Seismic Well Logging

the study of the seismic properties of rocks in boreholes by determining the velocities and the coefficients of reflection, transmittance, and absorption of elastic waves. The results are used to interpret seismic exploration data, study the lithological composition and physical state of rocks (for instance, the permeability and porosity), detect productive petroleum and gas beds, and monitor the engineering conditions of the well (for example, determine the quality of cementation).

Two techniques can be used in seismic well logging. In the first, the seismic source—usually an explosive source—is placed near the surface of the earth and the detectors are placed within the well. This technique is used to determine the average properties in layers more than 50–100 m thick and to study the pattern of vibrations from various seismic waves within the medium (profile shooting). Well seismographs and field recording equipment are used, and vibrations are recorded in the frequency range from 20 to 150 Hz.

In the second technique, the seismic source and the detectors are placed together inside the well. This technique is used to study the seismic properties in layers up to 1–2 m thick, and vibrations are recorded in the frequency range from 10 to 100 kHZ (acoustic and ultrasonic well logging).

Probes with magnetostriction or piezoelectric sources and sensors are used as electromechanical transducers of elastic vibrations. Recording is conducted on the surface of the earth in a mobile well-logging station. The electrical signals are transmitted along a cable from the probe to the station. Acoustic well logging is used in conjunction with other geophysical methods of studying wells.