Patent Publication Number: US-2015083422-A1

Title: Wellbore encasement

Description:
FIELD OF THE INVENTION 
     The present invention relates to the encasement of wellbores, and in particular to methods of depositing cement into an annulus between a newly-drilled borehole and reinforcing casing within the borehole. 
     BACKGROUND TO THE INVENTION 
     Conventionally, newly-drilled boreholes are reinforced by the insertion therein of a casing, which may comprise steel or concrete pipes, to provide structural integrity to the wellbore. Such casings are typically slightly smaller in diameter than the drill string and are secured in place by pumping cement into the annulus formed between the outer surface of the casing and the borehole. 
     As illustrated by reference to  FIG. 1 , cementing is usually performed by circulating a cement slurry through the inside of the casing and out into the annulus through a casing shoe at the bottom of a casing string. In order to deposit a correct quantity of the cement slurry on the outside of the casing, a plug is pumped with a displacement fluid behind the cement slurry column. When the plug reaches the casing shoe it blocks the flow path of the cement slurry and prevents further flow of fluid through the shoe. This stage can be seen at surface as a pressure spike at the cement pump. To prevent the cement from flowing back into the inside of the casing, a float collar above the casing shoe acts as a check valve and prevents fluid from flowing up through the shoe from the annulus. 
     Cementing is supposed to form an impenetrable seal to keep hot, gassy oil from surging up the well. However, as is well documented, a single flaw in that seal, perhaps a crack the size of a human hair, can be enough to cause a catastrophic leak. One known failure mechanism, suspected of being the cause of the Deepwater Horizon catastrophe, is gas bubbles getting into the cement and forming channels for pressurised gas or oil to surge uncontrollably up the well. The gas bubbles could originate from the initial cement slurry mix, which may include nitrogen, or could leak in through the borehole wall while the cement slurry is setting. 
     As illustrated by reference to  FIG. 2 , another known cause for inadequate cementing is because of the non-uniformity of the borehole walls. A predetermined volume of cement may be calculated for pumping into the wellbore to fill the annulus to a specific height. This can be problematic if the borehole wall includes voids or fissures, increasing the volume of the annulus over that expected such that the predetermined volume of cement would not reach the desired specific height. This has been overcome by top-up cement pumping operations to fill the space between the actual height of the cement in the annulus and the desired height. 
     Because of the extreme conditions that can be found in oil wellbores, it is important to monitor those conditions and their effects on the wellbore cement. Factors requiring monitoring can include cement integrity, cement placement, cement strength, and cement impermeability. 
     Important variables include stress/strain (providing information about geomechanical forces that may affect cement curing and bonding), pressure and temperature (being strong indicators of gas or liquid movement). Further parameters for monitoring include pH and gas/liquid phase. Accordingly, downhole sensors can be placed to monitor these variable parameters. Existing sensor technologies include distributed sensors, which use a fibre optic cable to take measurements along the length of the cable, which acts as both sensor and communication medium to relay the sensed data to the surface. 
     Another type of sensor is passive wireless sensor tags, which can be placed in hostile environments and which relay sensed data wirelessly to a transceiver at the surface and which require no power source. 
     A problem encountered in depositing cement in the annular gap between the casing and the wellbore surface is that residual drilling mud and mud filtrate cake can be stuck to the casing and formation which reduces cement bonding effectiveness. Accordingly, pre-cementing flushes can used to wash out the remaining drilling mud and remove the mud filtrate cake. 
     Another problem encountered in wellbore cementing is centralising the wellbore casing. One purpose of a casing centraliser is to act to support and centre the casing in the wellbore, so as to allow cement to be pumped up the annulus with least resistance around the casing and produce a robust cement seal, ensuring zonal isolation. If the centraliser is not strong enough to centre the pipe, or if it breaks, the consequences can be very expensive. If it breaks in a deviated well, centralisation is usually completely lost, rendering effective cementation impossible. Furthermore, the centraliser may jam the pipe down hole. 
     Whereas the above description of the prior art has focused on oil well technology, many of the principles apply to other types of wellbore, such as water wells. These may be of much larger diameter but shallower than oil well boreholes, but which must also be structurally sound. Rather than being at risk of high pressure fluids escaping through a casing, the walls of water well boreholes may be liable to inward collapse. 
     As such, there is a need for an improved method of encasing wellbores, and an associated need for a wellbore encasement device. There is furthermore a need for the provision of improved wellbore monitoring systems. 
     It is known to construct complex 3D structures through 3D printing, also known as additive manufacturing (AM), which comprises building up layers of material one after the other via a nozzle head that is controlled to ‘print’, i.e. deposit, the material. It is known to use such AM techniques to construct structures out of cement (concrete), as discussed for example in ‘Development of a Viable Concrete Printing Process’ by Sungwoo Lim of the Department of Civil &amp; Building Engineering, Loughborough University, UK. AM processes have advantages over conventional construction and manufacturing processes in that they do not require moulds, they offer design freedom, and they have the potential to include additional functionality into structures. 
     AM is in its infancy, especially when applied to the construction of concrete structures, and it has not been applied in the context of wellbores. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a method of lining a wellbore comprising the steps of:
         inserting a directional nozzle into the wellbore; and   controlling the direction of the nozzle and controlling flow through the nozzle to deposit at least one layer of lining material onto the interior surface of the wellbore.       

     The present invention provides a very effective method of lining a wellbore that applies 3D print technology to down-hole applications. Because the nozzle can be controlled both in terms of direction and flow (i.e. on/off, or to varying degrees between those extremes), the lining material can be deposited in a highly controlled and direct manner. This overcomes disadvantages with the known cement slurry pumping operations, and enables the exploitation of advantageous features of 3D printing technology. 
     The direction of the nozzle may be controlled so as to rotate about the longitudinal axis of the wellbore, for lining an entire circumference of the interior surface of the wellbore. The nozzle direction may further be controlled to be displaced along the longitudinal axis of the wellbore, for lining a length (height) of the wellbore. In some embodiments, the nozzle may be rotated relative to the longitudinal axis of the wellbore. Accordingly, it is possible to control the deposition of the lining material with precision to a specific target area. 
     The method preferably comprises depositing multiple layers of lining material onto the interior surface of the wellbore. This enables the exploitation of the benefits of a layered structure, providing an improved structural integrity to the lining. 
     In some embodiments, the nozzle is controllable to deposit different materials. Thus, different areas of the wellbore may be lined with different materials, or portions may be lined with multiple layers of different materials, so exploiting the advantages that can be obtained through the different properties of those materials, and the synergistic effects of combining them. 
     Multiple nozzles may be inserted into the wellbore, each controllable to deposit a different respective material. Typically, the multiple nozzles are mounted on a common printhead. 
     Different materials considered for application to the wellbore in methods of the invention include reinforcing materials such as cement, concrete, resins, plastics, metals, ceramics, and the like, and sealing materials such as rubber, plastics, bitumen, neoprene, and the like. 
     Although in some embodiments the lining material is deposited directly on to the interior surface of the wellbore and that deposited material forms the entire lining of the wellbore, in other embodiments a casing pipe inserted into the wellbore forms the final interior surface of the wellbore and the method is used to deposit the material into an annular gap formed between the interior surface of the wellbore and an exterior surface of the casing pipe. For the latter embodiments, the method includes a step of inserting a casing pipe into the wellbore, typically before the directional nozzle is inserted into the wellbore. The directional nozzle may be inserted through the interior of the casing pipe or, alternatively, on the exterior of the casing pipe. 
     When inserted through the interior of the casing pipe, the directional nozzle exits at a bottom end of the casing pipe and the nozzle is controlled to point towards the area of the wellbore surface to be lined. 
     The lining may be built up in radial layers, with the nozzle directed generally radially outwards. Alternatively, the lining may be built up in axial layers, with the nozzle directed generally upwards or downwards, depending on whether those axial layers are built up from above or from below. 
     To assist in depositing axial layers, the method may include a step of inserting a bung between the casing pipe and the interior surface of the wellbore, wherein the step of controlling the direction of the nozzle and controlling flow through the nozzle comprises depositing the at least one layer of lining material onto the bung and thereby onto interior surface of the wellbore. 
     In some embodiments, the topography of the borehole is determined, and the control of the direction of the nozzle and the control of the flow through the nozzle being dependent on the topography. This enables a bespoke deposition of the lining material to account for irregularities in the wellbore surface. 
     The method may include a step of accelerating a cure of the deposited material prior to deposition of a subsequent layer, so as to speed up the lining process whilst ensuring material integrity. 
     According to a second aspect of the present invention there is provided a device for depositing at least one layer of material onto an interior surface of a wellbore, comprising:
         a directional nozzle;   a source of material in connection with the nozzle;   means to control the direction of the nozzle; and   means to control the passage of the material through the nozzle, whereby to deposit at least one layer of lining material onto the interior surface of the wellbore.       

     The nozzle may be mounted for some or all of: rotation about a vertical axis, displacement along a vertical axis, and rotation relative to a vertical axis. 
     In some embodiments, the nozzle is selectively in connection with multiple sources of different materials, whereas in other embodiments the device comprises multiple nozzles, each in connection with a different respective source of material. In either instance, the device enables the deposition of different materials to take advantage of their different properties, particularly when combined. 
     The or each nozzle may be mounted on a common printhead, facilitating positioning of the nozzle(s) at the deposition site. 
     As described above in the context of the first aspect of the invention, in some embodiments a wellbore will be lined with a casing pipe, and the lining material deposited to fill the annular gap between the outside of the casing pipe and the inside of the wellbore surface. 
     For such embodiments, the device may be configured for insertion through a wellbore casing pipe. Typically, the or each nozzle is mounted on an arm that is able to bend so as to position the nozzle directed generally upwards into the annulus between the wellbore casing pipe and the interior surface of the wellbore, for deposition of axial layers of lining material from beneath. To facilitate this, the at least one nozzle may be connected to the associated source of material via a flexible conduit. 
     Alternatively, the device may be configured for insertion over a wellbore casing pipe, between the exterior of the wellbore casing pipe and the interior surface of the wellbore. Typically, the or each nozzle is mounted on a ring having a diameter substantially matching that of the wellbore casing pipe so as to position the nozzle directed generally downwards, for deposition of axial layers of lining material from above. Alternatively, the nozzle may be directed generally outwards, for the deposition of radial layers. 
     The device may include multiple printheads positioned at regular circumferential intervals, so providing faster deposition of materials and requiring less rotation of the device about the longitudinal axis of the wellbore for lining an entire circumference of the wellbore. 
     A controller is preferably included in the device to control the direction of the nozzle and the flow of material through the nozzle. The controller is preferably programmable, typically so as to deposit the material along an optimum path. In preferred embodiments, the device includes means for determining the topography of the borehole, and the optimum path is determined at least partly on the basis of the determined topography. The topography of the borehole may be determined electronically, such as via an emitter and associated detector, such as laser, radar, or the like, or may be determined mechanically, such as via a contour wheel. 
     In some embodiments, the device includes a UV source or other means for accelerating the curing of the deposited material. 
     Through suitable control of the operation of the nozzles, the lining may be built up in multiple layers and of different materials, and may include strategic voids in the final structure. Such voids can be used to place sensors or may run along a length of the wellbore for receiving cables—either for structural reinforcement or for monitoring purposes (e.g. fibre optic cables). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
         FIG. 1  shows a prior art wellbore cementing process; 
         FIG. 2  shows an irregular surfaced borehole and resultant incomplete cementing; 
         FIG. 3  shows a wellbore lined with multiple layers using a process of the invention; 
         FIG. 4  shows a detail view of a portion of the layered structure of  FIG. 3 ; 
         FIG. 5  shows a device according to one embodiment of the invention for depositing material into the wellbore; 
         FIG. 6  shows a dual media extrusion achievable using the device of  FIG. 5 ; 
         FIG. 7  shows a device according to another embodiment of the invention for depositing material into the wellbore; 
         FIG. 8  shows a device in situ in a wellbore and depositing a series of axial layers of material; 
         FIG. 9  shows a device according to another embodiment of the invention for depositing material into the wellbore; 
         FIG. 10  shows a device according to yet another embodiment of the invention for depositing material into the wellbore; 
         FIG. 11  shows a device according to even yet another embodiment of the invention for depositing material into the wellbore; 
         FIG. 12  shows an alternative application of a device according to the invention, for repairing casing walls; 
         FIG. 13  shows a device according to a further alternative embodiment of the invention for depositing material into the wellbore; and 
         FIG. 14  shows deposition of material using the device of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     In simple terms, the invention relates to the concept of depositing lining material to wellbores using 3D printing technology. A media dispensing apparatus including at least one nozzle is inserted down a borehole for depositing multiple layers of lining material to the interior surface of the borehole in a controlled manner. One embodiment is shown in  FIGS. 5 and 8 , in which the nozzle is mounted via a universal joint to a distal end of a hollow support rod. The support rod contains a primary flexible conduit for fluidly connecting the nozzle with a source of a first lining material. The support rod further contains a secondary flexible conduit for fluidly connecting the nozzle with a source of a second lining material, different to the first. As shown in  FIG. 6 , the nozzle and the conduits may be arranged to dispense the first and second materials simultaneously, in a form of extrusion. In other embodiments, only a single source of material is connected to the nozzle. 
     In certain embodiments, multiple different material sources may be connected to a single nozzle. The different sources may be selectively dispensed through the nozzle, for example through a selective valve block. In other embodiments, there may be multiple nozzles each connected to one or more sources of material. 
     The direction of the or each nozzle can be controlled so as to direct the flow of material through the nozzle at a desired target area. The flow of material through the or each nozzle can also be controlled, either by means of a binary on/off valve or by a variable valve. 
     The control of the nozzle operation is performed by a programmable controller, which may be within the printhead or remote therefrom. As is known in the art of 3D printing, material is deposited in layers built up one upon another to form a 3D structure. To ensure that the integrity of the structure is not compromised, it is important for the previous layer on which a subsequent layer is being deposited to have ‘gone off’ or cured, thus having sufficient strength to support the new layer without deformation. The curing time will be dependent on a number of factors, including the material being deposited, the thickness of each layer, and environmental conditions. The process may be accelerated by suitable means, such as the illumination of the layer by UV light. 
     In one embodiment, as shown in  FIG. 8 , the support rod is inserted into the wellbore to position the nozzle facing outwards towards the interior surface of the wellbore. The support rod may be held centrally in the wellbore by suitable centralizer means, as are well known in the art. 
     A first layer of lining material (e.g. cement) is deposited via the nozzle by rotating the support rod 360° about a longitudinal axis of the wellbore with the nozzle valve open. The longitudinal axis would typically be approximately vertical, but could be off vertical or even be horizontal. The deposited layer of material forms a ring around the circumference of the wellbore. The support rod is then raised to position the nozzle above the previous layer for depositing a subsequent layer above the previous one. The rings of lining material are thus built up axially from the bottom up to define a substantially contiguous lining. By being constructed of a series of essentially discrete layers, the rings of lining material act akin to the packing rings of a stuffing box, providing enhanced sealing properties and therefore improved resistance to the sort of catastrophic failure associated with a blow-out from gases escaping through imperfections in the lining structure. 
     In preferred embodiments, the axial rings may be built up in sections of different materials, as illustrated in  FIGS. 3 and 4 , which shows a section of the wellbore lined with axial strata of concrete, rubber or the like, foam and resins. As will be understood, the materials and their arrangement may be selected to make best use of their material properties, such as structural or sealing properties. 
     In addition, each axial ring could itself be formed of multiple layers of lining material, built up radially from the outside in. Again, those different layers could be formed of different materials. 
     As well as or instead of using fundamentally different materials, the layers can be built up of essentially the same materials but with different properties—such as cements of different densities. 
     A detail of the ‘printhead’ of a modification of the embodiment of  FIGS. 5 and 8  is shown in  FIG. 7 . This modified embodiment includes adjustable hinged guides at the nozzle outlet to assist in directing the flow of material from the nozzle to ensure that the material is deposited at the intended location. 
     The programmable controller control operation of the nozzle to deposit the lining material(s) according to the topography of the wellbore. The topography may be determined by different means, which may be incorporated into the printhead or be independent thereof. Examples of suitable topography-determining means include: a camera or other scanner, laser, radar, or the like, or a mechanical contour wheel. 
     Multiple printheads may be mounted to a single support arm, typically at regular circumferential intervals. For example, two printheads may be mounted 180° apart for dispensing material to opposite sides of the wellbore simultaneously, thus reducing by half the time to cover the entire circumference and also only requiring a 180° rotation of the support arm. The printheads need not be in the same plane as one another. 
     One particular advantage of 3D printing is the ability to form voids at specified locations. As shown in  FIGS. 3 and 4 , vertical channels (i.e. parallel to the longitudinal axis of the wellbore) can be formed in the lining structure for receiving wellbore monitoring, power, and communications equipment. One application would be to receive fibre optic cables for a distributed sensing system as described in the introduction. Another option would be to form pockets, either in communication with the channels or independent thereof, for receiving sensors such as the passive wireless sensors described in the introduction. The printhead could insert these sensors from a cartridge of them. It could insert them at predetermined distances, pressures, etc. It could locate more into regions of the wellbore where it is more critical to collect data. 
     In addition or instead of receiving the monitoring, power, and communications equipment, the channels could receive reinforcing structures, such as structural fibres, steel cables, extruded fibres, and the like. 
     The cables or fibres can be inserted into the channels during the deposition process, for example by being unloaded from spools, or could be inserted after the entire channel has been formed. For some structures, the cable could be extruded at the printhead during the deposition of the lining material(s). A heater may therefore be provided on the printhead for extrusion operations. 
     For other applications, the channels may be filled with a stent-like matrix, formed for example of sintered metal, which may be deposited at the same time as the rest of the lining material. The matrix can then be filled with a suitable material, such as a resin, to fill voids in the matrix and provide a structurally rigid reinforcement through the lining structure. 
     In some embodiments, and especially where the apparatus is used to fill the annular gap between a wellbore casing and the wellbore interior surface, rather than building the ring-like layers up from the bottom, the layers can be built up from the top down. To achieve this, the delivery device with the printhead is inserted down the interior of the casing. Exemplary embodiments are shown in  FIGS. 9 to 11 . 
     In the embodiment of  FIG. 9 , two printheads are inserted through the casing, each with a flexible conduit connecting a nozzle to a source of lining material at the surface. Each printhead is delivered to the distal end of the casing where it exits and, by virtue of the flexibility of the conduit and through a suitable drive system—which may incorporate wheel driven tracks—is able to be steered back on itself to direct the nozzle to point generally upwards. A flexible umbrella-like membrane structure is supported on the printhead surrounding the nozzle and is adapted to conform to the topography of the borehole to account for variations therein and to support the layer of material being deposited. 
     Each layer is deposited from below onto the bottom of the layer above. To provide a first layer onto which to deposit the subsequent layers, the printhead includes a mechanism for inserting a bung in the annular gap. One way to provide the bung is through use of an expanding foam-like material, which may be deposited in the gap by a two-pack resin module in conjunction with an aerosol. The resins and aerosol may be incorporated into the printhead and be operated under the control of the programmable controller. On actuation, the resins will be dispensed and mixed under the propulsion of the aerosol, thereby expanding from an outlet of the module. The foamy mixture will quickly harden sufficiently to support deposition of layers of the lining material onto its bottom surface. 
     Due to a partial vacuum and by virtue of inherent surface tension of the material being deposited, each layer will remain where deposited and will not for example drop due to gravity. 
     When depositing the lining material layers in water from below, the water may act to help keep the deposited material in place, if that material is buoyant in the water. In addition, the lining material(s) may be selected so that they are activated by contact with water, to accelerate the curing process or to improve adhesion, to expand, or to heat up, for example. 
     An alternative embodiment is shown in  FIG. 10 , in which the printhead has sprung tracks that conform to the gap between the casing and the interior surface of the wellbore. 
     Other alternative embodiments are shown in  FIG. 11 . One of the printheads shown here on the left may be guided by multi-positional wheels and by the reaction forces from the expulsion of a water jet from an end opposite to the nozzle for depositing the lining material. Instead of a water jet, the embodiment shown on the right uses an impeller or propeller to urge the printhead upwards. 
     In an alternative implementation, illustrated in  FIGS. 13 and 14 , rather than being sent down the inside of the wellbore casing, the printhead is sent down the outside of the casing. In this embodiment, the printhead comprises a ring structure, having a central aperture sized to be received around the casing. Conduits are connected to circumferentially spaced nozzle outlet vents through the ring structure for the delivery of lining material to deposit layers of the material into the gap between the exterior of the casing and the interior surface of the wellbore, from the bottom up. The printhead includes a drive unit incorporating wheels bearing against the exterior of the casing to drive the printhead vertically and rotatably, for example in a helical rising movement. 
     In any of the embodiments, the printhead can be adapted to act as a high pressure water/air/other fluid/gas jet to remove residual drilling mud to ensure a clean surface for the application of the lining layer(s). 
     An advantage of the provision of a nozzle whose direction of deposition of material may be controlled, and especially when mounted on a printhead that is directed into the annular gap between the casing and the interior surface of the wellbore is that it will allow the centralisation of the casing by several means. The very fact that the printhead is circulating around the outside of the casing will force the casing away from the surface of the wellbore, and when so spaced, the lining materials are deposited so as to keep the casing spaced away from the wellbore surface. Additionally, just by directing the printhead (or at least the nozzle(s) thereon) in a particular area, the reaction force of the material being ejected from the nozzle(s) will force the casing away from the wellbore surface. 
     One further application of the technology is in the repair of wellbore casings. As shown in  FIG. 12 , a printhead may be positioned to direct a nozzle towards a damaged or defective section of the casing. Material can be injected from the nozzle through the defect thereby filling it much like a rivet. 
     It will be understood that aspects of the various embodiments described above may be combined with aspects of other embodiments to provide further alternative implementations. 
     Whereas the above detailed description has been made in the context of oil wellbores, the technology can be applied to other application. One example is a large-diameter groundwater well, traditionally lined with bricks or with pre-cast sections of concrete pipe, which may be lined instead using the cement printing techniques, particularly of the type shown in  FIG. 8 . Another example is for the sealing of sewers. For such simple applications, just a single lining material may be used, although enhanced benefits may be obtained through combining multiple materials. 
     For some applications, at least one of the lining materials may comprise a reactive material that expands when certain conditions are met, such as coming into contact with water or a particular temperature or pressure. This may be an outside layer of the lining, and be reactive to the environmental conditions to break down over a predetermined period. For other applications, at least one of the lining materials may be hydrophilic, allowing water to flow through it at a given rate. This may be used in conjunction with a reactive substrate layer, wherein the reactive substrate reacts with the water.