Transducer for sonic logging-while-drilling

An acoustic transducer for mounting on a tubular drill string member for use in making sonic logging measurements in a borehole while drilling through a subterranean earth formation, said transducer comprising:

• a plurality of transducer elements mounted in an array around a surface on the circumference of said tubular drill string member, said transducer elements being located at substantially equal angular spacings and being arranged to excite and produce or detect acoustic waves that propagate through said earth formation, said transducer elements being mounted to an elastomer ring that is sized to fit in an external annular groove in said tubular drill string member.

An acoustic transmitter for use in sonic logging in a subterranean earth formation during the drilling of a borehole into said subterranean earth formation, said sonic logging including measurements of sonic velocity, earth formation porosity, seismic reflection/feature correlation, and reservoir potential evaluation, said acoustic transmitter comprising:

• a tubular drill collar having a longitudinal axis and defining a circumferential surface;
• a circumferential transducer array having a plurality of individual transducer elements mounted external to said drill collar and in spaced relation around said circumferential surface of said drill collar;
• and electrical circuit means for connecting said plurality of individual transducer elements of said circumferential transducer array so that an electrical excitation applied thereto causes said transducer elements to generate a monopole acoustic wave that propagates into the subterranean earth formation surrounding the borehole.

A sonic well logging apparatus for use in determining the velocity of acoustic energy through a rock formation surrounding a borehole during the drilling thereof with a bit on the lower end of a drill string, comprising:

• a tubular collar adapted to be connected in the drill string above the bit, said collar having a first circumferential array of transducer elements mounted thereon, said first circumferential array being mounted in a first external annular groove in said collar, and second and third circumferential arrays of transducer elements being mounted in respective ones of a pair of second annular grooves in said collar, shield means surrounding respective ones of said annular grooves and having individual windows formed therein radially outward of each of said transducer elements;
• means for electrically exciting said first circumferential array to generate acoustic waves that propagate out into the rock formation;
• and means for detecting the arrival of said acoustic waves at each of said second and third circumferential arrays, whereby the detected waves can be used to compute the velocity of acoustic energy through the rock formation.

A sonic well logging apparatus for use in determining the velocity of acoustic energy through a rock formation surrounding a borehole during the drilling thereof with a bit on the lower end of a drill string, comprising:

• a tubular collar adapted to be connected in the drill string above the bit;
• a transverse assembly of stacked transmitting transducer elements in said collar and adapted to generate acoustic waves that propagate outward into the rock formation;
• and at least one ring assembly of individual receiving transducer elements mounted in an external annular groove in said collar and having substantially equal annular spacings and being located on substantially equal radii from the longitudinal axis of said collar, said receiving transducer elements being longitudinally spaced from said transmitting transducer elements a selected distance for detecting the arrival of said acoustic waves from the rock formation to enable computation of the velocity of acoustic energy through the rock formation.

A method of generating and detecting acoustic waves in a borehole to obtain a log of the velocity of said waves through the rock formation surrounding the borehole while drilling, comprising of steps of:

• mounting first and second ring arrays of acoustic transducers in respective annular elastomer bodies, mounting said elastomer bodies in respective annular grooves in the exterior surface of a drill collar, using said first ring array of acoustic transducers to produce monopole acoustic waves that propagate out into the formation;
• using said second ring array of acoustic transducers to detect arrivals of said monopole acoustic waves from the rock formation.

A method of performing acoustic logging of a rock formation surrounding a borehole while drilling by determining the velocity of acoustic waves through said rock formation, said method comprising the steps of:

• using first and second longitudinally spaced assemblies of transducer elements, one of said assemblies being a ring array of individual piezo-electric transducer elements mounted externally around the circumference of a collar within a drill string and above a drill bit, and the other of said assemblies being a stacked array of individual piezo-electric transducer elements mounted within the collar in bilateral symmetry;
• generating acoustic waves with one of said first and second longitudinally spaced assemblies of transducer elements that propagate outward into the formation;
• and detecting arrivals of such acoustic waves with the other of said assemblies to enable computation of the velocity of said acoustic waves through the rock formation.

A method of producing sonic wave energy for use in making acoustic measurements of earth formations surrounding a borehole, said acoustic measurements including logging measurements of sonic velocity, earth formation porosity, seismic reflection/feature correlation, and reservoir potential evaluation, said method comprising the steps of:

• providing a plurality of transducer elements mounted in a ring array around the circumference of a collar connected within a drill string;
• and preferentially exciting said transducer elements in a mode such that the polarity of the sonic waves produced is of a multipole order.

A sonic well logging apparatus for use in determining the velocity of acoustic energy through a rock formation surrounding a borehole during the drilling thereof with a bit on the lower end of a drill string, comprising:

• a tubular collar defining a circumferential surface, and adapted to be connected in the drill string above the bit, said collar having a first circumferential array of transducer elements mounted around said circumferential surface, and second and third circumferential arrays of transducer elements mounted around said circumferential surface, said first, second and third circumferential arrays being disposed in axially spaced relation with one another;
• means for electrically exciting said first circumferential array around said circumference to generate acoustic waves that propagate out into the rock formation;
• and means for detecting the arrival of said acoustic waves at each of said second and third circumferential arrays of transducer elements, whereby the detected acoustic waves can be used to compute the velocity of acoustic energy through the rock formation.