1. Field of the Disclosure
This disclosure relates generally to directional drilling methods and, in particular, to methods for navigating a formation using a closed loop system using a downhole processor without access to a surface processor.
2. Brief Description of the Related Art
Boreholes are usually drilled with a drill string that includes a tubular member having a drilling assembly (also referred to as the bottomhole assembly or “BHA”) with a drill bit attached to the bottom end thereof. The drill string can be navigated or steered through the formation by changing the orientation of the drill bit while drilling. In general, in order to steer the drill string, various survey measurements may be taken to provide information related to the current location and orientation of the drill bit. These measurements may be obtained using downhole sensors but generally do not provide complete information, such as a position of the drill bit within the formation, required for directional drilling. The measurements are therefore sent a processor that is at a surface location. The surface processor generally has access to this additional information and determines a steering action to be taken at the drill bit. The surface processor then sends a steering signal downhole that may be implemented at the drill bit. As boreholes becomes longer and deeper, time delays and data degradation during communication limits the suitability of this method of drilling.
In one aspect the present disclosure provides a method of drilling a borehole, including: determining a length of the borehole between a surface location and a drill bit at a downhole end of a drill string in the borehole; obtaining an azimuth angle and inclination of the drill bit; and using a downhole processor to: determine a position and orientation of the drill bit from the determined distance, azimuth angle and inclination, and altering a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory for drilling the borehole.
In another aspect, the present disclosure provides a system for drilling a borehole, the system including: a drill string having a drill bit at a downhole end; a downhole clock at the downhole end of the drill string configured to record an arrival time at the downhole end of an acoustic pulse generated in the drill string at a surface location; and a downhole processor configured to: determine a length of the drill string using the recorded arrival time, determine a position and orientation of the drill bit using the determined length and, an obtained azimuth angle and inclination of the drill bit, and alter a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory of the borehole.
In yet another aspect, the present invention provides a drilling apparatus that includes: a drill bit at a downhole end of a drill string in a borehole; a receiver at the downhole end of the drill string configured to receive an acoustic pulse generated in the drill string at a surface location; a downhole clock configured to generate a time stamp when the acoustic pulse is received at the downhole receiver; and a downhole processor configured to: determine a length of the drill string using the time stamp, determine a position and orientation of the drill bit using the determined length, a obtained azimuth angle of the drill bit and an obtained inclination of the drill bit, and alter a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory.
Examples of certain features of the apparatus disclosed herein are summarized rather broadly in order that the detailed description thereof that follows may be better understood. There are, of course, additional features of the apparatus and method disclosed hereinafter that will form the subject of the claims appended hereto.
For detailed understanding of the present disclosure, references should be made to the following detailed description, taken in conjunction with the accompanying drawings in which like elements have generally been designated with like numerals and wherein:
The present disclosure relates to methods and systems for directional drilling of a borehole. The apparatus may include a downhole processor that determines an orientation and position of a drill bit and/or drilling assembly on a drill string in a borehole and alters a steering parameter of the drill bit to obtain a selected drilling trajectory for the drill string. In an embodiment, the downhole processor performs these actions without any related interaction with a surface processor. The present disclosure is susceptible to embodiments of different forms. The drawings show and the written disclosure describes specific embodiments of the present disclosure with the understanding that the disclosure is to be considered an exemplification of the principles of the disclosed herein, and that it is not intended to limit the disclosure to that illustrated and described herein.
In one aspect, a suitable drilling fluid 131 (also referred to as the “mud”) from a source 132 thereof, such as a mud pit, is circulated under pressure through the drill string 120 by a mud pump 134. The drilling fluid 131 passes from the mud pump 134 into the drill string 120 via a desurger 136 and the fluid line 138. The drilling fluid 131a from the drilling tubular 122 discharges at the borehole bottom 151 through openings in the drill bit 150. The returning drilling fluid 131b circulates uphole through the annular space or annulus 127 between the drill string 120 and the borehole 126 and returns to the mud pit 132 via a return line 135 and a screen 185 that removes the drill cuttings from the returning drilling fluid 131b. A sensor S1 in line 138 provides information about the fluid flow rate of the fluid 131. Surface torque sensor S2 and a sensor S3 associated with the drill string 120 provide information about the torque and the rotational speed of the drill string 120. Rate of penetration of the drill string 120 may be determined from sensor S5, while the sensor S6 may provide the hook load of the drill string 120.
In some applications, the drill bit 150 is rotated by rotating the drill pipe 122 using, for instance, the rotary table 114. However, in other applications, a downhole motor 155 (mud motor) disposed in the drilling assembly 190 rotates the drill bit 150 alone or in addition to the drill string rotation.
A surface control unit or controller 140 receives signals from the downhole sensors and devices via a sensor 143 placed in the fluid line 138 and signals from sensors S1-S6 and other sensors used in the system 100 and processes such signals according to programmed instructions provided by a program to the surface control unit 140. The surface control unit 140 displays desired drilling parameters and other information on a display/monitor 141 that is utilized by an operator to control various drilling operations. The surface control unit 140 may be a computer-based unit that may include a processor 142 (such as a microprocessor), a storage device 144, such as a solid-state memory, tape or hard disc, and one or more computer programs 146 in the storage device 144 that are accessible to the processor 142 for executing instructions contained in such programs. The surface control unit 140 may further communicate with a remote control unit 148. The surface control unit 140 may process data relating to various drilling operations, data from the sensors and devices on the surface, data received from downhole sensors and devices and may control one or more operations of such sensors and devices.
The drilling assembly 190 may also contain formation evaluation sensors or devices (also referred to as measurement-while-drilling, “MWD,” or logging-while-drilling, “LWD,” sensors) for obtaining various properties of interest, such as resistivity, density, porosity, permeability, acoustic properties, nuclear-magnetic resonance properties, corrosive properties of the fluids or the formation, salt or saline content, and other selected properties of the formation 195 surrounding the drilling assembly 190. Such sensors are generally known in the art and for convenience are collectively denoted herein by numeral 165. Such formation evaluation measurements are often indicative of formation lithology, hydrocarbon content, porosity, or other formation parameters that may indicate a presence of a hydrocarbon and which may therefore be used to alter a direction in which a borehole is being drilled. The drilling assembly 190 may further include a variety of other sensors and communication devices 159 for controlling and/or determining one or more functions and properties of the drilling assembly 190 (such as velocity, vibration, bending moment, acceleration, oscillations, whirl, stick-slip, etc.) and drilling operating parameters, such as weight-on-bit, fluid flow rate, pressure, temperature, rate of penetration, azimuth, tool face, drill bit rotation, etc. Additionally, the drilling assembly 190 may include one or more survey instruments 163, such as accelerometers, gyroscopes and/or magnetometers, that are configured to provide an inclination of the drilling assembly 190 and/or drill bit 150 and an azimuth or tool face angle of the drilling assembly 190 and/or drill bit 150.
Still referring to
Additionally, the drill string 120 may include a downhole control unit 170 which may include a downhole processor 172, a memory storage device 174, such as a solid-state memory, tape or hard disc, and one or more computer programs 176 in the storage device 174 that are accessible to the downhole processor 172 for executing instructions contained in such programs to perform the directional drilling methods disclosed herein.
The acoustic transmitter 202 generates an acoustic pulse in the drill string 120 at various times which are periodically spaced from each other. In one embodiment, the acoustic transmitter 202 generates the acoustic pulse by striking an object against the drill string 120. The first clock 204 may provide the time to the acoustic transmitter 202 and the acoustic transmitter 202 may generate the acoustic pulse at a selected time t. Alternately, the first clock 204 may provide a pulse generation signal at the selected time t to trigger the acoustic transmitter 202 to generate the acoustic pulse. The times at which the acoustic pulses are generated may be pre-selected and are generally periodically spaced by a selected time interval.
Thus, the acoustic transmitter 202 generates an acoustic pulse at time t. The acoustic pulse propagates through the drill string 120 and is received by the acoustic receiver 212. The second clock 214 records an arrival time t′ of the acoustic pulse at the acoustic receiver 212 and sends the recorded arrival time t′ to the downhole control unit 170. The downhole control unit 170 determines a travel time of the acoustic pulse between the acoustic transmitter 202 and the acoustic receiver 212 from the equation:
Δt=t′−t Eq. (1)
The travel time Δt may then be used to obtain a distance between the acoustic transmitter 202 and the acoustic receiver 212, thereby obtaining a length of the drill string 120 and/or a length of the borehole 126. In various embodiments, the travel time and a known speed of sound in the drill string is used to determine this distance. Known acoustic properties of the drill string such as the acoustic impedance of the drill string may be used to correct the calculation of the distance between the acoustic transmitter 202 and the acoustic receiver 212. The determined distance may then be used to determine a position of the drill bit 150 within the formation.
For example, the first clock may generate illustrative acoustic pulses 302 at every 10 seconds. (t0=0.00 seconds, t1=10.00 seconds, t2=20.00 seconds, t3=30.00 seconds) After propagation through the borehole, the acoustic pulses are received at the illustrative arrival times (t′0=3.42 seconds, t′1=13.48 seconds, t′2=23.51 seconds, t′3=33.55 seconds). The resulting difference between these times (e.g., Δt0=3.42 seconds, Δt1=3.48 seconds, Δt2=3.51 seconds, Δt3=3.55 seconds) are used to determine the distance travelled by the acoustic pulse and thus the position of the drill bit 150 within the formation 195. The downhole control unit 170 may receive a selected arrival time, e.g., t′1=13.48 seconds, and knows that the signal was generated by the acoustic transmitter 202 at t1=10 seconds because the pulse generation schedule for the first clock 204 is stored at the downhole control unit 170 and because the first clock 204 and the second clock 214 are synchronized to each other. As shown in
The drill string section 400 further includes a downhole motor 422 and a steering module 424. The drill bit may be attached to a lower end of the steering module 424. The downhole motor 422 may be used to rotate the steering module 424 and thus the drill bit around an azimuth of the drill string section 400. The downhole control unit 170 may therefore control the rotation of the downhole motor 422 to obtain a selected azimuth or tool face angle of the drill bit. The steering module 424 is equipped with various steering pads 426 which are placed at circumferential location around the steering module 424. Any selected number of steering pads 426 may be used. Each steering pad 426 may be independently extended or retracted from the steering module 424 to exert a force against a wall of the borehole, thereby altering an orientation of the steering module 424 and its attached drill bit. Thus, the downhole control unit 170 may control tool face angle and inclination of the drill bit.
The drill string section 400 further includes various formation evaluation sensors 410, 412 that may provide information to the downhole control unit 170. The downhole processor 172 may perform calculations using the information from the formation evaluation sensors 410, 412 to select a direction for future drilling and steer the drill bit accordingly, as discussed below.
In one embodiment, a selected drill path may be programmed into the downhole control unit 170 at the surface location prior to conveying the downhole control unit into the borehole. The downhole control unit 170 may then use the determined position and orientation of the drill bit 150 at various times during drilling of the borehole and used such determined position and orientation to determine an actual drill path of the drill bit 150. If a difference is observed between the actual drill path and the selected drill path, the downhole control unit 170 may alter an azimuth and/or inclination of the drill bit in order to select a path that reduces or minimizes the difference between the actual drill path and the selected drill path.
In another embodiment, a model of the formation may be programmed into the downhole control unit 170 prior to conveying the downhole control unit 170 into the borehole. The downhole control unit 170 may then map the determined position and orientation of the drill bit determined using the methods disclosed herein to the formation model. The downhole control unit 170 may then determine a drill bit trajectory for a subsequent drilling path using the mapped position and orientation of the drill bit and the formation model and alter the selected steering parameter (i.e., tool face angle and inclination) accordingly.
In yet another embodiment, the downhole control unit 170 may obtain formation evaluation measurements during drilling, using for example formation evaluation sensors 410 and 412. The downhole control unit 170 may then use the obtained formation evaluation measurements as well as the position and orientation determined using the methods disclosed herein to select a drill bit trajectory for a subsequent drilling path. For example, the drill bit may be drilling horizontally and the formation evaluation measurements may indicate that a hydrocarbon deposit may be found by drilling downward. The drill bit path may then be changed from drilling horizontally to drilling vertically, as determined by the downhole control unit 170.
In various embodiments, the downhole control unit 170 may use any combination of the steering methods disclosed above to steer or navigate the drill bit.
In one aspect of the present disclosure, the downhole control unit 170 is able to steer the drill bit using calculations that are performed entirely downhole. Thus, there is no need to send survey measurements uphole or for an operator at a surface location or an uphole processor to receive such measurements, select a drilling direction and send signals downhole to alter various steering parameters. As a result, the operator is not directly involved with the directional drilling process. Instead, the operator becomes merely an observer and/or administrator of the drilling process. To this end, the downhole control unit 170 may periodically send a progress report uphole for review and/or examination by the operator.
Therefore, in one aspect the present disclosure provides a method of drilling a borehole, including: determining a length of the borehole between a surface location and a drill bit at a downhole end of a drill string in the borehole; obtaining an azimuth angle and inclination of the drill bit; and using a downhole processor to: determine a position and orientation of the drill bit from the determined distance, azimuth angle and inclination, and altering a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory for drilling the borehole. The selected trajectory may be: (i) a preselected trajectory stored in a downhole memory location; (ii) a trajectory determined using a formation model stored at the downhole memory location and the determined position and orientation of the drill bit; and/or (iii) a trajectory determined by the downhole processor using in-situ formation measurements obtained downhole. A travel time for an acoustic pulse to traverse the borehole from the surface location to the drill bit is obtained in order to determining the length of the borehole. The acoustic pulse may be generated at the surface location according to a known schedule provided by a first clock. An arrival time of the acoustic pulse is recorded at a downhole acoustic receiver using a second clock at the downhole location. The travel time is then obtained using the recorded arrival time obtained from the second clock and the known schedule for generating the acoustic pulse. The first clock and the second clock are synchronized to each other. In various embodiments, the obtained travel time and a known previous position and orientation of the drill bit are used to determine the position of the drill bit. The acoustic impedance of the drill string may be used correct a calculation of a length of the drill string based on the measured travel time of the acoustic pulse through the drill string. In an exemplary embodiment, the steering parameter of the drill bit is altered using calculations performed entirely at the downhole processor.
In another aspect, the present disclosure provides a system for drilling a borehole, the system including: a drill string having a drill bit at a downhole end; a downhole clock at the downhole end of the drill string configured to record an arrival time at the downhole end of an acoustic pulse generated in the drill string at a surface location; and a downhole processor configured to: determine a length of the drill string using the recorded arrival time, determine a position and orientation of the drill bit using the determined length and, an obtained azimuth angle and inclination of the drill bit, and alter a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory of the borehole. The selected trajectory may be at least one of: (i) a preselected trajectory stored in a downhole memory location; (ii) a trajectory determined using a formation model stored at the downhole memory location and the determined position and orientation of the drill bit; and (iii) a trajectory determined by the downhole processor using in-situ formation measurements obtained downhole. The processor may determine the length of the drill string by obtaining a travel time for the generated acoustic pulse to traverse the drill string from a surface location to a downhole location. In one embodiment, an acoustic pulse generator at the surface location generates the acoustic pulse at a scheduled time and the downhole processor obtain the travel time using the recorded arrival time and a known schedule for generating the acoustic pulse. A surface clock may be used for controlling generation of the acoustic pulse at the acoustic pulse generator and the surface clock is synchronized with the downhole clock. The downhole processor may further determine the position of the drill bit using the obtained travel time and a known previous position and previous orientation of the drill bit. The downhole processor may further perform such calculations for altering the steering parameter of the drill bit without communication relevant data to or receiving instructions from an operator or a processor at the surface location.
In yet another aspect, the present invention provides a drilling apparatus that includes: a drill bit at a downhole end of a drill string in a borehole; a receiver at the downhole end of the drill string configured to receive an acoustic pulse generated in the drill string at a surface location; a downhole clock configured to generate a time stamp when the acoustic pulse is received at the downhole receiver; and a downhole processor configured to: determine a length of the drill string using the time stamp, determine a position and orientation of the drill bit using the determined length, a obtained azimuth angle of the drill bit and an obtained inclination of the drill bit, and alter a steering parameter of the drill bit using the determined position and orientation of the drill bit to obtain a selected trajectory. The selected trajectory may be at least one of: (i) a preselected trajectory stored in a downhole memory location; (ii) a trajectory determined using a formation model stored at the downhole memory location and the determined position and orientation of the drill bit; and (iii) a trajectory determined by the downhole processor using in-situ formation measurements obtained downhole. The downhole processor may determine the length of the drill string by obtaining a travel time for the generated acoustic pulse to traverse the drill string from a surface location to a downhole location. In one embodiment, an acoustic pulse generator at the surface location generates the acoustic pulse at a scheduled time and the downhole processor obtains the travel time using the recorded arrival time and a known scheduled time for generating the acoustic pulse. A surface clock synchronized with the downhole clock may be used to control generation of the acoustic pulse at the acoustic pulse generator. The downhole processor may further determine the position of the drill bit using the obtained travel time and a known previous position and previous orientation of the drill bit.
The foregoing description is directed to particular embodiments for the purpose of illustration and explanation. It will be apparent, however, to persons skilled in the art that many modifications and changes to the embodiments set forth above may be made without departing from the scope and spirit of the concepts and embodiments disclosed herein. It is intended that the following claims be interpreted to embrace all such modifications and changes.