HINZ Messtechnik announces a multilevel VSP tool string for depths up to 2500 m
Vertical seismic profile (VSP) data is generated by a surface source and recorded by geophones located at many depth levels spanning the entire borehole.
This multilevel tool string can be composed by a number of 3-component digital geophone units connected with inter tool cables of variable length. Useful numbers are 4 or 8 units, but can be more on demand.
An optional top unit contains gamma ray and casing collar locator to ensure accurate depth correlation.
The tool string is powered over 4-conductor logging cable. Line 1+3 is RS-485 bus, line 2+4 is +72 Volts DC, Armor is GND.
Common properties of all 3 C-Digital geophone units:
Dimensions: length = 60 cm, dia = 60 mm, weight = 6 kg
Three geophones arranged in an X-Y-Z pattern and an optional hydrophone
Motorised clamping arm. All arms open in parallel to reduce survey time. Full range clamping time is 30 sec.
Clamping force is software controlled, ratio force/mass is more than 5:1.
Clamping arms can easily be changed and adjusted in length and stiffness.
Four channel 24-bit ADC sampling with 48 ksps. 65.000 samples ringbuffer for each channel allows vibroseis recording.
Logical unit number and responses to RS-485 commands.
Downhole DSP handles oversampling and correlations.
An uphole trigger unit communicates via 2-line RS-485 bus with all downhole units. Transmission speed depends on length of logging cable and is selectable up to 250 kBaud. Voltage input to trigger unit is 12V, 0.5A DC. The uphole trigger unit supplies all downhole units with 72 Volt DC power. It is connected via USB and controlled by Windows recording software. The trigger unit also has four 24-Bit ADC-channels for uphole reference geophone recording. The RS-485 bus can be extended uphole to increase number of uphole channels.
When the seismic source at the surface fires, a precisely timed command is send from the trigger unit via RS-485 bus to all downhole units to syncronize data recording.
A depth counting unit in the trigger unit allows connection to different logging winches.