Apparatus and method for inducing longitudinal oscillations in subterranean drilling string

Abstract

A cavitation apparatus (CHRS) for use in subterranean drilling with a drilling rig, the rig having a drill bit and a drilling string mounted thereto through which a drilling fluid flows to the drill bit. The cavitation apparatus (CHRS) is adapted to be mounted in-line with the drilling string through which the drilling fluid flows. The CHRS has no moving parts and produces controlled low frequency, longitudinal fluctuations of at least a portion of a drill string to enhance the drilling rate of penetration (ROP). Optionally the entire drill string can be subjected to such controlled low frequency, longitudinal fluctuations.

What is claimed: 
     
         1 . A cavitation apparatus for use in subterranean drilling with a drilling rig, the rig having a drill bit and a drilling string mounted thereto through which a drilling fluid flows to the drill bit, the apparatus adapted to be mounted in-line with the drilling string through which the drilling fluid flows, the cavitation apparatus comprising:
 c. a hollow cylindrical body having an external diameter no greater than the external diameter of the drill string and an inlet end and an outlet end, each end adapted to be in fluid connection with the drilling string, the inlet end for receiving the drilling fluid from a downstream portion of the drill string and the outlet end through which the drilling fluid exits to an upstream portion of the drilling string,   d. the hollow cylindrical body having therein:
 i. a Venturi tube having an inlet opening and an outlet opening located between the inlet end and the outlet end of the cylindrical body, the Venturi tube having an interior diameter, 
 ii. a downstream cylindrical conical section having an inlet for receiving the drilling fluid from the inlet end of the hollow cylindrical body and an outlet for transferring the drilling fluid to the inlet opening of the Venturi tube, the diameter of the inlet to the downstream cylindrical conical section being greater than the outlet to the downstream cylindrical conical section, the outlet to the downstream cylindrical conical section in fluid communication with the Venturi tube inlet opening and of a diameter substantially equal to the Venturi tube interior diameter; 
 iii. an upstream cylindrical conical section, the upstream cylindrical conical section having an inlet for receiving the drilling fluid from the outlet opening of the Venturi tube and an outlet for transferring the drilling fluid to the outlet end of the hollow cylindrical tube, the diameter of the outlet to the upstream cylindrical conical section being greater than the inlet to the upstream cylindrical conical section, the inlet to the upstream conical section in fluid communication with the Venturi tube outlet opening and of a diameter substantially equal to the Venturi tube interior diameter, 
   wherein when the drilling fluid is passed through the drill string and the cavitation apparatus to the drill bit, low frequency longitudinal fluctuations are produced in at least a portion of the drill string to enhance the drilling rate (ROP) of the drilling string.   
     
     
         2 . A cavitation apparatus for use in subterranean drilling with a drilling rig, the rig having a drill bit and a drilling string mounted thereto through which a drilling fluid flows to the drill bit, the cavitation apparatus adapted to be mounted in-line with the drilling string through which the drilling fluid flows, the cavitation apparatus comprising:
 a. a hollow cylindrical body having an external diameter no greater than the external diameter of the drill string and an inlet end and an outlet end, each end adapted to be in fluid connection to the drilling string, the inlet end for receiving the drilling fluid from a downstream portion of the drilling string and the outlet end through which the drilling fluid exits to an upstream portion of the drilling string;   b. the hollow cylindrical body having therein:
 i. a Venturi tube having an inlet opening and an outlet opening located between the inlet end and the outlet end of the cylindrical body; 
 ii. a plurality of downstream cylindrical conical sections positioned in series and in fluid communication with each other and the inlet opening of the Venturi tube, each downstream cylindrical conical section having an inlet for receiving the drilling fluid from downstream that entered the inlet end of the hollow cylindrical body and an outlet end for transferring the drilling fluid upstream toward the inlet opening of the Venturi tube, the diameter of the inlet end of the downstream cylindrical conical section being greater than the outlet end of the downstream cylindrical conical section, the outlet to the downstream cylindrical conical section being in fluid communication with the inlet of another downstream cylindrical conical section positioned in closer proximity toward with the Venturi tube inlet opening, 
 iii. an upstream cylindrical conical section, the upstream cylindrical conical section having an inlet for receiving the drilling fluid from the outlet opening of the Venturi tube and an outlet for transferring the drilling fluid to the outlet end of the hollow cylindrical tube, the diameter of the outlet to the upstream cylindrical conical section being greater than the inlet to the upstream cylindrical conical section, the inlet to the upstream cylindrical conical section in fluid communication with the Venturi tube outlet opening and of a diameter substantially equal to the Venturi tube interior diameter, 
   wherein when the drilling fluid is passed through the drill string and the cavitation apparatus to the drill bit low frequency longitudinal fluctuations are produced in at least a portion of the drill string enhancing the drilling rate (ROP) of the drilling string.   
     
     
         3 . The cavitation apparatus of  claim 1 , further comprising an insert in the Venturi tube to further decrease the interior diameter of the Venturi tube to thereby enhance the longitudinal fluctuations. 
     
     
         4 . A subterranean drilling rig comprising:
 a. a drill bit for drilling a well hole;   b. a drilling string to transmit a drilling fluid to the drill bit;   c. the cavitation apparatus of  claim 1 , installed in-line as part of the drilling string between the drill bit and the drilling rig and acting as a source of peak frequency pressure fluctuations and imparting longitudinal pressure and mechanical fluctuations to at least a portion of the length of the drilling string.   
     
     
         5 . A subterranean drilling rig comprising:
 a. a drill bit for drilling a well hole;   b. a drilling string to transmit a drilling fluid to the drill bit;   c. a plurality of the cavitation apparatus of  claim 1 , each installed as part of the drilling string between the drill bit and the drilling rig and acting as a source of peak frequency pressure fluctuations and imparting longitudinal pressure and mechanical fluctuations to at least a portion of the length of the drilling string.   
     
     
         6 . The cavitation apparatus of  claim 1 , wherein the dimensions and configuration of the apparatus are selected to produce resonant frequency peaks in 100-20,000 Hz range with frequency peaks across 100 to 20,000 Hz spectrum in 500-5000 Hz intervals. 
     
     
         7 . A method of subterranean drilling comprising:
 a. providing a drill bit for drilling a well hole;   b. providing a drilling string to transmit a drilling fluid to the drill bit;   c. providing a plurality of the cavitation apparatus of  claim 1 , each installed as part of the drilling string between the drill bit and the drilling rig and acting as a source of peak frequency pressure fluctuations and, in doing so, imparting or conveying longitudinal pressure and mechanical fluctuations onto a part of or the entire the drilling string.   
     
     
         8 . A method of subterranean drilling comprising:
 a. providing a drill bit for drilling a well hole;   b. providing a drilling string to transmit a drilling fluid to the drill bit;   c. providing a plurality of the cavitation apparatus of  claim 1 , each installed as part of the drilling string between the drill bit and the drilling rig, one cavitation apparatus located adjacent to the drill bit to assist the drill bit in mechanical destruction of drilled formation by imparting longitudinal pressure and mechanical fluctuations of desired frequency onto the drill bit.   
     
     
         9 . The method of  claim 8 , wherein the cavitation apparatus reduces or eliminates occurrences of torsional vibration of the drilling string by inducing longitudinal pressure and mechanical fluctuations of desired frequency onto the drill bit. 
     
     
         10 . The method of  claim 8 , wherein the cavitation apparatus imparts longitudinal pressure and mechanical fluctuations onto the drill bit, with the longitudinal pressure and mechanical fluctuations reducing or eliminating propensity of drill bit to drift laterally during drilling process and improving lateral well dimension control.