Patent Publication Number: US-6708762-B2

Title: Methods and apparatus for forming a lateral wellbore

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/658,858 filed Sep. 11, 2000, now U.S. Pat. No. 6,536,525, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to apparatus and methods for forming a window in wellbore tubulars, more specifically the invention is related to forming a window in casing and drilling a lateral wellbore in a single trip. 
     2. Background of the Related Art 
     The practice of producing oil from multiple, radially dispersed reservoirs through a single primary wellbore has increased dramatically in recent years. Technology has developed that allows an operator to drill a vertical well and then continue drilling one or more angled or horizontal holes off of that well at chosen depth(s). Because the initial vertical wellbore is often cased with a string of tubular casing, an opening or “window” must be cut in the casing before drilling the lateral wellbore. The windows are usually cut using various types of milling devices and one or more “trips” into the primary wellbore is needed. Rig time is very expensive and multiple trips take time and add to the risk that problems will occur. 
     In certain multi-trip operations, an anchor, slip mechanism, or an anchor-packer is set in a wellbore at a desired location. This device acts as an anchor against which tools above it may be urged to activate different tool functions. The device typically has a key or other orientation indicating member. The device&#39;s orientation is checked by running a tool such as a gyroscope indicator or measuring-while-drilling device into the wellbore. A whipstock-mill combination tool is then run into the wellbore by first properly orienting a stinger at the bottom of the tool with respect to a concave face of the tool&#39;s whipstock. Splined connections between a stinger and the tool body facilitate correct stinger orientation. A starting mill is releasably secured at the top of the whipstock, e.g. with a shearable setting stud and nut connected to a pilot lug on the whipstock. The tool is then lowered into the wellbore so that the anchor device or packer engages the stinger and the tool is oriented. Slips extend from the stinger and engage the side of the wellbore to prevent movement of the tool in the wellbore; and locking apparatus locks the stinger in a packer when a packer is used. Pulling on the tool then shears the setting stud, freeing the starting mill from the tool. Certain whipstocks are also thereby freed so that an upper concave portion thereof pivots and moves to rest against a tubular or an interior surface of a wellbore. Rotation of the string with the starting mill rotates the mill. The starting mill has a tapered portion which is slowly lowered to contact a pilot lug on the concave face of the whipstock. This forces the starting mill into the casing and the casing is milled as the pilot lug is milled off. The starting mill moves downwardly while contacting the pilot lug or the concave portion and cuts an initial window in the casing. The starting mill is then removed from the wellbore. A window mill, e.g. on a flexible joint of drill pipe, is lowered into the wellbore and rotated to mill down from the initial window formed by the starting mill. The tool is then removed from the wellbore and a drill string is utilized with a drill bit to form the lateral borehole in the formation adjacent the window. There has long been a need for efficient and effective wellbore casing window methods and tools useful in such methods particularly for drilling side or lateral wellbores. There has also long been a need for an effective “single trip” method for forming a window in wellbore casing whereby a window is formed and the lateral wellbore is drilled in a single trip. 
     There is a need therefore, for a window forming apparatus that includes fewer mechanical components. There is a further need for a window forming apparatus that requires fewer trips into a wellbore to complete formation of a window in casing. 
     SUMMARY OF THE INVENTION 
     The present invention discloses and claims methods and apparatus for forming an opening or a window in a downhole tubular for the subsequent formation of a lateral wellbore. In one aspect of the invention, a container having an exothermic material is lowered into a wellbore to a predetermined depth. Thereafter, the exothermic material is ignited and a portion of the casing therearound is destroyed, leaving a window in the casing. In another aspect of the invention, the apparatus includes a run-in string or drill stem with a drill bit attached to a lower end thereof. A diverter, like a whipstock is attached temporarily to the drill bit with a mechanically shearable connection. At a lower end of the whipstock, a container is formed and connected thereto. The container is designed to house a predetermined amount of exothermic material at one side thereof adjacent the area of casing where the window or opening will be formed. A telescopic joint extends between the bottom of the container and an anchor therebelow and the telescopic joint is in an extended position when the apparatus is run into a wellbore. 
     In an aspect of the invention, the window is formed in the casing by first locating the apparatus in a predetermined location in the wellbore and setting the anchor therein. Subsequently, a thermite initiator is activated, typically by a hydraulic line between the initiator and hydraulic ports formed in the drill bit. The initiator activates a thermite fuse and the chemical process within the package of thermite begins producing heat for a given amount of time adequate to form the window or hole in the adjacent casing. As the thermite burns, the melted casing and thermite material is urged into the container by formations formed at the upper and lower edges of the container. As the thermite completes its burning process, a telescopic joint fuse connected between the lower portion of the thermite package and the telescopic joint is activated and the telescopic joint, having an atmospheric chamber formed therein, begins to retract. As the joint retracts, the shearable connection between the drill and whipstock fails and the container and whipstock move downward to a predetermined, second axial position within the wellbore. In the second position, the whipstock is properly placed to guide the drill bit through the newly formed window in the casing. As the container moves downward, the formations at the upper and lower edge remove any slag from the inside perimeter of the newly formed window. With the whipstock physically separated from the drill stem and drill bit and the whipstock properly located and anchored in a position appropriate for formation of the lateral wellbore, the drill stem and rotating drill bit are extended to form the lateral wellbore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a view of the apparatus of the present invention including a drill string, drill bit, whipstock, container portion, telescopic joint and anchor. 
     FIG. 2 is a view of the apparatus installed in a wellbore. 
     FIG. 3 is a top, section view of the container portion taken along a line  3 — 3  of FIG.  2 . 
     FIG. 4 is a section view of the apparatus after a window has been formed in the casing adjacent the container portion. 
     FIG. 5 is an enlarged view thereof. 
     FIG. 6 is a section view of the container portion taken along a line  6 — 6  of FIG. 5 showing a section of the container wall and casing wall removed by exothermic means. 
     FIG. 7 is a section view of the apparatus illustrating the whipstock positioned adjacent the casing window after the telescopic joint has retracted and a shearable connection between the whipstock and a drill bit thereabove has failed. 
     FIG. 8 is a section view showing the drill string and drill bit extending through the casing window to form the lateral wellbore in adjacent strata. 
     FIG. 9 is a top, section view of the whipstock and lateral wellbore taken along a line  9 — 9  of FIG.  8 . 
     FIG. 10 is a section view of the apparatus illustrating a thermite initiator assembly disposed between the whipstock and container portion. 
     FIG. 11 is an enlarged view thereof. 
     FIG. 12 is a section view showing a partially formed window in the wellbore casing. 
     FIG. 13 is a section view showing a fully formed window in the wellbore casing. 
     FIG. 14 is a section view of the telescopic joint in its first or extended position. 
     FIG. 15 is a section view of the telescopic joint showing a thermite-actuated break plug in greater detail. 
     FIG. 16 is a section view of the telescopic joint in the second or retracted position. 
     FIG. 17 is an alternative embodiment of the invention illustrating a container portion with apertures formed in a wall thereof. 
     FIG. 18 is a section view thereof. 
     FIG. 19 is a section view illustrating an alternative means of initiating the thermite process. 
     FIG. 20 is a section view showing a window formed in casing. 
     FIG. 21 is yet another embodiment of the invention illustrating a rocket member slidably disposed in a cased wellbore. 
     FIG. 22 is a section view of the apparatus of FIG. 21 illustrating the rocket member in a second, higher position within the apparatus. 
     FIG. 23 is a top section view of the embodiment of FIG.  21 . 
     FIG. 24 is an elevation view of an alternative embodiment of the invention illustrating an apparatus with container portion having apertures formed in a wall thereof and a slip assembly disposed thereabove. 
     FIG. 25 is a section view of the apparatus after a window has been formed in casing. 
     FIG. 26 is an alternative embodiment of the invention whereby the container portion forms an atmospheric chamber. 
     FIG. 27 is a section view of the embodiment of FIG. 26 after a window has been formed in the casing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an apparatus  100  of the present invention as a single unit as it would be lowered into a wellbore. The apparatus includes drill stem  110 , a drill bit  120  disposed at a lower end thereof, a diverter or whipstock  130  below the drill bit and attached to it with a shearable connection  132 , typically including a threaded member designed to fail upon a predetermined compressive or tensile force applied between the drill bit and the whipstock. Fixed at a lower end of the whipstock is a container portion  160  which is designed to house a quantity of an exothermic heat energy source, like thermite and also designed to house any casing or thermite material remaining after the thermite reaction burns a hole or window in the casing wall as will be described hereafter. At a lower end of the container portion  160  is a telescopic joint  200  disposed between the container portion  160  and an anchor  280  therebelow. The telescopic joint is designed to move the whipstock and container portion thereabove from a first position to a lower, second position within the wellbore after the casing window is formed. The anchor  280  fixes the assembly in the wellbore at a predetermined location and its use is familiar to those of ordinary skill in the art. 
     The drill stem  110  is typically a tubular used to rotate a drill bit and in this instance, is also used as a run-in string for the apparatus. The drill bit  120  is also typical and includes formations at a lower end to loosen material as a wellbore is formed. In one embodiment of the invention, the drill bit also includes apertures running longitudinally therethrough providing a channel for fluid injected from the well surface through the drill stem  110  and the drill bit  120  into the formation while drilling is taking place. The whipstock  130  is well known in the art and includes a sloped portion  135  having a concave formed therein made of material adequate to withstand abrasive action of the rotating drill  120  bit as it moves across the sloped portion towards a newly formed window in the casing to access that portion of the adjacent formation where the lateral wellbore will be formed. 
     FIG. 2 is a partial section view showing the apparatus  100  in a cased wellbore  105 . Thermite material, shown in dotted lines, is located along a recessed outside wall of the container portion  160  adjacent that area of the casing  310  where a window will be formed. FIG. 3 is a top, section view taken along a line  3 — 3  of FIG.  2 . Visible is the wellbore  105 , the casing  310  and a wall  164  of the container portion  160 . In the embodiment shown, the wall  164  of the container portion  160  is reduced in thickness on one side, creating a cavity  166  in the area adjacent the casing where the window will be formed. Thermite is housed in cavity  166  and is held at its outer surface by a thin sheet of mesh  167  wrapped therearound. It will be appreciated by those skilled in the art that the thermite material could be located and housed adjacent the casing wall in any number of ways so long as the proximity of the thermite to the casing permits the thermite process to effectively remove and displace or otherwise damage the casing material to form a window in the casing. 
     FIG. 4 is a partial section view of the apparatus  100  in a wellbore  105  after a window  312  has been formed in the casing and FIG. 5 is an enlarged view thereof. As illustrated, casing  310  remains above and below the window  312 . The shape of the window  312  is typically as depicted in FIG. 5, i.e., an elliptical shape adequate for drill bit  120  and drill stem  110  to pass through at a steep angle. At an upper and lower end of the container portion  160 , split rings  165  are located and are designed to urge the casing material and thermite to flow into the bottom of the container portion  160  as it melts and also to remove any remaining material on the inside of the window opening as the container portion  160  moves down across the window  312  after the window is formed, as will be more fully disclosed herein. 
     Window  312  is formed through a thermite process, including an exothermic reaction brought about by heating finely divided aluminum on a metal oxide, thereby causing the oxide to reduce. Thermite is a mixture of a metal oxide and a reducing agent. A commonly used thermite composition comprises a mixture of ferric oxide and aluminum powders. Upon ignition, typically by a magnesium ribbon or other fuse, the thermite reaches a temperature of 3,0000° Fahrenheit, sufficient to soften steel and cause it to flow. 
     One alternative to causing the spent thermite and the casing material to flow into a container is to leave a solidified mass of casing material in a state that is very fracturable and brittle and will break easily into small pieces which can then flow up the drill string with the flow of drilling fluids. This can be accomplished by supplying an excess of oxygen to the molten metal during combustion such that a portion of it is converted to oxide. The excess oxygen could also be obtained by altering the ratios of constituents making up the thermite or from an additive. Two additives that could be used to provide this excess oxygen are copper oxide (CuO) and cellulose. By performing a thermite operation with such an addition of oxygen, the casing material can be virtually destroyed but left in place or reduced to some state where it is easily broken up. In this embodiment therefore, no container portion for containing spent thermite or casing material is necessary. 
     FIG. 6 is a top, section view taken along a line  6 — 6  of FIG.  5 . Visible in FIG. 6 is the container portion  160  of the apparatus  100  after the window  312  has been formed in the wall of the casing  310 . Visible on the left side of the Figure is casing  310  and disposed annularly therein, the undamaged wall  162  of the container portion  160 . Visible on the right side of the drawing, the wall  162  of the container portion  160  and the casing  310  wall have been removed by the thermite process, leaving the interior of the container portion  160  exposed to the wellbore  105 . 
     FIG. 7 is an elevation view of the apparatus  100  illustrating the whipstock  130  in the wellbore  105  at a location adjacent the newly formed window  312  in the casing  310 . As will be more fully described herein, the telescopic joint (not shown) has moved to its second, retracted position causing the shearable connection  132  between the drill bit  120  and the whipstock  130  to fail. In this manner, the container portion  160  and the whipstock  130  move to a position whereby the whipstock is adjacent the window  312 . Visible also in FIG. 7 is the window left in the container wall by the thermite. From the position illustrated in FIG. 7, the formation of a lateral wellbore can begin with the rotating drill bit  120  moving down and along the sloped portion  135  of the whipstock  130 , through the casing wall window  312  and into a formation adjacent thereto. 
     FIG. 8 is a partial section view illustrating the drill bit  120  and drill stem  110  having traveled down the sloped portion  135  of the whipstock  120 , through the newly formed window  312  in the casing  310  and into formation  305  where the lateral wellbore  106  is formed. FIG. 9 is a section view taken along a line  9 — 9  of FIG.  8  and showing the drill stem  110  having exited the central wellbore  105  through window  312  to form the lateral wellbore  106 . 
     In one embodiment, the thermite reaction is initiated by a fluid power signal provided from the surface of the well through drill stem  110  and a hydraulic line extending from an aperture formed in the drill bit  120  to a thermite initiator assembly therebelow. FIG. 10 is an elevation view, partially in section, of the assembly  100  showing the hydraulic line  260  extending from the drill bit  120  to the thermite initiator assembly  265  located between the lower portion of the whipstock  130  and the upper container portion  160 . An aperture through drill bit  120  provides fluid communication between the drill stem  110  and the thermite initiator assembly  265  via the hydraulic line  260 . FIG. 11 is an enlarged section view of the thermite initiator assembly  265 . The initiator assembly  265  includes an initiator piston  267  housed in a body  269  and a primer  270  disposed therebelow to start the thermite reaction upon contact with the initiator piston  267 . The hydraulic line  260  is in fluid communication with a piston surface  268  through a port thereabove and the initiator piston  267  is fixed in a first position within the body  269  with at least one shear pin  271  designed to fail when a predetermined pressure is applied to the piston surface  268  via the hydraulic line  260 . Disposed below the primer  270  is a first fire mix  272  and therebelow a quantity of loose thermite powder  273 . Extending from the area of the loose thermite powder  273  through a bore  274  in the wall of the container portion  160  is a quantity of packed thermite which leads directly to thermite arranged in the cavity  166  formed in the container portion wall adjacent the casing wall as is illustrated in FIG.  3 . When a predetermined pressure is applied to piston surface  268  and the shear pin  271  fails, the piston  267  travels down the stroke of the body  269  and a formation  275  in the center of a lower surface of the piston  267  contacts primer  270  which then ignites the first fire mix  272  and the loose thermite powder  273  therebelow. Subsequently, the thermite located in cavity  166  is ignited. 
     FIG. 12 is a section view of the apparatus  100  in wellbore  105 , after the piston  267  has traveled downwards in body  269  and contacted primer  270  to begin the thermite process. A partially formed window  312  is visible in the Figure. As the thermite located in the cavity  166  begins burning in a top-down fashion, the material making up the casing  310  and that portion of container wall  164  adjacent cavity  166  is softened and through the action of time and heat is loosened sufficiently to flow to the bottom of the container portion  160  along with spent thermite material. The material  311  is visible housed in the bottom of the container portion  160 . In this manner, the casing is removed and window  312  is formed, leaving an opening in the casing  310  adequate for drill bit  120  and drill stem  110  to pass through. Specifically illustrated in FIG. 12 is the top down formation of the window  312  as the thermite located in cavity  166  burns from its point of ignition at the thermite initiator assembly  265  towards the lower end of the container portion  160  to form a substantially elliptical shape in the casing  310 . As the casing material is heated and melted, it flows into the bottom of the container portion and away from the newly formed window  312  and the wellbore  105 . FIG. 13 is a section view showing the completely formed window  312 . In this view, the thermite reaction has moved from the upper end of the container portion to a lower end, forming window  312 , the shape of which is determined by the shape of the thermite packed into the cavity  166  of the container portion  160 . 
     Also visible in FIGS. 12 and 13 is a means for causing the telescopic joint  200  (not shown) to move to its second position as the formation of window  312  is completed. A channel  202  formed in a lower wall of the container portion  160  leading from the lower end of the window  312  is constructed and arranged to house a fuse  204  or strip of thermite that will ignite as the formation of the window  312  is completed, carrying a burning charge to a lower area of the container portion  160 . The purpose of the thermite fuse  204  is to initiate the actuation of the telescopic joint  200 , causing the joint  200  to move from the first or extended position to the section or retracted position. 
     FIG. 14 is a section view illustrating the path of the fuse  204  from the bottom portion of the container portion  160  of the apparatus  100  to the telescopic joint  200  therebelow in the wellbore  105 . Thermite fuse  204  extends through a channel  202  formed in a central shaft  209  of the telescopic joint  200  and terminates at a break plug  210  which is designed to be fractured by the burning thermite fuse  204 . In FIG. 14, the fuse  204  is shown partially burned and terminates at a point  208  in channel  202 . The telescopic joint  200  is constructed and arranged with an upper atmospheric chamber  205  and lower atmospheric chamber  215 , both of which are formed between the exterior of the shaft  209  and an interior of a lower portion  212  of the telescopic joint  200 . Both atmospheric chambers  205 ,  215  are initially at atmospheric or surface pressure. When the break plug  210 , located in the upper atmospheric chamber  205  is fractured, the upper atmospheric chamber  205  is exposed to wellbore pressure. Wellbore pressure enters the interior of the channel  202  from a port  206  located in the bottom portion of the telescopic joint  200 . Fluid entering the port from the wellbore extends upwards in the telescopic joint  200  through channel  202  and enters the upper atmospheric chamber  205 . Thereafter, the higher pressure wellbore fluid acts upon a piston surface  207  in chamber  205  urging the piston downwards due to the pressure differential between the two chambers  205 ,  215 . A shear pin  216  keeps the telescopic joint  200  in its first position during run-in of the apparatus but is designed to fail upon a predetermined amount of pressure exerted on the piston surface  207  in the atmospheric chamber  205 . 
     FIG. 15 is an enlarged view illustrating the break plug  210  disposed in channel  202  of the telescopic joint  200  and providing a selectable fluid communication between fluid in the channel  202  and the upper atmospheric chamber  205  of the telescopic joint  200 . The plug  210  includes a passageway  211  therethrough to expose the atmospheric chamber  205  to the pressure in the interior of the telescopic joint upon fracturing of the break plug. FIG. 15 also illustrates the thermite fuse  204 , which extends into contact with the break plug  210 . FIG. 16 is a section view of the telescopic joint  200  shown in its retracted or second position. As is visible in the Figure, wellbore pressure has urged the central shaft  209  of the telescopic joint  200  to a lower position relative to the lower portion  212  of the joint, terminating in contact between an upper shoulder  217  of the telescopic joint  200  and the bottom  220  of the container portion  160  of the assembly. As the telescopic joint moves from the first to the second position, the shearable connection  132  between the drill bit  120  and the whipstock  130  fails allowing the container portion  160  of the assembly and the whipstock  130  to move to a lower, predetermined position within the wellbore (FIG. 7) whereby the sloped portion  135  of the whipstock  130  is accurately positioned in front of the newly formed window  312  in the casing  310 . 
     In operation, the apparatus  100  of the present invention operates as follows: The assembly  100 , including the drill stem  110 , drill bit  120 , whipstock  130  container portion  160 , telescopic joint  200  and anchor  280  are run into a wellbore  105  to a predetermined location where the anchor  280  is set, fixing the assembly  100  in the interior of the wellbore. A measurement-while-drilling (MWD) device may be used to properly orient the apparatus within the wellbore. Thereafter, using a hydraulic signal means via hydraulic line  260  running from the drill bit  120  to the thermite initiator assembly  265 , the thermite located in the wall  162  of the container portion  160  is ignited and through heat and time, a window  312  is formed in the casing  310  adjacent the wall of the container  160 . As the thermite completes its burning, a thermite fuse  204  adjacent a lower end of the window  312  ignites and subsequently causes a break plug  210  located in the telescopic joint  200  to fail, thereby exposing a piston surface  207  formed in an atmospheric chamber  205  to wellbore pressure. Wellbore pressure, acting upon the piston surface  207  is adequate to cause a shearable connection  132  between the drill bit  120  and the whipstock  130  to fail and the entire assembly below the drill bit  120  moves to a second, predetermined position as the telescopic joint  200  assumes its second position. Thereafter, the whipstock  130  is properly positioned in the wellbore  105  adjacent the newly formed window  312  in the casing  310  and the drill stem  110  and drill bit  120  can be lowered, rotated and extended along the sloped portion  135  of the whipstock and through the window  312  to form a lateral wellbore. 
     FIG. 17 is a plan view of an apparatus  400  in a wellbore  105  and illustrates an alternative embodiment of the invention wherein a container portion  405  of the apparatus includes a wall  407  having apertures  410  therethrough. In this embodiment, the thermite material, located inside the container portion, causes destruction of the adjacent wellbore casing without destroying the wall of the container. The wall  407  of the container  405  is formed of ceramic material or some other material resistant to the heat created by the burning thermite. As shown in FIG. 17, the container portion  405  of the apparatus in this embodiment is extended in length to include a lower portion having an opening  406  constructed and arranged to receive spent thermite and casing material as the thermite process is completed and a window is formed in the casing. FIG. 18 is a section view showing the thermite material  401  in the interior of the container portion  405  as well as the shape of the apertures  410  formed in the container wall. Each aperture includes a converge/diverge portion whereby during the thermite process, burning thermite is directed through each aperture where the velocity of the thermite increases in the converge portion. A diverge portion at the outer opening of each aperture allows the burning thermite to exit the container wall  407  in a spray fashion giving a sheet effect to the burning thermite as it contacts and melts the casing  310 . A lower portion container portion wall  407  includes a slanted face  408  also having apertures  410  formed therein. The shape of the slanted face  408  permits a pathway for flowing thermite and casing material into the opening  406  therebelow. Also visible in FIG. 18 is a thermite initiator assembly  425  relying upon an electrical signal to begin the thermite process (FIG. 19) and a thermite fuse  430  extending from the bottom of the container portion wall  407 , below the aperture  400  to a telescopic joint  200  (not visible) therebelow. 
     FIG. 19 is a section view of an electrical assembly  425  for initiating the thermite process. The assembly  425  includes two electrical conductors  426 ,  427  extending from the surface of the well and attached to an electrode  430  therebetween in a housing  429  of the thermite initiator  425 . At a predetermined time, an electrical signal is supplied from the surface of the well and the electrode  430  rises to a temperature adequate to initiate burning of thermite located proximate the electrode. Subsequently the thermite in the wall of a container portion burns to form the window in the casing. 
     FIG. 20 is a section view of the apparatus  400  after the window  312  in the casing  310  has been formed but before the telescopic joint  200  therebelow (not shown) has caused the whipstock  130  thereabove (not shown) to move adjacent the window  312 . Visible specifically is thermite and casing material  311  which has flowed into the opening  406  in the lower portion of container portion  405 . While a portion of the container wall is constructed of ceramic in the preferred embodiment, it will be understood that this embodiment of the invention could be constructed in a number of ways and the ceramic portion of the wall could consist only of inserts inserted in a metallic wall, with each insert including an aperture formed therein. 
     FIG. 21 illustrates yet another embodiment of the invention whereby a window in casing  310  is created by combustion of fuel in a rocket member  505  disposed in a container portion  510  of the apparatus  500 . In this embodiment of the invention, a window is formed by the combustion of solid fuel material, like thermite in the rocket member  505 . The products of the combustion are directed towards the casing wall by a slanted nozzle  515  as the rocket member  505  is propelled upwards in the container portion  510  of the apparatus  500 . Specifically, the rocket member with its slanted nozzle  515  is disposed in a lower area of the container  510  whereby the nozzle  515  is adjacent an area of the casing  310  where the bottom of the casing window will be formed. In the preferred embodiment, the rocket member is slidably disposed in the container portion  510  with a pin and slot arrangement whereby at least one pin  517  formed on the body of the rocket member is retained and moves within at least one slot  518  formed within the interior of the container portion  510 . During the thermite process, when the rocket member is expending fuel through the slanted nozzle  515 , the rocket member will be propelled upwards in the container portion  510  of the apparatus  500 . Visible also in FIG. 21 is a dampening member  560  disposed in an upper area of the container portion  510  whereby the rocket member  505 , upon reaching the upper area of the container will be slowed and stopped by the dampening member  560 . The dampening member  560  is located at that vertical position in the container portion whereby the nozzle  515  of the rocket member will be adjacent the upper portion of a window when the dampening member  560  stops the upward momentum of the rocket member  505 . 
     FIG. 22 is a section view of the apparatus  500  depicting the rocket member  505  having moved to an upper portion of the container  510  and a window  512  having been formed in the casing  310  by the rocket member fuel. The top of the rocket member has contacted dampening member  560 . In the embodiment shown, the apparatus includes a slip assembly  501  including two slip members  502 ,  503  that can be remotely actuated to fix the apparatus  500  in the wellbore. However, the apparatus could include a telescopic member therebelow and a thermite fuse with or without a time delay member can be located in a position whereby the fuse will begin burning as the formation of the window  512  is near completion. As with the other embodiments, the burning fuse initiates actuation of a telescopic joint therebelow, causing a whipstock to move into a position adjacent the newly formed window. FIG. 23 is a top section view taken along a lines  23 — 23  of FIG.  21 . FIG. 23 illustrates the relationship between the jet member with its two pins  517  and the slots  518  formed in the inner wall of the container portion  510  of the apparatus  500 . 
     FIG. 24 is an elevation view of an alternative embodiment of the invention providing a simple method and apparatus  600  for forming a window in downhole casing  310 . The apparatus includes a container portion  615  having apertures formed therein and a slip assembly  625  for fixing the apparatus in a wellbore. FIG. 25 is a section view of the embodiment of FIG. 24 after a window  612  has been formed in adjacent casing  310 . In this embodiment, the apparatus  600  containing thermite material is extended into the wellbore on wireline  605  to a predetermined position adjacent the area of the casing where the window will be formed. The container  615  has a predetermined amount of thermite disposed therein which is preferably disposed against a side of the container  615 . The container is preferably formed of ceramic material having a plurality of apertures  610  formed therein. The apertures are arranged as those of the embodiment described in FIGS. 17,  18  and  20  herein. Wireline  605  is capable of carrying the weight of the thermite container and also capable of passing an electrical charge sufficient to begin the thermite process through the use of a thermite initiator  617  disposed at an upper portion of the thermite container. Thermite initiator  617  is similar to the device described in relation to FIG. 19 herein. 
     In order to rotationally and axially fix the container  615  in the predetermined area of the wellbore  105 , slip assembly  625  is run into the wellbore  105  on wireline  605  along with the container  615 . In the preferred embodiment, the slip assembly  625  is disposed above the container and includes at least two slips  626 ,  627  which can be urged against the inside of the casing  310 , preferably by some gas means made possible by the burning thermite, thereby holding the apparatus  600  in place in the wellbore while the thermite process forms the window  612  in the casing  310 . In the preferred embodiment, the slip assembly  625  is gas actuated. Gas generated during the thermite process is communicated to the slip assembly  625  via channels  630 ,  631  connecting the slip assembly  625  to the container  615 . In the preferred embodiment, the slip assembly is constructed and arranged to become actuated simultaneously with the commencement of the thermite process. 
     FIG. 26 is a section view of an alternative embodiment of the invention whereby a container portion  760  of an apparatus  700  forms an atmospheric chamber which, when exposed to wellbore pressure, urges spent thermite and casing material into a lower area  761  of the container  760 . As with other atmospheric chambers, the pressure differential between the inside of the container portion and the wellbore create a suction when the interior of the container is breached and exposed to the wellbore pressure therearound. In this embodiment, a wall of the container portion adjacent the area of casing where a window will be formed includes an upper, thicker section  705  and a lower, thinner center section  708 . Corresponding to the thickness of the container wall is the cavity formed between the container wall and the casing which, when filled with thermite, results in a layer of thermite having an upper, thinner portion  710  and a lower, thicker portion  711 . The design of the present embodiment permits the thermite to burn in a top-down fashion melting the casing material without breaching the wall of the container  760 . As the burning thermite reaches the thinner wall section  708 , the thicker layer of thermite causes the wall section to melt, thereby exposing the atmospheric chamber in the interior of the container portion to wellbore pressure. The result is a suction which acts to urge spent thermite and casing material into the container portion. FIG. 27 is a section view of the embodiment of FIG. 26 showing a window  712  having been formed in casing  305 . Visible specifically in this view is the lower portion of the container which has been filled with spent thermite and casing material  711 . A fuse  722  running from the lower portion of the window to the telescopic joint assembly therebelow is partially burned. 
     While foregoing is directed to some embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.