Patent Publication Number: US-2011056704-A1

Title: Method and device for casing a bored well portion

Description:
The present invention relates to a method for casing a drilled (cylindrical) well, notably an oil or gas producing well. 
     It also relates to a device intended for applying the method. 
     The invention particularly but not necessarily, applies to the casing of a portion of a well which has already been drilled, and for which it is desired to continue with drilling after placing said casing, the latter being intended for sealing the already drilled portion, the wall of which is subject to fracturing phenomena. 
     The drilling of a well is usually performed by means of a rotary tool such as a bit mounted on the end of a drill rod and controlled from the surface. The operation is performed in the presence of mud which is permanently recycled inside the well. Mud is generally a fluid based on water or oil. One of its functions is to exert hydrostatic counter-pressure which is opposed to the thrusts of the fluids present around the wall of the well so as to stabilize the ground and thereby reduce the risks of collapses. Mud is injected at the end of the drill rod, under the bit, and flows upward to the surface with rock debris generated by the drilling. Another one of its functions is therefore to remove this debris. At the surface, the mud is decanted in order to remove the rock debris, and then re-injected into the well. The presence of the mud and its upward motion further ensure a control of the abnormalities which may occur during the drilling of the well (piercing a gas pocket for example), which then allows triggering of ad hoc safety systems, e.g. for closing the outlet of the well. 
     A difficulty likely to be encountered during drilling is a loss of circulation of the mud. This problem is in particular encountered when the well crosses a very permeable soil portion, having fractures, cracks or other channels which open out into large capacity passageways. 
     Under this assumption, indeed, the mud escapes towards the passageways instead of moving up to the surface, the supplies being insufficient for compensating the leaks. 
     Attempts to plug these fractures, which are generally made by acting on the composition and/or the grain size of the mud, possibly by enriching it with various granulates, are often vain. 
     The invention aims at solving these difficulties by proposing a method and a device with which it is possible to easily isolate at a reduced cost at least one fractured area encountered during drilling in order to avoid these losses and to allow drilling to subsequently continue with satisfactory circulation of the mud. 
     The object of the invention is therefore a method for casing a drilled well portion, notably a well for producing oil or gas. 
     According to the invention, for this, use is made of a cylindrical tube with a diameter slightly smaller than that of the borehole, at least the upper portion of which is ductile and radially expansible. This tube being provided at its base with a seal gasket itself radially expansible under the effect of the tube&#39;s own weight, this tube having a smaller length than that of the drilled well portion, but sufficient so that when its base bears against the bottom of the drilled well portion, said upper portion is positioned above the fractured area, and the following is performed:
         the tube is introduced axially into the drilled well portion in such a way that its base will bear against the bottom of the drilled well portion and causes radial expansion of the seal gasket, forcing the latter to be applied in a substantially leak-proof way against the well wall which surrounds it;   by means of an expander tool, it is proceeded with radial expansion of the upper portion of the tube beyond its yield strength, so as to apply it intimately against the well wall which surrounds it, at a level located above the fractured area.       

     A casing is thereby produced, the interior of which is perfectly isolated from the fractured area, by applying the expanded upper portion of the tube against the wall of the well on the one hand, by applying the seal gasket around the lower portion of the tube on the other hand. 
     According to other possible advantageous and non-limiting features of this method:
         it is proceeded with radial expansion of the upper portion of the tube by means of an expander tool in the form of an inflatable bladder;   it is proceeded with this expansion stepwise;   it is gradually proceeded with this expansion from the bottom to the top;   at the beginning of the operation, the expander tool is firmly attached to the tube and the whole is moved down into the well until the tube will rest on the bottom of the well, after which it is detached therefrom in order to proceed with the radial expansion of the upper portion of the tube.       

     The device intended for applying this method, which is also an object of the present invention, is characterized in that it comprises:
         a cylindrical tube with a slightly smaller diameter than that of the borehole, at least the upper portion of which is ductile and radially expansible, and which is provided at its base with a seal gasket itself radially expansible under the effect of the tube&#39;s own weight, this tube having a smaller length than that of the drilled well portion, but sufficient so that when its base will bear against the bottom of the drilled well portion, said upper portion is positioned above the fractured area;   an expander tool controlled from the surface and capable of achieving radial expansion of the upper portion of the tube beyond its yield strength, so as to apply it intimately against the well wall which surrounds it.       

     According to other possible advantageous and non-limiting features of this device:
         the expander tool and the tube are provided with mating connecting members allowing them to be coupled to each other in order to form an assembly within which both of these elements are easily separable from each other;   their mutual coupling is accomplished by screwing;   the expander tool is equipped at its lower end, with a threaded member capable of being screwed into a tapped ring positioned inside the tube, at the base of said ductile and radially expansible upper portion of the latter;   said seal gasket is a flexible and elastically deformable ring-shaped member;   the lower end portion of the tube includes two telescopic tubular elements between which this gasket is positioned, the relative displacement of both of these tubular elements causing the radial expansion thereof, when they are brought closer to each other.   said ductile and radially expansible upper portion of the tube is surrounded by at least one ring-shaped seal gasket.       

    
    
     
       Other features and advantages of the invention will become apparent upon reading the following description of a preferred embodiment of the invention. This description is made with reference to the appended drawings wherein: 
         FIG. 1  is an axial sectional view of a possible embodiment of a device according to the invention; for reasons of convenience of illustration, the left portion of the figure illustrates the upper portion (on the surface side) of the device, while its right portion illustrates the lower portion thereof (on the bottom side), both of these coaxial portions being connected at the points referenced as A 1 /A 2  (connected by a mixed dot and dash line which symbolizes their continuity); 
         FIG. 2  is an illustration, also in an axial section view of a vertical, partly drilled, cylindrical well with fractured area(s), the casing of which is desired according to the invention. 
         FIG. 1A  is a similar partial view which corresponds to the right portion of the device of  FIG. 1 , illustrating the way how the seal gasket which fits out the base of the tube is expanded. 
         FIGS. 3-7  are schematic views showing the main steps for casing the well of  FIG. 2  by means of the device of  FIG. 1 , thereby illustrating how the method of the invention is applied. 
     
    
    
     The device of  FIG. 1  comprises a substantially cylindrical tube  1  of great length. 
     Usually, it consists of an assembly of tube sections attached end-to-end, coaxially, for example by screwing the sections into each other. 
     Its length and its diameter are adapted to those of the well to be cased. 
     The material which makes it up and its wall thickness are selected so as to allow its radial expansion in the domain of plastic deformation (therefore beyond the elastic domain) under the effect of an internal pressure, notably generated by an inflatable hydraulic bladder, according to the teachings of FR-A-2 920 837 for example. 
     This is for example a relatively ductile stainless steel tube, the wall thickness of which is comprised between about 3 and 7 mm. 
     In  FIG. 1 , the central body of the tube  1  is designated by reference  10 , its upper end portion by reference  11  and its lower end portion by reference  13 . 
     Reference  12  designates an internal flange located at the base of the upper portion  11 . This flange  12 , preferably added onto the tube, is tapped interiorly. 
     The diameter of the upper  11  and lower  13  end portions is slightly larger than that of the central body. Further, preferably, the wall of the upper end portion  11  is thinner than that of the central body which promotes its capability of expanding radially. 
     The base of the tube  1  is provided with a telescopic tubular sleeve  7  force-fitted into the lower end portion  13  and axially mobile in the latter. Between both of these elements, on the external side, is interposed an annular gasket  2  in flexible, incompressible and elastic material of the rubber kind. It is adapted for expanding radially by a corner effect, between the facing beveled edges  70  of the element  7  and  14  of the portion  13 , when both of these elements are brought closer to each other. It then forms an annular bead. 
     This phenomenon is easily understood by simply observing  FIG. 1A  in which the arrows i symbolize the axial sliding of the sleeve  7  inside the tube  1 , the annular bead bearing reference  2 ′. 
     The portion  11  is surrounded by a series of flexible and elastically deformable (advantageously equidistant) rings  6  which, as this will be seen later on, also form seal gaskets. 
     In  FIG. 1 , reference  3  designates an initially unit assembly comprising an expander tool  5 , a connecting member  4  and the tube  1 . 
     The expander tool  5  is an inflatable hydraulic bladder, radially expansible of a known type (see for example the aforementioned FR-A-2 901 837) which is connected to the well head by an axial control rod  30   a  of great length. 
     The connecting member  4  is coaxially connected to the tool  5  by a rod section  30   b  of small length. It has a threaded wall  40 , capable of being screwed into the aforementioned flange  12 . 
     By maneuvering the rod  30   a  in a suitable way, it is possible to displace the assembly  3  axially in a well, rotate the tool  5  and the connector  4  which is firmly attached to it, around their common axis; this rod  30   a , preferably a tubular rod, is provided with suitable conduits required for hydraulic inflating and deflating the bladder  5 . 
     In  FIG. 2  is illustrated, in an axial sectional view, a vertical well with a cylindrical wall P and a flat bottom F, dug in a ground T containing a deposit of hydrocarbons, the exploitation of which is contemplated. 
     The borehole passes through at least one permeable area, or fracture area ZF, in which the wall has fractures, cracks, or similar channels, which are the causes of mud circulation losses, for the reasons exposed in the preamble above. 
     In order to be able to properly continue the drilling, a casing suitable for isolating the ZF area is set into place according to the invention, as this will now be explained. 
     As a simple indication, it will be assumed that the diameter of the well is about 300 mm and that the casing length required for achieving isolation of the ZF area(s) is of the order of 400 m. 
     A stainless steel tube is for example used, the main body  10  of which has a length of 400 m, an outer diameter of 244 mm and a well thickness of 6 mm. 
     The upper portion  11  has a length of 4 m, an outer diameter of 250 mm and a well thickness of 4 mm. 
     The inflatable bladder  5  has a length of 1 m and a diameter of 200 mm in the deflated condition. 
     The method is applied as explained hereafter. 
     The connecting member  4  having been connected by screwing, to the flange  12 , and the bladder  5  having been deflated, the assembly  3  is axially moved down inside the well, via the rod  30   a  (arrow D 1 ,  FIG. 3 ), until the lower portion of the tube will bear against the flat bottom. 
     The weight of the tube is relatively significant, of the order of 140,000 Newtons. 
     This is why, when it will bear against the bottom F (arrows D 2 ,  FIG. 4 ) a radial expansion of the gasket  2  (arrows Q) is observed, as explained above with reference to  FIG. 1A . 
     The initial diameter of this gasket and its expansion degree for the relevant load are selected in such a way that the gasket will be strongly applied against the surrounding wall P, so that the peripheral interval between the base of the tube  1  and the well is thereby sealed off. 
     The seal at the base of the tube is thereby obtained in a particularly simple and natural way, without requiring any hydraulic or other connection with the surface of the well. 
     The connector  4  is then unscrewed in order to detach it from the ring  12 , and therefore from the tube (arrows R and M 1 ,  FIG. 5 ). 
     Advantageously, the threading of the connector has a left hand thread, so that unscrewing is achieved by driving the rod  30   a  in the usual direction applied by the standardized control means installed in the well head. 
     Upon completion of unscrewing, the axial positioning of the expander tool  5  is perfectly defined; the tool is located exactly at the base of the upper portion  11  to be expanded. 
     Continuation of the operation is then under control. 
     The expansion may then begin by hydraulically inflating the constitutive bladder of the tool  5 . 
     The liquid which causes this inflation is introduced into the tool  5  via the rod  30   a , at sufficient pressure so that the radial expansion of its membrane pushes back the surrounding wall of the tube outwards, beyond its elastic deformation limit, by applying it intimately against the wall P (arrows G,  FIG. 6 ). 
     The bladder  5  (arrows H) is then deflated and the tool is moved up by the value of one step (arrow M 2 ). 
     This process, which alternates phases of inflation, deflation, and translational bottom-to-top displacement, is repeated in order to gradually expand the portion  11  over the whole of its length, after which the tool is removed (arrow J,  FIG. 7 ). 
     The interval between the tube  1  and the wall P is therefore sealed off in this way over the whole length of the widened upper portion of the tube  1 . The seal at this level is ensured or reinforced, by the presence of ring-shaped gaskets  6  which are compressed between the outer face of the tube and the wall of the well, which allows compensation for the inevitable surface irregularities of this wall. 
     Finally, a casing is obtained which completely isolates the ZF area from the internal space of the tube  1 . 
     It is then possible to continue drilling, by boring the bottom F, with application of the muds inside the tubing, which thus solves the problem of circulation losses. 
     What is important is that it deforms in order to automatically ensure a seal between the wall of the well and the base of the tube, under the action of the weight of the tube, when the latter abuts on the bottom of the well. 
     Moreover, various expansion methods, known per se, other than the one described here, may be applied for causing expansion of the upper portion  11 , for example in delimited areas (therefore partly) spaced apart from each other, continuously and/or with a mechanical expander tool with pressure rollers. 
     The different materials used, in particular for making up the tube  1  and the seal gaskets  2  and  6 , are naturally selected so as to be able to withstand on the long-term the various physico-chemical constraints (heat, pressure, corrosion . . . ) to which they will be exposed during their placement and during future operation of the well.