OPTICAL FEEDBACK TO MONITOR AND CONTROL LASER ROCK REMOVAL

Abstract

Methods, systems, and devices related to downhole wellbore operations such as drilling and completing wells in an earth formation that include a laser device. The method includes lasing a rock and detecting an optical response of the lased rock. It can be determined from the optical response whether the lased rock is responding as specified (e.g. spalling, melting, etc.) If the lased rock is not responding as specified, one or more laser parameters are adjusted to achieve the specified response. Spalling is determined by the detection of sparks, or other light that erratically changes in intensity over time, by an optical detector. The detection of steady light may indicate other types of rock removal mechanisms, such as melt or dissociation.

Description

FIELD

The present disclosure relates generally to rock removal using a laser, and more particularly, to adjusting laser power of rock removal based on optical feedback.

BACKGROUND

Once a wellbore has been drilled and one or more zones of interest have been reached, a well casing is run into the wellbore and is set in place by injecting cement or other material into the annulus between the casing and the wellbore. The casing, cement and formation are then perforated to enable flow of fluid from the formation into the interior of the casing. In some cases, the casing can be omitted.

SUMMARY

Aspects of the present disclosure are directed to systems, apparatuses, and methods for removing subterranean rock with a laser. Certain aspects of the implementations include, lasing subterranean rock around a well bore from inside the well bore. Emissions, such as optical and/or thermal emissions, can be detected from the lased rock. It can be determined whether the detected emissions from the lased rock indicates a specified material removal mechanism. If the detected emissions do not indicate the specified material removal mechanism is taking place, one or more laser cutting parameters can be adjusted until emissions detected from the lased rock indicates the specified material removal mechanism.

Certain aspects of the implementations are directed to a well laser system for use in a subterranean well. The system may include a laser apparatus configured to produce a laser beam, and direct the laser beam towards a subterranean rock. An optical detector may also be included and may be configured to detect light emitted from the rock. A controller may be communicatively coupled to the optical detector. The controller configured to receive a signal from the optical detector, determine from the signal whether the rock is responding as specified, and adjust a parameter of the laser if the rock is not responding as specified.

Certain aspects of the implementations are directed to a well apparatus for rock removal. The well apparatus may include a laser tool configured for insertion into the well and to direct laser energy onto rock. The laser tool may include a laser or may include optics that direct a laser beam produced by a terrestrially-located laser. The apparatus may also include a detector configured for insertion into the well and to detect emissions emitted from the rock. A controller can be configured to adjust power of a laser based on emissions detected from the rock.

Certain aspects of the implementations may include assessing an optical profile of the emissions detected from the lased rock for characteristic properties of the specified material removal mechanisms. A characteristic property of a material removal mechanism may include a detection of steady emissions. In other instances, a characteristic property of a specified material removal mechanism may include a detection of a rapidly time-varying emissions.

In certain aspects of the implementations, the detected emission intensity indicates that the lased rock is spalling.

In certain aspects of the implementations, the emission intensity indicate a specified material removal mechanism if the emissions fluctuate with a frequency above a specified threshold value.

In certain aspects of the implementations, adjusting the one or more laser parameters may include changing beam irradiance of the laser in response to the optical response profile of the emissions detected from the lased rock.

In certain aspects of the implementations, detecting emissions from the lased rock may include receiving light from the lased rock for a period of time.

In certain aspects of the implementations, detecting emissions from the lased rock may include detecting a steady emission intensity, the method further comprising determining that the lased rock is not spalling based on detecting the steady emission intensity. Certain implementations also may include determining that the rock is melting based on detecting the steady emissions. In some implementations, it may be determined that the rock is dissociating based on detecting the steady emissions.

In certain aspects of the implementations, lasing subterranean rock may include perforating a sidewall of the well bore.

In certain aspects of the implementations, lasing subterranean rock may include drilling the well bore.

In certain aspects of the implementations, the controller may include a processor communicatively coupled to the controller and configured to receive signals from the detector and output emissions information to the controller.

In certain aspects of the implementations, the controller is configured to automatically adjust the irradiance of the laser energy when the detected emissions from the rock indicate that the rock is not responding as specified. In certain aspects of the implementations, the light detected from the rock indicates that the rock is not spalling when the emissions have a varying intensity with respect to time below a threshold value.

In certain aspects of the implementations, the controller is configured to maintain the power of the laser when the emissions detected from the rock indicate that the rock is spalling.

In certain aspects of the implementations, the controller is configured to determine that the rock is spalling when emission intensity detected has varying intensities with respect to time, the variations in intensities occurring with a frequency above a threshold value.

Certain implementations may include a reflector configured to reflect a laser beam towards the rock and to reflect the emission from the rock to the light detector. Some implementations may include a dichroic reflector, the dichroic reflector configured to reflect a laser beam towards the rock and to transmit the light emitted from the rock to the light detector.

In certain aspects of the implementations, the optical detector may include a spot detector.

In certain aspects of the implementations, the optical detector may include a line detector.

In certain aspects of the implementations, the optical detector may include a two-dimensional detector array.

The details of one or more embodiments of the present disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side cross-sectional view of an example laser tool in accordance with the present disclosure depicted perforating a well bore.

FIG. 2 is a side cross-sectional view of an example laser tool constructed in accordance with the present disclosure depicted perforating a well bore.

FIG. 3 is a schematic block diagram of an example controller.

FIG. 4A is side cross-sectional view of an example laser tool illustrating an adjustable reflector.

FIG. 4B is a top cross-sectional view of the example laser tool of FIG. 4a illustrating the adjustable reflector.

FIG. 4C is a side cross-sectional view of an another example laser tool showing different trajectories of the laser beam typical in drilling a vertical well bore

FIG. 4D is a side cross-sectional view of another example laser tool showing different trajectories of the laser beam achieved using a fiber optic array.

FIG. 5A is a schematic diagram of a laser beam spot and a projection of an optical spot-detector location relative to the laser beam spot.

FIG. 5B is an example representation of the optical response of rock spallation.

FIG. 5C is a graphical representation of an example detector signal indicating spallation.

FIG. 5D is a graphical representation of an example detector signal indicating inefficient rock removal.

FIG. 6A is a schematic diagram of a laser beam spot and a projection of an optical line-detector location off-set relative to the laser beam spot.

FIG. 6B is a schematic diagram of a laser beam spot and a projection of an optical line-detector location intersecting the laser beam spot.

FIG. 6C is a schematic diagram of a laser beam spot and a projection of a location of a two-dimensional configuration of an optical detector.

FIG. 7 is a process flow chart for controlling laser parameters based on the optical response of a lased subterranean formation.

FIG. 8 is a graphical representation of laser power versus specific energy of a rock delineating the spallation zone and the melting zone.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

High power laser technology may be used for drilling and perforating downhole hydrocarbon formations. The amount of energy required to remove a given volume or mass of rock is defined as specific energy. An efficient rock removal process will result in a low specific energy while an inefficient process will exhibit a high specific energy. For a particular rock sample, the specific energy required to cut or drill through it depends on the laser parameters applied. These parameters include irradiance, laser power, spot size, laser on time, purge time, delay time between laser off and purge on.

Rock is often not a homogenous, isotropic material and its properties and composition change from well to well and from one location within a well to another and localized changes in physical or chemical composition, saturation, cracks or veins of dissimilar materials may require changing of the laser parameters in order to initiate a laser drilled hole and additional changes to the laser parameters may be required “on the fly” as the laser cut hole into the rock progresses.

The present disclosure is directed to systems, methods, and apparatuses for remotely detecting when laser drilling, perforating or other rock removal processes are efficient or inefficient. If an existing set of laser parameters results in inefficient removal, these parameters may be adjusted while the laser is down-hole until efficient removal is reestablished. In this way, a set of laser parameters resulting in efficient laser rock removal can be used at all times. This will result in quicker, more cost effective laser rock drilling, perforating or removal with improved hole geometry.

Several mechanisms exist for laser rock removal, including spallation, melting, dissociation, and vaporization. FIG. 8 is a graph 800 of specific energy versus average power (one of the laser parameters listed above) for a representative sandstone sample. The vertical line 802 in FIG. 8 marks the transition in laser power where the rock removal regime changes from spallation to melting. An abrupt increase in specific energy when the removal method switches from spallation and melt starts. Efficient (low specific energy) rock removal can be achieved by adjusting the laser power to the maximum level where spallation occurs, but below the power threshold where melting begins. Usually, it is desirable to operate in the power region where specific energy is minimum as shown in FIG. 8. Spallation is typically preferred to material removal by melting because spallation has a higher energy efficiency and results in an easier handling of debris.

Similar plots can be made where other laser parameters are changed and the remainder are held constant, however a general pattern emerges that specific energy increases when melting starts occurring.

Spallation and/or melting may be determined by the optical signature of the rock during laser illumination. The absorption of incident laser energy can result in rapid local heating of the rock surface. A portion of absorbed energy is re-radiated from the target region in the form of thermal emissions governed by Planck's law. Temperatures in excess of 800 C. are commonly attained in tenth-second timeframes when subjected to high power laser energy. Thermal emission's thus typically peak in the visible or near-IR region of the electro-magnetic spectrum. Current generation of high power lasers utilized in industrial applications are capable of delivering very high quality beams with near Gaussian intensity profiles, especially if delivered via a long spatially filtering fiber optic. Thermal emission from a flat, homogeneous rock surface impacted with such a laser beam resembles a solid circular glowing spot. Thermal emission and incident beam intensity profiles are highly correlated, with the region of brightest thermal emission coinciding with the peak of the incident beam profile. In practice, rough rock surfaces and non-uniform conductivity result in more complex thermal emission regions.

In the absence of material removal mechanisms, a constant incident laser power would be expected to yield increasingly bright thermal emission at lower wavelength until the energy input and output balance and a steady state temperature is attained. In practice, material removal processes typically initiate prior to obtaining steady state, provided a sufficiently high power laser is employed.

Under the most desirable material removal conditions, the sudden energy input resulting from laser incidence induces thermal stresses that shear rock grains and heat pore spaces in the rock matrix, causing grains and bits of rock matrix to be ejected from the surface. This condition is known as spallation. The ejected material often exhibits strong visible thermal emission signatures resulting in easy visual tracking of these particulates. The visual effect of observing many ejected grains rapidly moving radially outward from a central bright region at the site of laser incidence greatly resembles a type of burning firework known as a “sparkler”. A sparkler is a form of pyrotechnic comprised of a wire coated with a mixture containing an oxidizer; a fuel (e.g. charcoal and sulfur); a metal powder (e.g. iron, steel or aluminum); and a combustible binder (e.g. starch or sugar). When ignited at one end of the wire, this pyrotechnic burns slowly and releases a shower of white hot sparks.

Efficient spallation results in lower than otherwise observed thermal heating of the rock surface since much of the heated material is quickly ejected from the rock surface. Furthermore, this process typically maintains rock temperatures below the melt transition temperature. As such, key thermal emission signatures indicating spallation are a dynamic, low average intensity, longer wavelength signal corresponding to relatively low rock surface intensity in the presence of visible tracers of ejecta moving outward from the point of laser-rock interaction. FIG. 5B, discussed in more detail below, is an example representation of the optical image of rock spallation. In FIG. 5B, a laser is directed to the rock formation. The solidly glowing laser spot 502 is shown at the center of the heated mass. An optical detector can be positioned in a well tool so that it detects the optical response of the heated rock in a specified area. In certain instances, as shown in FIG. 5B, that specified projection location 554 is off-center from and not encompassing the laser spot 502. However, in other instances discussed in more detail below, the specified area can encompass the laser spot 502 and can be of different shapes and sizes. The optical detector (e.g., discussed herein) can be used to detect spallation by the white hot ejecta 556 coming off of the rock—looking for an erratic or irregular, unsteady optical response produced by the ejecta 556 as they pass in and out of the specified area, momentarily lighting the area or a portion of the area. See FIG. 5C. In certain instances, the optical detector can be used to look for time dependent variations in the optical response that occur with a frequency above a specified threshold value determined to indicate spalling and/or a certain specified degree of spalling.

In contrast, when the laser parameters result in rock melting, the visual effect is different from spallation. When melt is occurring, no sparks are observed; instead, the optical response is a steadily glowing center where melted material tends to puddle in the center. Occasional melted rock may drip out of the hole, but generally, the light emission observed from melting is much less dynamic that that observed during spallation. See FIG. 5D. The visual effect of dissociation is similar to that of melt.

Dissociation is a process by which rock is heated and then wet. The rock material can undergo a chemical reaction, turning the calcium carbonate into CaO₂. The CaO₂ is soluble in water. In some instances, dissociation may be desirable, and the optical response that indicates a rock that is undergoing dissociation can be identified using a detector to detect the emitted light from the rock.

The optical response of the lased rock can be detected and used to adjust laser parameters while the laser is down-hole. For example, an optical detector can receive the light emitted from the lased rock, and the variation in light intensity over time for a given spatial area of reference can be used to determine whether spallation is occurring (e.g., a high variation in light intensity over time) or whether melt is occurring (e.g., a low variation in light intensity over time) or whether neither is occurring.

Turning to FIGS. 1 and 2, FIG. 1 is a side cross-sectional view of an example laser tool 20 in accordance with the present disclosure depicted perforating a well bore. FIG. 2 is a side cross-sectional view of an example laser tool 20 constructed in accordance with the present disclosure depicted perforating a well bore. A cased well bore 10 in a subterranean zone 12 has a casing 14 affixed therein. A layer 16 of cement or similar material fills an annulus between the casing 14 and the well bore 10. An illustrative laser tool 20 is depicted in use perforating the well bore 10. The illustrative laser tool 20 is adapted to be inserted into the well bore 10 depending from a wireline 18 (FIG. 1) or a tubing string 19 (FIG. 2), and direct a laser beam 26. Although depicted as removing material from the subterranean zone 12 to form a perforation 22, the laser tool 20 can be adapted to also or alternatively drill a new well bore, extend an existing well bore, or heat material to emit light for use in laser induced breakdown spectroscopy (LIBS). As the illustrative laser tool 20 of FIGS. 1 and 2 is depicted perforating a cased well bore 10, it is directing the laser beam 26 onto the casing 14, the cement 16 and the subterranean zone 12. The illustrative laser tool 20 and related concepts described herein are equally applicable to an “open hole” well bore. An open hole well bore is one in which at least a portion of the well bore has no casing. Furthermore, the laser tool 20 may be used in perforating or drilling through various equipment installed in a well bore, and is not limited to perforating through casing, cement layers, and subterranean zone. When referring to a wall of a well bore herein, the wall can include any interior surface in the well bore, such as a sidewall or end/bottom wall thereof.

Power and/or signals may be communicated between the surface and the laser tool 20. Wireline 18 may include one or more electrical conductors which may convey electrical power and/or communication signals. Wireline 18 may additionally or alternatively include one or more optical fibers which may convey light (e.g. laser) power, optical spectra, and/or optical communication signals. Neither the communication of power, nor signals to/from the surface, are necessary for the operation of the implementations. In lieu of such communication, downhole batteries and/or downhole generators may be used to supply the laser tool 20 power. A downhole processor may be employed to control the laser tool 20, with relatively little (as compared to wireline) or no communication from the surface. For example, instructions for performing operations may be preprogrammed into the processor (ex. processor 44 in FIG. 3) before running the laser tool 20 into the well bore 10 and/or the laser tool 20 may respond to simple commands conveyed via surface operations such as rotary on/off, relatively low data rate mud-pulse, electromagnetic telemetry, and acoustic telemetry communication.

In implementations incorporating a tubing string 19, the tubing may be continuous tubing or jointed pipe and may be a drilling string. The tubing string 19 may incorporate a wireline 18 as described above. Tubing string 19 may be “wired drill pipe,” i.e. a tubing having communication and power pathways incorporated therein, such as the wired drill pipe. The tubing string 19 may contain a smaller tubing string within for conveying fluids such as those used in the fluid based light path described below or for conveying chemicals used by the laser.

As discussed above, the laser tool 20 may be configured for use in analyzing material using laser-induced breakdown spectroscopy (LIBS). In LIBS, at least a portion of the material being sampled is heated, for example to a plasma or an incandescent state, and the wavelength spectrum and intensity of the light it emits is measured to determine a chemical characteristic of the material, for example, the chemical elements of the material. The light may be in either or both of the visible and invisible spectrums. The laser tool 20 can also be configured to determine a physical characteristic of the material, such as its temperature or thermal properties. The laser tool 20 can operate to heat the rock of the subterranean zone 12 (or other material being analyzed) in situ, i.e. without removing the rock of the subterranean zone 12, using laser beam 26 while the laser tool 20 is operating to remove material (drilling or perforating) or apart from operation of the laser tool 20 to remove material.

If configured to both remove and analyze material, the laser tool 20 can be configured to remove material and heat the material being removed or the remaining material to emit light 36 during the same duty cycle or during separate cycles. For example, the laser tool 20 can remove material during a first duty cycle and operate to heat material, at the same location or a different location, in a second duty cycle.

The power of the laser beam 26 can be equal from cycle to cycle, vary from cycle to cycle, or the laser beam can be fired in non-cyclical pulses of varying power. For example, it may be desirable to use a multi-pulse technique to heat the subterranean zone 12 to enable use of a lower powered laser than is necessary to heat the subterranean zone in a single pulse. In a multi-pulse technique, a first laser beam pulse is fired toward the material being analyzed to generate a cavity in the material and/or the interceding or surrounding materials, such as well fluids and drilling mud, resulting from rapidly expanding vaporized material. A second, higher power pulse is then fired into the material being analyzed to heat the material to a plasma or incandescent state. The multi-pulse technique may also encompass firing the first laser beam in a higher power pulse than the second laser beam pulse (e.g. for blasting away interceding material). Additional laser beam pulses may be fired, of higher or lower power than the first and second laser beam pulses, as is desired. For example, a third laser beam pulse may be fired to perforate the subterranean zone rock.

As a heated portion of the subterranean zone may continue to emit light for a brief period of time after the laser beam has ceased being directed at the location, the optical detector 48 can be operated to receive emitted light 36 either (or both) while the laser beam 26 is being directed at the location and afterwards, for example during an off cycle of the laser beam 26 or while the laser beam 26 is being directed to heat or remove material in a different location. It is also within the scope of the disclosure to re-heat the subterranean zone at some time after the laser tool 20 has been operated to remove material at the location, and thereafter use the optical detector 48 to receive the emitted light 36.

In FIGS. 1 and 2, the illustrative laser tool 20 includes a laser beam device 24 that generates or relays a laser beam 26 into the subterranean zone 12. The laser tool 20 may optionally be provided with a focusing array 28 through which the laser beam 26 passes. The laser beam device 24 may generate the laser beam 26, and thus may be an electrical, electro-chemical laser or chemical laser, such as a diode laser or an excimer or pulsed Na:YAG laser, dye laser, CO laser, CO2 laser, fiber laser, chemical oxygen iodine laser (COIL), or electric discharge oxygen iodine laser (DOIL). The laser beam device 24 may relay the laser beam 26 generated remotely from the laser tool 20, such as a laser generated by a laser generator 29 on the surface and input into the laser beam device 24 via a transmission line 27 (FIG. 2), such as an optical fiber or light path. In some implementations it may be desirable to use a DOIL to increase service intervals of the laser tool 20, because a DOIL does not substantially consume the chemicals used in creating the laser beam and the chemicals need not be replenished for an extended duration. It is to be understood that the examples of particular lasers disclosed herein are for illustrative purposes and not meant to limit the scope of the disclosure.

The laser beam may be pulsed, cycled, or modulated by pulsing, cycling, or modulating the control signal, and/or using an optical chopper, shutter, digital micro-mirror device, Kerr cell, or other mechanical, electrical, or photonics based light switching device to shutter, pulse, cycle, or modulate the emitted beam. In some implementations, the laser pulse duration may be on the order of 10 nanoseconds. A Kerr cell is one electro-optical device that may be used to provide shuttering on the order of such speeds.

As discussed above, the laser beam 26 is generated by a laser 24. The laser beam 26 impinges a reflector 30 and is reflected towards the wall of the well bore 10. The laser beam 26 is directed through a window 54 in the casing 14. The laser beam 26 then impinges the layers of the well bore, as discussed above, to create the perforation 22. Put differently, lasing the subterranean rock includes perforating a sidewall of the well bore 10.

When the laser beam 26 impinges on the rock, the rock may respond optically. Light emitted by the rock can traverse a path towards the reflector 30 and towards optical detector 48. The optical response of the lased rock can be detected by the optical detector 48, which can send signals to a controller 38 (described in FIG. 3), across a communications path 50. The optical detector 48 can be configured to provide a signal representative of the detected light to a controller 38, and, in some instances, to a processor 44. Processor 44 can receive a signal or signals from the optical detector 48. The processor 44 can receive, analyze, interpret, or otherwise process the received signal(s) from the detector, and make a determination as to whether the rock is spalling or melting (or neither). The processor 44 can also perform Fourier transforms on optical data and apply filters to the data. The processor 44 can also automatically adjust the laser parameters accordingly. The processor 44 can also display a graphical analysis of the intensity over time to an operator, who can manually adjust the laser parameters.

In certain implementations, the optical detector 48 resides behind the reflector 30. As discussed above, reflector 30 may be dichroic, allowing the laser beam 26 to reflect towards the window 54, while allowing the emitted light from the rock surface and ejecta to transmit through the reflector 30. In other implementations, the detector 48 may reside at other locations in the well bore (e.g., within or outside of a down-hole tool). For example, the reflector 30 may reflect light from the ejecta towards the surface, and the detector can be positioned to detect light reflected from the reflector 30.

Turning briefly to FIG. 3, FIG. 3 is a schematic block diagram of an example controller 38. Controller 38 may reside down hole with the laser tool 20 or can reside at the surface and be in communication with the laser tool 20 and other components of the laser tool 20, such as detector 48. For example, the controller can receive optical information from the detector 48 by an optical communications line 50 which conveys optical measurements to the controller via either electrical and/or optical signals. If the controller is located downhole, it may contain the optical detector 48 thus obviating the need for line 50. The controller can communicate with the laser 24 and components on the surface across a wireline 40. The controller 38 includes a processor 44 and computer-readable media 46. The processor 44 can perform spectroscopic analyses based on light received from the detector 48 across optical communications line 50. The analyses can be stored on computer-readable media 46. The processor 44 and computer-readable media can communicate with surface equipment across wireline 40. In addition, the processor 44 can control the power of laser 24 based on the spectroscopic analysis. In certain implementations, the controller 38 can communicate with laser generator 29, shown in FIG. 2, to instruct the laser generator 29 to vary the laser parameters, such as the laser power, based on the spectroscopic analysis indicating a “melt” or rate of spallation optical response. The laser adjustments can be continuous and automatic. That is, the laser power adjustments can be made without human intervention.

Returning to FIGS. 1 and 2, focusing array 28 may include one or more optical elements or lenses configured to focus the laser beam 26 at a given focal length or adjustably focus the laser beam 26 to various focal lengths. Some examples of suitable devices for an adjustable focusing array 28 can include one or more electro-optic lenses that change focal length as a function of voltage applied across the lens or one or more fixed lenses and/or mirrors movable to change the focal length. It is understood that there are many suitable devices for manipulating an optical beam which can be actively manipulated, responding to mechanical, acoustical, thermal, electrical or other forms of input energy and numerous such devices are within the scope of the disclosure. The focusing array 28 focuses the laser beam 26 on the material being removed or heated.

Use of an adjustable focusing array 28 enables the laser beam 26 to be more precisely focused on the material being removed or heated than a fixed focusing array 28, for example, when there is movement of the laser tool 20 relative to the subterranean zone 12. An adjustable focusing array 28 also enables the laser beam 26 to be focused on the end wall of the material being removed as the end wall moves deeper into the subterranean zone. In removing material, the laser beam 26 can be first focused on the closest surface of the material to be removed then adjusted to maintain focus as the surface from which material is being removed moves deeper into the material. In the case of perforating a well bore 10, the laser beam 26 can be first focused on the interior of the casing 14 and adjusted to maintain focus at an end wall of the perforation 22 as the perforation deepens through the casing 14, the cement 16 and into the subterranean zone 12. In heating a material being analyzed to emit light, the laser beam 26 can be focused on the material being analyzed. The focal length and/or properties of the laser beam may be actively manipulated, for example to compensate for movement of the laser tool 20 relative to the material being heated or removed.

A length to the desired location can be determined using a distance meter, such as an acoustic or optical distance meter, configured to measure a distance between the laser tool 20 and the material being removed or analyzed. That length can then be used in determining a focal length at which to focus the adjustable focusing array 28. Optical distance meter (or range finding) technologies are known, for example using a laser beam and a photo diode to detect the light returned from the subterranean zone whose range is of interest wherein a modelable relationship exists between the distance to be measured, the focal point of the laser beam, and the intensity of the returns. By varying the focal point of the beam and monitoring the intensity of the returns, the distance to the subterranean zone may be inferred. Alternatively, a distance, relative distance, or change in distance may be inferred with a single focal point by correlating intensity to a model or experimental data, or monitoring intensity decrease or increase at different times during a process (e.g. the perforating) expected to result in a change in such distance. As another alternative, optical time domain reflectometry may be employed as is known to measure the time a flight of a pulse of light to and from the subterranean zone, from which distance may be determined. The laser beam used by the optical distance meter 66 may be from a laser beam device 24 used for removing or heating material, or maybe a separate beam from a separate device.

When using a fixed focusing array 28, constraining the relative tool/subterranean zone movement so that the distance from the well bore 10 wall to the fixed focusing array 28 remains fixed in relation to the focusing array's focal length ensures that the laser beam 26 will maintain the desired focus. In an adjustable focusing array 28, it may be desirable to constrain relative tool/subterranean zone movement to reduce the magnitude of focal length adjustments necessary to maintain focus. Relative laser tool/subterranean zone movement can be reduced by sizing the exterior of the laser tool 20 close to the diameter of the well bore 10 or by providing the laser tool 20 with one or more stabilizer fins that project to a diameter that is close to the diameter of the well bore 10. Movement of the laser tool 20 relative to the subterranean zone can be further reduced by providing one or more extendable stabilizers, that can be selectively expanded to reside close to or in contact with the wall of the well bore 10.

Although the laser beam device 24 can be oriented to fire directly towards the material being removed or heated in one or more trajectories, the illustrative laser tool 20 is configured with the laser beam device 24 firing into a reflector 30. The reflector 30 directs the laser beam 26 toward the subterranean zone 12 and may be operated to assist in focusing the laser beam 26 or operate alone in (when no focusing array 28 is provided) focusing the laser beam 26 into the material being removed. In the illustrative laser tool 20 of FIGS. 1 and 2, the laser beam 26 is directed substantially longitudinally through the laser tool 20 and the reflector 30 directs the laser beam 26 substantially laterally into the well bore 10. The laser tool 20 can be configured to fire the laser beam 26 in other directions, for example, down.

The laser beam 26 may be directed to remove material or heat various points around the well bore 10 and in varying patterns. In an illustrative laser tool 20 having a reflector 30, the reflector 30 can be movable in one or more directions of movement by a remotely controlled servo 32 to control the direction, i.e. trajectory, of the reflected laser beam 26. In a laser tool where the laser beam device 24 fires directly into the subterranean zone 12 or in a laser tool having a reflector 30, the laser beam device 24 can be movable by control servo to control the trajectory of the laser. In lieu of or in combination with a reflector 30, the laser beam can be directed into the subterranean zone 12 using a light path (see FIGS. 4D, discussed below), such as a fiber optic, that may optionally be movable by control servo to control the trajectory of the laser beam. The light path may include multiple paths, such as a fiber optic array, that each direct the laser beam in a different trajectory. The multiple paths can be used selectively, individually or in multiples, to direct the laser beam in different trajectories.

In the illustrative example of FIGS. 1 and 2, the laser beam 26 is directed using the reflector 30 and control servo 32, rather than or in combination with moving the laser tool 20. The control servo 32 can be configured to move the reflector 30, at least one of, about a longitudinal axis of the well bore 10 (see FIG. 4A), about a transverse axis of the well bore 10 (see FIG. 5B), or along at least one of the longitudinal and transverse axis of the well bore 10. FIG. 4A depicts the laser tool 20 firing the laser beam 26 through angle α about the well bore longitudinal axis. Depending on the application, it may be desirable to configure the laser tool 20 so that angle α may be as much as 360°. The reflector 30 can be adjusted by angle A to achieve a laser beam trajectory α. FIG. 4B depicts the laser tool 20 firing the laser beam 26 through angle β about the well bore transverse axis. Depending on the application, it may be desirable to configure the laser tool 20 so that angle β may be as much as 360°. The reflector 30 can be adjusted by angle B to achieve a laser beam trajectory β. The laser tool 20 can be appropriately configured so as not to fire the laser beam 26 upon itself. FIG. 4C depicts an illustrative laser tool 20 firing in multiple trajectories, through angle φ, typical for drilling a vertical well bore 10. Depending on the application, angle φ may be as much as 360° and may be oriented through 360° polar about the longitudinal axis of the laser tool 20. The reflector 30 can be adjusted by angle Φ to achieve a laser beam trajectory φ.

FIG. 4D depicts a illustrative laser tool 20 that uses a light path 104 comprised of multiple optical fibers 106 each oriented to fire in a different trajectory. The laser beam 26 may be directed through all of the multiple optical fibers 106 substantially simultaneously, or may be multiplexed through the multiple optical fibers 106, for example, as a function of duty cycle as is described below. Likewise, emitted light can be received through the multiple optical fibers 106 for use in material analysis as is described herein. Although depicted with a specified number of optical fibers 106 arranged vertically, the number and pattern of the optical fibers 106 can vary. For example, only one optical fiber 106 can be provided. In another example, the pattern in which the optical fibers 106 are arranged can additional or alternatively extend circumferentially about the laser tool 20 to reach circumferential positions about the well bore 10. The arrangement of optical fibers 106 can be configured to produce specified patterns in the material removed, heated, and/or analyzed.

By directing the laser beam 26 relative to the laser tool 20, with reflector 30, light path 104, or otherwise, the laser tool 20 can remain in a single position (without further adjustments or reorientation) and remove or heat material in multiple locations around the well bore 10. Accordingly, the number of adjustments and/or orientations of the laser tool 20 during an entire operation are reduced. Physically moving the laser tool 20 is time-consuming relative to adjustment of the laser trajectory using the configurations described herein (ex. by moving reflector 30). Therefore, the ability to reach multiple trajectories without moving the laser tool 20 reduces the amount of time necessary to perform operations (drilling, perforating, subterranean zone analysis).

According to the concepts described herein, the laser beam 26 can be manipulated with multiple degrees of freedom and focal points to remove material in many different patterns. So for example, a slice or thin wedge can be removed from the wall of the well bore 10, orthogonal to and along the length of the well bore 10, and orthogonal to a subterranean zone bedding plane, with a larger thickness at its distal end from the well bore 10, and exposing far more subterranean zone surface than traditional perforating operations. The concepts described herein enable a perforation hole to be shaped (such as by providing slots, rather than tubes or pits) to minimize fluid pressure down-draw. Multiple shapes can be envisioned within the implementations which may promote hydrocarbon recovery rate, total recovery and efficiency.

In the illustrative laser tool 20, the laser beam 26 can be directed to remove or heat material circumferentially about the well bore 10 by actuating the control servo 32 to rotate the reflector 30 about a longitudinal axis of the well bore 10 and/or actuating the reflector 30 to move along the transverse axis of the well bore 10. The laser beam 26 can be directed to remove or heat material along the axis of the well bore 10 by actuating the control servo 32 to rotate the reflector 30 about a transverse axis of the well bore 10 or move along the longitudinal axis of the well bore 10. The laser beam 26 can be directed to remove or heat material in an area that is larger than could be removed in a single trajectory, by actuating the reflector 30 to rotate about and/or translate along at least two axes, for example the longitudinal and transverse axis. The laser beam 26 would then be directed in two or more different trajectories to substantially adjacent locations on the material being heated or removed. For example, by directing the laser beam 26 to project on the material being removed or heated at quadrants of a circle, the laser beam 26 can substantially remove or heat the material in a circular shape. By directing the laser beam 26 in two or more trajectories at the same location, the laser tool 20 can remove material to form a conical perforation having a largest diameter at the opening or having a smallest diameter at the opening. Also, the laser beam 26 may be directed in one or more trajectories to form a perforation in the earth formation, and concurrently while forming the perforation or subsequently, be directed in one or more trajectories to widen the perforation. The laser beam 26 can also be directed in two or more different trajectories to remove or heat material of the earth formation in a substantially continuous area or two or more disparate areas.

The laser being directable can be also be used to drill more efficiently and/or with unique hole characteristics, as compared to both the classic drill-bit drilling and prior non-directable laser drilling. In drilling with the laser beam 26, the laser beam 26 would be directed axially rather than radially, and the laser beam tool 20 would be conveyed on the bottom of the bottom hole assembly in place of the drilling bit (see FIG. 5C). The beam path may also be selected to achieve directional drilling. A circular path could be swept by the laser beam 26, cutting (for example by spalling) a thin annular hole, approximately equal to a desired hole diameter. The resulting “core” sticking up in the middle would be periodically broken off and reverse circulated up the well bore 10, for example up the middle of the drill string 19, to the surface. The core may be lased for removal, as well. Accordingly, the laser energy is being used only to cut a small amount of rock (i.e. the annular hole). The same laser beam 26 directing configurations discussed above in the context of perforating could be applied to drilling. Because the material removal is not resulting from a mechanical bit being rotated, a circular cross-section hole is not necessary. For example, the laser beam 26 could be directed to sweep out elliptical, square, or other hole shapes of interest.

Using the directionality of the material removal allows formation of a specified hole or perforation section shape designed and executed for purposes of enhanced production. For example the hole or perforation can be formed in a rectangular, oval, elliptical, or other hole section with a longer axis aligned to expose greater (as compared to a circular cross-section) amount of the producing subterranean zone, or aligned to provide greater exposure to an axis of preferred permeability, or preferential production (or non-production) of oil, water, gas, or sand. Such specified hole or perforation section shape may be designed and executed for purposes of well bore or perforation stability, for example a rectangular, oval, or elliptical shape being employed with a longer axis aligned with the principal stress field, for increased stability and reduced tendency of collapse as compared to a circular cross-section.

The power of the laser beam 26 can be selected such that the duty cycle necessary to remove the material in the desired manner (crack, chip, spall, melt or vaporize) and/or heat the material to emit light allows enough time during off cycles of a given trajectory for the laser beam 26 to be directed in one or more additional trajectories. In other words, if the duty cycle necessary to remove and/or heat the material in the desired manner is 10%, the 90% off cycle can be utilized by re-directing the laser beam 26 to remove and/or heat material from one or more additional positions in the well bore 10. The duty cycle for the various positions can be substantially equal or one or more of the positions can have a different duty cycle. For example, the various positions may have a different duty cycle if one or more of the positions are a different material, if it is desired to remove material at a different rate in different positions, or if it is desired to remove material in one or more positions and merely heat material in one or more different positions to emit light. The laser beam 26 can be cycled or pulsed to achieve the required duty cycle or the laser beam 26 can be continuous and moved from position to position to achieve the duty cycle for each respective position. In either manner, the laser tool 20 operates to multiplex removal of material in one or more positions, for example to form one or more perforations 22, substantially concurrently. Likewise if it is desired to drill or perforate a hole that is larger than the laser beam 26 can form on a single trajectory or that otherwise must be formed with two or more trajectories, the same multiplexing technique can be used to remove material in the two or more trajectories substantially concurrently. More so, one or more positions on the earth formation can be heated to emit light substantially concurrently using this multiplexing technique.

In a laser tool 20 configured to analyze material, the optical detector 48 is provided to receive emitted light 36 from the subterranean zone 12. In an embodiment that communicates with the surface, the optical detector 48 is coupled to the surface by a communication link 40. The communication link 40 can be a fiber optic or light path for communicating data or light to the surface or can be an electrical or other type of link. The communication link 40 can be used to transmit wavelength spectra or signals indicative of wavelength spectra to the surface for analysis (ex. analysis using a surface based spectrometer and processor for determining the chemical characteristics of the material being analyzed). In an embodiment where the optical detector 48 determines the wavelength spectrum of the emitted light 36, the optical detector 48 can include a pyrometer and/or spectrometer 42 (FIG. 4). In addition to the spectrometer 42, if the optical detector 48 is configured to determine the chemical characteristics of the subterranean zone 12 (i.e. perform the LIBS), the optical detector 48 includes at least one processor 44. The optical detector 48 may contain memory or other computer readable media (hereinafter computer readable media 46) for logging the emitted light 36 wavelength spectrum information, logging the chemical and/or thermal characteristic information, and/or storing instructions for the processor 44 to operate at least a portion of the method of operation described herein.

In the illustrative embodiment of FIGS. 1-2, the reflector 30 is dichroic and configured to reflect the wavelength spectrum of laser beam 26 while passing other wavelengths. The laser beam device 24 is configured to emit a laser beam 26 in a wavelength spectrum that is different than the expected wavelength spectrum of the emitted light 36. The optical detector 48 is thus configured to receive the emitted light 36 that passes through the reflector 30. A lens assembly 49 can be provided behind the reflector 30 axially aligned with the incoming emitted light 36 and adapted to focus the emitted light 36 into a transmission path 50, such as a fiber optic, to the optical detector 48. The optical detector 48 can include a lens assembly 49 having one or more lenses, and optionally a filter, as is desired to condition the emitted light 36 before transmitting to the optical detector 48. Alternatively, the optical detector 48 can be configured to receive the emitted light 36 from a position adjacent the laser beam 26. In such an embodiment, the reflector 30 need not be dichroic, and the lens assembly 49 has a filter configured to filter out the wavelength spectrum of the laser beam 26.

Some or all of the components of the laser tool 20 can be encased in a housing 52. The housing 52 has one or more windows 54 adapted to allow passage of the laser beam 26 out of the housing 52 and emitted light 36 into the housing 52. The size and shape of the windows 54 accommodate the aiming capabilities of the laser beam 26 and receipt of emitted light 36. The windows 54 are further adapted to withstand the elevated pressures and temperatures experienced in the well bore 10. Some examples of materials for constructing the windows 54 may be silica, sapphire, or numerous other materials of appropriate optical and strength properties. The windows 54 may have anti-reflection coatings applied to one or both surfaces to maximize the transmission of optical power there-through while minimizing reflections. The windows 54 may comprise a plurality of optical fibers positioned to direct the laser beam 26 or collect emitted light 36 from multiple locations about the well bore 10, for example the optical fibers may be fanned radially about the laser tool 20.

FIG. 5A is a schematic diagram 500 of a laser beam spot 506 on a wall of the well bore and a projection of an optical spot-detector location 508 relative to the laser beam spot 506. The projection of the optical spot-detector location 508 shows the off-set position of the optical spot-detector relative to the laser beam spot 506. The optical spot-detector itself is located in the well bore and does not contact the wall. Diagram 500 shows an outline of a perforation 504 in the well bore surface 502, the outline of the perforation shown as having a radius 505. The laser beam spot 506 is shown having a radius 507. The projection of the spot-detector location 508 is shown to be at a specified distance 509 from the laser spot 506. The diagram 500 is not drawn to scale; however, the diagram 500 shows the position of the projection of the spot-detector location 708 as “off-set” from the position of the laser beam spot 506. The projection of the optical spot-detector location 508 is off-set from the laser beam spot 506 to avoid saturation by the laser beam spot, which allows for the detection of variations in the intensity of light. Spallation can be associated with light that is detected when, during laser irradiation, the received optical signal from the spot-detector is erratic or noisy (that is, the intensity of the light detected varies unpredictably over time; see FIG. 5B and FIG. 5C). Melt is associated with light that is detected when, during laser irradiation, the received optical signal from the spot detector is steady (that is, the detected light does not vary unpredictably over time or the change in intensity over time is within a threshold value). An essentially monotonic, smooth increase in detected signal intensity is expected as target material heats to the point of melt, where-at material temperature will plateau as energy is consumed by the state transition. See FIG. 5D. If no light is detected, the laser power may be too low for either spallation or melt. The laser power can be adjusted accordingly in that instance by receiving a “no-spallation” signal and comparing the actual laser power to the theoretical laser power shown in FIG. 8.

FIG. 5B is an example representation 550 of the optical response of rock spallation. The laser beam spot 552 is shown at the center of the lased rock. The projection 554 of the optical detector is shown offset from the laser spot 552. Also shown in FIG. 5B is an example of sparks 556. The sparks are also shown to intersect the optical detector projection 554. The sparks 556 represent ejecta from the lased rock formation, and would intersect the optical detector projection 554 randomly and intermittently. Therefore, the intensity of the light detected by the optical detector would also be random and intermittent. Detecting such light would indicate rock spallation.

FIG. 5C is a graphical representation 560 of an example detector signal indicating spallation. In graphical representation 560, detector signal (y-axis) is plotted against time (x-axis). First, the laser is activated 562. When the rock is heated, the detector signal indicates an increase in light emitted by the rock by an increase in the amplitude of the signal strength. If spallation occurs, the optical signal detected can resemble the erratic signal shown by 566, which indicates that the light emitted by the rock is erratic and time varying. Spallation stops after the laser is turned off 568. The optical signal then degrades slowly as the rock cools, indicating that the light emitted from the rock is gradually losing intensity 570. The detector level A1 572 indicates a detector intensity level for melt conditions, which is described in more detail below in conjunction with FIG. 5D.

FIG. 5D is a graphical representation 580 of an example detector signal indicating inefficient rock removal. Inefficient rock removal may include melt or dissociation. In FIG. 5D, the laser is activated 582. The light emitted from the rock increases, which is indicated on the plot by an increase in the amplitude of the detector signal. In this case, the amplitude of the detector signal exceeds the reference value A1 572. In general, the peak amplitude for melt conditions is higher than the amplitude for spallation. Additionally, during melt and dissociation, the peak signal does not vary erratically with time, as it would during spallation. The steady intensity is indicated by a relatively flat curve 584. Though curve 584 is relatively flat, low amplitude variations may be detected as the nature of the rock face changes. The low amplitude variations may be below the detection sensitivity of the detector, or may be out of scale given the peak amplitude of the detector signal. When the laser is turned off, the signal drops off, indicating that the intensity of the emitted light is decreasing. As the rock cools, the intensity of the light gradually fades, which is indicated by the gradual decline in signal strength/amplitude.

FIG. 6A is a schematic diagram 600 of a laser beam spot 506 and a projection of an optical line-detector location 602 off-set relative to the laser beam spot 506 by an amount 604 (from the center of the laser beam spot 506). In some implementations, the optical detector can be a line-detector, as opposed to a spot-detector. The off-set allows the optical detector to detect light from sparks emitted from the subterranean formation during spalling with a darker baseline than if the projection of the line-detector location were located closer to the laser spot 506. The distance should still be within a certain distance to detect a sufficiently high density of light at a high enough intensity to determine that spalling is occurring. The line-detector can be considered as a “line” of optical detectors or a one or two-dimensional array of photo-detectors. The line-detector can detect light across a larger area than a spot-detector. FIG. 6B is a schematic diagram 650 of a laser beam spot 506 and a projection of an optical line-detector location 652 relative to the laser beam spot 506. In FIG. 6B, the projection of the line-detector location 652 is across the laser beam spot 506. In this implementation, the line sensor will need to have a higher dynamic range when measuring across the center of the perforating tunnel than when measuring off center, outside of the central laser glow because of the constant and high intensity light from the laser spot 506 and the resulting glow emitted from the location of the subterranean formation lased by the laser.

FIG. 6C is a schematic diagram 660 of a laser beam spot 506 and a projection of a location 662 of a two-dimensional configuration of an optical detector relative to the laser beam spot 506. Two-dimensional detector configurations can track trajectories of ejecta propagating outward from the laser-rock interaction region. Additionally, two-dimensional detector configurations can count zero-crossings across a linear or circular line sensor. This implementation provides a quantized rate of spallation that can be further optimized by variation of cutting parameters. The detector projection 662 is shown to include a dotted box 664. The dotted box 664 is a projection of the interaction region, which may be an artificially drawn portion of the entire detector or detector array. Sparks that cross the boundary of the interaction region—entering the interaction region or leaving the interaction region—can be counted. The spark trajectories can be extrapolated as well.

FIG. 7 is a process flow chart 700 for controlling laser parameters based on the optical response of a lased subterranean zone. At the outset, a counter is set to zero (C=0) (701). A set of laser parameters is selected and applied to a laser. A laser beam is directed to impinge on a subterranean rock formation to perforate the subterranean zone (702). Lasing the subterranean rock can include perforating the well bore and/or drilling the well bore. The light emitted from the rock formation is detected for a period of time (704). A determination can be made based on the detected light whether the rock removal is considered to be efficient (706). For example, if the intensity of the light detected for a specified period of time at a specific location is erratic, noisy, irregular, or otherwise indicative of spallation, it can be determined that spallation is occurring, in which case, the rock removal is occurring efficiently. If the intensity of the light detected for a specified period of time at a specific location is steady or does not vary over time (or the variance of the intensity over time is below a threshold value), then it can be determined that melt is occurring, dissociation is occurring, or, more generally, that spallation is not occurring, and therefore, the rock removal is not occurring efficiently. In some implementations, spalling can be determined by detecting light that varies in intensity with respect to time, where the variation of intensity is detected at a frequency above a threshold value. For example, light can be detected by the optical detector and signals representative of the detected light sent to a controller. The data collected can be transformed from the time domain to the frequency domain (e.g., using a Fourier transform). A high-pass filter can be applied to the frequency-domain data, to filter any signals at frequencies lower than a threshold value defined by the high-pass filter. The high-pass filter could be designed such that the resulting data indicates the presence or absence of spalling—high volume data above the filter cut-off indicates spalling; low volume data above the filter cut-off indicates lack of spalling.

If efficient rock removal is detected, then the counter can be incremented (C=C+1) (712). Laser parameters can be maintained or further refined to optimize spallation signal strengths or rates, or overall process efficiency. A determination can then be made whether C=Cmax (714). Cmax is maximum number of laser shots or pulses for a particular lasing iteration. Cmax can be used to train the control system and can be used to ensure that sufficient sample space of data is collected to determine whether the rock removal is occurring efficiently. If the counter does not equal a maximum value, then lasing continues and the perforation depth can be monitored (716). It can be determined whether a desired depth is achieved (716). If the depth has not been achieved, the laser continues to perforate the well bore, and light detection continues from (704). If the depth is achieved, the laser can stop perforating (720), and other processes can commence (including those that use the laser, such as spectroscopic analyses).

If the counter is equal to its maximum value (and efficient rock removal is detected), then the counter is reset to zero (C=0) (708). The laser parameters can be adjusted (710). In this case, the laser parameters can be adjusted so that a new lasing area is chosen or new laser parameters are selected to test whether efficient rock removal can be achieved using different parameters.

If rock removal is determined to be inefficient (e.g., no spalling is detected), then the counter is reset to zero (C=0) (708). The laser parameters can be adjusted (710). The laser parameters include, among other things, laser power, irradiance (power/unit area), purge delay, orifice size on purge lance, purge velocity, the number of purges, etc. Laser power can be reduced to a point below that which would cause melt (see FIG. 8) or can be increased to enter the spallation zone. The active laser power can be compared to theoretical values, such as those presented in FIG. 8. The laser can then be started again to continue the process (702).

Other parameters can also be varied. For example, laser irradiance can be varied be changing the laser power or by changing the spot size area using lenses. The laser delay can also be varied. Delay may allow the melted rock to cool and solidify. The solidified rock can be removed to expose a “clean” rock surface for further lasing and removal. Cycle delay can also be varied (that is, the time between lasing and purging).

Various configurations of the disclosed systems, devices, and methods are available and are not meant to be limited only to the configurations disclosed in this specification. Even though numerous characteristics and advantages have been set forth in the foregoing description together with details of illustrative implementations, the disclosure is illustrative only and changes may be made within the principle of the disclosure. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A method for removing subterranean rock with a laser, the method comprising:

from inside a well bore, lasing subterranean rock around the well bore;

detecting emissions from the lased rock;

determining whether the detected emissions from the lased rock indicate a specified material removal mechanism; and

if the detected emissions do not indicate the specified material removal mechanism, adjusting one or more laser cutting parameters until emissions detected from the lased rock indicates the specified material removal mechanism.

2. The method of claim 1, further comprising assessing an optical profile of the emissions detected from the lased rock for characteristic properties of the specified material removal mechanisms.

3. The method of claim 2, wherein a characteristic property of a specified material removal mechanism comprises a detection of a rapidly time-varying emissions.

4. The method of claim 2, wherein a characteristic property of a material removal mechanism comprises a detection of steady emissions.

5. The method of claim 1, wherein the detected emissions indicate that the lased rock is spalling.

6. The method of claim 1, wherein the emission intensity indicate a specified material removal mechanism if the emissions fluctuate with a frequency above a specified threshold value.

7. The method of claim 1, wherein adjusting the one or more laser parameters comprises, in response to the emissions detected from the lased rock, changing one or more of beam irradiance of the laser, laser power, laser spot size, laser on time, purge time, or delay time between laser shut-off and purge turn-on.

8. The method of claim 1, wherein detecting emissions from the lased rock comprises receiving light from the lased rock for a period of time.

9. The method of claim 1, wherein detecting emissions from the lased rock comprises detecting a steady emission intensity, the method further comprising determining that the lased rock is not spalling based on detecting the steady emission intensity.

10. The method of claim 9, further comprising determining that the rock is melting based on detecting the steady emissions.

11. The method of claim 10, further comprising determining that the rock is dissociating based on detecting the steady emissions.

12. The method of claim 1, where lasing subterranean rock comprises perforating a sidewall of the well bore.

13. The method of claim 1, where lasing subterranean rock comprises drilling the well bore.

14. A well apparatus for rock removal, comprising:

a laser tool configured for insertion into the well and to direct laser energy onto rock;

a detector configured for insertion into the well and to detect emissions emitted from the rock; and

a controller configured to adjust power of a laser based on emissions detected from the rock.

15. The apparatus of claim 14, wherein the controller comprises a processor communicatively coupled to the controller and configured to receive signals from the detector and output emissions information to the controller.

16. The apparatus of claim 14, wherein, when the detected emissions from the rock indicate that the rock is not responding as specified, the controller is configured to automatically adjust one or more of an irradiance of the laser energy, laser power, laser spot size, laser on time, purge time, or delay time between laser shut-off and purge turn-on.

17. The apparatus of claim 16, wherein the detected emissions from the rock indicates that the rock is not spalling when the emissions have a varying intensity with respect to time below a threshold value.

18. The apparatus of claim 14, wherein the controller is configured to maintain the power of the laser when the emissions detected from the rock indicate that the rock is spalling.

19. The apparatus of claim 14, wherein the controller is configured to determine that the rock is spalling when emission intensity detected has varying intensities with respect to time, the variations in intensities occurring with a frequency above a threshold value.

20. The apparatus of claim 14, further comprising a reflector configured to reflect a laser beam towards the rock and to reflect the emission from the rock to the detector.

21. The apparatus of claim 14, further comprising a dichroic reflector, the dichroic reflector configured to reflect a laser beam towards the rock and to transmit the light emitted from the rock to the detector.

22. The apparatus of claim 14, further wherein the detector comprises one of an optical spot detector, an optical line detector, or a two-dimensional array detector.

23. A well laser system for use in a subterranean well comprising:

a laser apparatus configured to: produce a laser beam, and direct the laser beam towards a subterranean rock;

an optical detector configured to detect light emitted from the rock; and

a controller communicatively coupled to the optical detector, the controller configured to: receive a signal from the optical detector, determine from the signal whether the rock is responding as specified; and adjust a parameter of the laser if the rock is not responding as specified.

24. The system of claim 23, wherein the controller comprises a processor configured to receive signals from the optical detector and output instructions to the controller to adjust the power of the laser if the rock is not responding as specified.

25. The system of claim 23, wherein the controller is configured to automatically adjust the power of the laser when the light detected from the rock indicates that the rock is not spalling.

26. The system of claim 25, wherein the controller determines that the rock is not spalling when no sparks are detected by the optical detector.

27. The system of claim 26, wherein the controller further determines that the rock is dissociating when the light detected is a steady glow.

28. The system of claim 26, wherein the controller further determines that the rock is melting when the light detected is a steady glow.

29. The system of claim 23, wherein the controller is configured to maintain the power of the laser when sparks are detected by the optical detector.

30. The system of claim 23, wherein the laser apparatus further comprises a dichroic reflector, the dichroic reflector configured to reflect a laser beam towards the rock and to transmit the light emitted from the rock to the optical detector.

31. The system of claim 23, wherein the optical detector comprises a spot detector.

32. The system of claim 23, wherein the optical detector comprises a line detector.

33. The system of claim 23, wherein the optical detector comprises a two-dimensional detector array.