80 Well seismic surveying and acoustic logging 3.2.1 Necessary resources for data acquisition Listed below are the necessary resources in terms of equipment, vehicles and personnel. • Equipment: 1. logging unit, which includes: a number of probes, a winch with several hundred meters of cable, to which the probes are connected, a recording and digitization unit (digitization can be done at the sensor level), a system for the visualization and printing of the field recordings, and a depth measurement system. 2. one or more acoustic probes 3. a seismic source (weight drop), if a VSP operation is planned with the acoustic logging 4. a lifting system with pulleys to lower the logging (and VSP) probes 5. equipment should be checked periodically (maintenance, calibration). • Vehicles: 1. either: a logging unit (preferably all-terrain/off road), enabling the transport of personnel and equipment (logging probes and optional VSP probes...) 2. or: a logging unit and one vehicle or a trailer to transport the VSP source (if a VSP operation is planned with the acoustic logging). • Personnel and expertise: 1. two suitably qualified operators to execute the procedure (winch, lowering of logging probes, acquisition); 2. one geophysicist (Head of Mission) qualified for data quality control at acquisition and can also be an operator. 3.2.2 Implementation in the field In this section, we describe: 3.2.2.1 Description of an acoustic logging operation in a vertical borehole In vertical boreholes, it is assumed that there is a cylindrical symmetry of the geological formation with respect to the borehole axis. For this measurement, the hole must be in water (borehole mud). The acoustic probe is lowered using centralizers. It is recommended to first measure the borehole diameters (caliper). After setting the zero (probe reference) according to a reference plane (raft, rotary table...) or on the ground surface, the probe is lowered to a given depth chosen by the operator to make stationary measurements. These measurements enable the verification of the acoustic recordings, the correct operation of the tool, the repeatability of measurements, and the assessment of the signal-to-noise ratio and the
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