth of between 10 and 50m depending on the level of background noise.

Recording hydraulic fracturing events from the surface is not an easy task and is almost impossible to do with off the shelf equipment. Our engineers have therefore designed special equipment and software to do so. Our equipment works to minimise the electronic noise floor, increase the downhole gain and increase the sensor sensitivity. We achieve this by adding more geophones per channel to the downhole sensor.

Inside the sensor’s body there are four very high gain geophone elements in order to increase the signal gain and minimise the signal noise. The sensor’s configuration is able to record even events of negative magnitude. We can also support a double geophone configuration version with our S-200 sensor.

The characteristics of both sensors are shown below. Four different types of sensor have been manufactured and used according to the requirements of each application.

Spec
Sensor Model C200
Sensor Model C400
Geophones per axis (OMNI-2400 15 Hz)
2
4
Sensitivity
104 V/m/sec
208 V/m/sec
Coil resistance
2400 Ω
2400 Ω
Total Resistance
4800 Ω
9600 Ω
Damping
0.57
0.57

Table 1 – Sensor Specifications using OMNI-2400 geophone elements
 

Spec
Sensor Model C200
Sensor Model C400
Geophones per axis (ION SM6-UA10Hz)
2
4
Sensitivity
157.8 V/m/sec
315.6 V/m/sec
Coil resistance
3500 Ω
3500 Ω
Total Resistance
7000 Ω
10500 Ω
Damping
0.284
0.284

Table 2 – Sensor Specifications using ION SM6 UA10 geophone elements

 

Landtech’s Digitizer/Recorder

Landtech is proud to be able to offer the “state of the art” 32-bit resolution seismic digitizer. It is able to run on three or six analog input channels, offers extremely high resolution, especially in higher sampling rates from 250 to 1000 samples per second (sps.) The RMS effective resolution is 23.7 bits for a sampling rate of 250 sps, providing a dynamic range greater than 138db. Using data rates of lower than 100sps, a resolution of up to 32bits can be achieved.

The unit can be run for a week on just a single 7.2Ah Lead-Acid battery. All recordings are in CoRE32 format and captured directly to a FAT32 removable microSD flash card. Timing is monitored through a very accurate DPLL unit which is synchronised by a GPS receiver. The overall drift is extremely low (4*10-9 seconds) when the GPS is turned off. However, it is periodically switched on, usually once every hour for DPLL synchronisation. The digitizer provides real time data streaming in conjunction with the local recording through the Serial or Ethernet port or WiFi connection. The digitizer is ideal for micro-cracking monitoring, hydraulic fracking monitoring, micro-seismic monitoring and other applications where both high resolution and high dynamic ranges are required. When combined with the S-400 sensor, it can record even events at the surface with very small magnitude -1.8R.

Figure 2: The SRi32 32bit fracturing Digitizer/Recorder (front side)

Figure 3: The 32bit fracturing Digitizer/Recorder (back side)

Figure 4: Digitizer Noise Histogram @ 250sps data rate

Figure 5: Digitizer Signal Spectrum @ 250sps data rate
 

The SRi32 digitizer/recorder is based on a very powerful ARM type processor, similar to the processors that modern smartphones use. The firmware we employ is completely unique and not based on android or other Linux applications. Using a custom embedded operating system we can harness all the processor’s capabilities without wasting money on resources for unnecessary processes.

The firmware runs only the acquisition, filtering, time stamping, processing and storage functions. The data can be extracted any at time through the Serial/Ethernet ports. The data can then be transferred to any PC for real time processing.

Alternatively, the instrument can transmit only the times of the seismic event to the acquisition server. There, the local micro-earthquake magnitude and hypocenter location can be automatically calculated. The advantage of this configuration is that the transmitted data will be low volume and so there is no need to install a wide bandwidth communication channel. Any low data rate VHF or UHF channel can be used.

The unit’s total power consumption is extremely low. Only 0.7W for 3 channels continuous recording/processing. The instrument can operate for one week powered by a small 12V/7.2Ah rechargeable battery.

Figure 6: SRi32 Digitizer/Recorder and C400 sensor
 

Depending on the application required, the field engineer is able to setup the fracturing/microseismic network accordingly. VHF or UHF is generally the favoured method of communication between the seismic stations and server due to the ease of installation of the antennas which can be directional, omni-directional or vertical. Signals can be transmitted at great distance and transmission will not be affected by landscape anomalies or other physical barriers. The data rate is low, but more than ample when only P arrival time information has to be transmitted.

Additionally, data can be transmitted to the server in real time using a WiFi connection, or GPRS/3GH if the installation field has GSM coverage.

Figure 7: VHF and UHF telemetry modem

Figure 8: WiFi wireless bridge

Figure 9: GSM-3G industrial router
 

Real Time Data Telemetry via Seiscomp/Seedlink

Our digitizers/recorders support Seiscomp serial plugin. Our newest model also comes with a built-in Seedlink server. This means that data can be transferred via a robust and reliable Seedlink protocol. Using Seiscomp software the user can acquire the data from the seismic stations in real time and setup automatic processing. The software is a freeware, open source software, implemented from the GFZ Potzdam institute (https://www.seiscomp3.org/) and it runs under Linux OS.

Alternatively, you may prefer to use our specially designed telemetry software which can be run using MS Windows. Benefits of this software are:

  • Real time data acquisition from the remote seismic stations.
  • Data exported in CORE24 or MiniSEED format.
  • TCP/IP protocols.
  • Transmission error correction algorithm.
  • Seiscomp/Seedlink plug-in.
  • Sends user commands to the digitizer (seismometer lock/unlock, centering etc.)

Figure 10: Real Time Telemetry over Seiscomp/SeedLink

Figure 11: Real Time Telemetry Fracturing / Microseismic Network
 

Automatic Event detection Software

The micro-event detection process of the raw data is always a critical point of a micro-seismicity monitoring application. Special Software has been developed based on the following independent modules:

A. Trigger Module. The Trigger module applies our modified recursive STA/LTA algorithm to each data file and detects triggers regardless of if the trigger is generated by noise or seismic event.

B. Classifier Module. The Classifier module uses high order statistics to categorise whether the trigger is a noise or seismic event.

C. Association Module. The Association module compares the time stamp of the primary arrival of the seismic waves to all stations of the same group. If the time difference is less than a value in a predefined number of stations, the seismic wave is identified as an event.

D. Post Processor Module. The Post Processor Module gives the user the ability by plotting the files with the selected events, to confirm that the triggered data are seismic events. False triggers can be rejected by the user.

Figure 12: Real Time Telemetry Fracturing Network
 

Visit our Reservoir Monitoring web page at http://www.landtech-geophysics.com