DETAILED DESCRIPTION OF THE INVENTION

[0035] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.

[0036] Referring initially to FIG. 1, a pair of sand control screen assemblies used during the treatment of multiple intervals of a wellbore in a single trip and operating from an offshore oil and gas platform is schematically illustrated and generally designated 10 . A semi-submersible platform 12 is centered over a pair of submerged oil and gas formations 14 , 16 located below a sea floor 18 . A subsea conduit 20 extends from a deck 22 of the platform 12 to a wellhead installation 24 including blowout preventers 26 . Platform 12 has a hoisting apparatus 28 and a derrick 30 for raising and lowering pipe strings such as a work string 32 .

[0037] A wellbore 34 extends through the various earth strata including formations 14 , 16 . A casing 36 is cemented within wellbore 34 by cement 38 . Work string 32 includes various tools such as a sand control screen 40 which is positioned within production interval 44 between packers 46 , 48 and adjacent to formation 14 and sand control screen 42 which is positioned within production interval 50 between packers 52 , 54 and adjacent to formation 16 . Thereafter, a treatment fluid containing sand, gravel, proppants or the like is pumped down work string 32 such that formations 14 , 16 may be sequentially treated.

[0038] Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the sand control screen assemblies of the present invention are equally well-suited for use in wells having other directional orientations such as deviated wells, inclined wells or horizontal wells. Also, even though FIG. 1 depicts an offshore operation, it should be noted by one skilled in the art that the sand control screen assemblies of the present invention are equally well-suited for use in onshore operations. Also, even though FIG. 1 depicts two formations, it should be understood by one skilled in the art that the treatment processes of the present invention are equally well-suited for use with any number of formations.

[0039] Referring now to FIG. 2 therein is depicted a more detailed illustration of a sand control screen assembly of the present invention, such as, for example, sand control screen assembly 40 of FIG. 1 . Sand control screen assembly 40 includes a base pipe 56 that has a plurality of openings 58 which allow the flow of production fluids into sand control screen assembly 40 . The exact number, size and shape of openings 58 are not critical to the present invention, so long as sufficient area is provided for fluid production and the integrity of base pipe 56 is maintained.

[0040] Spaced around base pipe 56 is a plurality of ribs 60 . Ribs 60 are generally symmetrically distributed about the axis of base pipe 56 . Ribs 60 are depicted as having a cylindrical cross section, however, it should be understood by one skilled in the art that ribs 60 may alternatively have a rectangular or triangular cross section or other suitable geometry. Additionally, it should be understood by one skilled in the art that the exact number of ribs 60 will be dependant upon the diameter of base pipe 56 as well as other design characteristics that are well known in the art.

[0041] Wrapped around ribs 60 is a screen wire 62 . Screen wire 62 forms a plurality of turns, such as turn 64 and turn 66 . Between each of the turns is a gap through which formation fluids flow. The number of turns and the gap between the turns are determined based upon the characteristics of the formation from which fluid is being produced and the size of the gravel to be used during the gravel packing operation. Together, ribs 60 and screen wire 62 may form a sand control screen jacket which is attached to base pipe 56 by welding or other suitable techniques.

[0042] A one-way valve 70 is disposed within each opening 58 of base pipe 56 to prevent fluid flow from the interior to the exterior of the sand control screen assembly 40 . One-way valves 70 may be referred to collectively as a seal member 68 . Preferably, one-way valves 70 are mounted within openings 58 by threading, stamping or other suitable technique. Ball and seat type one-way valves have been found to be suitable, however, other types of one-way valves may also be used including poppet valves, sleeve valves and the like. One-way valves 70 prevent fluid flow from the interior to the exterior of sand control screen assembly 40 and are actuatable to allow fluid flow from the exterior to the interior of sand control screen assembly 40 . Accordingly, when one-way valves 70 are used within base pipe 56 of sand control screen assembly 40 during production, production fluids are allowed to flow through sand control screen assembly 40 through one-way valves 70 .

[0043] Referring now to FIG. 3 A, therein is depicted a sand control screen assembly that is generally designated 40 A. Sand control screen assembly 40 A is substantially identical to sand control screen assembly 40 described above as sand control screen assembly 40 A includes base pipe 56 that has a plurality of openings 58 , a plurality of ribs (not pictured) and a screen wire 62 . Together, the ribs and screen wire 62 form a sand control screen jacket that is attached using connectors 69 to base pipe 56 by welding or other suitable techniques.

[0044] One-way valves 70 A are disposed within each opening 58 of base pipe 56 to prevent fluid flow from the interior to the exterior of the sand control screen assembly 40 A. One-way valves 70 A may be referred to collectively as a seal member 68 . Preferably, one-way valves 70 A are flush mounted within openings 58 by threading, stamping or other suitable technique. One-way valves 70 A prevent fluid flow from the interior to the exterior of sand control screen assembly 40 A and are actuatable to allow fluid flow from the exterior to the interior of sand control screen assembly 40 A. Accordingly, when one-way valves 70 A are used within base pipe 56 of sand control screen assembly 40 A during production, production fluids are allowed to flow through sand control screen assembly 40 A through one-way valves 70 A.

[0045] Following the downhole treatment precesses discussed in detail below wherein fluid flow from the interior to the exterior of sand control screen assembly 40 A is prevented, the ability to flow fluids from the interior to the exterior of sand control screen assembly 40 A may be desirable, for example, to perform an acid treatment. Accordingly, one-way valves 70 A may be designed to lock out or be rendered inoperable under certain conditions such that one-way valves 70 A no longer prevent fluid flow from the interior to the exterior of sand control screen assembly 40 A. In such cases, after one-way valves 70 A have been operated into the lock out position, fluid flow is allowed from the exterior to the interior and from the interior to the exterior of sand control screen assembly 40 A. One method of locking out one-way valves 70 A is to expose one-way valves 70 A to a differential pressure above a predetermined threshold.

[0046] Referring now to FIG. 3 B, therein is depicted a sand control screen assembly that is generally designated 40 B. Sand control screen assembly 40 B is substantially similar to sand control screen assembly 40 A described above as sand control screen assembly 40 B includes base pipe 56 that has a plurality of openings 58 , a plurality of ribs (not pictured) and a screen wire 62 . Together, the ribs and screen wire 62 form a sand control screen jacket that is attached using connectors 69 to base pipe 56 by welding or other suitable techniques.

[0047] One-way valves 70 B are disposed within each opening 58 of base pipe 56 to prevent fluid flow from the interior to the exterior of the sand control screen assembly 40 B. One-way valves 70 B may be referred to collectively as a seal member 68 . Preferably, one-way valves 70 B are mounted within openings 58 by threading, stamping or other suitable technique. In the illustrated embodiment, one-way valves 70 B extend from openings 58 into base pipe 56 . Due to the thickness of the wall of base pipe 56 , it may be desirable to use one-way valves 70 B that are thicker than the wall of base pipe 56 . In this case, it has been found that one-way valves 70 B may extend into base pipe 56 and may reduce the inner diameter of base pipe 56 up to thirty percent without having a detrimental impact on the installation or operation of sand control screen assembly 40 B during treatment or production. Preferably, one-way valves 70 B may reduce the inner diameter of base pipe 56 between about ten and thirty percent.

[0048] As an alternative and as depicted in FIG. 3 C, one-way valves 70 C may be disposed within each opening 58 of base pipe 56 to prevent fluid flow from the interior to the exterior of the sand control screen assembly 40 C. One-way valves 70 C may be referred to collectively as a seal member 68 . Preferably, one-way valves 70 C are mounted within openings 58 by threading, stamping or other suitable technique. In the illustrated embodiment, one-way valves 70 C extend from openings 58 outwardly from base pipe 56 toward screen wire 62 . In his embodiment, the ribs (not pictured) must be positioned around base pipe 56 such that openings 58 may receive one-way valves 70 C that are thicker than the wall of base pipe 56 . In this configuration, base pipe 56 retains its full bore capabilities. Preferably, one-way valves 70 C may increase the outer diameter of base pipe 56 between about ten and thirty percent.

[0049] As yet an alternative and as depicted in FIG. 3 D, one-way valves 70 D may be disposed within each opening 58 of base pipe 56 to prevent fluid flow from the interior to the exterior of the sand control screen assembly 40 D. One-way valves 70 D may be referred to collectively as a seal member 68 . Preferably, one-way valves 70 D are mounted within openings 58 by threading, stamping or other suitable technique. In the illustrated embodiment, one-way valves 70 D extend inwardly and outwardly from openings 58 of base pipe 56 . In his embodiment, the ribs (not pictured) must be positioned around base pipe 56 such that openings 58 may receive one-way valves 70 D that are thicker than the wall of base pipe 56 . Preferably, one-way valves 70 D may increase the outer diameter of base pipe 56 between about ten and thirty percent and may reduce the inner diameter of base pipe 56 between about ten and thirty percent.

[0050] Referring now to FIG. 4 , therein is depicted an alternative embodiment of a sand control screen assembly that is generally designated 71 . Sand control screen assembly 71 includes base pipe 56 having a plurality of openings 58 with screen wire 62 wrapped therearound and attached to base pipe 56 with connectors 69 . Disposed within openings 58 of base pipe 56 are a plurality of plugs 72 that prevent fluid flow through openings 58 and serve as seal member 68 in this embodiment. Following the downhole treatment processes discussed in more detail below, plugs 72 are removed from openings 58 such that production fluids may flow to the interior of sand control screen assembly 71 .

[0051] Plugs 72 may be any conventional plugs known or unknown in the art, including metal plugs, such as aluminum plugs, ceramic plugs or the like. The techniques used to remove plugs 72 will depend upon the construction of plugs 72 . If plugs 72 are formed from an acid reactive material such as aluminum, an acid treatment may be used to remove plugs 72 . The acid may be pumped into the interior of sand control screen assembly 71 where it will react with the reactive plugs, thereby chemically removing plugs 72 .

[0052] Alternatively, regardless of the type of plug, plugs 72 may be mechanically removed. For example, a scraping mechanism may be used to physically contact plugs 72 and remove plugs 72 from the openings 58 . As another alternative, if plugs 72 are constructed from propellants, a combustion process may be used to remove plugs 72 . Likewise, if plugs 72 are constructed from friable materials such as ceramics, a vibration process, such as sonic vibrations may be used to remove plugs 72 . As a further alternative, plugs 72 may be removed by applying a preselected amount of differential pressure across plugs 72 .

[0053] Referring now to FIG. 5 , an alternative embodiment of a sand control screen assembly is illustrated and generally designated 73 . Sand control screen assembly 73 includes base pipe 56 having a plurality of openings 58 with screen wire 62 wrapped therearound. Disposed within base pipe 56 is a sleeve 74 having multiple ports 76 that serves as seal member 68 in this embodiment. When in a first position, ports 76 of sleeve 74 do not align with openings 58 of the base pipe 56 . When in a second position, ports 76 of sleeve 74 align with openings 58 of base pipe 56 . When sleeve 74 is in the first position, fluid flow from the exterior of sand control screen assembly 73 to the interior of sand control screen assembly 73 is prevented, as is fluid flow from the interior to the exterior of sand control screen assembly 73 . When sleeve 74 is in the second position, fluid flow from the exterior of sand control screen assembly 73 to the interior of the sand control screen assembly 73 is allowed, as is fluid flow from the interior to the exterior of sand control screen assembly 73 . Sleeve 74 can be displaced between the first position and second position by any conventional means such as axial displacement or rotational displacement. In an alternative embodiment, sleeve 74 can be a removable sleeve in which case ports 76 are not required.

[0054] Referring now to FIGS. 6 A- 6 B, therein is depicted another embodiment of a sand control screen assembly of the present invention that is generally designated 132 . Sand control screen assembly 132 includes a base pipe 134 that has a non perforated section and a perforated section that includes a series of openings 136 that are circumferentially spaced therearound. Sand control screen assembly 132 has a pair of screen connectors 138 , 140 that attach a sand control screen 142 to base pipe 134 . Screen connectors 138 , 140 may be attached to base pipe 134 by welding or other suitable technique. Sand control screen 142 may comprise a screen wire wrapped around a plurality of ribs as described above. Sand control screen 142 is disposed around the section of base pipe 134 that is not perforated.

[0055] Screen connectors 138 , 140 attach sand control screen 142 to base pipe 134 such that an annulus 144 is formed between sand control screen 142 and base pipe 134 . It should be noted that centralizers or other support members may be disposed within annulus 144 to support sand control screen 142 and maintain the standoff between sand control screen 142 and base pipe 134 . Screen connector 140 includes one or more fluid passageways 146 . Screen connector 140 also has an upper sealing surface 148 . Coupled to the upper end of screen connector 140 is a housing member 150 . Housing member 150 forms an annulus 152 with base pipe 134 adjacent to openings 136 . Disposed within annulus 152 is an annular sliding sleeve 154 having a sealing surface 156 which is preferably made from a resilient material such as an elastomer or polymer. Also disposed within annulus 152 is a spiral wound compression spring 158 that downwardly biases sliding sleeve 154 .

[0056] Together, spring 158 , sliding sleeve 154 and screen connector 140 form an annular one-way valve 160 that may be referred to as a seal member. One-way valve 160 prevents fluid flow from the interior to the exterior of sand control screen assembly 132 , as best seen in FIG. 6 A, and is actuatable to allow fluid flow from the exterior to the interior of sand control screen assembly 132 , as best seen in FIG. 6B . For example, during a treatment process as described below wherein a treatment fluid is pumped into the interior of sand control screen assembly 132 and is discharged into the wellbore annulus above sand control screen assembly 132 , fluid flow from the interior to the exterior of sand control screen assembly 132 is prevented. Specifically, the bias force of spring 158 and the force created by differential pressure across sliding sleeve 154 between the interior and the exterior of sand control screen assembly 132 both act downwardly on sliding sleeve 154 such that sealing surface 156 sealingly engages sealing surface 148 of screen connector 140 , thereby preventing fluid flow from the interior to the exterior of sand control screen assembly 132 .

[0057] During production, production fluids are allowed to flow from the exterior to the interior of sand control screen assembly 132 through a fluid flow path within sand control screen assembly 132 . Specifically, the fluid flows through sand control screen 142 , travels along base pipe 134 in annulus 144 , passes through fluid passageways 146 in screen connector 140 to unseat sliding sleeve 154 from sealing surface 148 of screen connector 140 by compressing spring 158 , then travels around sliding sleeve 154 , which may include a fluid bypass (not pictured), in annulus 152 and through openings 136 .

[0058] Following the downhole treatment precesses discussed below wherein fluid flow from the interior to the exterior of sand control screen assembly 132 is prevented, the ability to flow fluids from the interior to the exterior of sand control screen assembly 132 may be desirable, for example, to perform an acid treatment. Accordingly, one-way valve 160 may be designed to shear open or be rendered inoperable under certain conditions such that one-way valve 160 no longer prevents fluid flow from the interior to the exterior of sand control screen assembly 132 . For example, in the illustrated embodiment, when a sufficient differential pressure is placed across sliding sleeve 154 between the interior and the exterior of sand control screen assembly 132 , a ceramic disk 161 in bypass passageway 159 may rupture to permanently open bypass passageway 159 . In such cases, after one-way valve 160 has been rendered inoperable, fluid flow is allowed from the exterior to the interior and from the interior to the exterior of sand control screen assembly 132 .

[0059] Referring now to FIGS. 7 A- 7 B, therein is depicted another embodiment of a sand control screen assembly of the present invention that is generally designated 162 . Sand control screen assembly 162 includes a base pipe 164 that has a non perforated section and a perforated section that includes a series of openings 166 that are circumferentially spaced therearound. Sand control screen assembly 162 has a pair of screen connectors 168 , 170 that attach a sand control screen 172 to base pipe 164 . Screen connectors 168 , 170 may be attached to base pipe 164 by welding or other suitable technique. Sand control screen 172 may comprise a screen wire wrapped around a plurality of ribs as described above. Sand control screen 172 is disposed around the section of base pipe 164 that is not perforated.

[0060] Screen connectors 168 , 170 attach sand control screen 172 to base pipe 164 such that an annulus 174 is formed between sand control screen 172 and base pipe 164 . Screen connector 170 includes one or more fluid passageways 176 . Coupled to the upper end of screen connector 170 is a housing member 180 . Housing member 180 forms an annulus 182 with base pipe 164 adjacent to openings 166 . Disposed within annulus 182 is an annular sliding sleeve 184 . A seal 185 is positioned exteriorly of sliding sleeve 184 to provide a seal against the interior surface of housing member 180 . Likewise, a seal 186 is positioned interiorly of sliding sleeve 184 to provide a seal against the exterior surface of base pipe 164 . Preferably seals 185 , 186 are made from a resilient material such as an elastomer or polymer. Also disposed within annulus 182 is a spiral wound compression spring 188 that downwardly biases sliding sleeve 184 .

[0061] Together, spring 188 , sliding sleeve 184 , housing member 180 and base pipe 164 form an annular one-way valve 190 that may be referred to as a seal member. One-way valve 190 prevents fluid flow from the interior to the exterior of sand control screen assembly 162 , as best seen in FIG. 7 A, and is actuatable to allow fluid flow from the exterior to the interior of sand control screen assembly 162 , as best seen in FIG. 7B . Specifically, during a treatment process as described below, a differential pressure force and spring 188 downwardly biases sliding sleeve 184 such that seal 185 is in sealing engagement with the interior surface of housing member 180 and seal 186 is in sealing engagement with the exterior surface of base pipe 164 which prevents fluid flow from the interior to the exterior of sand control screen assembly 162 . During production, production fluids are allowed to flow from the exterior to the interior of sand control screen assembly 182 by passing through sand control screen 172 , traveling along base pipe 164 in annulus 174 , passing through fluid passageways 176 in screen connector 170 to shift sliding sleeve 184 such that seal 186 is out of sealing engagement with base pipe 164 by compressing spring 188 , then traveling around sliding sleeve 184 in the radially reduced section of base pipe 164 and through openings 166 .

[0062] Even though FIGS. 6 A- 7 B have been described as including annular sliding sleeves 154 , 184 , it should be understood by those skilled in the art that the illustrated sliding sleeves 154 , 184 could alternatively represent one or more pistons. For example, sliding sleeves 154 , 184 could alternatively be one or more semi-annular pistons that are acted upon simultaneously by a single spiral wound compression spring. As a further example, sliding sleeves 154 , 184 could alternatively be one or more rod type pistons each of which could be acted upon by a corresponding spring.

[0063] It should be understood by those skilled in the art that other type of seal members 68 may be used to temporarily prevent fluid flow from the interior to the exterior of a sand control screen assembly of the present invention during and following a treatment process of the present invention but allow the flow of production fluids from the exterior to the interior thereof without departing from the principles of the present invention.

[0064] Also, it should be understood by those skilled in the art that while FIGS. 2 - 7 B have depicted a wire wrapped sand control screen, other types of filter media could alternatively be used in conjunction with the apparatus of the present invention, including, but not limited to, a fluid-porous, particulate restricting material such as a plurality of layers of a wire mesh that are diffusion bonded or sintered together to form a porous wire mesh screen designed to allow fluid flow therethrough but prevent the flow of particulate materials of a predetermined size from passing therethrough.

[0065] Referring now to FIG. 8 , therein is depicted an embodiment of the present invention that is used during fracturing and frac packing treatments. As illustrated, sand control screen assembly 40 including one-way valves 70 , is positioned within casing 36 and is adjacent to formation 14 . Likewise, sand control screen assembly 42 including one-way valves 70 , is positioned within casing 36 and is adjacent to formation 16 . A service tool 78 is positioned within the work string 32 . As illustrated by the break between service tool 78 and sand control screen assemblies 40 , service tool 78 may be operably positioned several feet to several hundred feet uphole of sand control screen assembly 40 .

[0066] To begin the completion process, production interval 44 adjacent to formation 14 is isolated. Packer 46 seals the near end of production interval 44 and packer 48 seals the far end of production interval 44 . Likewise, production interval 50 adjacent to formation 16 is isolated. Packer 52 seals the near end of production interval 50 and packer 54 seals the far end of production interval 50 . Additionally, seal element 88 is coupled to service tool 78 . Seal element 88 contacts the interior of work string 32 forming a seal, thereby preventing fluid flow into the annulus between work string 32 and service tool 78 . Work string 32 includes cross-over ports 90 , 92 that provide a fluid communication path from the interior of work string 32 to production intervals 44 , 50 , respectively. Preferably, fluid flow through cross-over ports 90 , 92 is controlled by suitable valves that are opened and closed by conventional means.

[0067] Referring now to FIG. 9 , when the treatment operation is a frac pack, the objective is to enhance the permeability of the treated formation by delivering a fluid slurry containing proppants 96 at a high flow rate and in a large volume above the fracture gradient of the formation such that fractures may be formed within the formation 14 and held open by proppants 96 . In addition, a frac pack also has the objective of preventing the production of fines by packing production interval 44 with proppants 96 .

[0068] In the initial phase of the treatment process of the present invention, the interior of sand control screen assemblies 40 is filled with a sand plug 96 A. This is achieved by pumping treatment fluid downhole such as a relatively low viscosity oil or water based liquid including a high concentration of solid agents such as sand, gravel or proppants, that will fall out of the slurry relatively easily to form sand plug 96 A. Sand plug 96 A improves the ability of one-way valves 70 of sand control screen assembly 40 to prevent fluid flow from the interior to the exterior of sand control screen assembly 40 . In addition, sand plug 96 A prevents sand control screen assembly 40 from seeing the pressure spike that typically occurs at the end of a fracture operation. Accordingly, it is preferred that sand plug 96 A extend past the near end of sand control screen assembly 40 as illustrated. It should be noted that this initial phase of the treatment process may not be necessary if sufficient solid agents fall out of the treatment fluids during the fracture or frac packing operations.

[0069] Referring now to FIG. 10 , once sand plug 96 A is deposited in sand control screen assembly 40 , the second phase of the treatment process may begin. The treatment fluid used during the second phase of the treatment process, which is the fracture operation, may be any appropriate fracturing fluid such as oil, water, an oil/water emulsion, gelled water or gelled oil based fracture fluid having a relatively high viscosity to enhance the fracturing process. This treatment fluid may or may not include solid agents such as sand, gravel or proppants but will usually have a lower concentration of solid agents than the treatment fluid of the first phase of the treatment process.

[0070] In the illustrated embodiment, the treatment fluid of the second phase of the treatment process includes a low concentration of proppants indicated by reference character 96 B. The treatment fluid is pumped through service tool 78 and enters the near end of production interval 44 via cross-over ports 90 . As the treatment fluid is being continuously pumped at a high flow rate and in a large volume above the fracture gradient of formation 14 and as no returns are being taken, the treatment fluid fractures formation 14 as indicated by reference character 98 .

[0071] Referring now to FIG. 11 , prior to the point at which fractures 98 no longer propagate into formation 14 , the third phase of the treatment process begins. The treatment fluid used during this phase may be any suitable fluid such as oil, water, an oil/water emulsion, gelled water or gelled oil based fluid including a suitable solid agent such as gravel, sand or proppants. In this phase of the treatment process, the solid agents travel into the newly created fractures to prop the fractures open and create a path of high permeability back to wellbore 34 . In addition, the solid agents fill production interval 44 between sand control screen assembly 40 and casing 36 to form a gravel pack 96 C therein which filters particulate matter out of production fluids once production begins. Upon completion of the frac packing of production interval 44 , the valves associated with cross-over ports 90 are closed by conventional means.

[0072] Referring now to FIG. 12 , following completion of the first frac packing operation, service tool 78 is operably repositioned to frac pack formation 16 . As illustrated by the break between service tool 78 and sand control screen assembly 42 , the service tool 78 may be several feet to several hundred feet uphole of sand control screen assembly 42 . Once service tool 78 is positioned, a three-phase treatment process similar to that described above may begin.

[0073] Referring now to FIG. 13 , the low viscosity treatment fluid with a high concentration of solid agents is pumped into sand control screen assembly 42 to form sand plug 96 D. Fracture treatment fluid is then pumped through service tool 78 , as best seen in FIG. 14 . The treatment fluid enters the near end of production interval 50 via cross-over ports 92 . In the illustrated embodiment the fracture fluid contains a low concentration of proppants indicated by 96 E. As the fracture fluid is being delivered at a high flow rate and in a large volume above the fracture gradient of formation 16 and as no returns are being taken, the fracture fluids fracture formation 16 as indicated by fractures 100 .

[0074] Referring now to FIG. 15 , toward the end of the fracture operation, the composition of the treatment fluid is changed to include a higher concentration of solid agents. These solid agents are used to prop fractures 100 in formation 16 and to form a gravel pack 96 F in production interval 50 between sand control screen assembly 42 and casing 32 . This three-phase treatment process can be repeated for any number of formations by repositioning service tool 78 sequentially uphole relative to each of the formations requiring treatment. Once all of the formations are treated and prior to beginning production, sand plugs 96 A, 96 D must be washed out of sand control screen assemblies 40 , 42 . As seen in FIG. 16 , service tool 78 may be used to wash out the sand control screen assemblies 40 , 42 and work string 32 .

[0075] To wash out sand control screen assemblies 40 , 42 , liquid is delivered through service tool 78 to mix with the solid agents forming sand plugs 96 A, 96 D. The mixture is allowed to reverse out of work string 32 via the annulus between service tool 78 and work string 32 as indicated by arrows 105 . This process of circulating the solid agents to the surface and lowering service tool 78 farther into work string 32 continues until substantially all the solid agents in work string 32 have been removed.

[0076] As explained above, different compositions of treatment fluids are used in the above described method during the different phases of the treatment process. Preferably, the first treatment fluid has a higher concentration of solid agents than the second treatment fluid. The first treatment fluid requires a higher concentration of solid agents as it is intended to place a sand plug in the sand control screen assemblies. The second treatment fluid does not require such solid agents as it is intended to fracture the formations. Additionally, the first treatment fluid preferably has a lower density and lower viscosity than the second treatment fluid. The lower density and lower viscosity in the first treatment fluid allow the solid agents to fall out of the slurry easily. The higher density and higher viscosity of the second treatment fluid allows the second treatment fluid to effectively fracture the formation.

[0077] The third treatment fluid preferably has a higher concentration of solid agents than the second treatment fluid. The third treatment fluid props the fractures and gravel packs the production intervals surrounding the sand control screen assemblies. Therefore, a higher concentration of solid agents is desirable in the third treatment fluid. Additionally, the third treatment fluid may have a lower density and lower viscosity than the second treatment fluid. The lower density and lower viscosity in the third treatment fluid allow the solid agents to fall out of the slurry more readily.

[0078] As should be apparent to those skilled in the art, the above described method allows the use of a relatively simple service tool 78 that allows for the treatment of multiple formations that are relatively close together. This is achieved by using sand control screen assemblies 40 , 42 that include one-way valves 70 that prevent the flow of fluids from the interior to the exterior of sand control screen assemblies 40 , 42 . Accordingly, fewer tools are required between sand control screen assemblies 40 , 42 , thereby the distance between sand control screen assemblies 40 , 42 may be reduced. This reduced distance and the simplicity of service tool 78 allow relatively narrow and relatively closely spaced formations to be treated according to the present invention.

[0079] Referring now to FIG. 17 , therein is depicted an embodiment of the present invention that is used during a gravel packing treatment. As illustrated, sand control screen assembly 40 having one-way valves 70 is positioned within casing 36 and is adjacent to formation 14 . Similarly, sand control screen assembly 42 having one-way valve 70 is positioned within casing 36 and is adjacent to formation 16 . A wash pipe 104 extends through work string 32 traversing cross-over assembly 106 . Cross-over assembly 106 is positioned within work string 32 adjacent to crossover ports 90 that include valves therein as explained above.

[0080] Sand control screen assemblies 40 , 42 each have a filter medium associated therewith that is designed to allow fluid to flow therethrough but prevent particulate matter of sufficient size from flowing therethrough. The exact design of the filter medium of sand control screen assemblies 40 , 42 is not critical to the present invention as long as it is suitably designed for the characteristics of the formation fluids and the treatment fluids. One-way valves 70 of sand control screen assemblies 40 , 42 may be of any suitable type so long as they prevent fluid flow from the interior to the exterior of sand control screens 40 , 42 .

[0081] To begin the gravel packing completion process, production interval 44 proximate formation 14 and production interval 50 proximate second formation 16 are isolated. Packer 46 seals the near end of production interval 44 and packer 48 seals the far end of production interval 44 . Similarly, packer 52 seals the near end of production interval 50 and packer 54 seals the far end of production interval 50 . Initially, as illustrated, the cross-over assembly 106 is located proximate to sand control screen assembly 40 and aligned with cross-over ports 90 .

[0082] Referring to FIG. 18 , when the treatment operation is a gravel pack, the objective is to uniformly and completely fill production interval 44 between sand control screen assembly 40 and casing 36 with gravel. To help achieve this result, return fluid is taken through sand control screen assembly 40 , indicated by arrows 108 , and travels through wash pipe 104 , as indicated by arrows 110 , for return to the surface.

[0083] More specifically, a treatment fluid, in this case a fluid slurry containing gravel 112 is pumped downhole in work string 32 , as indicated by arrows 114 , and into production interval 44 via cross-over assembly 106 , as indicated by arrows 116 . As the fluid slurry containing gravel 112 travels to the far end of production interval 44 , gravel 112 drops out of the slurry and builds up from formation 14 , filling the perforations and production interval 44 around sand control screen assembly 40 forming gravel pack 112 A. While some of the carrier fluid in the slurry may leak off into formation 14 , the remainder of the carrier fluid passes through sand control screen assembly 40 through one-way valves 70 , as indicated by arrows 108 . The fluid flowing back through sand control screen assembly 40 , as explained above, follows the paths indicated by arrows 110 back to the surface.

[0084] After the gravel packing operation of production interval 44 is complete, cross-over assembly 106 and wash pipe 104 may be moved uphole such that other production intervals may be gravel packed, such as production interval 50 , as best seen in FIG. 19 . As the distance between formation 14 and formation 16 may be hundreds or even thousands of feet and as there may be any number of production intervals that require gravel packing, there may be a considerable amount of time between the gravel packing of production interval 44 and eventual production from formation 14 . It has been found that in conventional completions, considerable fluid loss may occur from the interior of sand control screen assembly 40 through gravel pack 112 A and into formation 14 . This fluid loss is not only costly but may also damage gravel pack 112 A, formation 14 or both. Using the sand control screen assemblies of the present invention, however, prevents such fluid loss using a seal member, in this case, one-way valves 70 , positioned within sand control screen assembly 40 . Accordingly, one-way valves 70 not only save the expense associated with fluid loss but also protect gravel pack 112 A and formation 14 from the damage caused by fluid loss.

[0085] Referring to FIG. 20 , the process of gravel packing production interval 50 is depicted. Wash pipe 104 is now disposed within sand control screen assembly 42 . Wash pipe 104 extends through cross-over assembly 106 such that return fluid passing through sand control screen assemblies 42 , indicated by arrows 118 , and travels through wash pipe 104 , as indicated by arrows 120 , for return to the surface.

[0086] The fluid slurry containing gravel 112 is pumped downhole through work string 32 , as indicated by arrows 122 , and into production interval 50 via cross-over assembly 106 and cross-over ports 92 , as indicated by arrows 124 . As the fluid slurry containing gravel 112 travels to the far end of production interval 50 , the gravel 112 drops out of the slurry and builds up from formation 16 , filling the perforations and production interval 50 around sand control screen assemblies 42 forming gravel pack 112 B. While some of the carrier fluid in the slurry may leak off into formation 16 , the remainder of the carrier fluid passes through sand control screen assemblies 42 through one-way valves 70 , as indicated by arrows 118 . The fluid flowing back through sand control screen assembly 42 , as explained above, follows the paths indicated by arrows 120 back to the surface. Once gravel pack 112 B is complete, cross-over assembly 106 may again be repositioned uphole to gravel pack additional production intervals. As explained above, using sand control screen assembly 42 prevents fluid loss from the interior of sand control screen assembly 42 to formation 16 during such subsequent operations.

[0087] As should be apparent to those skilled in the art, even though FIGS. 8 - 20 present the treatment of multiple intervals of a wellbore in a vertical orientation with packers at the top and bottom of the production interval, these figures are intended to also represent wellbores that have alternate directional orientations such as inclined wellbores and horizontal wellbores. In the horizontal orientation, for example, packer 46 is at the heel of production interval 44 and packer 48 is at the toe of production interval 44 . Likewise, while multiple production intervals have been described as being treated during a single trip, the methods described above are also suitable for treating a single production interval traversed by a wellbore or may be accomplished in multiple trips into a wellbore.

[0088] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.