Patent Publication Number: US-6659202-B2

Title: Steerable fluid hammer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/221,749 filed on Jul. 31, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to underground drilling machines. More particularly, the present invention relates to a steerable fluid hammer apparatus for use in directional drilling. 
     BACKGROUND OF THE INVENTION 
     Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular. 
     A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground. 
     In a typical rotational directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. By rotating the drill string and drill head, dirt and stone is ground and cut into pieces. The cutting mechanism is the action of the drill bit being rotated and pushed against the rock and soil. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool such as a drill bit) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore or bore-hole. 
     As an alternative to rotational drilling, impact cutting is employed to cut through especially hard substances like stone. Impact cutting involves the use of fluid pressure such as air or liquids to operate a fluid hammer. A fluid hammer includes a piston hammer which when activated by fluid pressure impacts repeatedly against the drill bit or a drill bit anvil, causing the cutting mechanism of the assembly to be a chipping or picking action rather than a grinding action. The drill bit used in impact drilling with a fluid hammer typically includes protrusions that function to reduce the effective surface area of the drill bit in contact with the rock. 
     In order to steer the apparatus during impact cutting, typically the drill bit is made unbalanced such that when not rotated it tends to deviate from a straight path and cuts in an arc. When drilling a curved bore the drill bit preferably is rocked so that the unbalanced protrusions on the drill bit eventually strike different portions of the rock face being drilled, gradually cutting an arced full bore. When a straight bore-hole is desired the drill bit is continuously rotated to prevent deviation from a straight path. Although effective, oscillating and rocking the drill string is a complicated, inefficient control technique. Furthermore, this method requires a more complex drill bit. 
     SUMMARY OF THE INVENTION 
     The present invention involves the use of a rotation means to rotate the fluid hammer and drill bit while the apparatus is being steered away from a straight path. By including in the drilling apparatus a means of rotation that may operate independently from the rotation of the drill string, a bent steering member may be held stationary by the drill string in order to steer the apparatus, while at the same time the fluid hammer and drill bit may be continuously rotated. Such an apparatus eliminates the need for complex drill bits. In addition, the method of operating and steering the apparatus is simplified by eliminating the need to rock the drill string. 
     One aspect of the present invention relates to a steerable directional drilling apparatus that includes a fluid hammer for impact cutting which is coupled to a bent steering member having a mud motor disposed therein. The mud motor is coupled to the fluid hammer such that the fluid hammer may be rotated even when the bent steering member is held stationary by a drill string. Thus, a balanced drill bit may be used with the fluid hammer which may be continuously rotated even when deviating from a straight path. 
     Another aspect of the present invention is directed towards a method for operating and steering a fluid hammer while drilling a bore-hole by coupling the fluid hammer to a bent steering member including a mud motor. In order to cut a straight bore-hole, pressurized fluid is supplied to activate the fluid hammer and the mud motor while the drill string is continuously rotated and advanced with limited force. The actual speed of rotation of the drill bit is the sum of the mud motor rotation and the drill string rotation. To deviate from a straight path, pressurized fluid is still supplied to activate the fluid hammer and the mud motor, but the drill string is held stationary to allow the bent steering member to force the apparatus to deviate. During deviation from a straight path, the fluid hammer and drill bit are rotated only at the speed supplied by the mud motor. 
     Another aspect of the present invention is directed towards a method for operating and steering a fluid hammer while drilling a bore-hole by coupling the fluid hammer to a pipe-in-pipe bent steering member including an inner pipe member and an outer pipe member. The inner pipe member can be rotated independently from the outer pipe member. The outer pipe member of the bent steering member may be positioned and held stationary by means of the outer pipe members of the drill string while the inner pipe member is rotated 
     A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an embodiment of a steerable drilling apparatus according to the according to the present invention having a fluid hammer and mud motor. 
     FIG. 2 is an embodiment of a steerable drilling apparatus according to the present invention having a fluid hammer and incorporating a pipe-in-pipe mechanism. 
     FIG. 3 is an enlarged view of the steerable drilling apparatus shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, a description of various exemplary aspects of the present invention will now be provided. 
     Referring now to FIG. 1 which illustrates a drilling apparatus  10  in accordance with the present invention. The apparatus includes a drill bit  14  coupled to a fluid hammer  12 . The fluid hammer  12  is coupled to a bent steering member  16 . The bent steering member  16  is bent at point  18 . The bent steering member includes a mud motor  36  which is coupled to the fluid hammer  12  near point  20 . The bent steering member  16  is coupled to a drill string  22 . The drill string  22  couples the drilling apparatus  10  to a directional drilling machine at the ground&#39;s surface. 
     FIGS. 2 and 3 include a more detailed depiction of a fluid hammer  12 . The fluid hammer  12  includes a hammer housing  28  which defines a lower piston chamber  34 . A valve housing  37  defines an upper piston chamber  35  and houses a spool valve  41 . A piston hammer  26  is slidably disposed in and separates the upper piston chamber  35  from the lower piston chamber  34 . As is known in the art, by way of spool valve  41  the upper piston chamber  35  is cyclically pressurized and depressurized to generate the forward and return stroke of the piston hammer  26 . The forward or work stroke of the piston hammer  26  impacts a target such as a drill bit  14  or drill bit anvil  42 . The return or rearward stroke of the piston hammer  26  is caused by depressurization of the upper piston chamber  35 , allowing the lower piston chamber  34 , that is preferably continuously pressurized, to generate the return stroke of the piston hammer  26 . Therefore, by application of fluid pressure to the piston chambers  34  and  35 , the piston hammer  26  reciprocates inside the piston chamber  34  repeatedly striking a drill bit anvil  42  and driving the drill bit  14  against the dirt and stone to be drilled. A mud hammer, which is a fluid hammer operated by liquid pressure, typically operates at liquid pressures ranging from 1000 to 3000 psi, typically around 2000 psi. A pneumatic hammer, which is a fluid hammer operated by gas pressure, typically operates at pressures ranging from 100 to 500 psi, often around 200 psi. 
     The present invention couples a fluid hammer  12 , such as the one described above, to a means of rotation that may rotate independently of the drill string rotation. FIG. 1 illustrates a drilling device wherein the independent means of rotation is a mud motor  36 , and FIGS. 2 and 3 illustrate an alternative embodiment of the drilling device wherein the independent means of rotation is a dual pipe drive mechanism as described below. 
     Mud motors, like fluid hammers, are powered by fluid pressure. A mud motor typically includes a rotating member that is powered with the drilling mud as it flows through an elongated body. Fluid-powered motors have been in use in drilling assemblies in the past. There are many different designs of mud motors, many of which include a fixed stator rotating rotor powered by fluid flow based on the original principles developed by Moineau. Mud motor  36 , for example may comprise a fluid-driven positive displacement (Moineau or vane-type) motor. 
     The mud motor  36  is coupled to the fluid hammer  12  so that when the mud motor  36  operates it rotates the fluid hammer  12 . The fluid pressure necessary to operate a mud motor typically falls within the range of 550 psi to 1100 psi. Therefore, if sufficient fluid pressure is to be available to motivate the fluid hammer  12  after the mud motor  36  is motivated, the total fluid pressure conveyed by the drill string  22  is preferably on the order of 2500 to 3100 psi. 
     By combining a fluid hammer  12  with a bent steering member  16  having a mud motor  36  disposed therein, the drill bit  14  may be continuously rotated even while the bent steering member  16  is held stationary via the drill string  22  during steering. The orientation of the bent steering member  16  and the fluid hammer  12  may be directed toward any desired path by rotating the drill string  22  to the desired position. The drill string  12  may then be held in position which, by means of the bent steering member  16 , will force the fluid hammer  12  and drill bit  14  to cut away from a straight path. Concurrently, however, the mud motor  36  may operate to rotate the fluid hammer  12  and drill bit  14 . When a straight path is desired, the drill string  22  may be continuously rotated to prevent the bent steering member  16  from directing the drilling apparatus  10  away from a straight path. 
     Other means may also be used to rotate the fluid hammer  12  while holding the bent steering member  16  stationary. In the alternative embodiment shown in FIGS. 2 and 3, a pipe-in-pipe design is employed to rotate the fluid hammer  12  independently from the bent steering member  16 . As is known in the art, a pipe-in-pipe drill string includes inner pipe members  30  disposed within outer pipe members  32 . The drill string, therefore, is comprised of a series of drill pipes, each drill pipe including two coaxial pipe members. The inner pipe members  30  of adjacent drill pipes are coupled, and the outer pipe members  32  of adjacent drill pipes are coupled. The inner pipe members  30  are coupled to an inner pipe drive mechanism at the ground surface, and the outer pipe members  32  are coupled to an outer pipe member drive mechanism also at the ground&#39;s surface. The inner pipe members  30  of the drill string can be rotated independently from the outer pipe members  32 . Thus, the pipe-in-pipe drill string is sometimes referred to as a dual drive drill string. 
     In the embodiment shown in FIGS. 2 and 3 the bent steering member  16  includes an outer housing  32 ′ and an inner pipe  30 ′. The inner pipe  30 ′ is coupled to the inner pipe members  30  of a pipe-in-pipe drill string. The outer housing  32 ′ is coupled to the outer pipe members  32  of a pipe-in-pipe drill string. Near point  18  where the outer housing  32 ′ is bent, the inner pipe  30 ′ is interrupted by a universal joint  31  which allows the inner pipe  30 ′ to rotate despite its change in direction. The inner pipe  30 ′ is coupled to the fluid hammer  12  near point  38 . Using the dual drive drill string, the fluid hammer  12  may be rotated via the inner pipe members and the inner pipe member drive mechanism while the bent steering member  16  is held stationary via the outer pipe members and the outer pipe drive mechanism. 
     Both embodiments of the present system shown in the figures convey fluid pressure from the ground surface to the fluid hammer  12 . Therefore, the drill string  22  typically defines an interior chamber  40  in order to supply fluid pressure to the bent steering member  16 . Pressurized drilling fluid may perform several functions including carrying away dirt and cuttings from the bore-hole as well as powering drilling components near the drilling end of the drill string. For example, in FIG. 1, the fluid pressure from the drill string  22  powers both a mud motor  36  and a fluid hammer  12 . In FIG. 3 the fluid pressure conveyed in the interior chamber  40  motivates the fluid hammer  12  but no mud motor. Therefore, the fluid pressure necessary to operate a pipe-in-pipe system as described above is much less than that necessary when a mud motor is used. The bent steering member  16  includes an internal conduit  24  which is in fluid communication with both the interior chamber  40  of the drill string  22  and the piston chamber  34  of the fluid hammer  12 . The internal conduit  24  conveys fluid pressure from the drill string  22  to the fluid hammer  12 . 
     The present invention may be applied as a method for steering a directional drilling apparatus and has been found to be superior to methods using grinding tricone drill bits. The preferred cutting action for cutting through rock formations is the impact breaking supplied by a fluid hammer which efficiently breaks up localized areas of the rock. A fluid hammer achieves this result with little or no grinding effect. By combining an independent rotation means with a fluid hammer, the present invention combines both the efficient cutting action of the fluid hammer  12  and the efficient steerability of a bent steering member  16  into one drilling apparatus  10  utilizing a balanced drill bit. 
     A sonde  44  may also be included in the bent steering member  16  in order to monitor the position and orientation of the apparatus. A sonde transmits electronic positioning signals to a worker typically by way of a hand-held complementary receiving device. Based on this positioning information, a user is able to monitor the orientation of the fluid hammer  12  and drill bit  14 , thereby improving steering accuracy. 
     The above specification provides a description of the present invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.