Patent Publication Number: US-9850714-B2

Title: Real time steerable acid tunneling system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to systems and methods for creating steerable lateral subterranean tunnels and for monitoring formation of tunnels in real-time at surface. 
     2. Description of the Related Art 
     Sidetracking operations create lateral tunnels that extend outwardly from a central wellbore, which is typically substantially vertically-oriented, but might also be horizontally-oriented or inclined. A number of tools and techniques can be used to create lateral tunnels. Included among these tools and techniques are devices that inject acid into the wellbore and surrounding formation in order to dissolve rock. Devices of this type are used, for example, in the StimTunnel™ targeted acid placement service which is available commercially from Baker Hughes Incorporated of Houston, Tex. These acid stimulation devices typically use a bottom hole assembly with a pivotable wand with a nozzle through which acid is dispensed under high pressure. The acid helps dissolve portions of the formation around the nozzle. The wand is typically provided with one or more knuckle joints that help angle the nozzle in a desired direction. Features of this type of tool are discussed in U.S. Patent Publication No. 2008/0271925 (“Acid Tunneling Bottom Hole Assembly”) by Misselbrook et al. [the &#39;925 reference]. The &#39;925 reference is herein incorporated by reference. 
     SUMMARY OF THE INVENTION 
     The present invention relates to devices and techniques for forming lateral tunnels from a subterranean wellbore using acid injection. Devices and methods of the present invention allow greater control of the direction and length of lateral tunnels being created than has been possible with conventional systems. Devices and methods of the present invention allow multiple lateral tunnels to be created radiating in different directions from a central, substantially vertical wellbore at a single depth or location along the wellbore. Devices and methods of the present invention allow for real-time monitoring, at surface, of details relating to the creation of lateral tunnels. 
     In accordance with particular embodiments, an acid tunneling system includes an acid-dispensing bottom hole assembly secured to a running arrangement for running into a wellbore. The bottom hole assembly includes a tunneling tool having a wand with a nozzle for injection of acid at desired locations to create lateral tunnels. 
     In preferred embodiments, the bottom hole assembly is provided with one or more downhole parameter sensors. The sensors are able to detect downhole parameters including pressure and temperature. In certain embodiments, the sensors are capable of detecting fluid flow parameters, such as density and viscosity. In a described embodiment, the sensors are retained within a sensor module that is incorporated into the bottom hole assembly. 
     In accordance with particular embodiments, a data/power cable is used to provide power to downhole components as well as a real-time data transmission system. Downhole parameters detected by the sensors is sent uphole by the cable to a controller. In accordance with preferred embodiments, the data/power cable is disposed within the central flowbore of the running string and may comprise a tube-wire type cable. 
     In a described embodiment, the acid tunneling system incorporates a casing collar locator (“CCL”) which is useful for determining the position of the bottom hole assembly within a cased wellbore. When the acid tunneling system is run into a wellbore having portions that are lined with casing having collared connection, the casing collar locator provides an indication of the bottom hole assembly&#39;s depth or location within the wellbore. Casing collar locator data is transmitted to the controller at surface using the data/power cable. 
     In particular embodiments, the acid tunneling system includes an inclinometer which can determine the angular departure from vertical of the bottom hole assembly at any given point within the wellbore. This data is transmitted to the controller at surface. Together with data from the casing collar locator, if used, the inclinometer can be used to locate the bottom hole assembly at a particular desired location in the wellbore. 
     In accordance with particular embodiments, an indexing tool is incorporated into the bottom hole assembly and is useful to rotate the tunneling tool portion of the bottom hole assembly within the wellbore. Preferably, the indexing tool can rotate the tunneling tool up to 180 degrees in either radial direction, allowing the tunneling tool to form lateral tunnels in any radial direction outwardly from the central wellbore. 
     In certain embodiments, a pulsating tool, such as a lower frequency EasyReach extended reach tool, is connected between the tunneling tool and upper portions of the bottom hole assembly. The pulsating tool creates pressure waves that are transmitted to the tunneling tool and, in response to each pulse, the wand and nozzle of the tunneling tool are flexed radially outwardly to permit acid to be dispensed toward the surrounding formation. 
     In accordance with particular embodiments, the pulsating tool is designed to provide pressure waves having a pre-set pressure profile for bending the tunneling tool in a prescribed manner to form enlarged diameter lateral tunnels. The pulsating tool is designed to provide pressure pulses or waves which will activate flexure or bending of the tunneling tool in a periodic manner. In a particular embodiment, radial flexure of the tunneling tool occurs when the pulse is applied (pressure wave increasing) and the tool unflexes when the pulse is stopped (pressure wave decreasing). This flexing and unflexing will alternatively bend and straighten the tunneling tool so that wider tunnels are created. The inventors have determined that creating wider tunnels will advantageously reduce friction between the bottom hole assembly and the formation rock. 
     In operation, the acid tunneling system of the present invention can be operated to form lateral tunnels which extends outwardly from the central wellbore into which the acid tunneling system is run. In accordance with an exemplary method of operation, the acid tunneling system is run into a wellbore down to a formation into which it is desired to create lateral tunnels. The approximate location of the bottom hole assembly within the wellbore is determined using a data from a casing collar locator, inclinometer, sensors and/or by other means known in the art. Acid is flowed down through the flowbore of the running string, and the fluid pressure of the acid actuates the pulsating tool. The pulsating tool, in turn, actuates the tunneling tool to flex and unflex as acid is injected into the wellbore and creates lateral tunnels. The pulsating tool is also instrumental in creating lateral tunnels having larger diameters and which provide less frictional resistance with the tunneling tool, thereby facilitating the tunneling process. 
     The acid tunneling system of the present invention is steerable since it can be used to create tunnels in particular directions and at particular depths or locations in the wellbore. In certain embodiments, the acid tunneling system is steered by raising and lowering the running string within the wellbore based upon data provided by a casing collar locator or sensors. Further, the tunneling tool can be radially oriented by the indexing tool to direct the nozzle of the tunneling tool in a particular radial direction. 
     In a further described embodiment, a steerable acid tunneling system is used in conjunction with a milling tool to form one or more lateral tunnels from a cased wellbore. In this embodiment, a milling tool is first run into the wellbore and cuts one or more windows in the wellbore casing at locations wherein it is desired to create lateral tunnels using acid tunneling. Thereafter, the acid tunneling system is run into the wellbore and the acid tunneling tool is steered to form one or more lateral tunnels through the one or more lateral windows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein: 
         FIG. 1  is a side, cross-sectional view of an exemplary wellbore containing an acid tunneling system in accordance with the present invention. 
         FIG. 2  is a side, cross-sectional view of a section of running string used with the acid tunneling system of  FIG. 1 . 
         FIG. 3  is a side, cross-sectional view of the wellbore and acid tunneling system of  FIG. 1 , now with the acid tunneling tool having been flexed to engage the wellbore wall. 
         FIG. 4  is a side, cross-sectional view of the wellbore and acid tunneling system of  FIGS. 1 and 3 , now with the acid tunneling tool creating a lateral tunnel in the wellbore wall. 
         FIG. 5  is a side, cross-sectional view of the wellbore and acid tunneling system of  FIGS. 1, 3 and 4 , now with the acid tunneling tool having been rotated to create a second lateral tunnel. 
         FIG. 6  is a side, cross-sectional view of the acid tunneling system forming an enlarged diameter lateral tunnel. 
         FIG. 7  is a flow diagram depicting steps in an exemplary acid tunneling system steering operation. 
         FIG. 8  is a side, cross-sectional view of an exemplary wellbore depicting a milling tool cutting a window in a cased wellbore. 
         FIG. 9  is a side, cross-sectional view of the wellbore shown in  FIG. 8  now with an acid tunneling system disposed within the wellbore to create a lateral tunnel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an exemplary wellbore  10  that has been drilled through the earth  12  from the surface  14  down to a hydrocarbon-bearing formation  16  into which it is desired to create lateral tunnels. The wellbore  10  has a portion that is lined with metallic casing  17 , of a type known in the art. An acid tunneling system, generally indicated at  18  is disposed within the wellbore  10  from the surface  14 . The acid tunneling system  18  includes a running string  20 , which is preferably coiled tubing of a type known in the art. 
     As  FIG. 2  illustrates, a central axial flowbore  22  is defined along the length of the running string  20 . A cable  24  for transmission of electrical power and/or data extends along the length of the flowbore  22 . According to preferred embodiments, the cable  24  is tube-wire. Tube-wire is a tube that contains an insulated cable that is used to provide electrical power and/or data to a bottom hole assembly or to transmit data from the bottom hole assembly to the surface  14 . Tube-wire is available commercially from manufacturers such as Canada Tech Corporation of Calgary, Canada. Telecoil is coiled tubing which incorporates tube-wire that can transmit power and data. 
     At surface  14 , a controller  26  receives data from the cable  24 . The controller  26  is preferably a programmable data processor having suitable amounts of memory and storage for processing data received from a bottom hole assembly as well as means for displaying such data. In currently preferred embodiments, the controller  26  comprises a computer. In preferred embodiments, the controller  26  is programmed with a suitable geosteering software which is capable of using data collected from downhole sensors and providing guidance to an operator in real time to permit on the fly changes or the position and orientation of the tunneling tool  40 . Suitable software for use by the controller  26  includes Reservoir Navigation Services (RNS) software which is available commercially from Baker Hughes Incorporated of Houston, Tex. 
     The acid tunneling system  18  includes a bottom hole assembly  28  that is secured to the running string  20  by a coiled tubing connector  30 . The bottom hole assembly  28  is designed for the injection of acid and preferably includes a sensor module  32  and a casing collar locator  34 . In the described embodiment, the bottom hole assembly  28  also includes an indexing tool  36  and a pulsating tool  38 . Additionally, the bottom hole assembly  28  includes an acid tunneling tool  40 . 
     In many respects, the acid tunneling tool  40  is constructed and operates in the same manner as the acid tunneling bottom hole assembly  100  described in U.S. Patent Publication 2008/0271925 by Misselbrook et al. The acid tunneling tool  40  includes a wand  42  and intermediate sub  44  which are affixed to the pulsating tool  38  by articulable knuckle joint  46 . A second articulable knuckle joint  48  interconnects the wand  42  and the intermediate sub  44  together. The wand  42  has a nozzle  50  at its distal end. A suitable device for use as the acid tunneling tool  40  is the StimTunnel™ targeted acid placement tool which is available commercially from Baker Hughes Incorporated of Houston, Tex. 
     The indexing tool  36  is disposed axially between the hydraulic disconnect  34  and the pulsating tool  38 . A suitable device for use as the indexing tool  36  is the coiled tubing Hi-Torque Indexing Tool which is available commercially from National Oilwell Varco. The indexing tool  36  is capable of rotating the pulsating tool  38  and acid tunneling tool  40  with respect to the running string  20  within the wellbore  10 . 
     The bottom hole assembly  28  also includes a pulsating tool  38 . A suitable device for use as the pulsating tool  38  is the EasyReach™ fluid hammer tool which is available commercially from Baker Hughes Incorporated of Houston, Tex. A fluid pulsing tool of this type is described in greater detail in U.S. Patent Publication No. 2012/0312156 by Standen et al. entitled “Fluidic Impulse Generator.” In operation, fluid, such as acid, is flowed down through the flowbore  22  of the running string, and through the pulsating tool  38  toward the acid tunneling tool  40 . The pulsating tool  38  creates pressure pulses within the fluid flowing to the acid tunneling tool  40 , and these pulses will cause the wand  42  and intermediate sub  44  to be flexed or bent upon the first and second knuckle joints  46 ,  48 . In currently preferred embodiments, the tunneling tool  40  will flex (flexed position shown in  FIG. 3 ) upon receipt of a pulse and unflex (unflexed position shown in  FIG. 1 ). Flexing of the tunneling tool  40  allows acid to be injected at an angle toward the wellbore  10  wall, as illustrated by  FIGS. 3-4 . Lateral tunnel  52  is shown in  FIG. 4  being created by the injection of acid from nozzle  50 . 
       FIG. 6  illustrates the use of the pulsating tool  38  to help in creating an enlarged diameter lateral tunnel  52 . In operation, the pulsating tool  38  generates a series of fluid pulses transmitted toward the tunneling tool  40 . As each pulse is transmitted, the wand  42  and intermediate sub  44  flex to the first position shown by the solid lines in  FIG. 6 . When the pulse passes, the wand  42  and intermediate sub  44  unflex to the second position indicated by the broken lines in  FIG. 6 . As a result, the surface area of the formation  16  over which acid is distributed in increased, thereby enlarging the lateral tunnel. In particular, the lateral tunnel  52  will have acid distributed onto an upper portion  54  and a lower portion  56 . Periodic flexing and unflexing, together with injection of acid, will create a lateral tunnel  52  having an enlarged diameter or wider portions as compared to acid tunneling tools which do not incorporate a pulsating tool. In addition, the enlargement of the lateral tunnel will result in reduced friction between the tunneling tool  40  and the formation  16  which will aid the process of forming the lateral tunnel  52 . 
     In certain embodiments, an inclinometer  58  is incorporated into the tunneling tool  40 . The inclinometer  58  is capable of determining the angular inclination of the tunneling tool  40 , or portions thereof, with respect to a vertical axis or relative to the inclination or angle of the wellbore  10 . The inclinometer  58  is electrically connected to the data/power cable  24  so that inclinometer data is sent to the controller  26  at surface  14  in real time. In addition, the sensor module  32  and casing collar locator  34  are electrically connected to the data/power cable  24  so that data obtained by them is provided to the controller  26  in real time. 
     The sensor module  32  includes sensors that are capable of detecting at least one downhole parameter. Preferably, the sensor module  32  includes sensors that are capable of detecting a variety of downhole parameters. Exemplary downhole parameters that are sensed by the sensor module  32  include temperature, pressure, gamma, acoustics and pH (acidity/alkalinity). These parameters can be used by the controller  26  or a user to identify the location and orientation of the bottom hole assembly  28  within the wellbore  10  in real time. For example, detected wellbore pressure or temperature can be correlated to a particular depth within the wellbore  10 . In particular embodiments, real time bulk and azimuthal gamma measurements provided to the controller  26  from the sensor module  32  are used by the controller  26  in a manner similar to geosteering drilling techniques for determining in real time if the lateral tunnel  52  being formed is being created in the desired direction from the wellbore  10 . In certain embodiments, sensed acoustics data is provided to the controller  26  from the sensor module  32  are used by the controller  26  for the same purpose. A pH sensor would be useful to provide information to the controller  26  which will help determine if acid is being spent effectively (i.e., reacting with formation rock) in forming lateral tunnel  52 . A user can, in response, adjust acid volume, pumping rate, temperature and/or pressure. 
     The controller  26  will provide a user with the information needed to steer the tunneling tool  40  in real time in response to information provided to the controller  26  by the sensor module  32 , inclinometer  58  and casing collar locator  34  used with the bottom hole assembly  28 . The casing collar locator  34  is capable of providing location data as a result of detection of axial spacing from a casing collar (i.e., connecting collars used with the cased portion  17  of the wellbore  10 . In the acid tunneling system  18  of the present invention, data from the casing collar locator  34  is provided to the controller in real time via data/power cable  24 . 
     In response to the information collected by the controller  26 , a user can steer the bottom hole assembly  28  in order to create lateral tunnels at desired locations and in desired directions. With reference to  FIG. 5 , it can be seen that the tunneling tool  40  has been rotated in the wellbore  10  from the creation of first lateral tunnel  52  so that a second lateral tunnel  60  is being created by acid from the nozzle  50 . The tunneling tool  40  has been rotated by the indexing tool  36  within the wellbore  10 . In certain embodiments, the indexing tool  36  is capable of rotating the tunneling tool  40  up to 180 degrees in either radial direction within the wellbore  10 , thereby providing the ability to orient the nozzle  50  of the tunneling tool  40  in any radial direction within the wellbore  10 . Such real-time steering of the tunneling tool  40  can also be used to guide and orient the nozzle  50  of the tunneling tool  40  initially for the creation of lateral tunnel  52 . 
     The invention provides systems and methods for steering a tunneling tool  40  in order to create lateral tunnels, such as tunnels  52 ,  60 . In accordance with particular embodiments, data from downhole sensors and devices is transmitted to the surface in real time and, in response thereto, the tunneling tool  40  is moved axially within the wellbore  10  and/or angularly rotated within the wellbore  10  to steer and orient the nozzle  50  of that acid is injected in a desired direction for creation of one or more lateral tunnels.  FIG. 7  provides an exemplary flow diagram depicting steps in an exemplary operation to steer the tunneling tool  40  to create lateral tunnels. In step  70 , the bottom hole assembly  28  is run into wellbore  10  on running string  20  to a first desired location within the wellbore  10 . In step  72 , acid is flowed to the bottom hole assembly  28  where the pulsating tool  38  is activated to flex and unflex the tunneling tool  40  as described above. Acid creates a first lateral tunnel at a first location within the wellbore  10 . 
     In step  74 , data from sensor module  32 , inclinometer  58 , and casing collar locator  34  is transmitted to controller  26 . It is noted that step  74  occurs during each of the steps  70  and  72 . In step  76 , the tunneling tool  40  is steered to orient the nozzle  50  to create a second lateral tunnel at a second location. A user steers the tunneling tool  40  in response to and based upon real-time downhole parameter data collected by the controller  26 . In steering the tunneling tool  40 , the bottom hole assembly  28  may be moved axially within the wellbore  10 . Also, the indexing tool  36  can steer the tunneling tool  40  by rotating it within the wellbore  10 . In step  78 , the tunneling tool  40  creates a second lateral tunnel in a second location within the wellbore  10 . In step  80 , acid is flowed to the bottom hole assembly  28 . The pulsating tool  38  flexes the tunneling tool  40  and directs the nozzle  50  radially outwardly so that a second lateral tunnel may be formed. 
       FIGS. 8-9  depict an embodiment wherein an acid tunneling system is used to create one or more lateral tunnels from within a wellbore  90  which is lined with metallic casing  92 .  FIG. 8  illustrates a window mill  94  having been run into the wellbore  90  on running string  96 . A whipstock  98  has been placed within the wellbore  90  deflects the mill  94  so that a window  100  is cut into the casing  92 . The window  100  is cut at a location within the wellbore  90  wherein it is desired to create a lateral tunnel. Although only a single window  100  is shown being cut, it should be understood that more than one window may be cut, allowing lateral tunnels to be created at multiple locations from wellbore  90 . 
     After the cutting of window  100  (or multiple windows, if applicable), the mill  94  and whipstock  98  are removed from the wellbore  90 . Thereafter, an acid tunneling system  18  is disposed into the wellbore  90  ( FIG. 9 ). The tunneling tool  40  of the acid tunneling system  18  is then steered, using the techniques described previously, to direct the nozzle  50  of the tunneling tool  40  toward the window  100  and surrounding formation  16 . Steering in this instance will preferably utilize at least data provided to the controller  26  by the casing collar locator  34  in order to assist in properly locating the tunneling tool  40  at the same depth or location in the wellbore  90  as the window  100 . Data from the inclinometer  58  is useful for directing the nozzle  50  through the window  100 . If there are multiple windows that have been cut in the casing, the tunneling tool  40  is steered to each of them using the techniques described previously. At each location, the acid tunneling tool is used to create a lateral tunnel through the window, such as window  100 . 
     Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.