Hydraulic impulse generator and frequency sweep mechanism for borehole applications

Apparatus for at least partially interrupting flow of a pressurized fluid that is circulating though a conduit, comprising:

• (a) a housing;
• and
• (b) a valve substantially enclosed by said housing, said valve comprising;
• (i) an inlet port configured to couple in fluid communication with the conduit through which the pressurized fluid is circulating;
• (ii) an outlet port configured to couple in fluid communication with the conduit through which the pressurized fluid is circulating;
• (iii) a plurality of fluid passages configured to selectively couple in fluid communication with said inlet port;
• (iv) a first member that is actuated by the pressurized fluid to cycle between an open position and a closed position, such that when in said closed position, said first member at least partially interrupts a flow of the pressurized fluid through the outlet port;
• and
• (v) a second member disposed within said first member, the second member being reciprocated back and forth between first and second positions during each cycle by the pressurized fluid, a position of said second member determining which of said plurality of fluid passages is coupled in fluid communication with said inlet port.

A method for generating pressure pulses within a conduit, comprising the steps of:

• (a) coupling a pressure activated flow interruption valve to the conduit, the valve being configured to periodically interrupt a flow of the pressurized fluid in the conduit, a flow of the pressurized fluid through the valve causing the valve to cycle between an open position and a closed position;
• (b) circulating a pressurized fluid through the conduit;
• and
• (c) directing the pressurized fluid through the valve to cyclically actuate the valve, thereby periodically interrupting a flow of the pressurized fluid in the conduit as the valve cycles between the open position and the closed position.

A method for imparting vibrations to a drillstring to reduce friction in vertical, horizontal, inclined, or extended reach wells by cyclically interrupting fluid flow through the drillstring, comprising the steps of:

• (a) inserting a drillstring into a well;
• (b) circulating a pressurized fluid through the well;
• and
• (c) periodically interrupting a flow of the pressurized fluid at a selected point within the well to produce pressure pulses, the pressure pulses imparting vibrations to the drillstring, thereby reducing friction between the drillstring and the well.

A method for reducing undesirable bit and drillstring motions including a whirl, a stick-slip, a wind-up, and bounce, comprising the steps of:

• (a) inserting a drillstring into a well;
• (b) circulating a pressurized fluid through the well;
• and
• (c) periodically interrupting a flow of the pressurized fluid at a selected point within the well to produce pressure pulses, the pressure pulses imparting vibrations to the drillstring, thereby reducing whirl, stick-slip, wind-up and bounce of the drillstring.

Apparatus for at least partially interrupting a flow of a pressurized fluid that is circulating though a conduit, to generate pressure pulses, a frequency of the pressure pulses varying in a repetitive pattern, comprising:

• (a) a valve substantially enclosed by a housing, said valve including:
• (i) a first member that is actuated by the pressurized fluid to cycle between an open position and a closed position, such that when in said closed position, said first member at least partially interrupts a flow of the pressurized fluid through an outlet port, thereby generating a pressure pulse;
• and
• (ii) a second member disposed within said first member, the second member being reciprocated back and forth between first and second positions during each cycle by the pressurized fluid, such that a position of said second member controls a timing of the valve changing between an open state and a closed state;
• and
• (b) a frequency modulator varies the timing of said valve by varying a stroke of said second member in a repetitive pattern, such that the frequency of the pressure pulses is varied in a manner corresponding to the repetitive pattern of the second member.

Apparatus for generating a series of impulsive pressure pulses having a repeat period between successive impulsive pressure pulses that is regularly varied, said impulsive pressure pulses propagating into a formation surrounding a borehole, comprising:

• (a) a housing adapted to be coupled into a drillstring, adjacent to a drill bit;
• (b) a valve substantially enclosed by said housing, said valve comprising a poppet whose position determines whether the valve is open or closed, and a pilot spool whose motion determines a timing of the valve, impulsive pressure pulses being generated each time said valve closes, the pilot spool and poppet cooperating to redirect a flow of drilling fluid to achieve a reciprocating motion within the housing to periodically open and close the valve;
• and
• (c) a variable flow restrictor substantially disposed within said housing, said variable flow restrictor regularly varying the timing of said valve by limiting an axial velocity of the pilot spool, each variation in the timing of the valve varying the repeat period between successive impulsive pressure pulses.

A seismic while drilling system, comprising:

• (a) a drillstring including a drill bit and a seismic source, said seismic source comprising:
• (i) a valve having a poppet whose motion and position determines whether the valve is open or closed;
• and a pilot spool whose motion and position determines a timing of the valve periodically opening and closing, seismic pressure pulses being generated each time said valve closes, the pilot spool and poppet cooperating to redirect a flow of drilling fluid to achieve a reciprocating motion;
• and
• (ii) a frequency modulator configured to regularly vary the timing of said valve by varying a stroke of said pilot spool in a repetitive pattern to achieve seismic pressure pulses having a frequency that is varied in a repetitive pattern;
• and
• (b) at least one seismic receiver for observing seismic waves caused by the seismic pressure pulses generated by said valve.

A method for performing seismic analysis while drilling, comprising the steps of:

• (a) inserting a drillstring including a drill bit into a borehole;
• (b) circulating a pressurized fluid through the borehole to activate the drill bit to start drilling;
• (c) during the drilling by the drill bit, periodically interrupting a flow of the pressurized fluid to the drill bit at a selected point within the well to produce seismic pulses;
• (d) periodically varying a timing between each successive interruption in a repetitive pattern;
• (e) collecting seismic data for the seismic pulses while drilling;
• and
• (f) analyzing the seismic data for the repetitive pattern used to generate the seismic pulses, to filter out seismic noise from other sources.

A method for generating seismic pulses to evaluate characteristics of a formation adjacent to a borehole, comprising the steps of:

• (a) circulating a pressurized fluid through a conduit that extends into the borehole;
• (b) periodically at least partially interrupting a flow of the pressurized fluid at a selected point within the borehole to generate seismic pulses, said seismic pulses radiating from the borehole into a formation adjacent to the borehole, a timing between successive interruptions of the flow being varied according to a repetitive pattern;
• and
• (c) redirecting at least a portion of said flow of the pressurized fluid within the conduit such that the step of partially interrupting a flow of the pressurized fluid at a selected point within the borehole does not completely interrupt a circulation of the pressurized fluid from an inlet of said conduit to said selected point, thereby preventing generation of a water hammer effect.

A method for removing scale from within a tube that extends through at least part of a borehole, comprising the steps of:

• (a) circulating a pressurized fluid through a conduit that extends into the tube;
• (b) periodically at least partially interrupting a flow of the pressurized fluid at a selected point within the borehole to generate negative pressure pulses, a timing between each successive interruption being varied according to a repetitive pattern;
• and
• (c) propagating the negative pressure pulses within the tube so that the scale is exposed thereto, said negative pressure pulses removing the scale from an internal surface of the tube.

A method for removing fines from a section of a wall of a borehole, comprising the steps of:

• (a) circulating a pressurized fluid through a high velocity flow course disposed in the borehole;
• (b) periodically reducing a flow of the pressurized fluid through the high velocity flow course to generate negative pressure pulses, a timing between each successive reduction being varied according to a repetitive pattern;
• and
• (c) propagating the negative pressure pulses into a wall of the borehole, said negative pressure pulses drawing the fines from the wall.

A method for clearing debris and fines from a plurality of perforations extending through a wall of a borehole, comprising the steps of:

• (a) circulating a pressurized fluid through a high velocity flow course disposed in the borehole;
• (b) periodically reducing a flow of the pressurized fluid through the high velocity flow course to generate negative pressure pulses, a timing between each successive reduction being varied according to a repetitive pattern;
• and
• (c) propagating the negative pressure pulses into the plurality of perforations extending through the wall of the borehole, said negative pressure pulses removing debris and fines from said plurality of perforations.

A method for weakening rock within a borehole, comprising the steps of:

• (a) circulating a pressurized fluid through a high velocity flow course that is disposed within the borehole;
• (b) periodically interrupting a flow of the pressurized fluid through the high velocity flow course to generate negative pressure pulses, a timing between each successive interruption being varied according to a repetitive pattern;
• and
• (c) propagating the negative pressure pulses toward the rock, said negative pressure pulses applying impulsive differential pressures of sufficient magnitude to the rock to weaken the rock, thereby enabling the rock to be more readily penetrated with a drill bit.

A method for detecting changes in pore pressure gradients within a borehole, comprising the steps of:

• (a) periodically producing both pressure and shear waves originating at the bottom of the borehole;
• (b) collecting data corresponding to the pressure and shear waves to generate pressure and shear wave velocity profiles;
• and
• (c) analyzing the shear wave velocity profiles to detect any change, a change in the shear wave profiles being indicative of a change in pore pressure gradients.