GB2289489A - Treating formations using alternative flowpaths - Google Patents

Abstract

Apparatus for treating multiple strata in a single operation from a single wellbore which penetrates a treatment interval which, in turn, includes a plurality of strata which, in turn, have different permeabilities. A treating fluid (e.g. consolidating agent, acid, etc.) is delivered directly to different levels within a section of the wellbore adjacent the interval to be treated through a plurality of alternate paths 31c, 32c; 31d, 32d which, in turn, lie substantially adjacent to the strata to be treated. <IMAGE>

Description

Method and Apparatus for Treating Formations Using Alternative Flowpaths The present invention relates to a method and apparatus for treating formations using alternative flowpaths. The method and apparatus are especially concerned with formations having strata of different pereabilities.

In producing hydrocarbons or the like from a well, it is not uncommon to treat the hydrocarbon-bearing formations to improve production and/or to extend the operational life thereof. For example, many producing reservoirs lie in unconsolidated and/or fractured formations which routinely produce large volumes of particulate material (e.g.

sand) along with the desired fluids.

If such formations are not treated, the continued production of particulates will generally create a variety of problems which result in added expense and considerable downtime of the well. That is, the production of particulates may cause (1) severe erosion of the well tubing and other production equipment; (2) partial or complete clogging or the flow from the well which requires workover of the well; (3) caving in the formation and collapse of the well casing; and (4) extra cost in processing the production fluids at the surface and disposal of the produced particulates. Accordingly, it is common to use sand control techniques to treat such formations to control this production of particulates.

One well knawn well treatment method used for sand control is generally referred to as "consolidating' the formation. In a typical sand consolidating method, a consolidating agent (e.g. thermosetting resin) is flowed down the wellbore under pressure and into the formation. The resin normally penetrates several inches into the formation where it occupies the pore spaces and envelopes the sand grains in the formation adjacent the wellbore. The formation temperature causes the consolidating agent to set and harden.As the resin hardens, it coats and cements the sand grains together but it also shrinks to about one-half to one-third of its original liquid volume thereby leaving open pore space, i.e. permeability, in the formation to allow production of formation fluids therethrough.

Other reservoirs lie in formations which are comprised prinarily of limestople or other carbonate materials which adversely affect the permeability of the formation. In these types of reservoirs, it is common to "acidize" the formation wherein an acid, e.g. hydrochloric acid, is injected down the wellbore and into the formation to dissolve at least part of the carbonate material to thereby increase the permeability and stunulate production.

In a typical well treatment method such as described above, the section of the wlellberre which lies adjacent the formation interval to be treated is isolated with packers ar the like and a tubing string is lowered into the isolated section. The treating fluid is flowed out of the lower end of the tubing and into the isolated wellbore section fran which it is forced under pressure into the formation being treated. Unfortunately, many hydrocarbon-bearing reservoirs (i.e.

producing interval) are composed of several different strata or zones of production which have varying permeabilities.

The mare permeable strata yield their formation fluids easily while the less permeable strata produce more slowly, if at all. When the full thickness of such a reservoir is subjected to treatment (e.g.

sand consolidation, acidizing, etc.) in a single operation, the treating fluid tends to take the path of least resistance and enters the more permeable strata or zone with little or no fluid entering the less permeable zones. Shen the well is returned to production, the untreated zones within the formation interval normally fail thereby allowing sand production where the well treatment is for sand control or continued decreased production where the well treatment is an acid treatment.

In known prior art treating methods of this type, the varying permeabilities of the strata have required that zones within the reservoir or formation interval be isolated or sealed off so that a particular zone can be treated individually. A tubing string is lowered to a point adjacent the isolated zone and the treating fluid is flowed from the lower end thereof to be delivered into the wellbore adjacent the isolated zone; usually the least permeable zone first. After the first zone is treated, a different zone is isolated and the procedure is repeated until all of the desired zones within the production interval are treated. It can be seen that such treatments can not be carried out in a single operation and are time-consuming and are generally very expensive to carry out.

According to one aspect of the invention there is provided apparatus for treating multiple strata within a treatment interval in a single operation from a single wellbore, said apparatus comprising a workstring having alternative path means for delivering treatment fluid directly to the respective, different strata of said interval to be treated.

In a first embodiment the workstring comprises a conduit adapted to be lowered from the surface to terminate within the interval to be treated; and said alternative path means comprises a plurality of openings spaced along that section of said conduit which lies substantially adjacent said different strata to be treated.

In a second embodiment the alternative path means comprises a plurality of conduits of different lengths adapted to terminate at different levels adjacent the respective strata to be treated. Preferably the workstring either comprises: an outer tubular member enclosing said plurality of conduits and being perforated along a section thereof which lies substantially adjacent the interval to be treated; or a central tubular member with means to mount said plurality of conduits on the outer surface thereof.

In a third embodiment the workstring comprises a conduit having a perforated section adapted to lie substantially adjacent the interval to be treated; and said alternative path means comprises a plurality of shunt tubes, said tubes having different lengths and being mounted within said perforated section of said conduit so that their upper ends lie substantially adjacent the upper and of the perforated section and their respective lower ends terminate at different levels within said perforated section.

In a fourth embodiment the workstring comprises a conduit adapted to extend downward into said wellbore to a point substantially adjacent the top of said interval to be treated; and said alternative path means comprises a plurality of tubes having different lengths fluidly connected to the lower end of said conduit whereby the respective lower ends of said tubes are adapted to terminate at different levels adjacent the respective strata to be treated.

According to another aspect of the invention there is provided a method for treating multiple strata in a treatment interval in a single operation from a single cased wellbore which penetrates said treatment interval and wherein said strata have different permeabilities, said method comprising: delivering treating fluid directly to different strata through alternative flowpaths to thereby treat the different strata.

Preferably the method includes the step of perforating said cased wellbore at different levels adjacent the different strata of the treatment interval, whereby said treating fluid can be delivered into a section of the wellbore adjacent said treatment interval through alternative flowpaths directly to the different levels within said section and through the perforations in the cased wellbore to thereby treat the different strata in said treatment interval.

Preferably the method includes the step of isolating a section of the wellbore substantially adjacent the treatment interval before delivering said treating fluid through said alternative flowpaths.

The treating fluid is desirably delivered simultaneously through all of the alternative flowpaths.

The treating fluid may be, for example, a sand consolidating agent, or an acid.

Reference is now made to the accompanying drawings, in which: Figure 1 is an elevational view, partly in section, of a well treating apparatus having alternative flowpaths in accordance with the present invention positioned in an operable position within a wellbore adjacent a formation to be treated; Figure 2 is an elevational view, partly in section, of an embodiment of the present well treating apparatus having different alternative flowpaths in accordance with the present invention; Figure 3 is an elevational view, partly in section, of a further embodiment of the present well treating apparatus; Figure 4 is an elevational view, partly in section, of still another embodiment of the well treating apparatus according to the invention; Figure 5 is an elevational view, partly in section, of a still further embodiment of the well treating apparatus according to the invention;; Figure 6 is an elevational view, partly in section, of an embodiment of the well treating apparatus according to the invention having shunt tubes as alternative flowpaths; and Figure 7 is an elevational view, partly in section, of an embodiment of the invention wherein the well treatment method is carried out within a previously gravel-packed interval of the wellbore.

Referring more partiollarly to the drawings, Figure 1 illustrates the lower end of a producing and/or injection well 10. Well 10 has a wellbore 11 which extends from the surface (not shown) through treatment interval 12. wel1bo 11 is typically cased with a casing 13 which, in turn, is cemented (not shown) in place. While the present invention is illustrated in relation to a vertical, cased wellbore, it should be recognised that it can equally be used in open-hole and/or underred completions as well as in inclined and horizontal welibares, as the situation dictates.

As illustrated, treatment interval 12 is comprised of a plurality (only two shown) of zones 14, 15 which have different pereabilities.

casing 13 is perforated at different levels to provide at least two sets of perforations 16, 17 which lie substantially adjacent zones 14, 15, respectively. Since the present invention is applicable in horizontal and inclined wellbores, the terms "upper and lower", "top and bottan', as used herein are relative te:rs and are intended to apply to the respective positions within a particular wellbore while the term "zones" is meant to refer to respective positions lying along the wellbore between the terminals of the treatment interval.

Well treating apparatus 20 of the present invention is positioned in wellbore 11 substantially adjacent treatment interval 12. Fracturing apparatus 20 is comprised of a tubing or workstring 21 which is closed at its lower end 22 and which extends to the surface (not shown).

Tubing string 21 has a plurality of openings (e.g. upper and lower sets of openings 23, 24, respectively) which are spaced above the lower end 22 to coincide roughly with casing perforations 16, 17, repectively. Appropriate packers 25 and 27 or other means, e.g.

columns of liquid in the well annulus, "isolate" the section 26 of wellbore 11 which lies adjacent treatment interval 12. As used herein, the term "isolated section" refers to the section of the wellbore which lies adjacent the interval to be treated.

In operation, a treating fluid, e.g. consolidating agent (resin, sodium silicate, or the like) or acid (hydrochloric, etc.) is pumped down wcrkstrm g 21 and out through upper and lower openings 23, 24 into the isolated section 26 of welIrore 11. As section 26 fills with treating fluid and the pressure in=eases, the treating fluid is forced through casing perforations 16, 17 and contacts zones 14, 15 of the treatment interval 12. However, since, as illustrated, zone 15 has a higher permeability, the treating fluid takes the path of least resistance and substantially all of the fluid will flow into zone 15.

In a conventional well treating operation where the treating fluid only exits through the lower end of a workstring, the treating fluid will continue to flow into zone 15 with little or no fluid being forced through the upper casing perforations 16 into zone 14. This uneven distribution of treating fluid over the treatment interval results in little or no treatment of the less permeable zones in the treatment interval. This, in turn, results in the other zones having to be individually isolated, the workstring having to be repositioned within these zones, and treatment fluid having to be flowed separately to each of these zones in order to adequately treat the entire treatment interval 12.

In the present invention, even while the treating fluid is flowing into the more permeable zone 15, treating fluid will also continue to flow through upper openings 23 (i.e. alternative flowpaths) in the tubing string 21 to be delivered directly adjacent the less permeable zones to thereby treat the lesser permeable zone 14 through casing perforations 16. While only two zones in the treatment interval and two sets of openings in both the workstring and casing have been illustrated, it should be understood that the workstring and casing may have openings at more than two levels to service more than two zones in the desired treatment interval.The important feature is to provide alternative flow paths for the treating fluid to the different levels or zones of the treatment interval so all of the zones can be treated in a single operation from a single tubing string. That is, the treating fluid will continue to be delivered to the respective levels in the interval to treat the respective zones until all of the zones have been treated regardless of the permeabilities of the respective zones.

While in most operations the treating fluid will flow simultaneously through all of the alternative flowpatns to all of the different levels within the treatment interval, there may be tines that it will be desired to treat the strata of a particular treatment interval in a preferred sequence. Accordingly, the respective openings in the workstring can be sized so that the treating fluid will seek the path of least resistance and sustatially flow primarily through larger zings in the workstring which are positioned adjacent the first strata to be treated.After the first strata has been substantially treated, the pressure builds up adjacent the large opening wherein the bulk of the fluid will then flow through a second set of smaller openings positioned adjacent a second strata, and so forth until all of the strata have been treated. Also, valve means (not shown), e.g.

discs which rupture at different pressures, may be used to close selected openings in the workstring at particular levels so that no flow will occur through these openings until a desired pressure is reached within the workstring.

Figure 2 illustrates another embodiment of the present well treating apparatus. Treating apparatus 20a is cO'prised of a bunile or plurality of conduits 31, 32 (only two shown) which are monted and encased within perforated carrier tube 33 which, in turn, provides structural in*xyrity and support for the conduits 31, 32. Conduits 31, 32 may be of different lengths (as shown) so that they terminate at different levels within tube 33 and open only at their lower ends or they may be of equal or varying lengths with openings (not shown) at different levels to coincide substantially with the different perforations in casing 13a.

As seen in Figure 2, treating fluid is delivered aut the lower ends of the individual conduits 31, 32 to fill the lower end of carrier tube 33. The fluid flows out of the perforations in tube 33 and fills isolated section 26a of the wellbore. As described. above, the fluid initially enters the more permeable zone 15a. When this occurs, the treating fluid continues to be delivered through conduit 32 to treat the second zone in the treatment interval.

Figure 3 illustrates a well treating apparatus 30b having a plurality of conduits 31a, 32a which are mounted on and carried by a central tubular member 33a. Bands 34 or the like secure the conduits onto the outer surface of central member 33a. The conduits 31a, 32a terminate at different levels and are used to carry aut the well treatment operation in the same manner as described above in relation to the well treating apparatus 20a.

Figures 4 and 5 illustrate further din,ts of the present invention wherein well treating apparatus 30c is comprised of a workstring 21b, 21c, respectively, which is adapted to extend dorarard into the wellbore to a point which is substantially adjacent the top of the treatment interval (not shown). In Figure 4, a single, reduced diameter conduit 35 is connected to the bottan of workstring 21b and includes openings 36, 37 (alternative flowpaths) which are spaced to lie adjacent the zones to be treated when the apparatus 30c is in an operable position within the well.In Figure 5, a plurality of conduits 31c, 32c (only two shown) having different lengths are connected to the bottom of workstring 21c and are in fluid csnunication therewith. When apparatus 30c is in an operable position within the welibore, conduits 31c, 32c will terminate at different levels within the wellbore adjacent different zones of the treatment interval. Each of the conduits 31c, 32c are perforated along their respective lower ends to provide a plurality of openings 40, 41, respectively.Treating fluid flows down tubing string 21c and is delivered directly to different levels within the isolated section 26c through the openings in the conduits (i.e. alternative paths) to carry out the treating operation as described above.

Still another embodiment of the present invention is shown in Figure 6 wherein the well treating apparatus 30d is comprised of a carrier tube 33d having a perforated lower section which is adapted to lie subsently adjacent to treatment interml when apparatus 30d is in an operable position within wellbore 11d. A plurality of shunt tubes 31d, 32d (only two shown) of different lengths are mounted within the perforated section of the workstring with their upper ends lying substantially adjacent the upper end of the perforated section and their respective lower ends terminating at different levels within the perforated section.The shuts tubes are open at both their upper and lower ends to allay fluid flow rethrough.

In operation, treating fluid flows down the workstring and out the perforated section at the lower end thereof. At the same time, treating fluid is flowing through the shunts tubes 31d, 32d (i.e.

alternative paths) and the adjacent openings in the perforated section to be delivered directly to the respective different levels. Even as the treating fluid is flowing into the more permeable zones, treating fluid is also flowing through the other shunt tubes 31d, 32d to treat the other zones within the treatment interval.

Figure 7 discloses the present invention as carried out in a previously gravel-paciçed section of the wellbore. A screen 50 is set adjacent the perforations in the casing 13 and is surrcsrded with a mass of gravel 51. Workstrirg 52 having a perforated conduit 53 muted on the lower end thereof is run into and landed on screen 50.

Treating fluid is then flowed down the tubing and out through the openings in the conduit 52 to deliver treating fluid directly to the different levels within the screen. The fluid will flow out the screen and through the gravel at the respective levels to treat the different zones in the treatment interval in the same manner as described above.

Claims (14)

1. Apparatus for treating multiple strata within a treatment interval in a single operation from a single wellbore, said apparatus comprising a workstring having alternative path means for delivering treatment fluid directly to the respective, different strata of said interval to be treated.

2. Apparatus according to claim 1, wherein said workstring comprises a conduit adapted to be lowered from the surface to terminate within the interval to be treated; and said alternative path means comprises a plurality of openings spaced along that section of said conduit which lies substantially adjacent said different strata to be treated.

3. Apparatus according to claim 1, wherein said alternative path means comprises a plurality of conduits of different lengths adapted to terminate at different levels adjacent the respective strata to be treated.

4. Apparatus according to claim 3, wherein said workstring comprises an outer tubular member enclosing said plurality of conduits and being perforated along a section thereof which lies substantially adjacent the interval to be treated.

5. Apparatus according to claim 3, wherein said workstring comprises a central tubular member; and means to mount said plurality of conduits on the outer surface thereof.

6. Apparatus according to claim 1, wherein said workstring comprises a conduit having a perforated section adapted to lie substantially adjacent the interval to be treated; and said alternative path means comprises a plurality of shunt tubes, said tubes having different lengths and being mounted within said perforated section of said conduit so that their upper ends lie substantially adjacent the upper end of the perforated section and their respective lower ends terminate at different levels within said perforated section.

7. Apparatus according to claim 1, wherein said workstring comprises a conduit adapted to extend downward into said wellbore to a point substantially adjacent the top of said interval to be treated; and said alternative path means comprises a plurality of tubes having different lengths fluidly connected to the lower end of said conduit whereby the respective lower ends of said tubes are adapted to terminate at different levels adjacent the respective strata to be treated.

8. A method for treating multiple strata in a treatment interval in a single operation from a single cased wellbore which penetrates said treatment interval and wherein said strata have different permeabilities, said method comprising: delivering treating fluid directly to different strata through alternative flowpaths to thereby treat the different strata.

9. A method according to claim 8, further comprising perforating said cased wellbore at different levels adjacent the different strata of the treatment interval, whereby said treating fluid can be delivered into a section of the wellbore adjacent said treatment interval through alternative flowpaths directly to the different levels within said section and through the perforations in the cased wellbore to thereby treat the different strata in said treatment interval.

10. A method according to claim 8, further comprising isolating a section of the wellbore substantially adjacent the treatment interval before delivering said treating fluid through said alternative flowpaths.

11. A method according to claim 8, wherein said treating fluid is delivered simultaneously through all of the alternative flowpaths.

12. A method according to claim 8, wherein said treating fluid is a sand consolidating agent.

13. A method according to claim 8, wherein said treating fluid is an acid.

14. A method according to claim 8, wherein said treating fluid is delivered to said alternative flowpaths through a workstring which is positioned in the wellbore.