Abstract:
A system for enhancing oil production and reducing contamination thereof by such things as water breakthrough in unconsolidated horizontal wells comprises gravel packing, zonal isolation and selective flow control in combination. The significant control provided by the system enables the well operator to create a uniform pressure drop form heel to toe of the horizontal well and avoid commonly experienced water coning and early breakthrough of the horizontal borehole. An intelligent completion string including one or more flow control devices and one or more sensors is installable to enhance zonal isolation and control.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part application of U.S. Ser. No. 09/411,686, now U.S. Pat. No. 6,318,465, filed Oct. 4, 1999 which claims the benefit of an earlier filing date from U.S. Provisional Application No. 60/107,266 filed Nov. 3,1998. 
    
    
     BACKGROUND 
     Horizontally disposed wellbores have been employed in growing numbers in recent years to access oil reservoirs not previously realistically producible. Where the formation is consolidated, relatively little is different from a vertical wellbore. Where the formation is unconsolidated however, and especially where there is water closely below the oil layer or gas closely above, horizontal wells are much more difficult to produce. 
     Pressure drop produced at the surface to pull oil out of the formation is at its highest at the heel of the horizontal well. In an unconsolidated well, this causes water coning and early breakthrough at the heel of the horizontal well. Such a breakthrough is a serious impediment to hydrocarbon recovery because once water has broken through at the heel, all production from the horizontal is contaminated in prior art systems. Contaminated oil is either forsaken or separated at the surface. Although separation methods and apparatuses have become very effective they still add expense to the production operation. Contamination always was and still remains undesirable. Zonal isolation has been attempted using external casing packers and open hole packers in conjunction with gravel packing techniques but the isolation of individual zones was not complete using this method and the difficulties inherent in horizontal unconsolidated formation wells have persisted. 
     Another inherent drawback to unconsolidated horizontal wells is that if there is no mechanism to filter the sand prior to being swept up the production tubing, a large amount of sand is conveyed through the production equipment effectively sand blasting and damaging the same. A consequent problem is that the borehole will continue to become larger as sand is pumped out. Cave-ins are common and over time the sand immediately surrounding the production tubing will plug off and necessitate some kind of remediation. This generally occurs before the well has been significantly depleted. 
     To overcome this latter problem the art has known to gravel pack the horizontal unconsolidated wells to filter out the sand and support the bore hole. As will be recognized by one of skill in the art, a gravel packing operation generally comprises running a screen in the hole and then pumping gravel therearound in known ways. While the gravel effectively alleviates the latter identified drawbacks, water coning and breakthrough are not alleviated and the horizontal well may still be effectively occluded by a water breakthrough. 
     Since prior attempts at enhancing productivity in horizontal wellbores have not been entirely successful, the art is still in need of a system capable of reliably and substantially controlling, monitoring and enhancing production from unconsolidated horizontal wellbores. 
     SUMMARY 
     The above-identified drawbacks of the prior art are overcome or alleviated by the unconsolidated horizontal zonal isolation and control system disclosed herein. 
     The invention teaches a zonally isolated horizontal unconsolidated wellbore where packers are not employed on the outside of the basepipe but a reliable zonal isolation is still created. Zones are created by interspersing blank basepipe with slotted or otherwise “holed” basepipe. The blank pipe is not completely blank but rather includes closeable ports therein at preselected intervals. Screens are employed over these ports and (as conventional) over the slotted basepipe. Upon gravel packing, a near 100% of pack is achieved over the blank pipe section because of the closeable ports. Only about 60% is achievable without the ports. With a full gravel pack of a preselected distance, i.e., the distance of the blank pipe, and the ports closed, isolation is assured with fluid produced for a bad zone being virtually completely prevented from migrating to the next zone. By shutting off production from the undesirable zone, then, through production string seals, only the desired fluid is produced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross section view of an unconsolidated zonal isolation and control system of the invention; 
     FIG. 1A is a schematic cross section as in FIG. 1, illustrating the washpipe; 
     FIG. 2 is a schematic cross section view of a horizontal gravel packed zonal isolation system with dehydration ports in a blank pipe section; 
     FIG. 3 is an enlarged schematic cross section view of a dehydration section from the invention of FIG. 2; and 
     FIG. 4 is a cross section view of FIG. 3 taken along section line  4 — 4 . 
    
    
     DETAILED DESCRIPTION 
     In order to most effectively produce from a hydrocarbon reservoir where a horizontal wellbore in an unconsolidated formation is indicated, a gravel pack is ideally constructed. Moreover, the gravel packed area is most desirably zonally isolatable for reasons discussed above. Such zonal isolation preferably is effected by creating unfavorable flow conditions in the gravel pack at selected areas. To complete the system, a number of alternatives are possible: a production string including flow control devices may be run into the hole, each zone being isolated by a locator and a seal; production may commence directly from the base pipe and bridge plugs may be added later to seal certain offending zones; or a straddle packer which extends from blank pipe to blank pipe may be installed on an offending zone. The latter two alternatives are installed conventionally. The various components of the system are illustrated in FIGS. 1 and 1A wherein those of skill in the art will recognize a liner hanger or sand control packer  10  near heel  12  of horizontal wellbore  14 . From liner hanger or packer  10  hangs a production string including flow control device  16  which may be hydraulic, mechanical, electrical, electromechanical, electromagnetic, etc. operated devices such as sliding sleeves and seal assemblies  18 . Seal assembly  18  operates to create selectively controllable zones within the base pipe of a horizontal wellbore  14 . Seal assemblies  18  (in most cases there will be more than one though only one is depicted in FIG. 1) preferably seal against a polished bore in the original gravel packing basepipe  22  which remains in the hole from the previous gravel packing operation. Not visible in FIG. 1 but shown in FIG. 1A for clarity is washpipe  20  which is conventional and known to the art for many years. Additionally, a shifting profile  21  is illustrated in FIG. 1A depending from washpipe  20 . The shifting profile may be of any conventional or unconventional type. Shifting profiles in general are known in the art. Still referring to FIGS. 1 and 1A, one of skill in the art will recognize conventional holes  23  in the base pipe and production string  25 . Although the seal assemblies on the inside of the basepipe are effective and controllable, the gravel pack is generally a source of leakage zone to zone as hereinbefore noted. 
     In a preferred zonal isolation embodiment of the invention, referring to FIG. 2, one will recognize the open hole wall  50  and the gravel pack  52 . Centered within the packed gravel  52  are several sections of attached pipe. On the left and right sides of the drawing are standard gravel pack zones  54  and  55  which include a slotted or otherwise “holed” base pipe with screen thereover. Between these zones  54  is an elongated section of essentially blank pipe  56 . The blank pipe does, however, have what is referred to herein as a dehydration zone which comprises short sections of screen  58  over at least one, preferably several, closeable port(s). The ports enable full packing of gravel around the blank pipe  56 . Without the dehydration ports, only about 60% of the annular region surrounding a blank pipe will be packed. Since this provides a 40% open annulus, zonal isolation would be impossible. With a full pack (about 100%), very good zonal isolation is achieved. The isolation between zones is created by the length of blank pipe. Whatever that length be, undesired fluid would have to travel through the gravel pack in the annulus in order to get to a producing zone once the production pipe has shut off the offending zone. For example, if water had been produced from zone  55  but not from zone  54  the answer would be to shut off zone  55  from production in some conventional way and continue to produce from zone  54 . Although it is possible to move fluids from zone  55  to zone  54  through the pack  52 , it requires a tremendous pressure differential to move any significant volume of fluid. Tests have indicated that at 1500 psi of differential pressure and 40 feet of gravel packed annulus, only 0.6 barrels of the unwanted fluid will migrate to the producing zone through the gravel pack per day. Since in reality it is unlikely that more than 200-300 psi of differential pressure could exist between the zones, the leakage is so small as to be negligible. 
     As stated above, gravel packing blank pipe is generally an unsuccessful venture. This is because there is no leak-off of the gravel carrier fluid. When there is no leak-off, the velocity of the fluid stays high and the gravel is carried along rather than deposited. Thus, with respect at least to the β wave of the gravel packing operation, very little sand or gravel is deposited in the annulus of the blank pipe. To slow the gravel carrier fluid down, leak-off must occur. With slower fluid, gravel deposition occurs and the desired result is obtained. 
     The purpose of the blank pipe is zonal isolation. If there can be leak-off in the blank pipe, the zones will be not be isolated. The inventor of the present invention solved the problem by supplying the temporary leak-off paths introduced above as dehydration zones. Referring to FIG. 3, one of the dehydration zones is illustrated in an enlarged format to provide an understanding thereof to one of ordinary skill in the art. The screen  58  is an ordinary gravel pack screen employed as they are conventionally i.e. wrapped around a length of pipe to screen out particles. Under the screen is the essentially blank pipe  56  but which includes one of preferably several ports  60  which operate identically to a selected base pipe in a conventional gravel pack assembly while the ports  60  are open. Ports  60  allow for leak-off and therefore cause gravel to deposit. 
     When the gravel packing operation is complete and the otherwise conventional washpipe is withdrawn, a profile on the end thereof (not shown but any type of shifting profile is acceptable) is pulled past closing sleeve  62  to close the same. The sleeve  62  completely shuts off port  60  with the sleeve and it seals  64  and is not permitted to open again because of any number of conventional locking mechanisms such as dogs, collet, lock ring, etc. existing preferably at  66 . The locking arrangement is needed only to prevent accidental opening of the closing sleeve  62  after it has been closed. Once the closing sleeve  62  is closed, the pipe  56  is indeed completely blank pipe and is a zonal isolator. 
     Preferably the screen  58  is about one foot in length. Ports  60  may be distributed in many different patterns thereunder with as many ports as desired. One preferred embodiment employs four one quarter inch holes radially arranged about the circumference of the pipe. With respect to the blank pipe section length between the dehydration zones, a range of about five feet to about ten feet is preferred. 
     Since the provision of different zones and flow control devices in the invention allow the metering of the pressure drop in the individual zones, the operator can control the zones to both uniformly distribute the pressure drop available to avoid premature breakthrough while producing at a high rate. Moreover, the operator can shut down particular zones where there is a breakthrough while preserving the other zones&#39; production. 
     After construction of one of the assemblies above described, and the washpipe has been removed, a production string is installed having preferably a plurality of the seal assemblies with at least one tool stop mechanism to locate the seal assemblies at points where the basepipe is smooth and the inner diameter is not reduced. Location may also be assured based upon the liner hanger. The seal assemblies allow different zones to be created and maintained so that selective conditions may be generated in discrete zones. 
     In an alternative embodiment of the dehydration ports, the closing sleeve  62  is not locked and remains operable so that if needed, individual closing sleeves may be opened. This alternative embodiment provides the invention with even more utility in that it allows the well operator to contaminate selected sections of the gravel pack to even more strongly hamper the ability of fluid to move longitudinally through the gravel pack. More specifically, the sleeve  62  would be opened by a shifting tool and an injection tool (one of many known to the art) would be used to apply a contamination fluid through the open port  60 . The contamination fluid could be cement, drilling mud, epoxy, etc. and once injected into the gravel pack through the port it would fill all interstitial spaces in the pack making it even more impermeable. 
     Referring back to FIG. 1, particularly valuable with respect to achieving maximum benefits of the zonally isolated gravel pack taught herein is an intelligent completion string  25  having one or more intelligent control devices  70  and one or more sensors  72  for temperature, pressure, flow rate, chemical composition, etc. which when installed operates in concert with the construction of the zonally isolated pack to further enhance controllability of different zones and isolation therebetween. Controllability includes the ability to control fluid movement both into or out of a particular zone for purposes such as production of fluids, remediation or even modification of the gravel pack or the formation by various methods. More specifically, an intelligent completion string  25  provided with one or more relevant sensors as elucidated above will query incoming fluid for chemical composition and if not acceptable may execute a program in a downhole processor which is part of string  25  to determine an appropriate action and then take action. Actions taken may be such as closing a flow control device, calling for or carrying out injection of a substance into the gravel pack and or into the formation or simply modifying the flow rate for such reasons as controlling the advance of a steam front from an associated injection well, for example. Moreover, the string may include a communication capability for communication with a remote location including but not limited to a surface location. It will be understood that both communication and control may be carried out by wire conductor, optic fiber conductor, acoustically, hydraulic line or wirelessly. 
     The combination of the disclosed gravel pack and method for forming the same and advanced completion strings such as the above discussed intelligent completion string provides a synergistic effect relative to the enhancement of hydrocarbon well systems in vertical, deviated and even horizontal configurations. The combined disclosed elements create a versatile, function changeable system having significant benefit to the hydrocarbon recovery industry in both economy and efficiency. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.