WO2002024771A2

WO2002024771A2 - Subterranean wellbore and formation sealing compositions

Info

Publication number: WO2002024771A2
Application number: PCT/EP2001/010909
Authority: WO
Inventors: Keng S. Chan
Original assignee: Sofitech NV; Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Holdings Ltd
Current assignee: Sofitech NV; Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Holdings Ltd
Priority date: 2000-09-20
Filing date: 2001-09-20
Publication date: 2002-03-28
Anticipated expiration: 2003-03-20
Also published as: AU2002224768A1; WO2002024771A3

Abstract

Sealing compositions useful in subterranean wellbore completion and remedial operations are provided. The compositions generally comprise a cationic monomer, a cross-linker, a polymerization initiator, and a thixotropic agent. The compositions can further comprise a delaying agent, a gel stabilizer, or a complexing agent. The disclosed compositions provide desirable properties for use in a number of sealing and isolation applications, and are particularly well suited for use in the completion of horizontal or highly deviated wells.

Description

Subterranean Wellbore and Formation Sealing Compositions

Technical Field of the Invention This invention relates generally to the sealing and isolation of subterranean wellbores and formations, and, more particularly, to improved sealing compositions useful in selectively isolating zones of oil wells.

Background of the Invention Various types of sealing compositions have been used in well completion operations, such as the primary bonding of casing and liner in the wellbore, preventing corrosion of steel pipes, or consolidating gravel packs or incompetent sands in formations. Sealing compositions have also been widely used for remedial operations, such as sealing leaks, cracks, or voids either in the formation or in casing and liners, placing plugs in the wellbore or in zones or formations containing undesirable fluids, placing temporary plugs in lieu of ■ • packers to isolate zones or formations, or filling external casing packers.

For example, in conventional well completion, a tubular liner or casing is run into the well after it is drilled, and a sealing compositions such as cement is pumped between the casing and the wellbore wall and allowed to set. This isolates the various zones of the well from each other and so prevents, for example, oil from entering aquifers which might be at lower pressure. Where it is desired to allow formation fluids such as oil or gas to enter the well, the lining and cement are perforated by an explosive charge in order to provide a channel for the fluid to enter the lining so that it can pass more sensitive zones without causing damage or pollution.

This technique generally works well in wells that are more or less vertical, since it is straightforward to run the liner into the well, to ensure it is centralized, and to ensure that cement is placed evenly around the liner and bonds to both the liner and the wellbore. However, when the well is deviated from vertical—particularly when highly deviated, even horizontal-certain problems can occur. In particular, it is often difficult to ensure that the liner remains central in the well before the cement is placed. There is a tendency for the liner to lie on the lower side of the well such that when the cement is pumped it flows easily along the high side of the liner, but little if any penetrates around the low side. This can lead to bonding problems. Also, the tools used to perforate the liner and cement can become eccentric, and then do not operate efficiently. The horizontal parts of deviated wells are often arranged so as to remain within a producing formation, and therefore in these sections good communication between the formation and the liner is required, whereas in the vertical sections leading to the surface good zonal isolation is required. One technique that is used in such horizontal situations is to provide a perforate liner—for instance, a slotted, perforated, or predrilled liner, or a screen or a pre-packed screen—in the horizontal section of the well without any cementing to bond the liner to the wellbore. The annular gap between the liner and the wellbore is either left "empty" or (as may be preferable in certain circumstances) is packed with suitably-sized gravel. However, problems can arise if it is desired to perform a selective well treatment on, or produce selectively from, one zone in the horizontal section. This is because inside a perforate liner there is no way of isolating the zone in question from the remainder of the well by using packers, as with conventional liners, because fluid can by-pass the plug by exiting the liner into the annular space therearound.

One technique that has been proposed to overcome this problem is to provide one or more packers around the outside of the liner (external casing packers) which contact the wellbore and provide localized restriction to communication outside the liner. This then allows packers inside the liner to be used to isolate a portion of the well. Unfortunately, there are also problems associated with the use of external casing packers. For example, they must be sealed against the wellbore, they must be positioned in advance, and they substantially increase the cost of the completion.

For chemical sealing or isolation applications, various requirements must be met. For example, a sealing fluid composition useful in wellbore applications is preferably one that can be pumped through fine screens, gravel-packs, slotted liners, etc., in a one-way path, without flowing back. The sealing compositions are desirably solid-free or contain only very small particles that can pass through a fine screen or penetrating porous subterranean formation (i.e., are essentially solid-free). Materials that have been used to form solid-free gels include cross-linkable monomer or polymer solutions, however such materials do not generally provide sufficient gel strength for withstanding the high differential pressure experienced in a wellbore. To achieve higher gel strength, higher polymer or monomer concentrations are needed. However, at high polymer concentrations, the fluid becomes unacceptably viscous and can become waxy and/or semi-solid. In view of the ever increasing demand for improved well completion and remedial operation techniques, the present invention provides improved sealing compositions which overcome, or at least reduce the effects of, one or more of the aforementioned problems.

Summary of the Invention In one aspect of the present invention, there are provided sealing compositions for completion or remedial operations in subterranean zones penetrated by a borehole. The sealing compositions comprise polymerizable monomer systems in combination with thixotropic materials. Preferably, the polymerizable monomer system includes:

( 1 ) a polymerizable monomer, (2) a polymerization initiator effective for causing the formation of a polymer from said monomer;

(3) a cross-linking agent effective for cross-linking the polymer once it has polymerized; and, to the extent necessary,

(4) a delaying agent.

According to another aspect of the present invention there is provided a method of forming a plug in a region in a well, in which method a volume of a sealing composition in accordance with this invention is pumped, conveniently via a suitable packer apparatus such as a pair of region delimiting packers, into the region, which volume is sufficient to displace substantially all other fluids from the region to be plugged.

According to another aspect of the invention, there is provided a method of placing a plug in a region around a perforate liner in a wellbore, e.g., a horizontal wellbore, the method comprising: placing a pair of packers inside the liner where the plug is to be positioned, the packers being spaced apart so as to define both a chamber inside the liner which includes a perforation and also a region to be plugged outside the liner; and pumping a predetermined volume of sealing composition in accordance with this invention into the chamber and, via the perforation, into the region to be plugged, which predetermined volume of material is sufficient to displace substantially all other fluids from the region to be plugged.

According to another aspect of the invention, a method is provided for cementing a casing or pipe in a borehole, comprising introducing into the annular space between the outer surface of the casing or pipe and the wall of the borehole a sealing composition of this invention; and allowing the material to set.

Brief Description of the Drawings The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

Figure 1 illustrates the shear thinning behavior of an illustrative sealing composition of the present invention;

Figure 2 illustrates the effect of delaying agent concentration on the gelling time of an illustrative sealing composition according to the present invention; and

Figure 3 illustrates the gel extrusion strength as a function of time for an illustrative sealing composition of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description of Illustrative Embodiments

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The sealing fluid compositions of the present invention find use generally in subterranean wellbore and formation isolation, such as those discussed above, and find particular application in known techniques for the completion of horizontal wells employing slotted or predrilled liners.

The sealing compositions of the invention broadly employ the use of polymerizable monomer systems in combination with thixotropic materials. The polymerizable monomer system will generally include:

(1) a polymerizable monomer,

(2) a polymerization initiator effective for causing the formation of a polymer from said monomer;

(4) a delaying agent.

Polymer science is a well developed art and numerous polymerizable monomer systems will be readily apparent to the skilled individual. For the applications addressed by this invention, those monomers that will find particular utility will include, for example, dimethyldiallylammonium chloride, hydroxymethlylacrylamide, hydroxylethylacrylate, Ca- diacrylate, trimethanolpropanetriacrylate and other like materials.

The sealing compositions will further comprise one or more polymerization initiators. The selection of polymerization initiator will vary depending on the particular monomer that is used, and the compatibility of various monomers and initiators will be understood by those skilled in the art. Illustrative examples of polymerization initiators employable herein can include oxidizing agents, persulfates, peroxides, azo compounds such as 2,2'-azobis(2- amidinopropane)dihydro-chloride and oxidation-reduction systems.

The sealing compositions of the present invention further comprise one or more cross- linking agents. The cross-linking agent or agents used in the sealing compositions of this invention is selected so as to be capable of cross-linking the polymer that is formed following polymerization of the monomers described above. Many cross-linking systems are known in the art and may be used in accordance with this invention, including, without limitation, known metallic and/or organic cross-linkers, e.g., methylenebisacrylarnide which is commercially available, triallylamine, and the like. The compatibility of a cross-linking agent with specific types of polymer is also known. Thus, the selection of cross-linking agent will depend on the particular polymer that is to be produced from the polymerizable monomers discussed above.

Moreover, to the extent necessary, the sealing compositions will also comprise one or more delaying agents. Many monomers useful in accordance with this invention will polymerize very rapidly in the presence of an appropriate initiator. This is undesirable for most wellbore isolation applications since the duration of a particular isolation procedure may be much longer than the polymerization time for a given monomer/initiator combination. Consequently, in order to controllably delay the polymerization of the monomer for a predetermined duration of time, known delaying agents can be used in the sealing compositions of this invention. As illustrated in Figure 2, the gelling time of the compositions can be manipulated by varying the concentration of delaying agent that is present.

Delaying agents suitable for use in the present composition will vary depending on the monomer system being utilized. Illustrative examples of such agents can include, for example, potassium ferricyanide, hydroquinone, thiosulfate, and the like.

In order that the sealing composition can meet the various requirements for subterranean applications, it is desirable in many instances that the compositions have thixotropic properties. This is because during pumping the confining pressure keeps the fluid tight against the borehole walls and liner surface. However, once pumping stops there are no containment pressures so the plug must become substantially "self-supporting" very quickly so as not to move significantly along the annulus.

Therefore, the sealing compositions of this invention, in addition to the monomer system described above, will generally further comprise one or more thixotropic agents. Such agents are particularly useful in applications where it is desired to prevent the compositions from sagging or slumping under gravity, such as for operations in extended horizontal and/or other wells deviated from vertical. Such agents are well known and can include, for example, chemical systems containing microfine clay particles, chemically treated clay particles, mixtures of these clay particles, polymer systems such as hydroxy ethyl cellulose polymers, alkyl quaternary ammonium bentonite, or alkyl quaternary ammonium montmorillonite, and other like materials. By thixotropic, it is meant that the shear yield strength must be such that under the likely ambient conditions the fluid flows readily when being pumped and yet rapidly gels when pumping stops. Naturally, acceptable values will depend upon the physical parameters of the well, of the wellbore, and of any tubing therein.

The selected chemicals should be compatible. However, preferred order of mixing is to mix the polymerizable materials and their associated polymerization initiators, cross- linkers, and stabilizers first as a base fluid before adding thixotropic agents and their associate complexing agents.

The sealing compositions will generally be essentially solid-free and therefore readily pumpable through screens and openings less than about 75 microns. The sealing compositions are generally pumpable through pipe or tubing as small as about 4 mm in diameter. Moreover, the sealing compositions will also typically have high initial yield stress and can retain the form last pumped with little or no backflow through the screens and openings under normal wellbore pressure conditions. Also," the sealing compositions have high gel strength in the bore hole or casing annulus, yielding higher extrusion pressure gradients than other gel systems in comparable wellbore completion and flow geometries.

In certain illustrative embodiments of the invention, the sealing compositions will be comprised of about 10-90 wt.%, more preferably about 30-60 wt.%, of the one or more monomers, about 0.1-2 wt.%, preferably about 0.25-1 wt.%, of one or more cross-linking agent; about 0.01-2 wt.%, preferably from about 0.05-0.5 wt.%, of one or more polymerization initiators, about 0.1-10 wt.% of one or more delaying agents, and about 1-10 wt.%, of one or more thixotropic agents. These levels are intended to be illustrative only and the skilled individual will recognize that the levels of each component present in the sealing compositions described above can be readily varied to suit the needs of a given implementation.

Numerous additives for use in sealing compositions are known in the art and may also be formulated with the sealing compositions of this invention if desired. Of course, it will be preferred that any additives employed do not adversely impact the ability of the sealing compositions to function in their intended applications. Additives that one skilled in the art might consider employing in the sealing compositions include, for example, gel stabilizers, delaying agents, antioxidants such as zirconium lactate, tetrasodium ethylenediaminetetraacetic acid, sodium hydroxide, potassium ferricyanide, hydroquinone, or thiosulfate.

Therefore in many illustrative embodiments, the sealing compositions will further comprise one or more complexing agents and/or gel stabilizing agents for improving the thixotropic properties and gel strength. Again, the examples are zirconium lactate, tetrasodium ethylenediaminetetraacetic acid, sodium hydroxide.

The sealing compositions disclosed herein are suitable for use in any of a variety of subterranean applications, such as the primary bonding of casing and liner in the wellbore, preventing corrosion of steel pipes, or consolidating gravel packs or incompetent sands in formations. They are particularly well suited for various remedial operations, such as sealing leaks, cracks, or voids either in the formation or in casing and liners, placing plugs in the wellbore or in zones or formations containing undesirable fluids, placing temporary plugs in lieu of packers to isolate zones or formations, or filling external casing packers. It will be appreciated, of course, that it may be necessary to formulate a sealing composition that is suited to the variety of liner being employed, for certain sealing compositions will be more compatible with some types of liners than others. Which sealing compositions are suitable for which liner variety will be evident to those skilled in the art.

Therefore, one aspect of this invention provides a means for achieving zonal isolation in a well with a perforate liner. The perforate liner can take any suitable form. Typically, it is a slotted liner or a pre-packed screen. This is achieved by pumping a fluid sealing composition of the present invention into the relevant annular region between the liner and the wellbore and allowing the sealing composition to set to form a plug that prevents communication from one side to the other except via the liner. The sealing compositions can be conveniently pumped either from the surface to the chamber via a tube, or by means of a downhole pump from a reservoir located near the packers in the wellbore.

In one particularly illustrative embodiment, the present invention provides a method of placing a plug in a region around a perforate liner in a wellbore, the method comprising placing a pair of packers inside the liner where the plug is to be positioned, the packers being spaced apart so as to define a chamber inside the liner which includes a perforation and also a region to be plugged outside the liner. A predetermined volume of sealing composition is then pumped into the chamber and, via the perforation, into the region to be plugged, which predetermined volume of sealing composition fluid is sufficient to displace substantially all other-fluids from the region to be plugged.

Additionally, the volume of the fluid sealing composition employed is preferably such that when in the annulus it does not extend beyond the limit of the packers, but nevertheless it is possible for the fluid to extend past them. However, to prevent the fluid from then re- entering the liner, it is often desirable that the critical pressure drop along the annular region being plugged does not exceed the pressure drop across the slots in the liner, i.e. no fluid enters the liner beyond the packer.

Thus, the sealing composition preferably will have rheological properties effective to displace other fluids when pumped into the region and to remain there while it sets so as to seal against the wellbore and the casing and form an impermeable plug.

The sealing compositions preferably have a characteristic gelling time that is shorter than or comparable to the time taken to displace the fluid into the region, and the gel strength or viscosity of the material is sufficient to eliminate gravity-induced flows. The required gel strength and gelling time are calculated to achieve optimum displacement for the specific geometry of the region, the pumping time and the density difference between the fluid and the oil/water initially filling the region for each job.

Prior to use of the sealing compositions, it may be desirable to pump a wash fluid through the chamber and region to be plugged. These wash fluids and their pumping rates are well-known in the field of sealing and well treatment, and are designed according to the particular nature of the job at hand.

Moreover, after the sealing composition is in place in the annulus it will normally be the case that the residue of the fluid in the chamber (and possibly in the liner outside the packer pair) needs to be washed out. Again, suitable wash fluids and their pumping rates are well-known in the field of cementing and well treatment, and need no further description here.

The techniques described above mostly require that the sealing fluid be pumped from the surface to the region in question. However, in various alternative embodiments, the fluid can be held in a downhole reservoir near the region, and pumped through the chamber using a downhole pump. This lessens the strict rheological requirement of the fluid, and allows downhole mixing of two-part fluids or the like which can set rapidly in the region without causing problems in the tubing itself. In some instances, a downhole source of radiation such as UV or heat might be provided near the region to trigger or aid, for example, in facilitating the setting of the sealing composition. Moreover, triggering of downhole pumps or sources can be achieved by in situ measurements-for example, the conductivity of fluids passing through the tool.

The techniques described above provide a single plug around the liner. To effect treatment to a particular zone of a well having a perforate liner it is typically necessary to set two or more such plugs, such that there is one plug on either side of the zone in question. Packers can then be run into the liner and sealed against the plugs so as to isolate the zone therebetween and allow a selective treatment to be applied to that zone. It will be appreciated that if the treatment zone is near the bottom of the well or another plug, it may only be necessary to set a single plug to define the zone.

Therefore, in a further embodiment of the invention, a method is provided for isolating a zone of a well that is lined with a perforate liner, this method comprising: placing plugs on either side of the zone according to the method of the invention; and then setting a packer in the liner adjacent each plug.

There are occasions other than when dealing with the special problems posed by perforate liners when it may be desirable to form a plug in the well (perhaps in the well itself, or possibly in the annular region between the wellbore wall and some tubing within the. wellbore), and the compositions and techniques disclosed herein may be useful for this purpose as well. Such occasions include, for example, selective abandonment of a section of the well, as well as the regulated fill of a washout.

Accordingly, in a further aspect the invention provides a method of forming a plug in a region in a well, in which method a volume of sealing composition is pumped into the region, conveniently via suitable packer apparatus such as a pair of region-delimiting packers, which volume is sufficient to displace substantially all other fluids from the region to be plugged.

The following examples are provided to demonstrate certain illustrative embodiments of this invention. It should be appreciated by those skilled in the art that the techniques disclosed in the examples which follow represent those found by the inventors to function in the practice of the invention and thus can be considered to constitute examples of illustrative modes for its practice. However, those skilled in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Examples

The following represents an illustrative sealing composition of this invention, conveniently formulated using commercially available products:

Recorded lab tests showed the fluid injectable through pipe and tubing. Witnessed . injection and screen squeeze tests demonstrated that the said formulation fluid can be squeezed through a 200 Mesh screen (75 micron or 0.003" openings) at a rate of 20 ml/min and at 50 Psi back pressure via a 4 mm ID tubing. The pipe extrusion measurements showed that the set gels were solid and could withstand 30 to 50 Psi/ft pressure gradient in 1" ID pipe.

In addition, as illustrated in Figure 1, the above mentioned fluid system exhibits a strong shear thinning behavior and relatively low viscosity around 500 cP at 170 1/sec shear rate. This ensures the system is pumpable through production tubings or pipes or coiled tubing which are commonly used in the oilfield.

As illustrated in Figure 2, the gel setting time for the above mentioned fluid system can be controlled by using a delay agent, in this case, potassium ferricyanide. This provides sufficient working time for pumping and placement of this gel system in the wellbore. A pressure test was performed on a 12" long iron pipe of 0.5" internal diameter. The sample was heated to 120°F, then remained for 24 hours. A differential pressure was then applied to the test pipe and held for several minutes. The pressure was increased in stepwise fashion to determine the differential pressure at which the gel extrudes from the pipe. As illustrated in Figure 3, the gel holds 65 psi/ft but fails or extrudes at 72 psi/ft. This provides adequate hydraulic seal in pipe, or annulus between the pipe and open-hole, or rock matrix.

Claims

WHAT IS CLAIMED IS:

1. A sealing composition for completion or remedial operations in subterranean zones penetrated by a borehole, said composition comprising • at least one polymerizable monomer;

• at least one polymerization initiator effective for causing the formation of a polymer from said monomer;

• a cross-linking agent effective for cross-linking said polymer once formed;

• a thixotropic agent.

2. The sealing composition according to claim 1, comprising

• about 30-60 wt.% of said at least one polymerizable monomer;

• about 0.05-0.5 wt.% of said at least one polymerization initiator;

• about 0.25-1 wt.% of said at least one cross-linking agent;

• about 0.5-10 wt.% of at least one thixotropic agent.

3. The sealing composition according to any of claims 1 to 2, wherein the monomer is a cationic monomer.

4. The sealing composition according to any of claims 1 to 2, wherein the monomer is_* selected from the group consisting of dimethyldiallylammonium chloride, hydroxymethlylacrylamide, hydroxylethylacrylate, Ca-diacrylate, and trimethanolpropanetriacrylate.

5. The sealing composition according to any of the preceding claims, wherein the polymerization initiator is selected from the group consisting of persulfates, peroxides, azo compounds such as 2,2'-azobis(2-amidinopropane)dihydro-chloride and oxidation-reduction systems.

6. The sealing composition according to any of the preceding claims, wherein the cross- linking agent is selected from the group consisting of methylenebisacrylamide and triallylamine.

7. The sealing composition according to any of the preceding claims, further comprising a delaying agent.

8. The composition according to claim 7, wherein said delaying agent is selected from the group consisting of potassium ferricyanide, hydroquinone, and thiosulfate.

9. The composition according to claim 7 or 8, comprising about 0.5-4wt.% of said delaying agent.

10. The sealing composition according to any of the preceding claims, wherein the thixotropic agent is selected from the group consisting of hydroxy ethyl cellulose polymer, microfine clay particles and mixture thereof.

11. The sealing composition of claim 10, wherein the thixotropic agent comprises cationic surfactant-treated microfine clay particles selected from alkyl quaternary ammonium bentonite and alkyl quaternary ammonium montmorillonite.

12. The sealing composition according to any of the preceding claims, further comprising a gel stabilizer.

13. The sealing composition according to claim 12, wherein said gel stabilizer is a thiosulfate.

14. The sealing composition according to claim 12 or 13, comprising 0.1-lwt.% of said gel stabilizer.

15. The sealing composition according to any of the preceding claims, further comprising a complexing agent.

16. The sealing composition according to claim 15, wherein said complexing agent is selected from the group consisting of zirconium lactate, tetrasodium ethylenediaminetetraacetic acid, and sodium hydroxide.

17. The sealing composition according to claim 15 or 16, comprising 0.1-lwt.% of said complexing agent.

18. A method of forming a plug in a region in a well, comprising pumping a volume of a sealing composition according to anyone of claim 1 to 17, said volume sufficient to displace substantially all other fluids from the region to be plugged.

19. The method according to claim 18, further including placing packers to deliminate said region.

20. The method according to claim 19, whereby said region is around a perforate liner, and wherein the packers are being spaced apart so as to define both a chamber inside the liner which includes a perforation and also a region to be plugged outside the liner and whereby the sealing composition is pumped into the chamber and, via the perforation, into the region to be plugged.

21. The method the method according to any of claims 18 to 19, wherein the wellbore is a horizontal wellbore.

22. A method of cementing a casing or pipe in a borehole, comprising introducing into the annular space between the outer surface of the casing or pipe and the wall of the borehole a sealing composition according to anyone of claim 1 to 17; and allowing the material to set.