Acoustic geosteering in directional drilling

Abstract

A method for acoustic geosteering in directional drilling is provided. The method includes measuring a response from an optical fiber distributed acoustic sensor disposed on a bottom hole assembly and determining a location of the bottom hole assembly from seismic waves received from a surface source. A subsurface formation structure proximate the bottom hole assembly is determined from reflections of locally generated acoustic waves. An adjustment to a geosteering vector for the bottom hole assembly is determined based at least in part on the location and the subsurface formation structure.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Patent Application No. 16 / 838,479, filed April 2, 2020, the entire contents of which are incorporated herein by reference. Background Technology

[0003] The production of crude oil and other hydrocarbons begins with drilling a wellbore in a hydrocarbon reservoir. In many cases, hydrocarbon reservoirs are narrow layers of material in the subsurface environment, making efficient wellbore targeting crucial for productivity. Therefore, directional drilling is frequently used to guide the drill bit to form a wellbore within the reservoir.

[0004] Drilling can be performed using a rotary drill string, which uses the rotation of the drill string to power the drill bit and cut through the subsurface. Changing the drill bit's orientation for directional drilling can be done using a mud motor, for example, by stopping the drill string's rotation, then starting the mud motor to power the drill bit while simultaneously sliding the drill string forward along the well, with the bending section of the bottomspin assembly orienting the drill string in the new direction. Numerous other techniques have been developed for directional drilling.

[0005] Recent developments have focused on directional drilling using coiled tubing. Directional drilling with coiled tubing can be achieved by using a mud motor in conjunction with a hydraulic actuator to change the direction of the drill bit.

[0006] Controlling the direction of the drill string in directional drilling (referred to herein as geosteering) can be accomplished using any number of techniques. In earlier techniques, drilling was stopped, and downhole instruments, connected to the surface by wirelines, were lowered into the drill string. These wireline instruments were used to gather information about the inclination and magnetic azimuth of the drill string tip. This information was then used in conjunction with the depth at the drill string tip (e.g., measured by the length of the wireline or drill string) to determine the location of the drill string tip at a given point in time; this is called surveying. Numerous surveys are required to determine the changes needed to geosteering the drill string toward the reservoir during drilling operations. Summary of the Invention

[0007] The implementation described herein provides a method for acoustic geosteering in directional drilling. The method includes measuring the response from fiber-optic distributed acoustic sensors mounted on a bottom drill assembly and determining the location of the bottom drill assembly based on seismic waves received from a surface source. The subsurface structure adjacent to the bottom drill assembly is determined based on the reflection of locally generated acoustic waves. A geosteering vector for the bottom drill assembly is adjusted, at least in part, based on this location and the subsurface structure.

[0008] Another implementation provides a system for acoustic geological guidance in directional drilling. The system includes a bottom drill string assembly comprising: a fiber-optic distributed acoustic sensor including optical fibers spirally wound around the bottom drill string assembly; a drill bit; and an acoustic transducer positioned close to the drill bit. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of a method for geologically guiding a well during directional drilling using sound waves.

[0010] Figure 2 This is a drawing of an instrumented bottom hole assembly (BHA) that can be used for geological guidance in directional drilling during coiled tubing (CTD).

[0011] Figure 3 This is a schematic diagram of BHA, which shows the use of sound waves to assist in geological guidance.

[0012] Figure 4 This is a process flowchart for a method of geological guidance using sound waves.

[0013] Figure 5 This is a block diagram of a system that can be used to geologically guide BHA based at least in part on data from seismic acoustic waves from ground sources and reflections of locally generated acoustic waves.

[0014] Figure 6 This is a block diagram of an optical fiber time domain reflectance measurement (OF-TDR) system, which can be used in a BHA to measure acoustic waves striking optical fibers. Detailed Implementation

[0015] This paper presents techniques for geosteering downhole assemblies during directional drilling. In these techniques, a bottom drill assembly (BHA) mounted on the coiled tubing used for coiled tubing drilling (CTD) has optical fibers mounted along the assembly to sense acoustic waves. When the CTD equipment is not rotating during drilling, the optical fibers can be used to transmit information to the surface, thus eliminating the need for downhole electronics. Acoustic sources are placed at the surface and along the BHA near the drill bit. Acoustic waves from the surface source are used to update the geological model and structural stratification, as well as to determine the location of the BHA. The acoustic sources on the BHA near the drill bit, acting as deeper acoustic propagation sources, are used to determine the structure of the subsurface layers adjacent to the BHA. Geosteering of the well can be achieved in real time using the measured data, adjusting the drilling trajectory by using location and layer information, to target drilling within the most productive reservoirs.

[0016] Figure 1This is a schematic diagram of a method 100 for geological guidance of a well during directional drilling using acoustic waves. In method 100, a drill string 106 leading to a reservoir 108 is drilled using a drill rig 102 at the surface 104. In this diagram, the reservoir 108 is bounded by an upper layer 110 (e.g., a caprock) and a lower layer 112 (e.g., an aquifer).

[0017] Drilling rig 102 is connected to a coiled tubing 114 used for drilling. A control shed 116 can be connected to the coiled tubing 114 via a cable 118, which includes fiber optic cables, transducer power lines, and other control lines. Cable 118 can pass through or run parallel to the coiled tubing 114 to an end 120 of the wellbore 106, where it connects to the BHA used for drilling the wellbore 106. In the embodiment described herein, the BHA emits acoustic waves 122 that can be used for layer identification (e.g., reflections from upper layer 110 and lower layer 112) to allow determination of the proximity of the BHA to each of these layers 110 and 112.

[0018] Seismic waves 128 and 130 are emitted using seismic sources 124 and 126 located at ground level 104. These seismic waves are detected by an optical fiber on the BHA located at end 120 of the wellbore 106. Detection of the seismic waves 128 and 130 received from different ground sources allows for triangulation of the BHA's location. This information, along with information about the structure of layers 110 and 112, is used to adjust vector 132 to locate the wellbore 106 within reservoir 108.

[0019] Figure 2 This is a drawing of an instrumented bottom drill assembly (BHA) 200, which can be used for geological guidance in directional drilling during coiled tubing (CTD). The BHA 200 is encased in a fiber optic cable 202 (e.g., helically oriented), which acts as a fiber optic distributed acoustic sensor (DAS). The helical orientation reduces the directionality of seismic and acoustic signals. The fiber optic cable 202 can be wound around the coiled tubing to the ground, or it can be wound around the BHA 200 and connected to the ground via a straight fiber optic cable 204 laid along the coiled tubing. The use of the fiber optic cable 202 allows for the instrumentation of several feet of coiled tubing. The fiber optic cable 202 or the straight fiber optic cable 204 is connected to the ground 104 (…). Figure 1 Optical systems (such as lasers and photodetectors) at the location.

[0020] The fiber optic cable 202 may be a multi-layered structure including an outer wire mesh over other protective layers surrounding the cable, which includes optical fibers and any other cables used for communication and power. These cables may include, for example, power cables for supplying power to a transducer 206 positioned near the drill bit 208 to locally generate sound. In some embodiments, the transducer 206 may be powered by a mud flow passing through the BHA 200. In these cases, the fiber optic cable 202 may consist solely of optical fibers within the protective sheath.

[0021] For reference Figure 3 Further discussion suggests that transducer 206 can be used to transmit sound waves to an area close to BHA 200, thereby allowing the determination of the layer structure based on sound waves reflected back from the layers surrounding BHA 200. Fiber optic cable 202 will also be used to pick up sound waves from ground-based seismic sources.

[0022] Figure 3 This is schematic diagram 300 of BHA200, which illustrates the use of acoustic waves to assist in geological guidance. Similar numbered entries are as follows... Figure 1 and Figure 2 As described. Figure 3 As shown, acoustic waves 122 emitted from transducer 206 are reflected from nearby subsurface layers (e.g., upper layer 110 and lower layer 112). The reflected acoustic waves 302 and 304 are detected by the optical fibers of fiber optic cable 202. The reflected acoustic waves 302 and 304 can be used to determine the proximity of BHA 200 to layers 110 and 112, thereby allowing BHA 200 to be guided within reservoir 108 between layers 110 and 112.

[0023] Seismic sources 124 and 126 (e.g., controlled sources) are used to emit seismic waves 128 and 130 at ground level 104. As used herein, a controlled source is a truck-mounted system that uses a large oscillating mass block to generate seismic waves. The controlled source can be manually controlled, for example, by an operator receiving communication from the system described herein to activate it. Seismic waves 128 and 130 are detected by optical fibers in fiber optic cable 202. Seismic waves 128 and 130 can be used for triangulation of the location of BHA 200. Determining the proximity of BHA 200 to layers 110 and 112, combined with the location of BHA 200, is used to support geological guidance within reservoir 108.

[0024] Figure 4 This is a process flow diagram for method 400, which uses acoustic waves for geological guidance. Method 400 begins at box 402: measuring the response from a fiber optic distributed acoustic sensor. The measurement will acquire both the reflections of seismic waves emitted from the ground and the locally generated acoustic waves.

[0025] At box 404, triangulation is performed to determine the position of the bottom drill string assembly based on ground seismic waves detected by optical fiber. At box 406, the layer structure near the bottom drill string assembly is determined based on the reflection of locally generated acoustic waves. At box 408, adjustments to the geological steering vector are determined. These adjustments can be used to change the direction of wellbore drilling.

[0026] Figure 5 This is a block diagram of system 500, which can be used for geological guidance of a BHA based at least in part on data from seismic acoustic waves from a surface source and reflections of locally generated acoustic waves. System 500 includes a controller 502 and a BHA sensor / actuator 504. As discussed herein, the BHA sensor / actuator 504 includes an optical fiber 506, which may be encased in a protective cladding. A transducer element 508 is used to generate localized acoustic waves from a drill bit approaching the BHA. In some embodiments, a guiding actuator 510 (e.g., a hydraulic head) is used to guide the drill bit in a new direction.

[0027] The BHA sensor / actuator 504 is coupled to the controller 502 through a number of different units. For example, a laser power supply 512 powers a laser 514 that transmits light via an optical fiber 506. The light is detected by a photodetector 516. A high-speed digital-to-analog converter (DAC) 518 is used to convert the light (e.g., a signal detected from a light pulse) into a signal that can be processed by the controller 502. (See also...) Figure 6 Further details are discussed below. The optical pulses are used to detect acoustic waves (such as seismic waves and locally emitted sound waves) striking the optical fiber 506. Although the optical fiber 506 is shown as coupled between the laser 514 and the photodetector 516, as referenced... Figure 6 The fiber optic cable 506 discussed can be coupled to a single optical system (such as an optical circulator) at the ground, wherein the fiber optic cable 506 is deployed in a single direction downward along the continuous tube to the bottom drill assembly 200. Figure 2 ).

[0028] Transducer element 508 may be coupled to transducer power supply 520, for example, via a cable. In some embodiments, as discussed herein, transducer element 508 is not powered by a power cable from the ground, but by a flow of slurry that flows through a continuous pipe to the BHA.

[0029] If present, the guide actuator 510 can be powered by a hydraulic or electrical line from the ground. For example, the guide control unit 522 can provide electrical or hydraulic actuation for the guide actuator 510. In some embodiments, geological guidance is performed using other techniques, such as including bend joints in the BHA.

[0030] Controller 502 may be installed in control shed 116 ( Figure 1 This can be a separate unit within the BHA, such as part of a programmable logic controller (PLC), a distributed control system (DCS), or another computer control unit for controlling the drilling. In other embodiments, controller 502 may be a virtual controller running on a processor in a DCS, on a virtual processor in a cloud server, or using other real or virtual processors. In one embodiment, controller 502 is included in an instrument package attached to the BHA, such as in a housing having transducer element 508.

[0031] Controller 502 includes processor 524. Processor 524 may be a microprocessor, multi-core processor, multi-threaded processor, ultra-low voltage processor, embedded processor, or virtual processor. In some embodiments, processor 524 may be part of a system-on-a-chip (SoC), in which processor 524 and other components of controller 502 are formed as a single integrated electronic device package. In various embodiments, processor 524 may include components from Santa Clara, California. The processors used can be from the company, from Advanced Micro Devices, Inc. (AMD) of Sunnyvale, California, or from ARM Holdings, Ltd. of Cambridge, UK. Any number of other processors from other suppliers may also be used.

[0032] Processor 524 can communicate with other components of controller 502 via bus 526. Bus 526 can include any number of technologies, such as Industry Standard Architecture (ISA), Extended ISA (EISA), Peripheral Component Interconnect (PCI), Extended Peripheral Component Interconnect (PCIx), PCI Express (PCIe), or any other technologies. Bus 526 can be a dedicated bus, such as those used in SoC-based systems. Other bus technologies can be used in addition to or instead of the technologies described above. For example, the interface system may include I... 2 C-bus, Serial Peripheral Interface (SPI) bus, fieldbus, etc.

[0033] Bus 526 can couple processor 524 to memory 528. In some embodiments, such as in a PLC and other processing control units, memory 528 is integrated with data storage area 530 for long-term storage of programs and data. Memory 528 includes any number of volatile and non-volatile memory devices, such as volatile random access memory (RAM), static random access memory (SRAM), flash memory, etc. In smaller devices, such as a PLC, memory 528 may include registers associated with the processor itself. Data storage device 530 is used for permanent storage of information such as data, applications, operating systems, etc. Data storage device 530 may be non-volatile RAM, solid-state drive, or flash memory drive, etc. In some embodiments, data storage device 530 will include hard disk drives, such as micro hard disk drives, general hard disk drives, or hard disk drive arrays, for example, associated with a DCS or cloud server.

[0034] Bus 526 couples processor 524 to controller interface 532. Controller interface 532 can be a device bus (such as fieldbus, I / O bus, etc.). 2 Interfaces such as C-bus, SPI bus, etc. are available. Controller interface 532 couples controller 502 to laser power supply 512, transducer power supply 520, and (if present) guidance control unit 522. This allows controller 502 to generate light pulses from laser 514, activate transducer element 508 to generate acoustic waves from BHA 504, and activate guidance actuator 510 to redirect the drill bit for directional drilling.

[0035] Sensor interface 534 couples controller 502 to high-speed DAC 518 to collect measurements from photosensor 516. In some embodiments, sensor interface 534 is an integrated unit including high-speed DAC 518.

[0036] If the controller 502 is located in the field, a local human-machine interface (HMI) can be used to input control parameters and view results from the distributed acoustic sensors. The local HMI can be coupled to a display (such as a multi-line LCD display) or a monitor screen. A small keypad can be coupled to the local HMI to input control parameters such as the frequency of light pulses and the wavelength of detected light.

[0037] In some embodiments, controller 502 is linked to communicator 536 via network interface controller (NIC) 538. Communicator 536 may be a router, Ethernet coupling, wireless network interface, or device bus interface (such as a fieldbus).

[0038] Data storage device 530 includes blocks of stored instructions that, when executed, instruct processor 524 to perform the functions of controller 502. Data storage device 530 includes a block 540 of instructions that instruct the processor to initiate sound generation. This can be done, for example, by powering transducer element 508 to emit local sound waves at BHA 504, by instructing an operator of a controllable seismic source to initiate the generation of seismic waves, or by both.

[0039] Data storage device 530 includes a block 542 that instructs a processor to measure the response from optical fiber 506, thereby allowing the processor to determine the acoustic response detected by the optical fiber. For example, these instructions could instruct the processor to activate laser power supply 512 to cause laser 514 to emit a series of pulses into optical fiber 506. Changes in light passing through or reflected back from optical fiber 506 can be detected by photodetector 516, which converts the light into electrical signals. These electrical signals are digitized in high-speed DAC 518 for processing by controller 502. This can be achieved through [reference needed]. Figure 6 Many different techniques are described further.

[0040] The data storage device 530 also includes a block 544 that instructs the processor to perform triangulation on the location of BHA 504 in the underground environment. This can be done by detecting and identifying seismic waves from multiple controlled sources and comparing the arrival times of the signals to perform triangulation on the location of BHA 504.

[0041] The data storage device 530 also includes a block 546 that instructs the processor to determine the layer structure adjacent to BHA 504. This can be accomplished by analyzing the reflection of sound waves emitted by transducer element 508. This analysis can be performed using seismic analysis techniques based on, for example, the intensity and time of arrival of the reflected sound waves.

[0042] Data storage device 530 includes a block 548 that instructs the processor to determine adjustments to the steering vector used for geological guidance of BHA 504. This can be done, for example, by comparing the location of BHA 504, determined based on triangulation of seismic waves from a controlled seismic source, with a seismic map of the reservoir. Further adjustments can be made by comparing the layer structure with the current location of BHA 504 to determine the proximity of the upper and lower layers defining the reservoir to BHA 504. The drilling direction can then be adjusted to move the wellbore closer to the desired boundaries. In an automated system, data storage device 530 may include a block 550 that instructs the processor to adjust the steering vector, for example, based on adjustments determined by the current location of BHA 504.

[0043] Figure 6This is a block diagram of an OF-TDR (Optical Frequency-Domain-Reflectance) system 600, which can be used in a BHA to measure acoustic waves striking optical fibers. Similar numbered items are shown in the reference. Figure 5 As described, an OF-TDR-based sensor system can be used to obtain information about the location, frequency, and amplitude of sound impacting an optical fiber 506.

[0044] In this embodiment, laser 514 sends an optical pulse into optical circulator 602, which guides the pulse along optical fiber 506. Acoustic waves striking the optical fiber change its refractive index, causing light to scatter back towards optical circulator 602. The light received from optical fiber 506 in optical circulator 602 is guided to photodetector 516 for analysis. The photodetector may include other optical systems such as an interferometer or monochromator to determine the wavelength of the detected light.

[0045] The time-of-flight of the light received from fiber optic cable 506 can be used to determine the location of the received sound, thus allowing fiber optic cable 506 to act as a fiber optic distributed acoustic sensor (DAS). Depending on the length of fiber optic cable 506, this can be analogous to having an acoustic detector every meter along the fiber. Arranging the fiber in a spiral around the BHA increases the number of detection points along the BHA and makes it easier to determine the direction of the sound source, as the detected sound will repeat along the fiber at a distance determined by the radius of the BHA.

[0046] The frequency of the sound can be determined by the phase shift of the light pulse received at photodetector 516. This can be used to identify the source of the sound, such as a controlled vibration source or a local transducer.

[0047] The techniques described in this paper are not limited to OF-TDR, as other optical measurement techniques can also be used. These other optical measurement techniques include the use of fiber Bragg gratings (FBGs) formed in optical fibers, which allows each FBG to act as a detection point. In the application described in this paper, FBGs can be formed near the BHA, thereby increasing the signal power of the acoustic signal received at the BHA. Other techniques can be used, such as interferometry, including Sagnac interferometry. However, these techniques may also increase the complexity of the system, as two optical fibers are typically used for detection.

[0048] The implementation described herein provides a method for acoustic geosteering in directional drilling. The method includes measuring the response from fiber-optic distributed acoustic sensors mounted on a bottom drill assembly and determining the location of the bottom drill assembly based on seismic waves received from a surface source. The subsurface structure adjacent to the bottom drill assembly is determined based on the reflection of locally generated acoustic waves. A geosteering vector for the bottom drill assembly is adjusted, at least in part, based on this location and the subsurface structure.

[0049] On one hand, locally generated acoustic waves are produced by the transducer of the drill bit near the bottom of the drill assembly. On the other hand, seismic waves are generated at the ground source. Seismic waves are also generated by a controlled seismic source.

[0050] On one hand, laser pulses are sent into the optical fiber, and the light backscattered from the optical fiber is measured to measure the response.

[0051] On the one hand, adjustments are used to change the direction of drilling into the wellbore.

[0052] On the one hand, the subsurface structure is determined by seismic analysis of the reflections of locally generated sound waves. On the other hand, the location of the bottom drill assembly is determined by triangulation of sound waves received from different surface sources.

[0053] On the one hand, the orientation of the bottom drill string assembly is changed, at least in part, by adjusting the position of the bottom drill string assembly. On the other hand, the orientation of the bottom drill string assembly is adjusted automatically.

[0054] Another implementation provides a system for acoustic geological guidance in directional drilling. The system includes a bottom drill string assembly comprising: a fiber-optic distributed acoustic sensor including optical fibers spirally wound around the bottom drill string assembly; a drill bit; and an acoustic transducer positioned close to the drill bit.

[0055] On one hand, the system includes a continuous drilling rig. On another hand, the system includes an optical fiber cable that couples an optical fiber to an optical system located on the ground. On yet another hand, the system includes: a pulsed laser for emitting light pulses into the optical fiber; and a photodetector for detecting light from the optical fiber.

[0056] On one hand, the system includes an optical time-domain reflectometry system, in which a photodetector is used to detect light backscattered from the optical fiber. On the other hand, the system includes a Sagnac interferometry system.

[0057] On one hand, the system includes a guide actuator for changing the orientation of the bottom drill assembly.

[0058] On one hand, the system includes a controller, which comprises a processor and a data storage device. The data storage device includes instructions that, when executed, direct the processor to: measure responses from distributed acoustic sensors; perform triangulation of the position of the bottom drill assembly based on seismic acoustic waves received from a ground source; and determine the layer structure near the bottom drill assembly based on reflections of locally generated acoustic waves emitted by acoustic transducers on the bottom drill assembly. The data storage device further includes instructions that, when executed, direct the processor to determine adjustments to the steering vector based at least in part on the position of the bottom drill assembly and the layer structure near the bottom drill assembly.

[0059] On one hand, the data storage device includes instructions that, when executed, instruct the processor to initiate sound generation from the sound transducer. On the other hand, the data storage device includes instructions that, when executed, instruct the processor to guide the operator of the seismic source to generate seismic sound waves.

[0060] On one hand, the data storage device includes instructions that, when executed, guide the processor to adjust the steering vector. On the other hand, the data storage device includes instructions that, when executed, guide the processor to send signals to the steering actuator to change the orientation of the bottom drill assembly.

[0061] On one hand, the instructions that guide the processor to measure the response from the distributed acoustic sensors include the following instructions, which, when executed, guide the processor to: enable the laser power supply to cause the laser to emit light pulses into the optical fiber; receive data from a high-speed digital-to-analog converter, wherein the high-speed digital-to-analog converter receives a signal from a photodetector that measures the light from the optical fiber; and determine the acoustic signal based on the data.

[0062] On the one hand, the instructions that guide the processor to perform position triangulation include the following instructions, which, when executed, guide the processor to: detect seismic sound waves from multiple controlled seismic sources; and compare the arrival times of signals from multiple controlled seismic sources to perform position triangulation of the bottom drill assembly.

[0063] On the one hand, the instructions that guide the processor to determine the layer structure include the following instructions, which, when executed, guide the processor to perform seismic analysis on the reflections.

[0064] Other implementations are also within the scope of the following claims.

Claims

1. A method for acoustic geological guidance in directional drilling, the method comprising: Measure the response from fiber-optic distributed acoustic sensors mounted on the bottom drill assembly; The location of the bottom drill assembly is determined based on seismic waves emitted from a ground source detected by fiber optic distributed acoustic sensors. The subsurface structure approaching the bottom drill assembly is determined based on reflected sound waves generated by local acoustic waves from an acoustic transducer mounted on the bottom drill assembly, detected by a fiber optic distributed acoustic sensor, and the reflected sound waves produced by the subsurface. The adjustment of the geological steering vector for the bottom drill assembly is determined, at least in part, based on the location and the subsurface structure.

2. The method of claim 1, further comprising the local acoustic wave generated by a transducer of the drill bit near the bottom drill assembly.

3. The method of claim 1, further comprising generating seismic waves at a ground source.

4. The method of claim 3, wherein, A ground source is a controllable seismic source.

5. The method of claim 1, further comprising transmitting a laser pulse along the optical fiber and measuring the light backscattered from the optical fiber to measure the response.

6. The method of claim 1, further comprising using the adjustment to change the direction of the drilling wellbore.

7. The method of claim 1, further comprising determining the underground structure by performing seismic analysis on the reflected acoustic wave.

8. The method of claim 1, further comprising determining the location of the bottom drill assembly by triangulation of seismic waves emitted from different ground sources.

9. The method of claim 1, further comprising at least in part changing the orientation of the bottom drill assembly based on the adjustment.

10. The method of claim 9, further comprising automatically adjusting the orientation of the bottom drill assembly.

11. A system for acoustic geosteering in directional drilling, the system comprising a bottomscrew assembly including: A fiber optic distributed acoustic sensor comprising an optical fiber spirally wound around the bottom drill assembly; drill; A sound transducer is positioned close to the drill bit. as well as Controller, wherein the controller includes: Processor; and A data storage area, wherein the data storage area includes instructions that, when executed, direct the processor: Measure the response from the fiber optic distributed acoustic sensor; The position of the bottom drill assembly is triangulated based on seismic waves emitted from a ground source detected by fiber optic distributed acoustic sensors. The subsurface structure approaching the bottom drill assembly is determined based on reflected sound waves generated by the local acoustic waves produced by the acoustic transducer on the bottom drill assembly and reflected by the subsurface, detected by a fiber optic distributed acoustic sensor; and The adjustment of the steering vector is determined at least in part based on the location of the bottom drill assembly and the subsurface structure adjacent to the bottom drill assembly.

12. The system of claim 11, further comprising a coiled tubing drilling apparatus.

13. The system of claim 11, further comprising an optical fiber cable that couples the optical fiber to an optical system located on the ground.

14. The system of claim 11, further comprising: A pulsed laser, which is used to emit light pulses into the optical fiber; as well as A photodetector, used to detect light from the optical fiber.

15. The system of claim 14, further comprising an optical time-domain reflectometry system, wherein, The photodetector is used to detect light backscattered from the optical fiber.

16. The system of claim 14, further comprising the Sagnac interferometry system.

17. The system of claim 11, further comprising a guide actuator for changing the orientation of the bottom drill assembly.

18. The system of claim 11, wherein, The data storage area includes instructions that, when executed, instruct the processor to initiate the sound wave generation of the sound transducer.

19. The system of claim 11, wherein, The data storage area includes instructions that, when executed, instruct the processor to direct the operator of the ground source to generate the seismic waves.

20. The system of claim 11, wherein, The data storage area includes instructions that, when executed, guide the processor to adjust the guide vector.

21. The system of claim 17, wherein, The data storage area includes instructions that, when executed, direct the processor to send signals to the guide actuator to change the orientation of the bottom drill assembly.

22. The system of claim 14, wherein, Instructions that guide the processor to measure the response from the distributed acoustic sensor include the following instructions, which, when executed, guide the processor: Turn on the laser power supply to make the pulsed laser emit light pulses into the optical fiber; Receives data from a high-speed digital-to-analog converter, wherein the high-speed digital-to-analog converter receives a signal from a photodetector that measures the optical pulse; and The acoustic signal is determined based on this data.

23. The system of claim 11, wherein, The instructions that guide the processor to perform triangulation at this location include the following instructions, which, when executed, guide the processor: Seismic waves from multiple controlled sources were detected using fiber optic distributed acoustic sensors; and The arrival times of signals from the multiple controlled seismic sources are compared to triangulate the position of the bottom drill assembly.

24. The system of claim 11, wherein, The instructions that guide the processor to determine the underground structure include the following instructions, which, when executed, guide the processor to perform seismic analysis on the reflected sound waves.

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