Abstract:
A method for locating placement of a guide stock in a multilateral well wherein the guide stock is properly aligned with the lateral borehole. The method employs an impression packer with a scribed reference line to provide information at the surface regarding the lateral borehole&#39;s exact location and orientation with respect to the originally installed whipstock packer. This information is then employed to make up a guide stock and orientation sub to properly orient the diverter face of the guide stock with the lateral borehole. There are tool embodiments for inflating the impression packer to a preset relatively low internal pressure. In one embodiment, the inflation fluid is carried downhole in the tool and is released to the packer on set down pressure, the fluid being drawn back out of the packer upon pick up. In another embodiment, the impression packer is outfitted with an automatically closing valve. The valve can be mechanically electromechanically or electrically activated and may work in combination with a controller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of an earlier filing date from U.S. Provisional Application Ser. No. 60/066,607, filed Nov. 26, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to oil well tools. More particularly the invention relates to proper placement of a guide stock in a wellbore for diverting tools into a lateral borehole. 
     2. Prior Art 
     When a lateral borehole is to be drilled a certain sequence of events is known and practiced regularly. First a packer is set within a primary wellbore at a location downhole of the desired exit point for a lateral borehole. A whipstock is then run and inserted in the anchor, the whipstock having an orientation sub thereon which orients the face of the whipstock in the desired direction of the proposed lateral borehole. A drill is run and the lateral borehole created. The drill is removed, the whipstock is removed and a guide stock is stabbed into the original packer. Since the guide stock is provided with the same type of orientation sub it orients in the same direction that the whipstock originally did. This is an old and well-known sequence of events and would seem to indicate that the diverter face of the guide stock should be aligned with the lateral borehole. Unfortunately, however, during the kicking off of the drill from the whipstock, the whipstock tends to move due to the tremendous torque placed on the whipstock by the drill. Since the whipstock is in this (contorted to some degree) condition when the drill leaves the primary bore the exact angle and orientation of the window thereby created is somewhat different than planned. The movement does not translate to the packer and so when the whipstock is replaced by a guide stock for feeding other tools into the lateral borehole, it may not be aligned. The orientation of the guide stock, not having any torque loads thereon is that of what was originally planned and may not coincide with the actual orientation of the lateral borehole itself. For this reason it has always been challenging to properly orient the guide stock to align with the lateral borehole. 
     Prior art methods for aligning the guide stock include, as the most common and ubiquitous method, experience of the drill team. More specifically, upon removing the whipstock from the hole an inspection is made which to a skilled and experienced eye will indicate about how far off the planned orientation the lateral borehole has been drilled. This is accomplished by examining marks made on the whipstock by the drill bit such as how deep the marks are, where on the diverter face the marks are located, etc. These marks tell the experienced driller where the bit bound and kicked off the whipstock diverter face and thus in which direction drilling began. From these determinations the drill team will reorient the guide stock by attaching the orientation sub to the guide stock differently. This modifies the orientation of the diverter surface so as to be more likely to be aligned with the lateral borehole. While skill and experience are of the most important assets in making a well work, the guestimate method of placing a guidestock leaves exactness to be desired. 
     SUMMARY OF THE INVENTION 
     The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the method and apparatus for placing a guide stock of the invention. 
     A guide stock can be reliably and precisely placed and aligned with respect to a lateral borehole by first obtaining an impression of the actual borehole window through the casing of the primary well including its exact orientation with an impression packer having an orientation sub attached thereto for engagement with the original packer installed in the primary well in preparation for drilling the lateral borehole. Upon inflation of the impression packer, the soft casing is urged into the lateral borehole opening and an impression of the window is recorded in the soft covering on the impression packer. The impression packer is then tripped out of the hole and can be reinflated at the surface to measure the impression of the lateral borehole. The impression is an exact duplicate showing angle, orientation, chord length, etc. of the window. Armed with this information a guide stock may be specifically tailored with an orientation sub and space-out subs to perfectly align with the lateral borehole. Enhancing the ability to measure the window impression is the act of scribing a line in the impression cover to employ as a reference. 
     In another aspect of the invention an impression packer having its own inflation reservoir is disclosed. While a standard impression packer known to the prior art may be employed in the method of the invention, certain inherent drawbacks exist. Although standard impression packers regularly function correctly, there are times when inflation is not completed or deflation is not possible. This is generally due to the employment of a rig pump at a great distance from the tool to inflate the tool and the length of the fluid column with respect to deflation. For preferred employment with the method of the invention is an impression packer having its own on-board inflation source. 
     The self-inflation impression packer of the invention provides more certainty that the packer will inflate to the desired pressure (approximately 200 psi) without significantly exceeding that pressure and will deflate reliably and without difficulty. The self-inflation device carries a predetermined quantity of inflation fluid which is urged into the element upon set down weight. The device automatically deflates the impression packer upon pick up. The arrangement avoids prior art inflation and deflation problems associated with pressuring up from the surface to deploy the packer. In another embodiment of the invention, the over pressure problem is avoided by installing a valve which closes at a specific predetermined pressure rating (e.g. 200 psi). A valving system is disclosed. 
     The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
     FIG. 1 is a cross sectional elevation view of a primary wellbore illustrated with a drill string being deflected by a whipstock to drill a lateral borehole; 
     FIG. 2 is a cross sectional elevation view of the primary wellbore and lateral borehole with an impression packer installed therein; 
     FIG. 3 is a cross sectional elevation view similar to FIG. 2 but with the impression packer inflated; 
     FIG. 4 is a view of the impression packer, removed from the wellbore and reinflated to provide a representation of the drilled window in the impression rubber; 
     FIG. 5 is a cross sectional elevation view of the well with the guide stock installed; 
     FIGS. 6-11 illustrate a cross sectional view of the valve assembly of the invention in an inflation tool;. 
     FIGS. 12-15 illustrate a cross sectional view of the valve assembly of the invention in an alternate position; 
     FIGS. 16-19 illustrate a cross sectional view of the valve assembly of the invention in an alternate position; 
     FIGS. 20-23 illustrate a cross sectional view of the valve assembly of the invention in another alternate position; 
     FIG. 24 is an enlarged view of the valve of the invention; 
     FIG. 24A-1 is a cross sectional view taken along section line A—A in FIG. 24; 
     FIG. 24A-2 is the section of FIG. 24A-1 but in an alternate position; 
     FIG. 24A-3 is the section of FIG. 24A-1 but in an alternate position; 
     FIG. 24B-1 is a cross sectional view taken along section line B—B in FIG. 24; 
     FIG. 24B-2 is the section of FIG. 24 b - 1  but in alternate position; 
     FIG. 24C is a cross sectional view taken along section line C—C in FIG. 24; 
     FIG. 24D is a cross sectional view taken along section line D—D in FIG. 24; 
     FIG. 24E is a cross sectional view taken along section line E—E in FIG. 24; and 
     FIG. 25 is a cross sectional view of the self-inflating sub for an impression packer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 it becomes apparent why placement of a guide stock is a difficult matter. FIG. 1 represents a primary wellbore  10  to having a packer  12  installed therein for drilling of a lateral borehole. A whipstock  14  is installed in packer  12  as is conventionally known, until this point the relative orientation of the parts is known and is relatively precise. Upon introduction of the drill string  16  however, with drill bit  18 , certainty of location and orientation is lost to some degree. Drill bits, as is known to those familiar with oil well drilling, are large and course as well as heavy and driven with incredible torque. Upon a drill bit  18  contacting the face of whipstock  14 , it gouges the face and puts tremendous downward and lateral forces as well as torsional forces on the whipstock as bit  18  kicks off to drill a lateral borehole  20 . These forces tend to distort and move whipstock  14  away from the precisely set orientation it had when installed since during drilling, the whipstock is not in the predetermined position, the lateral borehole is not being drilled precisely as it was intended to be. The degree of distortion is generally not substantial however it is sufficient to render a guide stock not properly aligned with the borehole  20 . This can and does often make installing lateral tools difficult 
     Referring to FIGS. 2,  3  and  4 , the method of the invention allows the rigger to gather precise information about the location and orientation of the drilled lateral borehole  20 . With this information a guide stock may be designed to align with borehole  20  exactly. The method of the invention may employ a conventional impression packer (commonly commercially available) or may employ impression packers of the invention which are disclosed in detail hereunder. In the method of the invention, prior to running impression packer  22 , the packer  22  is inflated to a circumference matching the circumference of the borehole in which it will be deployed to take an impression. In this condition a straight line is scribed where the window is expected to be (i.e. aligned with the orientation sub) on the outside diameter of the impression rubber of the packer  22  preferably the line is also painted onto the packer for ease of visibility. This is a reference line that will be employed post impression to provide an accurate measurement of the window. The line is visible in FIG.  4 . The line is preferred due to possible twisting of the packer during removal from the well. The impression packer  22 , (conventional impression packers being currently commercially available from Baker Oil Tools Houston, Tex.), is first deflated and then run in the hole with an orientation sub  24  attached to the bottom thereof which is engageable with packer  12 . The packer  22  will be conventionally run on tool string  26 . Upon landing the impression packer  22  in the packer  12 , packer  22  is inflated to a pressure in the range of from about 100 psi to about 300 psi and preferably to about 200 psi to urge the impression rubber of the packer  22  against the window  28  to create an impression in the impression rubber. It should be noted that the psi range of about 100 to about 300 with a preferred pressure of about 200 psi has been determined by the inventor hereof to create well-defined impressions of the window  28  without seriously damaging the packer  22 . Those skilled in the art will note the dramatic reduction in pressure employed from conventional use of impression packers for their originally intended purpose. More specifically, impression packers were developed to acquire impressions of casing erosion and cracking or fissures in open holes and employ a preferred working pressure of about 1000 psi. Because the window  28  being courted in the present invention is vastly larger than the features previously sought by impression packer use, the pressure had to be significantly reduced to prevent destruction of the tool including possibly bursting the inflatable element into the lateral borehole  20 . In the conventional impression packer embodiment of the invention pressure is regulated at the surface while in the new impression packers of the invention pressure is regulated downhole for more precision. 
     Returning to the method of the invention, packer  22  having been inflated to about 200 psi is locked off and allowed to hold pressure for a period of time of preferably at least 30 minutes. Although it is possible to obtain an impression in less than 30 minutes it is not advisable for if a viable impression is not retrieved, a significant amount of time and money will have been lost. At a time after about 30 minutes (preferably) from the time impression packer reaches about 200 psi, the packer is deflated by allowing the fluid supply to drain out of the inflatable element. Preferably about 30 minutes is allowed to drain off the conventional impression packer. Subsequent to drainage the packer  22  is removed from the well to be examined. 
     At the surface, packer  22  (see FIG. 4) is reinflated to a circumferential dimension equaling that of the hole in which it was set so that measurement can be made with the rubber of the inflatable element expanded to the same degree as it was when the element was inflated downhole. Preferably, and if the whipstock  14  did not move too much during drilling of the lateral borehole  20 , the scribed line  30  will be close to the center axis of the impression  32  on the impression rubber  33 . Measurements are taken, using line  30  as a reference, at approximately one foot increments to get an accurate set of dimensions of window  28 . The dimensions and orientation of the impression provide information such as the outer periphery dimensions of the window, the orientation and the distance from the original packer  12  that the window begins. These measurements are used to make up a guide stock that will align with the window. 
     Referring to FIG. 5, a guide stock  40  is illustrated in a position properly oriented to the lateral borehole  20 . The guide stock  40  is made up to align with window  28  exactly by adjusting the orientation of the guide stock  40  on the orientation sub  42  and providing any spacers necessary to properly place the guide stock. The setting of the original whipstock  14  has thus been adjusted to meet the alignment requirements of borehole  20  occasioned by the forces of drilling on whipstock  14  as discussed previously. All measurements are provided accurately by impression  32  to perfectly align guide stock  40  with borehole  20  when guide stock  40  is stabbed in packer  12 . 
     Preferably the impression packer  22  is long enough to provide an impression surface that will cover the entire window  28  with one impression. It is possible, however, to employ more than one impression packer for different areas of the window. By changing the length of space-out subs on the impression packer, different areas of the window may be queried. All of the impressions can then be recombined at the surface by measurement of distance from the packer  12  which is known. A single packer  22  long enough to cover the window is preferable due to a shorter period of time necessary to obtain the whole impression, less calculation work and fewer opportunities for error with a single impression. 
     With respect to the impression packer itself, referring to FIGS. 6 through 25, two embodiments of the invention are illustrated. In the discussion above, possible difficulties with conventional impression packers were noted such as problems associated with inflation and deflation. Another possible problem while employing conventional impression packers in the method of the invention is an over pressure situation. Keeping in mind the low pressures at which the method of the invention is effective, as set forth above, one of skill in the art will readily recognize the potential for an over pressurization situation where the element may rupture or other damage could occur. Over pressurization may be exacerbated by a long fluid column above the device which makes accurate pressurization difficult. Thus the invention discloses two embodiments of impression packers which reduce or avoid any over pressurization potential. 
     In a first embodiment; illustrated in FIGS. 6-24E, a conventional impression packer is modified by the addition of a pressure sensitive valve. The valve is intended to close at the time the pressure of fluid internal to the impression packer is at or about 200 psi. Once the valve is closed fluid pressure from the column, or ultimately the surface, will not be added to the interior of the packer. With this safety feature, over pressurization concomitant a surface fed system is unlikely. The valve is preferably mechanically actuated by providing a port open to internal element pressure and to a closure valve assembly whereby internal element pressure upon overcoming the bias of a spring closes the valve. This is designed to occur at about 200 psi. It should be noted that the valve may also be electromechanically or electrically actuated and may be associated with downhole sensor(s) and a processor of other type or controller. 
     In a second embodiment of the impression packer of the invention, reference being made to FIG. 25, over pressurization is virtually impossible due to the inflation fluid being carried within an inflation tool connected to the impression packer itself. Set down weight on the packer causes shearing of a retaining member whereafter the set down weight forces fluid out of a reservoir and into the element. The amount of fluid contained in the reservoir is sufficient only to create an internal pressure within the impression packer of about 200 psi. Picking up on the device creates an opposite reaction and draws fluid back into the reservoir thus deflating the element. 
     In FIG. 25, the reservoir is identified by numeral  82 . Reservoir  82  is bounded by housing  80  circumferentially, inflation sub  84  at the downhole end threaded into housing  80 , piston  86  at the uphole end, fluid sealingly slideable within housing  80  and washover pipe  88  centrally. As is then apparent, reservoir  82  is annular. Piston  86  is slidable within housing  80  to either expel fluid from the reservoir or draw fluid back in similar to a hypodermic needle. Piston  86  is operated through movement of mandrel  90  which is coaxially located within housing  80 . Mandrel  90  is supported radially, preferably by a plurality of torque bearings  92  arranged circumferentially therearound although it should be understood that other support structure could be substituted. The torque bearings number preferably six, but more or fewer may be employed if desired. Torque bearings  92  ride in semicircular grooves  94  in mandrel  90  and are maintained in contact with mandrel  90  by being held into holes  96  in top sub  98  with set screws  100 . Mandrel  90  terminates at the uphole end thereof preferably with a box thread connector  102  for connection a to tubing string (not shown). It should be noted that the stroke of piston  86  is preferably from top sub contact face  97  to the uphole end of pin thread  104  where housing  80  connects to inflation sub  84 . 
     During run in, reservoir  82  is filled with an amount of fluid appropriate to fill the selected size of the impression packer to about 200 psi and to the predetermined circumference (equal to the hole in which the packer will be inflated). Mandrel  90  is prevented from moving piston  86  during run in by a shearable connection. The connection is preferably at least two shear screws  106 . Upon set down, however, of the orientation sub for the impression packer, screws  106  are sheared and the fluid in reservoir  82  is urged through the several inflation ports  108  by piston  86  due to downward movement of mandrel  90 . When the piston  86  has fully stroked, the fluid displaced from reservoir  82  into the impression packer is the quantity of fluid that will create about 200 psi in the packer. The movement is caused by additional set down weight from the tubing string above. The fluid is expelled from reservoir  82  through inflation ports  108  and into the impression packer connected to the self-inflating device of the invention. The inflation ports  108  are preferably drill holes through inflation sub  84 . Preferably at least two are provided. Inflation ports  108  remain in open fluid communication with the inflatable element of the impression packer. This is important because it provides for automatic deflation of the packer as well as inflation. More specifically, upon picking up on mandrel  90 , piston  86  moves uphole and creates a vacuum within reservoir  82  which draws fluid out of the impression packer causing it to deflate. By the time the pick up force reaches the 30-40 thousand pounds to disengage the orientation subs on the impression packer, the mandrel  90  is in its fully extended position, piston  86  has been stroked fully uphole within the tool and all of the fluid in the inflatable element has been removed. The tool then can be easily tripped out of the wellbore for examination as discussed hereinabove. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.