Patent Publication Number: US-8985209-B2

Title: High pressure jet perforation system

Description:
BACKGROUND 
     Many types of wells are perforated and stimulated to facilitate production of well fluids. Perforation techniques may involve the use of shaped charges or the use of high-pressure jets to create perforations through surrounding casing and into the formation. When using high pressure jets to create sequential perforations at different well zones, a sand plug is created downhole for a given well zone after each perforation and well stimulation operation. If the sand plug interferes with the region to receive the next set of perforations, the excess portion of the sand plug is removed. Difficulties can arise in removing the excess sand, and sometimes the perforating string needs to be pulled out of hole so that a motor/mill can be run in hole to break loose the excess sand. 
     SUMMARY 
     In general, the present disclosure provides a system and method which facilitate removal of excess sand during a jet perforating operation without requiring that the perforating string be pulled out of hole. A jet perforating tool is provided with at least one perforating nozzle for creating perforations in a well via high-pressure fluid. The jet perforating tool also comprises at least one wash nozzle oriented to direct fluid under pressure against a sand plug to break loose excess sand. A pair of seats and plug members may be used in the jet perforating tool to control the flow of pressurized fluid through the perforating jet nozzle and/or the wash nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein, and: 
         FIG. 1  is a schematic illustration of an example of a well system comprising a jet perforating tool, according to an embodiment of the disclosure; 
         FIG. 2  is a cross-sectional view of an example of a jet perforating tool, according to an embodiment of the disclosure; and 
         FIG. 3  is a flowchart illustrating an example of a methodology for creating perforations and removing excess sand from sand plugs if needed, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of some illustrative embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The disclosure herein generally relates to a system and methodology which facilitate removal of excess sand from a sand plug to enable creation of a subsequent set of perforations with a jet perforating tool. The removal of excess sand may be accomplished during a jet perforating operation without requiring that the perforating string be pulled out of hole. The jet perforating tool comprises a perforating nozzle for creating perforations in a well via high-pressure fluid which may be directed through a surrounding casing and/or other well components and into the formation. The jet perforating tool also comprises a wash nozzle which may be used to direct fluid under pressure against a sand plug to break loose excess sand, thus allowing the excess sand to be removed, e.g. reverse circulated, from the sand plug area. In many applications, a plurality of perforating nozzles and a plurality of wash nozzles are used in the jet perforating tool to create multiple pressurized fluid streams. 
     In some applications, a slurry of fluid and solids is directed at high differential pressures through the jet perforating tool. The resulting high velocity fluid stream is capable of perforating casing, liner, cement, debris, and other materials before entering into the formation rock. After formation of the perforations, a stimulation operation, such as a fracturing operation, can be performed. By way of example, a fracturing operation may be performed by directing fracturing fluid downhole through an annulus formed between the well casing and the coiled tubing on which the jet perforating tool is deployed. 
     A sand plug may be placed in the wellbore after the stimulation procedure to create isolation between stimulation stages. For example, the sand plug may be placed by adding sand to a flush fluid following a fracturing treatment. Excess sand may be cleaned up through the coiled tubing string by reverse circulating, thus reducing the volume of fluid used and the time incurred during cleanouts. However, if the excess sand has become compacted or otherwise difficult to remove, the wash nozzle or nozzles of the jet perforating tool can be used to break loose the excess sand of the sand plug. The loosened, excess sand may then be removed via reverse circulation. 
     In some fracturing applications, for example, a fracture operation is performed after a first jetting, e.g. after formation of the first set of perforations, and depending on the fracture geometry it is possible to have high wellhead pressure. This high wellhead pressure can cause the sand plug to consolidate, thus creating difficulty in cleaning out the sand and dressing the sand plug by reverse circulation cleaning without first breaking loose the excess consolidated sand. The jet perforating tool can be used to direct fluid under pressure through the wash nozzles to help remove the excess sand from the consolidated layer without having to pull the perforating string out of hole. 
     In general, compaction of the sand plug isolating fracture stages can be caused by a variety of factors, including high fracturing pressure or overpressure of the sand plug when a pressure test is performed. In these situations, removal of any excess sand via reverse circulating can become very difficult. The ability to selectively use the jet perforating tool to remove the excess sand without pulling the perforating string out of hole greatly enhances the efficiency of the perforating and stimulating operation. 
     Referring generally to  FIG. 1 , an example of one type of application utilizing a perforating string to facilitate perforating and stimulating of a plurality of well zones is illustrated. The example is provided to facilitate explanation, and it should be understood that a variety of perforating systems, stimulation systems, and other well or non-well related systems may utilize the methodology described herein. The well string and the jet perforating tool may comprise a variety of components arranged in various configurations depending on the parameters of a specific perforating/stimulating operation. 
     In  FIG. 1 , an embodiment of a well perforating and stimulating system  20  is illustrated as comprising a jet perforating tool  22  deployed on a tubing string  24 , such as a coiled tubing string having coiled tubing  26 . Additionally, the tubing string  24  may comprise a variety of additional and/or alternate components, depending in part on the specific perforating and stimulating application, the geological characteristics, and the well type. In the example illustrated, the tubing string  24  is deployed in a wellbore  28 , illustrated as a generally vertical wellbore  28  lined with a casing  30 . However, various types of downhole equipment may be used in the well perforating and stimulating system  20 . Additionally, the tubing string  24  may be deployed in other types of wellbores, including deviated, e.g. horizontal, single bore, multilateral, cased, and uncased (open bore) wellbores. 
     In the example illustrated, wellbore  28  extends down through a subterranean formation  32  having a plurality of well zones  34 . Each of the well zones  34  may be selectively perforated to form a plurality of perforations  36 . Additionally, each of the well zones  34  may be stimulated, e.g. fractured, via an appropriate stimulation operation following perforation of the well zone  34 . In the example illustrated, perforations  36  are formed by high-pressure jets of fluid discharged through at least one perforating jet nozzle  38  of jet perforating tool  22 . In the example illustrated, the jet perforating tool  22  comprises a plurality of perforating jet nozzles  38  which direct perforating jets of fluid laterally, e.g. radially, outward through casing  30  and into the formation  32  at the desired well zone  34 . 
     After perforating a desired well zone  34 , a sand plug  40  may be formed by delivering sand downhole through, for example, an annulus  42  formed between tubing string  24  and well casing  30 . In a perforating and fracturing operation, for example, the sand plug is created after stimulating each zone to establish isolation between fracture stages. In this example, the sand plug may be placed in the previously perforated and stimulated well zone to block the perforations  36  and to thus isolate that region of the wellbore for performance of the perforating and stimulating operation at the next sequential well zone  34 . In at least some fracturing operations, the sand plug  40  may be formed by adding sand to the flush fluid delivered downhole after the fracturing treatment. 
     If excess sand is delivered downhole, it is desirable to clean or remove the excess sand before the next stage of perforating and stimulating. As discussed above, however, the excess sand may become compacted and difficult to remove via reverse circulation at least prior to loosening the compacted excess sand. It should be noted that in many applications, reverse circulation is achieved by circulating fluid down through annulus  42  and up through an internal flow passage of tubing string  24  to remove the excess sand. However, other techniques may be applied to remove the excess sand from the zone to be perforated. In the embodiment illustrated, jet perforating tool  22  comprises at least one wash nozzle  44  through which a pressurized stream of fluid may be directed to break up and loosen the excess compacted sand from sand plug  40 . For example, fluid may be directed down through tubing string  24  and through a plurality of wash nozzles  44  which are oriented to direct the pressurized fluid against the excess sand of sand plug  40 . Once loosened, the excess sand can be reversed circulated from the region to facilitate the next perforating and stimulating procedure. 
     Referring generally to  FIG. 2 , an embodiment of jet perforating tool  22  is illustrated. In this embodiment, the jet perforating tool  22  comprises a tool housing  46  which may be made up of a plurality of sections join together by, for example, threaded engagement. In the example illustrated, the tool housing  44  comprises a lead end  48  which may be formed as a bull nose  50  designed to guide the jet perforating tool  22  along the wellbore  28 . The lead end  48  may be coupled with a reverse check valve assembly section  52  which, in turn, is coupled to a perforating jet section  54  via a sub section  56 . The perforating jet section  54  also may be coupled with a mechanical connection end  58  designed to enable coupling of the jet perforating tool  22  into tubing string  24 . Depending on the specific application, however, the various sections used to form tool housing  46  and jet perforating tool  22  may be substituted, reconfigured, or otherwise changed to facilitate a given perforation and stimulation operation. 
     In the example illustrated, a primary internal flow passage  60  is disposed longitudinally through an interior of tool housing  46  to enable flow of fluids, e.g. reverse circulation fluids and high-pressure jetting fluids, through the jet perforating tool  22 , as represented by arrows  62 . Along the primary internal flow passage  60 , a first seat  64  is disposed in, for example, lead end  48 . Additionally, a second seat  66  is disposed along the primary internal flow passage  60  in, for example, check valve assembly section  52 . The first seat  64  and the second seat  66  may be selectively and sealingly engaged by corresponding first plug member  68  and second plug member  70 , respectively. By way of example, the first plug member  68  and the second plug member  70  may be in the form of balls designed to seat and seal against the corresponding first seat  64  and second seat  66  to selectively block flow along primary internal flow passage  60 . 
     In the embodiment illustrated, second seat  66  has a larger diameter than first seat  64 . The seat diameters are selected so that the first plug member  68 , e.g. the first ball or plug member  68 , passes through the second seat  66  and engages and seals against first seat  64  when delivered through jet perforating tool  22  along the primary internal flow passage  60 . The second ball or plug member  70 , e.g. the second plug member  70 , has a larger diameter than the first plug member  68  so as to engage and seal against the second seat  66 . 
     The wash nozzle or nozzles  44  may be disposed in lead end  48  such that the nozzles extend from primary internal flow passage  60  to an exterior  72  of the jet perforating tool  22 . Although the wash nozzles  44  may be arranged in a variety of orientations, the illustrated example provides a plurality of the wash nozzles  44  extending from primary internal flow passage  60  in a generally forward direction (e.g. generally parallel to a longitudinal axis defined by the flow passage  60 ) to a location along exterior  72  ahead of first seat  64 , i.e. on an opposite side of first seat  64  relative to second seat  66 . This allows pressurized fluid to be discharged in the forward direction toward the excess compacted sand of sand plug  40  when first plug member  68  is delivered into engagement with first seat  64 . The first plug member  68  is used to block flow of pressurized fluid through primary internal flow passage  60  so as to force the pressurized fluid through wash nozzles  44  and against the sand plug  40 . The wash nozzles  44 , e.g. four wash nozzles, are designed to give the discharged fluid enough velocity to jet the consolidated layer of excess sand with sufficient power to deconsolidate the excess sand. It should be noted that in some applications, additional nozzles  74  may be deployed between first seat  64  and second seat  66  to facilitate removal of sand. 
     The second plug member  70  also may be selectively delivered downhole through jet perforating tool  22  along primary internal flow passage  60 . Second plug member  70  is delivered into engagement with second seat  66  to enable discharge of high-pressure fluid through the perforating jet nozzle or nozzles  38 . For example, second plug member  70  may be delivered downhole into engagement with second seat  66  prior to a perforation procedure in which high-pressure fluid is delivered down through primary internal flow passage  60  for discharge in a lateral, e.g. radial, direction to form perforations  36  in a desired well zone  34 . In some applications, the second plug member  70  may be retained in a plug cavity  76  by a retention member  78 , such as a pin. However, the retention member  78  is omitted or removed in applications when second plug member  70  is reversed circulated out of jet perforating tool  22  to enable deployment of first plug member  68  down through primary internal flow passage  60  to first seat  64 . 
     The jet perforating tool  22  and the overall well perforation and stimulation system  20  may be used in a variety of applications. However, an example of a perforating and fracturing application is described with reference to  FIG. 3  to facilitate explanation of the jet perforating tool  22  and a methodology for operating the jet perforating tool  22 . In this example, an initial jetting operation is performed downhole at an initial well zone  34 , e.g. the lowermost well zone, as represented by block  80 . The jetting operation involves discharge of high pressure fluid jets through perforating jet nozzles  38  to create perforations  36 . A stimulation and sand plug operation is then performed, as represented by block  82 . For example, a fracturing procedure may be performed by pumping fracturing fluid into the perforations  36  to fracture the surrounding formation. Sand is then delivered downhole with the flush fluid after the fracturing treatment to create the sand plug  40 . 
     Once the sand plug  40  is formed, a determination is made whether a cleanup is required, as represented by block  84 . If no sand removal is required, the subsequent jetting operation may be performed at the next subsequent well zone  34  (see block  80 ); although in some applications, pressure tests may be formed on the sand plug to verify sand plug integrity prior to perforating the next well zone. If, on the other hand, cleanout is required, a reverse circulation is initiated to reverse out the larger, second plug  70 , e.g. ball, (see block  86 ) and to establish a reverse circulation fluid flow, as represented by block  88 . A determination is then made as to whether the reverse circulation has been successful in cleaning out the excess sand, as represented by decision block  90 . 
     If the region is sufficiently clean of sand, a pressure test may be performed on the sand plug  40 , as represented by block  92 , and a determination is made as to whether the sand plug holds the pressure, as represented by decision block  94 . If the sand plug  40  does not hold, additional sand may be pumped down through the coiled tubing  26 , as represented by block  96 . The sand plug  40  is then again pressure tested (see block  92 ). If the sand plug holds under pressure testing, the larger, second plug member  70  may be pumped down into engagement with the corresponding second seat  66 , as represented by block  98 . Once the second plug member  70  is seated, pressurized fluid may be applied against the second plug member  70  such that high-pressure fluid jets are discharged through perforating jet nozzles  38  for perforation of the next sequential well zone  34  (see block  80 ). 
     Returning to decision block  90 , if the reverse circulation fluid flow is unsuccessful in cleaning the excess sand, the smaller first plug member  68  is pumped down coiled tubing  26 , through primary internal flow passage  60  of jet perforating tool  22 , and into engagement with first seat  64 , as represented by block  100 . Once the first plug member  68  is properly seated against first seat  64 , pressurized fluid may be directed down through coiled tubing  26 , along primary internal flow passage  60 , and out through wash nozzles  44 , as indicated by block  102 . The high-pressure stream of fluid discharged from the wash nozzles  44  deconsolidates the excess sand of the sand plug  40  for removal without pulling the perforating string  24  out of hole. 
     Once the excess sand is loosened, a reverse circulation of fluid is initiated to reverse out the first plug member  68 , e.g. ball, (see block  104 ) and to establish a reverse circulation fluid flow, as represented by block  106 . Following the reverse circulation stage, a pressure test is performed on the sand plug  40 , as represented by block  108 . A determination is then made as to whether the sand plug is able to hold the pressure, as represented by decision block  110 . If the sand plug does not hold, additional sand may be pumped down through the coiled tubing  26 , as represented by block  112 . The sand plug is then again pressure tested (see block  108 ). If the sand plug holds under pressure testing, the larger, second plug member  70  may be pumped down into engagement with the corresponding second seat  66 , as represented by block  114 . Once the second plug member  70  is seated, pressurized fluid may be applied against the second plug member  70  such that high-pressure fluid jets are discharged through perforating jet nozzles  38  for perforation of the next sequential well zone  34  (see block  80 ). 
     The system and methodology described herein may be employed in non-well related applications which require deconsolidation of compacted material. Similarly, the system and methodology may be employed in many types of well applications, including many types of vertical and lateral well applications involving perforating procedures combined with various stimulation procedures, e.g. fracturing procedures, chemical injection procedures, proppant procedures, or other stimulation procedures. Furthermore, other types of well string components may be added, substituted and/or modified with respect to the overall well system  20  to facilitate perforation and stimulation operations in a variety of environments. Components of the jet perforating tool  22  also may be added, substituted and/or modified to facilitate a given perforating and stimulating operation without requiring that the tubing string be pulled out of hole. 
     Although only a few embodiments of the system and methodology 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 disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.