Southwest Research Institute® (SwRI®) News

Seismic Velocity Logging Probe

San Antonio, Texas -- Sept. 21, 1978 -- A seismic velocity logging probe of innovative design and unusual capabilities, developed by Southwest Research Institute® (SwRI®), has been honored as one of the 100 most significant new technical products of the year.

The new probe, Institute officials said, is the first of its kind to be capable of: working in either dry or fluid-filled boreholes, and providing direct, high-precision measurements of both compressional (P, or pressure) waves and shear (S) waves in geologic materials.

The system has been selected as a winner in the 1978 I-R 100 competition sponsored by Industrial Research magazine, officials of the publication announced Thursday in Chicago.

Accurate information on P and S wave velocities, along with data on density of material involved, can be used to provide valuable information on the geological and engineering characteristics of earth structures, said Dr. Thomas E. Owen, director of the SwRI Department of Geosciences.

Conventional probes, he said, are dependent on fluid in the borehole for their operation, using it as a coupling medium to relay seismic energy pulses between probe and surrounding material.

The new probe operates differently, he explained. Its transducers for sending and receiving seismic pulses are mounted on hydraulically actuated pistons which are extended to make direct contact with the borehole wall, thus eliminating need for fluid couplant and at the same time improving the accuracy of measurement.

Key figure in the SwRI development team working on the probe are engineers Sidney A. Suhler of the Department of Geosciences, program leader, and Edgar C. Schroeder of the Department of Mechanical Sciences, in charge of mechanical design.

The probe, developed for the U.S. Geological Survey Branch of Special Projects at Denver, is housed in a cylinder 2 inches in diameter and 17.7 feet long. It is connected by data logging cable to a surface control unit. Seismic signals are transmitted in analog waveform.

The device can be operated in horizontal as well as vertical exploratory holes, and can function in any borehole from 3 to 6 inches in diameter (using an extender beyond the 4-inch range). The probe is centralized in a borehole by extension of reaction pistons placed generally opposite the transducer pistons, as well as by bowspring modules at top and bottom.

Downhole equipment includes a transmitter module and a receiver module, separated by an acoustic isolator section. They may be used in one assemblage, or as two units operated in separate boreholes to evaluate intervening materials.

Development of the operational system grew out of an earlier SwRI program conducted for the Bureau of Mines Denver Mining Research Center, in which investigators demonstrated feasibility of the concept as applied to evaluation of materials associated with mining operations.

A second operational probe of similar design, 2-3/4 inches in diameter, is now under development for the Denver Mining Research Center, intended for use in coal-related research.

Owen emphasized the new probe's accuracy of measurement. Operating with errors of less than about 2 percent, he said, it provides a high quality of data surpassing that previously available. Furthermore, there is no need for computer data processing of the kind usually required in conventional probe operation to distinguish between types of seismic wave. The direct physical contact between transducers and borehole wall is responsible for this advantage, he said. He explained:

In a logging system using fluid as a coupling medium, P waves will propagate through the fluid from the probe, but S waves will not. The system, therefore, must rely on wave-type conversion at the fluid-rock interface, and on signal processing to separate the P and S waves in the received seismic pulses.

While operators using a conventional system frequently must wait for interpretation of their data at a remote computer facility, users of the new system can interpret their data directly at the test site.

"With our equipment on the site," Owen said, "you can see the P wave and the S wave arrivals distinctly in the raw data."

For more information about the Seismic Logging Probe, contact Joe Fohn, Communications Department, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas, 78228-0510, Phone (210) 522-4630, Fax (210) 522-3547.

SwRI News separate.gif (834 bytes) SwRI Home