Patent Publication Number: US-2011056690-A1

Title: Well Repair Using Swellable Material in a Remedial Matrix

Description:
BACKGROUND OF THE INVENTION 
     In many well-related applications, unwanted migration of fluids may be problematic. In some wells, fluids such as gas, oil, and/or water migrate along the annulus formed outside the well casing and through the formation proximate the wellbore. The migrating fluids can detrimentally affect production operations and other well-related operations. 
     For example, when gas migrates along a given well, the well may have a problem exhibited as a surface casing vent flow or gas migration. Remediation techniques are sometimes employed in an attempt to block the unwanted gas migration. Available techniques employ a variety of equipment and fluids that can be pumped downhole to remediate unwanted fluid flows. For example, cement squeezes have been used to limit unwanted fluid migration. However, available techniques often are limited in their ability to substantially block the fluid migration in many types of well applications and well environments. 
     BRIEF SUMMARY OF THE INVENTION 
     In general, the present invention provides a system and methodology for performing remedial treatments to block unwanted fluid migration in a well. A slurry is formed with a swellable material, and the slurry comprising the swellable material is pumped downhole. The slurry is directed to a remediation site and deposited in a manner that establishes a desired remediation treatment able to block unwanted migration of downhole fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a schematic view of a well system used to deploy a slurry containing swellable material at a remediation site along a wellbore, according to an embodiment of the present invention; 
         FIG. 2  is a schematic view similar to that of  FIG. 1  but showing a reverse flow to remove unwanted material from the wellbore, according to an embodiment of the present invention; 
         FIG. 3  is a schematic illustration of one sequence of treatment substances directed downhole to the remediation site, according to an embodiment of the present invention; 
         FIG. 4  is a schematic illustration of another sequence of treatment substances directed downhole to the remediation site, according to an alternate embodiment of the present invention; 
         FIG. 5  is a flowchart illustrating one example of a procedure for carrying out the remediation treatment, according to an embodiment of the present invention; and 
         FIG. 6  is a flowchart illustrating another, more detailed, example of a procedure for carrying out the remediation treatment, according to an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to a system and methodology for carrying out a remediation treatment in a subterranean environment. The remediation treatment involves deploying slurry containing a swellable material to a specific remediation site or sites disposed along a wellbore. In one example, the slurry comprises a cement matrix having a swellable material and designed for remedial cementing. The swellable materials are deployed in the cement system to remediate a wellsite by enhancing the ability of the cement to shut off unwanted fluid migration, such as annular fluid migration. In some applications, the cement matrix, including the swellable materials, is used to shut off the unwanted annular flow of gas, such as shallow gas. 
     In another embodiment, the present system and methodology comprise squeezing an activating agent, such as an oil-based spacer fluid, ahead of the slurry containing the swellable material. In this example, the swellable material is selected to swell upon contact with a hydrocarbon activating agent, such as oil. In some environments, a preparatory fluid, such as an acid, may also be squeezed into the formation initially to enhance the penetration of the remedial cement system. One preparatory fluid comprises hydrochloric acid and is sometimes referred to as a mud acid. 
     By injecting the activating fluid, e.g. an oil-based fluid, into the matrix ahead of the cement slurry, the activating agent is able to enhance the swelling of the swellable materials contained in the self-healing cement upon placement of the cement slurry at a well remediation site. Placement of the activating agent enhances the self-healing/swelling capabilities of the cement. Consequently, the cement has an improved functionality in the presence of migrating fluids, such as gas. In a variety of applications, for example, the swellable materials help block the unwanted migration of pure methane, nearly pure methane, and other gases that do not necessarily induce swelling of the swellable material. The activating agent injected prior to the cement may comprise a variety of materials, including diesel fuel, crude oil, mineral oil, condensate, and/or other oils. The activating agent also may comprise other materials, such as liquid natural gas, ethane, propane, butane, other gases, and other materials. 
     Referring generally to the schematic example of  FIG. 1 , one embodiment of a well system  20  is illustrated as deployed in a wellbore  22 . The well system  20  may comprise a variety of components for use in many types of wells and well environments. The well system  20  also can be used in cooperation with many types of completion equipment, casings, liners, and other components used in various well applications. To facilitate explanation, however, well system  20  is illustrated as comprising a treatment tubing  24  deployed downhole within a surrounding tubing, such as a well casing  26 . A plurality of perforations  28  may extend through well casing  26 , through a surrounding annulus  30 , and into a surrounding formation  32 . 
     Treatment fluids are delivered down through treatment tubing  24 , as represented by arrows  34 . The treatment fluids comprise a swellable material  36  which is delivered downhole to a desired remediation site  38  for use in a remediation process to limit the unwanted flow of well fluids along specific areas. As described above, for example, the swellable material  36  can be used in a cement slurry for remedial cementing along surrounding annulus  30  to prevent the undesired migration of gas and/or other fluids along well casing  26 . Unused portions of the treatment fluids can be reverse circulated out of wellbore  22  by a reverse fluid flow, as represented by arrows  40  in  FIG. 2 . In this particular example, the reverse fluid flow  40  is initially delivered into an annulus  42  between treatment tubing  24  and the surrounding tubing  26 , e.g. well casing. The reverse fluid flow  40  is routed down along annulus  42 , proximate remediation site  38 , and up through treatment tubing  24  to remove excess treatment fluids. 
     The treatment fluids  34  may be delivered in stages, as illustrated in the example of  FIG. 3 . By way of example, the fluid stages may be delivered immediately sequentially or with gaps between the sequential fluid stages. In the embodiment illustrated in  FIG. 3 , an activating agent  44  is initially delivered downhole to remediation site  38 . As described above, the activating agent may be delivered through an appropriate tubing, such as treatment tubing  24 . In some applications, treatment tubing  24  may comprise coiled tubing conveyed downhole within a surrounding casing, completion, or other downhole component. 
     Following activating agent  44 , a slurry  46  containing swellable material  36  is delivered downhole to remediation site  38 . In the embodiment illustrated, slurry  46  comprises a cement slurry for use in remedial cementing. The slurry  46  contains swellable material  36  which may be in the form of swellable particles  48  dispersed throughout the slurry. The activating agent  44  is selected to cause swelling of the swellable material  36 , e.g. swellable particles  48 , upon deposit of the slurry  46  at remediation site  38 . 
     The particular type of activating agent  44  chosen for a given remediation procedure depends on the swellable material  36  used in slurry  46 . By way of example, the swellable material, e.g. swellable particles  48 , can be formed from a material that swells in the presence of a hydrocarbon based fluid, such as oil. Examples of oils that can serve as activating agent  44  include diesel fuel, crude oil, mineral oil, or condensate. The activating agent also may comprise other hydrocarbon fluids, including liquid natural gas. Other types of activating gases can also be used in the activating agent  44 . In still other applications, the swellable material  36  can be selected to swell in the presence of water and/or in the presence of a specific chemical or chemicals. 
     The swellable material  36  may be formed from one or more materials that swell in the presence of a suitable activating agent. A few specific examples of swellable materials comprise swelling elastomers and nitrile mixed with salt or hydrogel. Additionally, a material available from Schlumberger Technology Corporation of Sugar Land, Texas, USA and sold under the trade name FUTUR also comprises a swellable material that can be pumped downhole as slurry  46 . In many of these applications, the swellable material  36  is used as part of a cement matrix to facilitate remedial cementing at remediation site  38 . 
     In the embodiment illustrated in  FIG. 4 , a preparatory fluid  50  is initially delivered downhole to remediation site  38 . By way of example, preparatory fluid  50  may be squeezed into the formation at remediation site  38  to enhance penetration of the remedial slurry  46  containing swellable material  36 . As described above, preparatory fluid  50  may comprise a suitable acid, such as a mud acid, delivered downhole through tubing  24  or along another appropriate delivery route. 
     After delivering preparatory fluid  50  to remediation site  38 , activating agent  44  also may be delivered downhole to the remediation site. In some applications, activating agent  44  may be delivered immediately following preparatory fluid  50 . As described above, the activating agent also may be delivered through tubing  24  or via another suitable route. 
     In this embodiment, the slurry  46  containing swellable material  36  is subsequently delivered downhole to remediation site  38 . Again, the slurry comprises swellable material  36  which may be in the form of swellable particles  48  or in other forms dispersed throughout the slurry. The activating agent  44  serves to cause swelling of the swellable material  36  upon deposit of the slurry  46  at remediation site  38 . 
     The procedure for performing a remedial application at remediation site  38  may vary according to the remediation site size and location, the equipment deployed downhole, the wellbore environment, and other factors. However, a general procedure for carrying out a remedial operation can be described with reference to the flowchart in  FIG. 5 . In this example, a remedial cementing operation is carried out by initially injecting an acid downhole to a remediation site, as indicated by block  52 . The acid may comprise a variety of acids, such as hydrochloric acid, a combination of hydrochloric acid and hydrofloric acid (e.g. 12:3 mud acid), or organic acid (e.g. citric acid). 
     Subsequently, an oil is injected downhole to the remediation site  38  to serve as the activating agent, as indicated by block  54 . By way of example, the oil may comprise diesel fuel, synthetic oil, or mineral oil that is deposited at the remediation site  38  to enable or at least facilitate expansion of swellable material  36 . Following injection of the oil, the slurry  46  is delivered downhole. In this embodiment, a self-healing cement is injected downhole to remediation site  38 , as indicated by block  56 . Self-healing cement comprises swellable material  36  which may be in the form of swellable particles  48  dispersed throughout the cement slurry. Furthermore, the various treatment fluids may be injected downhole through an appropriate tool deployed on tubing, such as coiled tubing. 
     The treatment fluid amounts, rates, spacing, and other injection parameters may vary depending on the remediation site, the equipment downhole, and the well environment. In some applications, for example, roughly equal amounts of acid, oil, and the self-healing cement may be directed downhole to the remediation site. By way of specific example, approximately 1 cubic meter of each treatment fluid may be pumped downhole to the remediation site  38 . Of course, these amounts can vary depending on the size and nature of the remedial cementing required for a given operation. 
     Referring generally to the flowchart of  FIG. 6 , another example is provided for a treatment procedure used to perform a remedial treatment able to limit the unwanted migration of downhole fluids at a remediation site. It should be noted that in some applications, the remediation site may extend a substantial distance along the wellbore. Furthermore, the procedure described in reference to  FIG. 6  is one specific example of a remedial treatment procedure, however, the order, length, content, and materials used to carry out the procedure can be changed and adjusted to accommodate the needs of particular remedial operations. 
     In the example illustrated, a cement retainer is initially set at depth within wellbore  22 , as indicated by block  58 . A stinger is then run on tubing to a desired downhole location, as indicated by block  60 . The operator can then rig in cementing equipment for performing a cement squeeze, as indicated by block  62 . A safety and procedure evaluation may be conducted prior to initiation of pressure testing, as indicated by block  64 . 
     Once this initial equipment is in place, the treating lines, e.g. tubing  24 , can be pressure tested, as indicated by block  66 . Furthermore, water may be dispersed downhole and further pressure testing may be conducted by, for example, moving the stinger to a blank spot in the cement retainer, as indicated by block  68 . Following the pressure testing, the operator is able to sting into the cement retainer and establish a suitable feed rate, as indicated by block  70 . 
     In some applications, it may not be necessary to inject a preparatory fluid  50 . However, in the example provided in  FIG. 6  a preparatory fluid  50 , e.g. an acid, is pumped downhole to the remediation site  38  to improve the injection of slurry  46  with swellable material  36 , as indicated by block  72 . After injecting the preparatory fluid, the operator can sting out of the cement retainer, as indicated by block  74 , and an activating agent  44 , e.g. oil, is circulated into the tubing, as indicated by block  76 . By way of example, the activating agent  44  may be delivered downhole via treatment tubing  24 . 
     The operator then again stings into the cement retainer and squeezes activating agent, e.g. oil, into the surrounding formation, as indicated by block  78 . Upon completion of the activating agent squeeze, the operator can sting out of the retainer, as indicated by block  80 . Subsequently, the slurry  46 , which may comprise self-healing cement containing swellable material  36 , is circulated into the tubing, as indicated by block  82 . 
     The operator again stings into the cement retainer, as indicated by block  84 . This enables a squeeze of the self-healing cement until a final squeeze pressure is attained, as indicated by block  86 . Subsequently, the operator is able to sting out of the cement retainer, as indicated by block  88 , and the tubing may be backwashed, as indicated by block  90 . The backwashing can be conducted by establishing a reverse fluid flow  40 , as described above. 
     Depending on the material used to prepare slurry  46 , e.g. the type of cement used to prepare the slurry, the slurry is allowed to cure over a desired time period, as indicated by block  92 . For example, a 24-hour period may be provided to allow the cement to sufficiently cure. Upon deposit of the slurry, the swellable material  36  within the slurry is acted on by the activating agent  44  which causes the swellable material  36  to swell and expand. The swelling better enables the cement to block unwanted migration of fluids, e.g. gases, past remediation site  38 . 
     It should be noted that the well remediation technique may be adjusted to suit a variety of wells, environments, and types of equipment. Furthermore, the swellable material can be deployed in a variety of slurries and with a variety of supporting treatment fluids. In some applications, well repair is accomplished using swellable material in a cement matrix. Additionally, well system  20  may be formed with many types of components for use with many types of well systems. Similarly, various stingers and tubings or other passages may be used for injecting fluids. The remediation technique also may be carried out in cooperation with many configurations of existing downhole equipment. Some applications benefit from a preparatory fluid, while other remediation operations can be conducted without the preparatory fluid. Additionally, a variety of activating agents and slurry materials may be employed. Similarly, the type, size, disbursement, concentration, shape, and other factors related to the swellable material may be adjusted as desired for a given application. 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.