Apparatus and method for progressively treating an interval of a wellbore

This invention relates in general to the treatment of a production interval of a wellbore to stimulate hydrocarbon production and prevent the production of fine particulate materials and, in particular, to an apparatus and method for progressively gravel packing or progressively frac packing the production interval of the wellbore.

It is well known in the subterranean well drilling and completion art that relatively fine particulate materials may be produced during the production of hydrocarbons from a well that traverses an unconsolidated or loosely consolidated formation. Numerous problems may occur as a result of the production of such particulate. For example, the particulate cause abrasive wear to components within the well, such as tubing, pumps and valves. In addition, the particulate may partially or fully clog the well creating the need for an expensive workover. Also, if the particulate matter is produced to the surface, it must be removed from the hydrocarbon fluids using surface processing equipment.

One method for preventing the production of such particulate material is to gravel pack the well adjacent the unconsolidated or loosely consolidated production interval. In a typical gravel pack completion, a sand control screen is lowered into the wellbore on a work string to a position proximate the desired production interval. A fluid slurry including a liquid carrier and a relatively coarse particulate material, such as sand, gravel or proppants which are typically sized and graded and which are typically referred to herein as gravel, is then pumped down the work string and into the well annulus formed between the sand control screen and the perforated well casing or open hole production zone.

The liquid carrier either flows into the formation or returns to the surface by flowing through a wash pipe or both. In either case, the gravel is deposited around the sand control screen to form the gravel pack, which is highly permeable to the flow of hydrocarbon fluids but blocks the flow of the fine particulate materials carried in the hydrocarbon fluids. As such, gravel packs can successfully prevent the problems associated with the production of these particulate materials from the formation.

It is sometimes desirable to perform a formation fracturing and propping operation prior to or simultaneously with the gravel packing operation. Hydraulic fracturing of a hydrocarbon formation is sometimes necessary to increase the permeability of the production interval adjacent the wellbore. According to conventional practice, a fracture fluid such as water, oil, oil/water emulsion, gelled water or gelled oil is pumped down the work string with sufficient volume and pressure to open multiple fractures in the production interval. The fracture fluid may carry a suitable propping agent, such as sand, gravel or proppants, which are typically referred to herein as proppants, into the fractures for the purpose of holding the fractures open following the fracturing operation.

The fracture fluid must be forced into the formation at a flow rate great enough to fracture the formation allowing the entrained proppant to enter the fractures and prop the formation structures apart, producing channels which will create highly conductive paths reaching out into the production interval, and thereby increasing the reservoir permeability in the fracture region. As such, the success of the fracture operation is dependent upon the ability to inject large volumes of hydraulic fracture fluid along the entire length of the formation at a high pressure and at a high flow rate.

It has been found that it is difficult to achieve a complete gravel pack of the desired production interval either independent of or as part of a fracturing operation, particularly in long or inclined/horizontal production intervals. These incomplete packs are commonly a result of the liquid carrier entering the permeable portions of the production interval causing the gravel to form a sand bridge in the annulus. Thereafter, the sand bridge prevents the gravel pack slurry from flowing to the remainder of the annulus which, in turn, prevents the placement of sufficient gravel in the remainder of the annulus.

Therefore a need has arisen for an apparatus and method that are capable of creating fractures along the entire length of a production interval. A need has also arisen for such an apparatus and method that can produce a complete gravel pack of the wellbore adjacent to the production interval either independent of or as part of the fracturing of the production interval. Further, a need has arisen for an apparatus and method that are capable of stimulating the production interval to enhance production and gravel packing the production interval to prevent the production of fine particulate materials when production commences.

The present invention disclosed herein comprises an apparatus and method that is capable of enhancing production from a production interval by creating fractures throughout the entire interval and producing a substantially complete gravel pack of the wellbore adjacent to the production interval to prevent the production of fine particulate materials when production commences. The apparatus and method of the present invention achieves these results by progressively treating the production interval from one end to the other.

The apparatus comprises a sand control screen that is positioned within the wellbore and a fluid delivery tubular positioned adjacent to sand control screen in the wellbore. The fluid delivery tubular progressively allows fluid communication from the interior of the fluid delivery tubular to the exterior of fluid delivery tubular from a first end to a second end of the interval, thereby delivering the treatment fluid along the entire length of the interval.

The fluid delivery tubular may comprises a plurality of actuatable members. The actuatable devices may be rupture disks, pressure actuated one-way valves or other pressure actuated devices that are positioned along a portion of the length of the fluid delivery tubular such that the pressure required to actuate the actuatable members progressively increases from the first end to the second end of the interval. Alternatively, the actuatable device may be progressively actuated from the first end to the second end of the interval using signals sent from the surface using hard wire connections, fiber optics, hydraulics or wireless telemetry.

The fluid delivery tubular may alternatively comprise a perforated pipe having a plurality of removable members positioned on the interior or the exterior thereof. The removable members may be propellants or other combustible material members each having an initiator. The initiators may be activated using signals. Alternatively, the initiators may have pressure activated firing devices that are positioned such that the pressure required to fire the pressure activated firing devices progressively increasing from the first end to the second end of the interval.

The removable members may alternatively be friable members that are progressively removable from the first end to the second end of the interval. Each friable member may include a pressure actuated vibration generator. In this case, the pressure actuated vibration generators are positioned such that the pressure required to activate the pressure actuated vibration generators progressively increasing from the first end to the second end of the interval. Alternatively, each of the friable members may have a vibration generator that activated by a signal sent from the surface.

The method of the present invention comprises traversing the formation with the wellbore, locating a sand control screen eccentrically within the wellbore proximate the formation, positioning a fluid delivery tubular adjacent to the sand control screen within the wellbore, injecting a treatment fluid into the fluid delivery tubular, progressively establishing fluid communication between the interior of the fluid delivery tubular and the exterior of the fluid delivery tubular from the first end to the second end of the interval and terminating the injecting when the interval is treated.

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:

FIG. 1 is a schematic illustration of an offshore oil and gas platform operating an apparatus for progressively treating an interval of a wellbore of the present invention;

FIG. 2 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention in its initial position;

FIG. 3 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention after the first progression of the apparatus;

FIG. 4 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention after the second progression of the apparatus;

FIG. 5 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention after the third progression of the apparatus;

FIG. 6 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention after the next to last progression of the apparatus;

FIG. 7 is a half sectional view of an apparatus for progressively treating an interval of a wellbore of the present invention after the last progression of the apparatus;

FIG. 8 is a half sectional view of another embodiment of an apparatus for progressively treating an interval of a wellbore of the present invention after the first progression of the apparatus; and

FIG. 9 is a half sectional view of another embodiment of an apparatus for progressively treating an interval of a wellbore of the present invention in its initial position.

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.

Referring initially to FIG. 1, an apparatus for progressively treating an interval of a wellbore operating from an offshore oil and gas platform is schematically illustrated and generally designated 10 . A semi-submersible platform 12 is centered over a submerged oil and gas formation 14 located below sea floor 16 . A subsea conduit 18 extends from deck 20 of platform 12 to wellhead installation 22 including blowout preventers 24 . Platform 12 has a hoisting apparatus 26 and a derrick 28 for raising and lowering pipe strings such as work string 30 .

A wellbore 32 extends through the various earth strata including formation 14 . A casing 34 is cemented within wellbore 32 by cement 36 . Work string 30 includes various tools including a sand control screen assembly 38 which is positioned within wellbore 32 adjacent to formation 14 . Also extending from platform 12 through wellbore 32 is a fluid delivery tubular 40 having a fluid discharge section 42 positioned adjacent to formation 14 which is used to frac pack or gravel pack the production interval 48 between packers 44 , 46 . When it is desired to treat interval 48 , work string 30 and fluid delivery tubular 40 are lowered through casing 34 until sand control screen assembly 38 and fluid discharge section 42 are positioned adjacent to formation 14 including perforations 50 . Thereafter, a treatment fluid containing sand, gravel, proppants or the like is pumped down delivery tubular 40 to progressively treat interval 48 .

Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the apparatus for progressively treating an interval of a wellbore of the present invention is equally well-suited for use in 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 apparatus for progressively treating an interval of a wellbore of the present invention is equally well-suited for use in onshore operations.

Referring now to FIG. 2, therein is depicted a more detailed illustration of interval 48 . As illustrated, screen assembly 38 is eccentrically positioned within casing 34 and is adjacent to formation 14 . A wash pipe 52 is positioned within screen assembly 38 . Wash pipe 52 extends into a cross-over assembly 54 which is connected to work string 30 extending from the surface. Screen assembly 38 is designed to allow fluid to flow therethrough but prevent particulate matter of sufficient size from flowing therethrough. The exact design of screen assembly 38 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. For example, as illustrated, screen assembly 38 includes a perforated base pipe 56 having a wire 58 wrapped directly thereon. Alternatively, a plurality of ribs may be placed around the base pipe to provide stand off between the base pipe and the wire wrap. It should be noted by those skilled in the art that even though FIG. 2 has depicted a wire wrapped screen, other types of filter media could alternatively be used without departing from the principles of the present invention. For example, a fluid-porous, particulate restricting, sintered metal material such as a plurality of layers of a wire mesh that are sintered together to form a porous sintered wire mesh screen could alternatively be used.

In the illustrated embodiment, fluid discharge section 42 of fluid delivery tubular 40 includes a plurality of progressively actuatable members 60 A- 60 E. Suitable actuatable members 60 A- 60 E include rupture disks or valves and are preferably one-way valves that selectively allow fluid to flow from the interior of fluid delivery tubular 40 to the exterior of fluid delivery tubular 40 . Actuatable members 60 A- 60 E may be progressively actuated using a variety of known techniques such as sending a signal via a direct electrical connection, fiber optics, hydraulics, wireless telemetry including pressure pulses, electromagnetic waves or acoustic signals and the like. Actuatable members 60 A- 60 E are preferably pressure actuated one-way valves as explained in more detail below.

To begin the completion process, interval 48 adjacent to formation 14 is isolated. Packer 44 seals the near end of interval 48 and packer 46 seals the far end of interval 48 . Cross-over assembly 54 is located adjacent to screen assembly 38 , traversing packer 44 with portions of cross-over assembly 54 on either side of packer 44 . As illustrated, when the treatment operation is a gravel pack, the objective is to uniformly and completely fill interval 48 with gravel. To help achieve this result, wash pipe 52 is disposed within screen assembly 38 . Wash pipe 52 extends into cross-over assembly 54 such that return fluid passing through screen assembly 38 , indicated by arrows 62 , may travel through wash pipe 52 , as indicated by arrow 64 , and into annulus 66 , as indicted by arrow 68 , for return to the surface.

The fluid slurry containing gravel 70 is pumped down fluid delivery tubular 40 . In the illustrated embodiment, the fluid slurry containing gravel 70 travels to the far end of interval 48 through fluid delivery tubular 40 . As illustrated, a portion of fluid slurry containing gravel 70 exits the open end of fluid delivery tubular 40 . As gravel 70 builds up at the far end of interval 48 , the pressure within fluid delivery tubular 40 will begin to increase. Alternatively, the far end of fluid delivery tubular 40 could be closed in which case the pressure also increases in fluid delivery tubular 40 when the fluid slurry containing gravel travels to the far end.

Once the pressure in fluid delivery tubular 40 increases to a sufficient level, the progressive operation of the present invention may begin. Specifically, as best seen in FIG. 3, actuatable member 60 A is actuated which allows the fluid slurry containing gravel 70 to travel from fluid delivery tubular 40 through actuatable member 60 A into interval 48 . As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 A and interval 48 around the far section of screen assembly 38 forming the initial portion of the gravel pack. Some of the carrier fluid in the slurry may leak off through perforation 50 A into formation 14 while the remainder of the carrier fluid passes through screen assembly 38 , as indicated by arrows 62 , that is sized to prevent gravel 70 from flowing therethrough. The fluid flowing back through screen assembly 38 , as explained above, follows the paths indicated by arrows 64 , 68 back to the surface.

As the initial portion of the gravel pack becomes tightly packed, the pressure in fluid deliver tubular 40 again increases. At this point and as best seen in FIG. 4, actuatable member 60 B is actuated which allows the fluid slurry containing gravel 70 to travel from fluid deliver tubular 40 through actuatable member 60 B. As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 B and interval 48 around the adjacent section of screen assembly 38 forming the next portion of the gravel pack. While some of the carrier fluid in the slurry may leak off through perforation 50 B into formation 14 , the remainder of the carrier fluid passes through screen assembly 38 , as indicated by arrows 62 and returns to the surface as indicated by arrows 64 , 68 .

As this portion of the gravel pack becomes tightly packed, the pressure in fluid delivery tubular 40 again increases. At this point and as best seen in FIG. 5, actuatable member 60 C is actuated which allows the fluid slurry containing gravel 70 to travel from fluid delivery tubular 40 through actuatable member 60 C. As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 C and interval 48 around the adjacent section of screen assembly 38 forming the next portion of the gravel pack. While some of the carrier fluid in the slurry may leak off through perforation 50 C into formation 14 , the remainder of the carrier fluid passes through screen assembly 38 , as indicated by arrows 62 and returns to the surface as indicated by arrows 64 , 68 .

This process continues to progress from the far end of interval 48 toward the near end of interval 48 . Specifically, as best seen in FIG. 6, actuatable member 60 D is actuated which allows the fluid slurry containing gravel 70 to travel from fluid delivery tubular 40 through actuatable member 60 D. As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 D and interval 48 around the adjacent section of screen assembly 38 forming the next portion of the gravel pack. While some of the carrier fluid in the slurry may leak off through perforation 50 D into formation 14 , the remainder of the carrier fluid passes through screen assembly 38 , as indicated by arrows 62 and returns to the surface as indicated by arrows 64 , 68 .

As this portion of the gravel pack becomes tightly packed, the pressure in fluid delivery tubular 40 again increases. At this point and as best seen in FIG. 7, the last actuatable member, actuatable member 60 E, is actuated which allows the fluid slurry containing gravel 70 to travel from fluid delivery tubular 40 through actuatable member 60 E. As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 E and interval 48 around the adjacent section of screen assembly 38 to packer 44 forming the last portion of the gravel pack. While some of the carrier fluid in the slurry may leak off through perforation 50 E into formation 14 , the remainder of the carrier fluid passes through screen assembly 38 , as indicated by arrows 62 and returns to the surface as indicated by arrows 64 , 68 .

As can be seen, using the present invention for progressively treating an interval of a wellbore, a gravel pack may progress from one end of an interval toward the other end of an interval as fluid communication is progressively established along the entire length of the interval. Also, as should be apparent to those skilled in the art, even though FIGS. 2-7 present the progressive gravel packing of an interval of a wellbore in a vertical orientation with packer 44 at the top of interval 48 and packer 46 at the bottom of interval 48 , 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 44 is at the heel of interval 48 and packer 46 is at the toe of interval 48 .

Likewise, even though FIGS. 2-7 present the progressive gravel packing of an interval of a wellbore as being progressively performed from the far end of the interval to the near end of the interval, those skilled in the art will understand that the progressive gravel packing process of the present invention can alternatively be performed from the near end of the interval to the far end of the interval.

As stated above, there are numerous ways to progressively actuate actuatable members 60 A- 60 E. In the preferred method described above, the pressure created by the fluid slurry within fluid delivery tubular 40 progressively triggers the actuation of actuatable members 60 A- 60 E. One way to implement this method is to position actuatable members 60 A- 60 E within fluid delivery tubular 40 such that the pressure required to actuate actuatable members 60 A- 60 E progressively increases from the one end of interval 48 to the other end of interval 48 . For example, each adjacent actuatable member may be set to actuate at an incremental pressure above the prior actuatable members such as at increments of between about 50-100 psi. This assures a proper progression of the gravel pack by preventing any out of sequence activations. In addition, this approach is particularly advantageous in that the incremental pressure increase of adjacent actuatable members helps to insure that each section of the gravel pack is tightly packed prior to initiating the gravel packing of subsequent sections.

Alternatively, a hard wired or wireless telemetry system may be used to progressively actuate actuatable members 60 A- 60 E. For example, each actuatable member may be actuated by sending a signal addressed to a specific actuatable member. This assures a proper progression of the gravel pack by preventing any out of sequence activations. The signals may be manually or automatically sent based upon time or the pressure response in fluid delivery tubular 40 . For example, the signal to actuate the next actuatable member may be sent each time the pressure within fluid delivery tubular 40 reaches a particular level or each time the pressure within fluid delivery tubular 40 reaches the next preselected pressure increment. As with the direct pressure response method, the particular actuation sequence should insure that each section of the gravel pack is tightly packed prior to initiating the gravel packing of subsequent sections.

Referring now to FIG. 8, therein is depicted another embodiment of the present invention that is used for frac packing interval 48 . As illustrated, screen assembly 138 is eccentrically positioned within casing 34 and is adjacent to formation 14 . A wash pipe 152 is positioned within screen assembly 138 . Wash pipe 152 extends into a cross-over assembly 154 which is connected to work string 30 extending from the surface. Cross-over assembly 154 includes a valve 150 that is used to selectively allow and prevent the flow of return fluid to the surface via wash pipe 152 . Alternatively, a surface valve (not pictured) may be used to prevent the flow of return fluid. As illustrated, screen assembly 138 includes a perforated base pipe 156 having a wire 158 wrapped directly thereon, however, other types of filter media may alternatively be used.

In the illustrated embodiment, fluid discharge section 142 of fluid delivery tubular 140 includes a plurality of progressively actuatable members 160 A- 160 E which are preferable valves, such as pressure actuated one-way valves that selectively allow fluid to flow from the interior of fluid delivery tubular 140 to the exterior of fluid delivery tubular 140 . Actuatable members 160 A- 160 E may alternatively be progressively actuated using a variety of known techniques such as sending a signal via a hard wire connection, fiber optics, hydraulics, wireless telemetry including pressure pulses, electromagnetic waves or acoustic signals and the like.

To begin the completion process, interval 48 adjacent to formation 14 is isolated. Packer 44 seals the near end of interval 48 and packer 46 seals the far end of interval 48 . Cross-over assembly 154 is located adjacent to screen assembly 138 , traversing packer 44 with portions of cross-over assembly 154 on either side of packer 44 . As illustrated, when the treatment operation is a frac pack, the objective is to enhance the permeability of formation 14 by delivering a fluid slurry containing proppants 170 at a high flow rate and in a large volume above the fracture gradient of formation 14 such that fractures may be formed within formation 14 and held open by the proppants 170 . In addition, a frac pack also has the objective of preventing the production of fines by packing interval 48 with the proppants 170 . To help achieve these results, valve 150 of cross-over assembly 154 is initially in the closed position to prevent returns from flowing therethrough.

The fluid slurry containing proppants 170 is pumped down-fluid delivery tubular 140 . In the illustrated embodiment, the fluid slurry containing proppants 170 travels to the far end of interval 48 through fluid delivery tubular 140 . At this point, the fluid slurry containing proppants 170 may exit the far end of fluid delivery tubular 140 if it is open or builds up in fluid delivery tubular 140 if it is closed at the far end. In either case, the pressure within fluid delivery tubular 140 will begin to increase.

Once the pressure in fluid delivery tubular 140 increases to a sufficient level, the progressive operation of the present invention may begin. Specifically, as best seen in FIG. 8, actuatable member 160 A is actuated which allows the fluid slurry containing proppants 170 to travel from fluid delivery tubular 140 through actuatable member 160 A into interval 48 . As the fluid slurry containing proppants 170 is being delivered at a high flowrate and in a large volume above the fracture gradient of formation 14 and as valve 150 is closed, the fluid slurry fractures formation 14 as indicated by fracture 172 . As this portion of interval 48 begins to screen out, the pressure within fluid delivery tubular 140 will rise causing the progressive actuation of actuatable members 160 B- 160 E in the manner described above with reference to FIGS. 3-7. It should be noted that as the frac pack operation progresses some of the proppants 170 in the fluid slurry will remain in interval 48 , thereby packing interval 48 around screen assembly 138 . This packing process may be enhanced by reducing the flow rate of the fluid slurry toward the end of the treatment process and opening valve 150 to allow some returns to flow to the surface as described above.

Referring now to FIG. 9, therein is depicted another embodiment of an apparatus for progressively treating an interval of a wellbore. As illustrated, screen assembly 238 is eccentrically positioned within casing 34 and is adjacent to formation 14 . A wash pipe 252 is positioned within screen assembly 238 . Wash pipe 252 extends into a cross-over assembly 254 which is connected to work string 30 extending from the surface. Screen assembly 238 is designed to allow fluid to flow therethrough but prevent particulate matter of sufficient size from flowing therethrough. The exact design of screen assembly 238 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. For example, as illustrated, screen assembly 238 includes a perforated base pipe 256 having a wire 258 wrapped directly thereon. Other types of screen assemblies having other types of filter media may alternatively be used.

In the illustrated embodiment, fluid discharge section 242 of fluid delivery tubular 240 includes a plurality of perforations 244 A- 244 J that are selective blocked by removable members 260 A- 260 E. Removable members 260 A- 260 E may be constructed from a variety of materials such as combustible materials, referred to herein as propellants, that are removable by combustion, friable materials, including ceramics, that are removable by disintegration, or other materials that are removable in a downhole environment.

When removable members 260 A- 260 E are constructed from propellants, suitable initiators are attached to each removable member 260 A- 260 E such that the combustion process of each removable member 260 A- 260 E may be triggered independently. The initiators may be operated using a variety of known techniques including pressure actuation, electrical actuation, acoustic actuation or the like. For example, as explained in more detail below, the pressure generated by the treatment fluid can be used to trigger the initiators. Alternatively, a signal may be sent to trigger each of the removeable members 260 A- 260 E via a hard wired connection, fiber optics, hydraulics, a wireless telemetry system utilizing pressure pulses, electromagnetic waves or acoustic signals and the like.

When removable members 260 A- 260 E are constructed from friable materials, suitable vibration generators are attached to each removable member 260 A- 260 E such that the disintegration process of each removable member 260 A- 260 E may be triggered independently. The vibration generators may be operated using a variety of known techniques such as those described above.

To begin the completion process, interval 48 adjacent to formation 14 is isolated. Packer 44 seals the near end of interval 48 and packer 46 seals the far end of interval 48 . Cross-over assembly 254 is located adjacent to screen assembly 238 , traversing packer 44 with portions of cross-over assembly 254 on either side of packer 44 . As illustrated, when the treatment operation is a gravel pack, the objective is to uniformly and completely fill interval 48 with gravel. To help achieve this result, wash pipe 252 is disposed within screen assembly 238 . Wash pipe 252 extends into cross-over assembly 254 such that return fluid passing through screen assembly 238 , indicated by arrows 262 , may travel through wash pipe 252 , as indicated by arrow 264 , and into annulus 66 , as indicted by arrow 268 , for return to the surface.

The fluid slurry containing gravel 70 is pumped down fluid delivery tubular 240 . In the illustrated embodiment, the fluid slurry containing gravel 70 travels to the far end of interval 48 through fluid delivery tubular 240 . At this point, a portion of fluid slurry containing gravel 70 exits the open end of the fluid delivery tubular 240 if this end is open to flow.

As the pressure in fluid delivery tubular 240 increases to a sufficient level, the progressive operation of the present invention may begin. Specifically, removable member 260 A is removed which allows the fluid slurry containing gravel 70 to travel from fluid delivery tubular 40 through perforations 244 A- 244 B into interval 48 . As the fluid slurry containing gravel 70 enters interval 48 , the gravel 70 drops out of the slurry and builds up from formation 14 , filling perforation 50 A and interval 48 around the end section of screen assembly 238 forming the initial portion of the gravel pack. Some of the carrier fluid in the slurry may leak off through perforation 50 A into formation 14 while the remainder of the carrier fluid passes through screen assembly 238 , as indicated by arrows 262 , that is sized to prevent gravel 70 from flowing therethrough. The fluid flowing back through screen assembly 238 , as explained above, follows the paths indicated by arrows 264 , 268 back to the surface.

As the pressure within fluid delivery tubular 140 increases, removable member 260 B is removed which allows fluid flow through perforations 244 C- 244 D into interval 48 which packs perforation 50 B and the section of screen assembly 238 adjacent thereto. This process progresses from the far end of interval 48 to the near end of interval 48 by progressively removing removable member 260 C, which exposes perforations 244 E- 244 F, removable member 260 D, which exposes perforations 244 G- 244 H, and removable member 260 E, which exposes perforations 244 I- 244 J. Accordingly, the entire interval 48 is progressively gravel packed. After the treatment process is completed, a valve (not pictured) in fluid delivery tubular 240 may be closed to prevent the flow of fluids, for example production fluids, to the surface therethrough.

As stated above, there are numerous ways to remove removable members 260 from fluid discharge section 242 of fluid delivery tubular 240 to progressively establish fluid communication between the interior of fluid delivery tubular 240 and the exterior of fluid delivery tubular 240 . One preferred method allows the pressure created by the treatment fluid within fluid delivery tubular 240 to progressively trigger the removal of removable members 260 . For example, when the removable members 260 are constructed of propellant material, pressure activated firing devices may be attached to initiators that are coupled on each of the removable members 260 . The pressure activated firing devices are then positioned within fluid delivery tubular 240 such that the pressure required to fire the pressure activated firing devices progressively increases from, for example, the far end of interval 48 toward the near end of interval 48 . Each adjacent pressure activated firing device may be set to fire at an incremental pressure above the prior pressure activated firing device such as at increments of between about 50-100 psi. This assures a proper progression of the gravel pack by preventing any out of sequence activations. In addition, this approach is particularly advantageous in that the incremental pressure increase of adjacent pressure activated firing devices helps to insure that each section of the gravel pack is tightly packed prior to initiating the gravel packing of subsequent sections.

Alternatively, a signal may be used to progressively trigger the removal of removable member 260 . For example, when the removable members 260 are constructed of a friable material, vibration generators may be coupled on each of the removable members 260 . Each vibration generator may be activated by a particular signal addressed specifically for that vibration generator. This assures a proper progression of the gravel pack by preventing any out of sequence activations. The signals may be manually or automatically sent based upon time or the pressure response in fluid delivery tubular 240 . For example, the signal to remove the next removable member 260 may be sent each time the pressure within fluid delivery tubular 240 reaches a particular level or each time the pressure within fluid delivery tubular 240 reaches the next preselected pressure increment. As with the direct pressure response method, the particular removal sequence should insure that each section of the gravel pack is tightly packed prior to initiating the gravel packing of subsequent sections.

Even though FIG. 9 has depicted removable members 260 A- 260 E as being positioned on the interior of fluid delivery tubular 240 , it should be understood by those skilled in the art that removable members could alternatively be positioned on the exterior of fluid delivery tubular 240 without departing from the principles of the present invention. Also, even though the embodiment of the apparatus for progressively treating an interval of a wellbore described in FIG. 9 referred to permanently removing the removable members, other types of removable members that are temporarily removed may alternatively be used, including, but not limited to, sliding sleeves and the like, without departing from the principles of the present invention.

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.