Patent Application
20080066958
The invention and its advantages may be more easily understood by reference to the following detailed description and the attached drawings, in which:
While the invention will be described in connection with its preferred embodiments, it will be understood that the invention is not limited to these. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents that may be included within the scope of the invention, as defined by the appended claims.
The rig 11 includes a derrick 13 that is supported on the ground above a rig floor 15. The rig 11 includes lifting gear, which includes a crown block 17 mounted to the derrick 13 and a traveling block 19. The crown block 17 and the traveling block 19 are interconnected by a cable 21 that is driven by a draw works 23 to control the upward and downward movement of the traveling block 19. The traveling block 19 carries a hook 25 from which is suspended a top drive 27. The top drive 27 rotatably supports a drill string, designated generally by reference numeral 35, in a well bore 33. The top drive 27 can be operated to rotate the drill string 35 in either direction.
According to one embodiment of the present invention, the drill string 35 can be coupled to the top drive 27 through an instrumented top sub 29, although this is not a limitation on the scope of the invention. A surface drill string torque sensor 53 can be provided. However, the location of the surface torque sensor 53 is not a limitation on the scope off the present invention. A surface drill pipe orientation sensor 65 that provides measurements of drill string angular position or surface tool face can be provided. However, the location of the surface drill pipe orientation sensor 65 is not a limitation of the present invention.
The surface torque sensor 53 may be implemented as a strain gage in the instrumented top sub 29. The torque sensor 53 may also be implemented as a current measurement device for an electric rotary table or top drive motor, or as a pressure sensor for a hydraulically operated top drive, as previously explained. The drill string torque sensor 53 provides a signal which may be sampled electronically. Irrespective of the instrumentation used, the torque sensor 53 provides a measurement corresponding to the torque applied to the drill string at the surface by the top drive or rotary table, depending on how the drill rig is equipped. Other parameters which may be measured, and the corresponding sensors used to make the measurements, will be apparent to those skilled in the art.
The drill string 35 includes a plurality of interconnected sections of drill pipe (not shown separately) and a bottom hole assembly (BHA) 37. The bottom hole assembly 37 may include stabilizers, drill collars and a suite of measurement while drilling (MWD) instruments, including a directional sensor 51. As will be explained in detail below, the directional sensor 51 provides, among other measurements, tool face angle measurements that can be used according to the present invention, as well as bore hole azimuth and inclination measurements.
A steerable drilling motor 41 is connected near the bottom of the bottom hole assembly 37. The steerable drilling motor 41 can be, but is not limited to, a positive displacement motor, a turbine, or an electric motor that can turn the drill bit 40 independently of the rotation of the drill string 35. As is well known to those skilled in the art, the tool face angle of the drilling motor is used to correct or adjust the azimuth and inclination of the bore hole 33 during slide drilling. Drilling fluid is delivered to the interior of the drill string 35 by mud pumps 43 through a mud hose 45. During rotary drilling, the drill string 35 is rotated within the bore hole 33 by the top drive 27. As is well known to those skilled in the art, the top drive 27 is slidingly mounted on parallel vertically extending rails (not shown) to resist rotation as torque is applied to the drill string 35. During slide drilling, the drill string 35 is held rotationally in place by the top drive 27 while the drill bit 40 is rotated by the drilling motor 41. The drilling motor 41 is ultimately supplied with drilling fluid by the mud pumps 43 through the mud hose 45 and through the drill string 35.
The driller can operate the top drive 27 to change the tool face orientation of the drilling motor 41 by rotating the entire drill string 35. A top drive 27 for rotating the drill string 35 is illustrated in
The discharge side of the mud pumps 43 includes a drill string pressure sensor 63. The drill string pressure sensor 63 may be in the form of a pump pressure transducer coupled to the mud hose 45 running from the mud pumps 43 to the top drive 27. The pressure sensor 63 makes measurements corresponding to the pressure inside the drill string 35. The actual location of the pressure sensor 63 is not intended to limit the scope of the invention. Some embodiments of the instrumented top sub 29, for example, may include a pressure sensor.
Screen 71 includes a tool face indicator 73, which displays the tool face angle derived from the output of the steering tool. In the illustrated embodiment, the tool face indicator 73 is implemented as a combination dial and numerical indicator. Screen 71 includes a pump pressure indicator 75, an off-bottom pressure indicator 77, and a differential pressure indicator 79. The pump pressure indicator 75 displays drilling fluid pressure information derived from the pressure sensor 63 (
As is well known to those skilled in the art, differential pressure is related to weight on bit. The higher the weight on bit is, the higher the differential pressure is because the torque exerted by the drilling motor increases correspondingly. In directional drilling, it is often difficult to determine the weight on bit directly from measurements of the weight of the drill string made at the earth's surface because of friction between the drill string and the wall of the bore hole. Accordingly, weight on bit is typically inferred from differential pressure. Before commencing rotary drilling according to the present invention, the driller begins circulating drilling fluid while the drill bit is off the bottom of the bore hole. The driller can input the off-bottom drilling fluid pressure to the system. The off-bottom pressure is displayed in the off-bottom indicator 77 and used to calculate the differential pressure for display in the differential indicator 79. The off-bottom pressure indicator 77 is accompanied by off-bottom pressure controls. An up arrow control 81 increases the off-bottom pressure when activated, while a down arrow control 83 decreases the off-bottom pressure when activated.
Screen 71 includes a RSM (Rotary Steerable Motor) Control Set 85. The RSM Control Set includes six combination controls with both up arrow and down arrow controls and numerical displays. The controls and displays are for the trigger value 87, the range 89 for the trigger value, the left torque value 91, the idle percent 93, the slide time 95, and the rotate time 97. An actual trigger indicator 101 displays the measured result for the driller. A trigger value selector 105 allows the driller to choose which type of trigger to use.
Screen 71 also displays the inclination indicator 107, azimuth indicator 109, and torque indicator 111 beneath and to the right of the tool face indicator 73. A graphical display 113 shows plots of differential pressure vs. time 115 and torque vs. time 117 for the driller. Surface rate of penetration, bit depth, and hook load (weight of the drill string measured at the earth's surface) are displayed in indicator boxes 119, 121, and 123, respectively.
The invention in general terms is a method for directionally drilling a bore hole with a steerable drilling motor. The method includes alternating between two drilling modes with two different drill string rotation rates to keep the tool face angle near a desired orientation for as much of the time as possible. The method sets targets to aid in determining when drilling at a particular drill string rotation rate has continued long enough. The method uses triggers to determine when to take a specific action, such as changing from the first to the second drill string rotation rate. For example, a first target is checked to determine when the drilling at the first rotation rate has gone on long enough. Then a first trigger is checked to determine when to change to the second rotation rate. Then, a second target is checked to determine when drilling at the second rotation rate has gone on long enough. The method returns to the first rotation rate to continue the process of alternating between the two drilling rotation rates.
At 41, rotary drilling is initiated. The procedures for initiating rotary drilling are described below with reference to the flowchart in
At 42, rotary drilling is continued at a first rotation rate until a first target is met. In one embodiment, the first target for determining when to start checking for the first trigger is a parameter that is based on weight on bit. This parameter would include, but not be limited to, weight on bit itself, differential pressure (defined above), or downhole reactive torque. In an alternative embodiment, the first target is a pre-selected time period. The procedures for determining whether the first target is met are described below with reference to the flowchart in
At 43, the first rotation rate is changed to a second rotation rate when a first trigger is substantially met. In one embodiment, the drill string rotation rate of the rotary drilling is decreased to a slower rate. In the present embodiment, the rotation speed for rotary drilling alternates between a first, high rotation rate, such as about 40 revolutions per minute (rpm), and a second, low rotation rate, such as about 5-10 rpm. The slow down in rotation rate is not enough to change the drilling mode from rotary drilling to slide drilling. The slow down only causes the surface applied torque to the drill string to temporarily decline below rotary drilling torque (the amount of surface applied torque needed to keep the drill string rotating) during the drilling at the second rotation rate for a short period of time. The purpose of slowing the rotation rate of the drill string is to spend more time drilling within a range, for example 90°, of a desired tool face angle than drilling in a range away from the desired tool face angle.
In one embodiment, the first trigger for determining when to change from the first rotation rate to the second rotation rate is a measurement of tool face angle. In an alternative embodiment, the first trigger for changing rotation rates is substituted by making the changes after preselected time periods. The procedures for determining whether the first trigger is substantially met are described below with reference to the flowchart in
At 44, drilling is continued at the second rotation rate until a second target is substantially met. In one embodiment, the drilling rate is a slow rotation rate as described above and so the drilling mode remains rotary drilling. In another embodiment, the second rotation rate is substantially zero and so the drilling mode is slide drilling. In this second embodiment, the drilling mode is changing from rotary drilling at the first rotation rate to slide drilling at the second, substantially zero rotation rate and then back to the first rotation rate.
In one embodiment, the second target for changing back to rotary drilling at the first rotation rate is a parameter that is based on weight on bit. This parameter would include, but not be limited to, weight on bit itself, differential pressure, or downhole reactive torque. In an alternative embodiment, the second target for changing back is a pre-selected time period. The procedures for determining whether the second target is substantially met are described in more detail below with reference to the flowchart in
If the drilling method described above is repeated in a consistent manner, then the tool face angle during the second rate of rotation should be substantially the same every time. By changing any one of the target and trigger values, the tool face during the second rate of rotation can be sufficiently controlled. For example, the first trigger point may be adjusted until the tool face angle during the second rate of rotation (typically slide drilling) begins to fall into a desired tool face window.
At 45, the process returns to 42 to repeat elements 42-44, thus alternating between rotary drilling at the first rotation rate and rotary or slide drilling at the second rotation rate. The method of the invention, as described herein, may be performed manually or automated. Automation increases the accuracy and repeatability of the process, which thus increases the success rate or effectiveness of using the present invention.
At 55, axially advancing the drill string (drilling ahead) is initiated. At 56, the rate of advancing the drill string is adjusted to a desired operating advancing rate. The operating advancing rate is preferably the rate that maintains the desired differential pressure or weight on bit (hook load). Alternatively, the operating advancing rate is the rate that maintains a desired surface-measured rate of penetration. At 57, on-bottom pump pressure is monitored. At 58, differential pressure is calculated from the difference of the off-bottom pressure from 54 and the on-bottom pressure from 57. At 59, torque is monitored. At 60, drill pipe orientation angle (surface tool face angle) is monitored.
At 61, the drill string is rotated at the first rotation rate. In a preferred embodiment, the first rotation rate is a desired operating rotation rate. The driller brings the rate of rotation of the drill string up to the operating rate.
At 62, the drill string is axially advanced at an operating advancing rate. The driller brings the rate of drill string advancement up to the operating rate. The operating advancement rate is preferably the rate that maintains the desired differential pressure or weight on bit. Alternatively, the operating advancing rate is the rate that maintains a desired surface rate of penetration.
At 63, it is determined when the first target value is substantially met. In one embodiment, the first target is differential pressure. The driller can monitor the differential pressure on the driller's screen until a desired target value is substantially met. The target differential pressure value is preferably the recommended operating differential pressure of the drilling motor, perhaps less a safety factor. The target differential pressure value may be defined within a range of the first target value.
In an alternative embodiment, the first target is time. A time value can be preset. Typically, this time value may be of the order of approximately 10 seconds. This time value is preferably selected so that the differential pressure has had sufficient time to rise to the desired level.
For any of the embodiments of first target value, when the first target value is substantially met, then the process continues to step 64 to begin checking for the first trigger value.
At 64, it is determined when the first trigger value is substantially met. Preferably, the first trigger value to be met is defined within a range on both sides of the trigger value. Using a range is a more realistic approach to meeting a trigger value.
In a preferred embodiment, the first trigger is tool face angle. The driller may monitor tool face angle from the driller's screen and determine from steering tool measurements the prevailing tool face angle during the second rotation rate (typically slide drilling). Although the desired tool face angle of the current drilling cycle is the desired end, the first trigger tool face angle will have to be a different value to account for the inertia of the drill string. Stopping rotation of the drill string at the surface does not instantly stop the drill string at the bit. Thus the first trigger value will have to be a value of the tool face angle that leads to the desired tool face angle when the tool face stops changing orientation. Discovering an appropriate trigger value may take a process of trial and error or may be gleaned from previous experience.
In an alternative embodiment, the first trigger is not based on a given parameter, but is simply a random action. As an example, if randomly stopping the rotation of the drill string brings about a tool face angle substantially close to the desired tool face angle, then slide drilling continues. In one embodiment, substantially close is defined as within a pre-selected range of the desired tool face angle.
In another embodiment, torque can be a trigger. Torque may be measured at the bottom-hole, at the surface, or anywhere in the bore hole.
For any of the embodiments of trigger value, when the first trigger value is substantially met, then the process continues to step 65 to change over to drilling at the second rotation rate.
At 65, the rate of rotation of the drill string is changed to the second rotation rate. In one embodiment, the rate of rotation is decreased from a relatively higher first rotation rate to a relatively lower second rotation rate. In another embodiment, the second rotation rate is substantially zero. In this embodiment, the drilling mode at a zero rotation rate is now slide drilling instead of rotary drilling. The rate of advance of the drill string is kept constant. Alternately, the surface rate of penetration of the drill string is kept constant.
At 66, a left hand torque is applied. This is an optional step that is applied when needed. Left hand torque, also called a left torque bump, is the amount of counter-clockwise (“to the left”, as it is known in the art) torque applied to the drill string at the surface. Since normal rotation of the drill pipe is clockwise (“to the right”, as it is known in the art), left hand torque is a opposite direction drill pipe rotation. A left torque bump is an extra small amount of left hand torque applied to hold the drill string relatively motionless during the slide drilling step. In practice, the left hand torque is applied until a second trigger, a preset left torque value, is reached before settling to the second rotation rate.
At 67, the drill string is axially advanced at the operating advancing rate. As described above, the operating advancing rate may be the rate that maintains a desired differential pressure, weight on bit, or surface rate of penetration.
At 68, it is determined when the second target value is substantially met. In one embodiment, the second target is differential pressure. The driller can monitor the differential pressure on the driller's screen until a desired target value is substantially met. The differential pressure value is decreasing and the driller can pick a value close to zero as the second target value. The target differential pressure value may be defined within a range of the second target value.
In an alternative embodiment, the second target is time. A time value can be preset on the driller's screen. Typically, this time value may be of the order of approximately 10 seconds. This time value is preferably selected so that the differential pressure has had sufficient time to decrease to the desired level. When the second target value is substantially met, then the process returns to 61 to repeat rotary drilling at the first rotation rate again.
At 69, the first trigger value is adjusted, if needed. The first trigger value is adjusted until the tool face angle during the second rate of rotation begins to fall into the desired tool face window. This adjustment may take a few cycles of trial and error. As a consequence, the downhole tool face during the second rate of rotation can be controlled sufficiently to be substantially the same every time.
It should be understood that the preceding is merely a description of specific embodiments of this invention and that numerous changes, modifications, and alternatives to the disclosed embodiments can be made in accordance with the disclosure here without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.
