Down hole periodic seismic generator

A down hole periodic seismic source for operation within a bore hole to produce seismic shear waves through surrounding earth strata comprising

• an elongated housing adapted for lowering into the bore hole by a cable means;
• clamping means carried by the housing for selectively rigidly clamping said housing to the wall of the bore hole;
• pneumatic oscillator means carried by the housing for producing vertical seismic vibration in the housing;
• a pneumatic pressure source carried by the housing for providing air under pressure;
• and
• a variable speed electro-mechanical drive means operably connected between the pneumatic pressure source and the pneumatic oscillator means for producing seismic vertical shear waves over a discrete low frequency range.

A down hole periodic seismic source for operation within a bore hole to produce seismic shear waves through surrounding earth strata comprising

• an elongated housing;
• means for lowering said housing into a bore hole;
• clamping means carried by the housing for selectively, rigidly clamping said housing to the wall of the bore hole;
• self-contained pneumatic reservoir means carried by the housing;
• a longitudinal pneumatic oscillator carried by the housing;
• and
• value means operably connected between the reservoir and the oscillator for reciprocally driving said oscillator longitudinally with respect to the bore hole at low frequencies to produce predominantly vertical shear waves,
• whereby vibratory seismic vertical shear waves are transmitted through the clamping means into the surrounding earth strata and wherein said clamping means comprises a plurality of radially spaced shoe members engageable with the wall of the bore hole, a reversible servo motor, and scissor-jack screw means operably connected between the servo motor and the shoe members for selectively retracting or extending said shoe members into rigid engagement with the wall of the bore hole.

A down hole periodic seismic source for operation within a bore hole to produce seismic shear waves through surrounding earth strata comprising

• an elongated housing;
• means for lowering said housing into a bore hole;
• clamping means carried by the housing for selectively, rigidly clamping said housing to the wall of the bore hole;
• self-contained pneumatic reservoir means carried by the housing;
• a longitudinal pneumatic oscillator carried by the housing;
• and
• value means operably connected between the reservoir and the oscillator for reciprocally driving said oscillator longitudinally with respect to the bore hole at low frequencies to produce predominantly vertical shear waves,
• whereby vibratory seismic vertical shear waves are transmitted through the clamping means into the surrounding earth strata and wherein the selfcontained pneumatic reservoir means comprises an elongated pneumatic air chamber, an electric motor carried by the housing, a rotatable shaft operably connected to the motor and extended into the air chamber and including means for converting rotary motion into reciprocal motion, an air piston reciprocally disposed in the chamber and operably connected to said shaft and pneumatic porting means carried by the housing and having a pressure passageway operably connected between the air chamber and the valve means whereby longitudinal travel of said piston forces air under pressure through the pneumatic porting means to the valve means.

A down hole periodic seismic source for operation within a bore hole to produce seismic shear waves through surrounding earth strata comprising

• an elongated housing;
• means for lowering said housing into a bore hole;
• clamping means carried by the housing for selectively, rigidly clamping said housing to the wall of the bore hole;
• self-contained pneumatic reservoir means carried by the housing;
• a longitudinal pneumatic oscillator carried by the housing;
• and
• valve means operably connected between the reservoir and the oscillator for reciprocally driving said oscillator longitudinally with respect to the bore hole at low frequencies to produce predominantly vertical shear waves,
• whereby vibratory seismic vertical shear waves are transmitted through the clamping means into the surrounding earth strata and wherein the longitudinal pneumatic oscillator comprises an elongated cylindrical chamber, first air passageway means operably connected between a first end of the chamber and the valve means, second air passageway means operably connected between second opposite end of the chamber and the valve means and an air hammer member reciprocally disposed in the chamber, said valve means being capable of selectively providing pressurized burst of air alternatively through said first and second air passageway means causing said hammer to oscillate within the chamber to provide periodic seismic vibration within the housing.

A down hole periodic seismic source for operation within a bore hole to produce seismic shear waves through surrounding earth strata comprising

• an elongated housing adapted for lowering into the bore hole by a capable means;
• clamping means carried by the housing for selectively, rigidly clamping said housing to the wall of the bore hole;
• pneumatic oscillator means carried by the housing for producing vertical seismic vibration in the housing;
• a pneumatic pressure source carried by the housing for providing air under pressure;
• and a variable speed electromechanical drive means operably connected between the pneumatic pressure source and the pneumatic oscillator means for producing seismic vertical shear waves over a discrete low frequency range and wherein the variable speed electromechanical drive means comprises a variable speed electric motor, a rotary valve connected to the output of the electric motor and pneumatically connected between the pressure source and the oscillator whereby the amount of air provided to the valve decreases as the oscillator frequency increases and including means carried by the oscillator to produce a substantially flat seismic power output over said discrete frequency range.