Abstract:
An apparatus and method for facilitating eversion of a flexible liner down a borehole when an artesian head condition is producing a rate of water flow out of the top of the borehole. A bypass pipe channels artesian flow, moving upward in the borehole and/or well casing, past an everting flexible liner to a wellhead fixture. Artesian flow arriving at the wellhead fixture is pumped away to ameliorate resistance to liner eversion otherwise presented by the water flow. A heavy mud may be disposed inside the everting liner further to promote its downward eversion past the artesian flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 61/783,281 titled “Method of Installation of Flexible Borehole Liner Under Artesian Conditions” filed on 14 Mar. 2013, and of the filing of U.S. Provisional Patent App. Ser. No. 61/853,096 titled “Method of Installation of Flexible Borehole Liner Under Artesian Conditions” filed on 28 Mar. 2013, both the specifications of which are incorporated herein by reference. This application is related to U.S. Provisional Patent App. Ser. No. 61/793,548 entitled “Method for Sealing of a Borehole Liner in an Artesian Well” filed on 15 Mar. 2013, and the specification thereof also is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to the installation of everting flexible borehole liners into boreholes in geologic formations with shallow water tables or in geologic formations exhibiting artesian hydraulic head conditions. 
     Background 
     A “borehole” is a hole, e.g., a shaft or well, drilled into the Earth&#39;s subsurface. The hydraulic conductivity profiling techniques described in U.S. Pat. No. 6,910,374 and U.S. Pat. No. 7,281,422 have been used in over 400 boreholes since 2007. These patents, whose complete teachings are incorporated herein by reference, describe methods for determining the hydraulic transmissivity profile of the geologic formations surrounding borehole by carefully measuring the eversion of a flexible borehole liner into an open, stable, borehole. Other installations of flexible liners into boreholes, by the eversion of the liners, are disclosed in a number of other patents, such as U.S. Pat. Nos. 6,283,209, 6,794,127, and 7,896,578, obtained by this inventor. Such liners are usually installed into the open boreholes using a water level inside the liner which is significantly higher than the water table in the formation penetrated by the borehole. 
     However, when that required excess pressure head (difference between ambient water table level and water level supplied to the liner interior) is not available at a particular borehole, a scaffold plus an extension of the surface casing may be used to achieve the needed higher water level within the liner. In some situations of very shallow water tables, or in situations where the head within the borehole would rise above the ground surface if the surface casing were extended above the surface, the required scaffold is so high as to be very inconvenient or even dangerous, and use of scaffolds often exposes the installation personnel to freezing winter winds. 
     With the foregoing background, the presently disclosed invention was developed. 
     SUMMARY OF THE INVENTION 
     The invention described hereafter allows the transmissivity profiling procedure, and the installation of flexible liners used for other measurements or purposes, to be accomplished without the need for extensive scaffolding above the borehole. Furthermore, the presently disclosed apparatus and method allow the liner installation when the artesian head condition in the borehole is producing a very high rate of water flow out of the top of the borehole. Using previously known techniques, the installation of everting flexible liners into boreholes was limited to situations of less than approximately five feet of artesian head above the ground surface, even when scaffolding was employed. In contrast, the present invention greatly extends the circumstances of successful use of everting flexible liners, even to situations involving natural artesian heads twenty feet above the ground&#39;s surface. Furthermore, the method of the present disclosure allows easier installations under the more commonly encountered conditions of shallow water tables. Additional benefits will be described hereafter. 
     There is disclosed hereby a method and apparatus to reduce the effective water table beneath an everting flexible borehole liner, and to provide a higher pressure within the liner, in order to allow the liner eversion into the borehole, despite the existence of high artesian pressures. The method is accomplished without the extension of the borehole surface casing far above the surface to obtain the necessary driving pressure within the liner. An advantage of the presently disclosed method is that it allows the normal artesian flow out of the borehole to bypass the liner during its installation, thereby preventing the normal development of a high water pressure beneath the liner (i.e., between the descending eversion point of the liner and the bottom of the borehole). A further advantage is that in those boreholes which produce a natural gas flow to the surface, the gas is not trapped beneath the everting liner, which trapped gas hinders everting liner propagation down the borehole. 
    
    
     
       BRIEF DESCRIPTION OF THE VARIOUS VIEWS OF THE DRAWING 
       The attached drawings, which form part of this disclosure, are as follows: 
         FIG. 1  is a side sectional view of a typical everting liner installation according to known techniques; 
         FIG. 2  is a side sectional view of three examples of water table conditions of increasing difficulties addressed according to the present invention; 
         FIG. 3  is a side sectional diagrammatic view of a borehole, showing the location of a bypass pipe and wellhead fixture according to the present invention, to allow the water table in the hole to be lowered and the artesian flow to be directed past the everting liner; 
         FIG. 4  is a side sectional diagrammatic view of a borehole similar to  FIG. 3 , showing the addition of a weighty but flowable mud to the interior of the liner and the presence of selected components of the apparatus system according to the present invention; 
         FIG. 5  is a view similar to that seen in  FIG. 4 , showing the extension of the mud-filled liner past the bypass pipe; and 
         FIG. 6  is a view similar to that seen in  FIG. 5 , showing the further descent of the liner, with the artesian flow ascending adjacent to the liner and being removed at the wellhead fixture. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An everting liner installation according to known techniques is shown in  FIG. 1 . The liner  11  has been attached to the top of the casing  12  at location  13 . The liner in the borehole  14  is filled to the level  15 , which is above the water table  16  in the formation  17 . The water within the borehole  14  beneath the liner (i.e., between the bottom of the liner and the bottom of the borehole) is displaced into available flow paths in the formation  17  allowing the liner  11  to propagate by eversion of the liner at the bottom everting end of the liner. The driving pressure to evert the liner  11  is due to the difference between the head at the water level  15  in the liner and the head at the water table  16  in the formation  17 . 
     If the pressure head at the level  16  in the formation  17  is higher than the head at level  15  inside the liner  11 , the liner will be collapsed by the formation water pressure, and the liner cannot propagate down the borehole. A minimum pressure difference, between level  15  and level  16 , is needed to cause the liner to propagate in the eversion process. That minimum eversion pressure is greater for smaller borehole diameters than for larger diameter boreholes. For the liner  11  to be easily everted down the borehole, the water table  16  in the open borehole must be a sufficient distance below the top of the surface casing  12  to allow a water fill of the liner to drive the eversion process. For some boreholes, the minimum water table depth in the formation  17  must be at least five feet below the top of the casing  12 . In other situations of smaller boreholes, a water table  16  of at least twenty feet below the top  13  of the casing  12  may be required to supply an adequate liner driving pressure. If the water table  16  in the formation is less than the necessary depth distance below the top  13  of the casing  12 , the above-ground height of the casing  12  can be extended upward to obtain a higher water level  15  inside the liner  11 . However, there are practical safety limits as to how high the casing can be extended, with the associated surrounding scaffolding, and still allow safe working space for the installation personnel. In some situations, for safety reasons there are prohibitions against the use of any scaffolding. 
       FIG. 2  illustrates several static water tables as may be seen in three hypothetical boreholes  26 ,  27 ,  28  extending into a geologic formation  25 . In a commonly encountered circumstance, the water table level  21  is in the borehole  27  a considerable (e.g., more than about ten to fifteen feet) below the surface  29 . A more troublesome situation is when the natural water level  22  is near the surface  29  (below the top end of a casing  210 ), as seen in the middle borehole  26  of  FIG. 2 . The degree of difficulty in pressure-everting a liner into such a borehole will depend somewhat upon the diameter of the borehole; generally, such a troublesome “shallow condition” involves a natural water table less than about five to about ten feet below the top end of the well casing. The more difficult situation for installing everting liners, seen in the borehole  28  on the right side of  FIG. 2 , is when the level  23  of the water table in the formation intersected by the borehole  28  is above the top of the well casing, perhaps many feet above, and thus substantially above the ground&#39;s surface  29 . This is an artisan condition; in this disclosure, “artesian flow conditions” refers to the spontaneous (without artificial pumping), upward movement of water, under hydrostatic pressure in rocks or unconsolidated material beneath the earth&#39;s surface, to an elevation above the earth&#39;s surface. In this latter case, if the height of the casing were below the level  23 , the water from the subsurface formation(s)  25  would flow over the top of the surface casing (i.e.,  210  in the figure) onto the surface of the ground. If the natural level  23  is very high above the surface  29 , and the transmissivity of the formation  25  is a large value, the flow rate out of the top of the (too-short) casing  210  would be large. Such flows, which can exceed 100 gal/min, normally are extremely undesirable at the borehole installation site. 
     In the borehole  27  seen at the left side of  FIG. 2 , where the natural water level  21  is a significant distance below the surface of the ground, a typical liner installation can be effected by known techniques, as indicated in  FIG. 1 . In the circumstance of the middle borehole  26  in  FIG. 2 , with the water level  22  near the surface  29 , a casing extension is needed. In the third situation seen in the right borehole  28  of  FIG. 2 , an everting liner installation normally would not be attempted. Whereas this invention is most useful in allowing a liner to be installed at a borehole, such as borehole  28  with an elevated artesian water level  23  see in  FIG. 2 , the invention also facilitates installation in the situation of a borehole  26  with a natural water level  22  modestly above the ground&#39;s surface  29  without scaffolding or a casing extension; the method and apparatus thus is an improvement beyond currently known practices, due to safety concerns about tall scaffolding and the inconvenience of personnel working on scaffolding. 
     This disclosure is not a contention that it has not previously been known to use a heavy mud, in lieu of water, to pressurize and install by eversion a flexible borehole liner. Rather, the present apparatus and method are an innovative combination of processes for allowing the installation of everting liners under challenging conditions such as water levels  23  elevated many feet above the ground surface  29  such as generally described in reference to borehole  28  in  FIG. 2 . Such circumstances, called artesian head conditions, normally prohibit the safe installation of everting flexible liners. Some key features of the present apparatus are the bypass pipe, the mud fill, the bulbous wellhead fixture, and the wellhead pump, all as described hereafter. 
       FIG. 3  shows a borehole  36  in fractured rock formation  35  with a surface casing  37  extending some depth into the fractured rock.  FIG. 3  shows a partial system according to this disclosure, prior to initial completed installation. The artesian condition is shown as an upward flow  38  (directional arrows) allowing water flow over the top of the surface casing  37  above the ground&#39;s surface. A hollow wellhead fixture  39  is attached to the top of the casing  37  to support an everting liner (described further hereinafter). The fixture  39  preferably is “bulbous,” meaning that it is roughly spherical in shape to enclose an interior space, and in horizontal size (i.e. horizontal dimension or diameter) is substantially larger than the diameter of the casing  37 . The larger bulbous shape of the fixture  39  provides some working space within the fixture interior (e.g., for placing and arranging a liner preparatory to liner eversion), and the provision of a discharge outlet  311  in and on the fixture. A bypass pipe  310  of sufficient diameter to accommodate the entire artesian flow  38  is lowered into position in the borehole  36 , and situated proximate to and extending up above the top of the surface casing  37  as seen in  FIG. 3 . Preferably installed, the bypass pipe  310  is intermediately overlapping between the casing  37  and an interior of the fixture  39 , with an open bottom end of the bypass pipe extending a distance into the borehole and an open top end of the bypass pipe extending into the interior of the fixture. As a result, any water flowing upward in the borehole toward the casing  37  can flow upward through the bypass pipe  310  and into the interior of the fixture  39 . 
     The bypass pipe  310  may be lowered, supported, and adjustably positioned with a suitable cable or other device (not shown), which supports the upper open end of the bypass pipe near a discharge outlet  311 , which may be about horizontal, on and for the bulbous wellhead fixture  39 . The vertical elevation of the bypass pipe  310  may be adjustable relative to the casing  37  and/or fixture  39 , as with a retractable cable extending from the top of the bypass pipe to a winch (not shown) at or near the fixture  39 . The bypass pipe  310  can be any conduit or tube suitable for transmitting a liquid flow, and preferably is rigid against radial collapse. As suggested by the figures, the axis of the bypass pipe  310  preferably is oriented substantially vertically, and the pipe is placed in close adjacency with, or in contact with, the casing  37 . 
     Referring to  FIG. 4 , which shows the initial stages of installation, a pump  41  is connected with a hose  42  to be in fluid communication with the discharge outlet  43  (corresponding to outlet  311  in  FIG. 3 ), of the bulbous wellhead fixture  44  (corresponding to fixture  39  in  FIG. 3 ). The pump  41  has a sufficient discharge rate to draw off the water  45  rising (see directional arrows in well bore in  FIGS. 3 and 4 ) under artesian pressure from the well or borehole  412 . The pumping, with the pump  41 , of water from the interior of the fixture  44  at a rate at least equaling the flow  45  of water from the borehole  412  via the bypass pipe  413 , lowers or reduces the effective water table elevation (e.g., elevation  23  in  FIG. 2 ); this pumping and effective reduction in the natural water table elevation promotes the eversion of a liner into a borehole under artesian conditions, so as to allow a mud-filled liner  46  to descend to the open bottom of a bypass pipe  413 . 
     A flexible liner  46  is wound upon a reel  47  next to the wellhead on a short platform. The liner  46  is inside-out on the reel  47  as described in U.S. Pat. No. 7,281,422 and as shown in  FIG. 1  herein. In  FIG. 4 , the pump  41  is actuated to draw the water level in the bulbous wellhead fixture  44  to the level of the outlet  43 . An open-ended bypass pipe  413  is provided proximate to the borehole&#39;s surface casing (as also described in reference to  FIG. 3 ). The open end of the liner  46  is then slipped over the bulbous wellhead fixture at upper location  48  and secured tightly with, e.g., a hose clamp (not shown) to the top of the wellhead fixture  44 . The liner  46  is then pushed into the wellhead fixture  44  a short distance (e.g., about arms length, approximately two to three feet) to form an annular pocket  49  as seen in  FIG. 4 . A heavy water-based mud mixture such as may be confected of bentonite and powdered barite is then added, as by pouring into the annular pocket  49 , causing the liner  46  to evert past the open top end of the bypass pipe  413 . For purposes of this disclosure, the mud mixture preferably has a weight of between about 9.0 lbs/gal and about 15 lbs/gal, although these are by way of example; mud density may be customized to the conditions of the well. As indicated in  FIGS. 4 and 5 , the bypass pipe preferably is between the liner and the casing, or between the liner and the wall of the borehole, as the liner descends toward the bottom of the borehole. 
     As indicated in  FIGS. 3 and 4 , the open top end of the bypass pipe  310 ,  413  preferably extends above the top of the casing and into the hollow interior of the bulbous wellhead fixture  39 ,  44  that is secured atop the casing. The bypass pipe  413  of  FIG. 4  is of sufficient vertical length that the heavy mud column inside the liner  46  will develop a hydrostatic pressure in the lower, everting, end  411  of the liner  46 , which pressure exceeds the artesian head in the borehole  412  when the liner  46  has propagated downward in the borehole past the bottom end of the bypass pipe  413 . 
     Prior to the liner everting to the open bottom end of the bypass pipe, however, the upward flow  45  in the borehole  412  is diverted, via the bypass pipe, past the everting liner  46  to the pump extraction outlet  43  in the bulbous fitting  44 . The water flowing upward in the well (i.e., flow  45  in  FIG. 4 ) flows up through the bypass pipe, through the interior of the bulbous wellhead fixture  44 , and is pumped off (especially if artesian pressure is insufficient) through the outlet  43  by the action of the pump  41 . Accordingly, the liner&#39;s downward eversion is resisted little, nearly not at all, by the high pressure upward flow in the borehole  412 , until the liner  46  has reached the depth of the bottom end of the bypass pipe  413 . 
     As indicated by  FIG. 4 , the top of the bulbous fixture  44  preferably is open, to allow the disposition of the liner  46  into the fixture interior and the addition of the heavy water-based mud  49  into the liner interior to pressure the liner interior. If desired or necessary in a very fast-flowing artesian well, a short (e.g., 3 feet to about 5 ft) casing extension may be sealably provided upon the open top of the wellhead fixture  44  to extend upward there from, and the free end of the liner attached to the top end of such casing extension, to permit the heavy-mud filled liner  46  to extend above the fixture  44 . 
       FIG. 5  illustrates the system after liner eversion has progressed some distance down the borehole  56 .  FIG. 5  shows that when the liner  57  filled with mud  51  everts past the lower open end  52  of the bypass pipe (i.e.,  413  in  FIG. 4 ), the filled liner  57 , under the pressure of the contained mud  51 , presses tightly against the borehole wall below the lower end  52  of the bypass pipe. The mud-filled liner  57  thus shuts off the upward flow of water in the bypass pipe, because the mud column pressure (inside the liner  57 ) is greater than the artesian pressure in the formation  55  of  FIG. 5 . At that point, the mud column  51  pressure within the liner  57  is greater than the artesian head, and the liner  57  can continue to evert further down the borehole  56  in the usual manner. 
       FIG. 6  shows that as the portion of the liner  611  that contains the mud  61  everts past the borehole elevation  62  at which the artesian flow enters the borehole, the corresponding artesian pressure originating at the formation  65  tends to collapse that portion of the liner  611  not sufficiently dilated with the heavy mud  61 , or without sufficient mud head  63  ( FIG. 6 ) to exceed the artesian pressure at elevation  62 . Such a situation as seen in  FIG. 6  allows the artesian flow discharge to resume and to flow upward in a space  64  between the borehole wall and liner  611  to the bypass pipe  66  as the liner is everted to the bottom of the hole  67 . The above-ground flow  68  ( FIG. 6 , dashed directional line) travels from the pipe  66  (or adjacent to the pipe) to the elevation of the bulbous wellhead fixture, and then through the fixture interior and exits the fixture outlet. Note that the bulbous wellhead fixture  610  allows water rising anywhere between the upper portion of the liner  611  and the casing  612  to be collected and drawn off by the pump  69 . The discharge outlet of the bulbous wellhead fixture  610  allows the pump  69  rapidly to draw off the water that would otherwise tend to collapse the liner  611 , because the top end of the liner is sealed to the bulbous fitting  610  at location  613 . In this manner, the pump  69  can greatly reduce any tendency of the liner to be collapsed by the artesian flow above the mud-filled portion of the liner in the vicinity of elevation  62 . Use of this method and technique, including the operation of the foregoing components, including a bypass pipe  66 , a bulbous wellhead fixture  610 , a pump  69 , and weighted mud fill  61  have allowed everting liners to be installed into boreholes while performing the measurements described in U.S. Pat. No. 7,281,422, and with extreme artesian flow conditions of over 100 gallons/min., and even with artesian heads greater than 20 feet above the surface. 
     If the liner is a temporary liner it can be inverted from the borehole in the reverse of the procedure described above, except that the pump is still used to reduce the collapse of the liner. If the liner is to be a relatively permanent installation, the liner is filled with a weighted mud or with a grout fill. The grout fill results in an essentially permanent installation and prevents the artesian pressure collapse of the liner. The grout fill involves a special procedure to assure that the liner does not collapse as the grout is curing. 
     Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. The present inventive method can be practiced by employing generally conventional materials and equipment. Accordingly, the details of such materials and equipment are not set forth herein in detail. In this description, specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, as one having ordinary skill in the art would recognize, the present invention can be practiced without resorting strictly only to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention. 
     Only some embodiments of the invention and but a few examples of its versatility are described in the present disclosure. It is understood that the invention is capable of use in various other combinations and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Modifications of the invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents.