Electroacoustic pulse source for high resolution seismic prospectings

• US 4,734,894 A
• Filed: 06/04/1986
• Issued: 03/29/1988
• Est. Priority Date: 12/13/1984
• Status: Expired due to Fees

• Current Assignee: Consiglio Nazionale Delle Ricerche (Repubblica Italiana)
• Original Assignee: Consiglio Nazionale Delle Ricerche (Repubblica Italiana)
• Inventors: D'Ottavi, Enrico, Cannelli, Giovanni B., Santoboni, Silvio
• Primary Examiner(s): Kyle, Deborah L.
• Assistant Examiner(s): Steinberger, Brian S.
• Application Number:
  US06/878,377
• Time in Patent Office: 664 Days
• Field of Search: 367/137, 367/138, 367/147, 367/148, 367/151, 367/171, 367/174, 181/108, 181/110, 181/113, 181/114, 181/116, 181/119, 181/118, 376/144, 376/145, 372/86, 315/241 P, 315/308
• US Class Current: 367/147
• CPC Class Codes: G01V 1/157 using spark discharges; using exploding wires

Abstract

A seismic source consists of an electroacoustic transducer having a metallic structure, shaped like an empty round paraboloid (1) closed at the base by means of an elastic diaphragm and filled with a proper liquid. Around the focus of the paraboloid two main electrodes (5) are set and an auxiliary electrode (6) is put between the first ones. The main electrodes (5) are connected to a set of capacitors (C_o) supplied by a high-voltage power supply (HT). One of the main electrodes (5b) and the auxiliary electrode (6) are connected to a trigger pulse generator (EHT) driven by a remote control (4) via a synchronization pulse generator (3). The discharge between the main electrodes (5) primed by a preliminary spark, generates an acoustic pulse through the liquid medium of the transducer on the ground where the paraboloid (1) is engaged. So the transducer generates seismic waves utilized for shallow prospecting both on land and underwater.

Claims

1. A seismic source adapted for high resolution seismic prospecting comprising:

an electroacoustic transducer including a metallic hollow bell-shaped structure having a closed head and an open base that is closed by an elastic diaphragm, and being filled with a dielectric liquid, the structure having an inner reflective surface in the shape of a circular paraboloid having a vertical axis and a focal point, the structure further enclosing a pair of main electrodes positioned near the head on opposite sides of the focal point and with a gap therebetween, an auxiliary electrode positioned in the gap between the two main electrodes, and means for moving the main and auxiliary electrodes vertically along the vertical axis to vary their distance from the focal point and for moving the main electrodes horizontally normal to the axis to vary the width of the gap;

first circuit means for storing energy in a capacitor bank for maintaining a voltage across the main electrodes insufficient for initiating a discharge across the gap so long as the dielectric liquid in the gap is not ionized, and;

second circuit means connected between one of the main electrodes and the auxiliary electrode for establishing therebetween controllably a voltage sufficient to ionize the dielectric liquid in the gap whereby there is triggered an electrical discharge between the two main electrodes across the gap for exciting an acoustic wave in the dielectric liquid directed at the elastic diaphragm at the base end of the hollow structure.

2. A seismic source in accordance with claim 1 in which the first circuit means include a bank of capacitors of which selected ones may be connected in parallel for storing energy to be supplied to the main electrodes for creating the discharge across the gap.

3. A seismic source in accordance with claim 2 in which the first circuit means includes an inductor.

4. A seismic in accordance with claim 1 in which the first circuit means provides a voltage of about several thousand volts to the main electrodes and the second circuit means provides a voltage of at least a hundred thousand volts between the auxiliary electrode and one of the main electrodes.

5. A seismic source according to claim 1 which further includes means for adjusting the spacing of the main electrodes about the focal point.

6. A seismic source according to claim 5 which further includes means for adjusting the axial position of the main and auxiliary electrodes relative to the focal point.