Dowhole orbital seismic source

Claim 2

A downhole seismic source for the simultaneous generation of orbital shear wave seismic energy and compression wave seismic energy into a fluid-filled borehole wall comprising: an elongated cylindrical frame means having a central axis and an outer wall supportable at a point along said borehole wall; and drive means disposed in said frame means and ener­gizable to impart an orbital motion to at least a portion of the frame means outer wall thereby to generate an orbital shear wave in said bore­hole wall.

Claim 3

A downhole seismic source as set forth in claim 1 wherein said cylindrical frame means comprises: a cylinder having continuous outer wall in contact with the borehole fluid; and top and bottom end cap structure secured to opposite ends of the cylinder.

Claim 4

A downhole seismic source as set forth in claim 1 or 2 wherein said drive means comprises: a drive motor providing rotational output; and first and second eccentric rotors receiving said rotational output, said rotors being equi­spaced along the central axis of said frame means and aligned in parallel and radial align­ment for synchronous eccentric rotation.

Claim 5

A downhole seismic source as set forth in claim 3 wherein said first and second eccentric rotors each com­prises: a circular disk having an eccentrically displaced shaft hole for receiving input of rotation.

Claim 6

A downhole seismic source as set forth in claim 3 or 4 wherein: said drive motor is a variable speed electric motor which includes a feedback encoder.

Claim 7

A downhole seismic source as set forth in claim 1 or 2 wherein said cylindrical frame means comprises: at least two cylindrical frames of relatively heavy mass secured in axial alignment by a largely open peripheral structural cage and defining a cylindrical cavity therebetween; a pliable boot enclosing said cavity outer wall and retaining fluid therein; and first and second end cap means secured to opposite ends of the secured cylindrical frames.

Claim 8

A downhole seismic source as set forth in claim 6 wherein said drive means comprises: a drive motor providing rotational output along said central axis; and a rotor disk having selected thickness and being driven eccentrically by said rotational output, said disk being disposed in said cavity to distend said boot in orbital manner relative to the borehole wall.

Claim 9

A downhole seismic source as set forth in claim 6 or 7 wherein said structural cage comprises: at least two peripherally disposed equi-spaced struts secured longitudinally between the respective frames.

Claim 10

A downhole seismic source as set forth in claim 6, 7 or 8 wherein said pliable boot comprises: a generally cylindrical elastomer membrane sealingly secured about the periphery of respective frames adjacent said cylindrical cavity.

Claim 11

A downhole seismic source as set forth in claim 7 wherein: said drive motor is a variable speed electric motor with at least one built-in feedback encoder.

Claim 12

A downhole seismic source as set forth in claim 1 or 2 wherein said drive means comprises: at least two equal first reaction masses having opposite ends and being secured in parallel juxtaposition and transverse alignment generally centrally in said frame means; at least two equal second reaction masses having opposite ends and being secured adjacent on each side of said first reaction masses but in right angle alignment relative to the first masses; a plurality of piezoelectric elements each bonded in affixure on respective ends of said first and second reaction masses and to the frame means cylinder; and means for energizing said piezoelectric elements in selected phase relationship to exert predeter­mined rotational transverse thrust to said cylindrical frame means.

Claim 13

A downhole seismic source as set forth in claim 11 which further includes: at least four linear bearings secured to support said first and second reaction masses.

Claim 14

A downhole seismic source as set forth in claim 1 or 2 wherein said drive means comprises: at least four electromagnetic coils having upper and lower pole pieces of metal having high magnetic permeability, said coils being held in quadra­ture array with the upper and lower pole pieces each being circularly aligned and with all pole pieces being secured within the mass of said cylinder; a non-magnetic ring of selected outer diameter bonded around said cylinder in the circular area between the circularly arrayed pole pieces; an iron ring of selected inside diameter greater than said non-magnetic ring outer diameter and disposed concentrically thereto; fluid-tight pliable boot means secured to said cylinder means on each side of said non-­magnetic ring to retain said iron ring in concentricity; fluid of selected viscosity and compressibility disposed within said boot means; and means for energizing said electromagnetic coils in selected quadrature phase relationship to displace said soft iron ring in rotational transverse thrust relative to said cylindrical frame means.

Claim 15

A downhole seismic source for generation of orbital shear wave seismic energy in a fluid-filled borehole, comprising: an elongated frame means of relatively heavy mass defining an interior space and having a circum­feral opening formed generally centrally therealong; means disposed in said interior space in com­munication through said circumferal opening for generating an elliptically polarized shear wave in the adjacent borehole wall; and means for supporting said frame means at a selected location in said borehole.

Claim 16

A downhole seismic source for generation of orbital shear wave seismic energy in a fluid-filled borehole, comprising: an elongated frame means of relatively heavy mass defining an interior space and having a circum­feral opening formed generally centrally therealong; means disposed in said interior space in com­munication through said circumferal opening for generating an elliptically polarized shear wave in the adjacent borehole wall; and means for supporting said frame means at a selected location in said borehole.