WO2015152859A1

WO2015152859A1 - Compositions and methods for well completions

Info

Publication number: WO2015152859A1
Application number: PCT/US2014/032303
Authority: WO
Inventors: Anthony Loiseau
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited; Schlumberger Technology Corporation
Priority date: 2014-03-31
Filing date: 2014-03-31
Publication date: 2015-10-08

Abstract

Cement compositions with reduced porosity and improved strength comprise water, a hydraulic cement and an encapsulated silicate. The silicate may be released from the capsules by exposure to mechanical stress, heat, dissolution, swelling or coating degradation. Upon release, the silicate reacts with calcium hydroxide in the cement matrix to form calcium silicate hydrate. The formation of additional calcium silicate hydrate may fill voids in the set cement.

Description

COMPOSITIONS AND METHODS FOR WELL COMPLETIONS BACKGROUND

[0001] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0002] This disclosure relates to compositions and methods for treating subterranean formations, in particular, compositions and methods for decreasing the porosity and increasing the strength of well cements.

[0003] During the construction of subterranean wells, it is common, during and after drilling, to place a tubular body in the wellbore. The tubular body may comprise drillpipe, casing, liner, coiled tubing or combinations thereof. The purpose of the tubular body is to act as a conduit through which desirable fluids from the well may travel and be collected. The tubular body is normally secured in the well by a cement sheath. The cement sheath provides mechanical support and hydraulic isolation between the zones or layers that the well penetrates. The latter function is important because it prevents hydraulic communication between zones that may result in contamination. For example, the cement sheath blocks fluids from oil or gas zones from entering the water table and polluting drinking water. In addition, to optimize a well's production efficiency, it may be desirable to isolate, for example, a gas-producing zone from an oil-producing zone.

[0004] The cement sheath achieves hydraulic isolation because of its low permeability. In addition, intimate bonding between the cement sheath and both the tubular body and borehole is necessary to prevent leaks. However, over time the cement sheath can deteriorate and become permeable. Alternatively, the bonding between the cement sheath and the tubular body or borehole may become compromised. Principal causes of deterioration and debonding include physical stresses associated with tectonic movements, temperature changes and chemical deterioration of the cement.

[0005] There have been several proposals to deal with the problems of cement-sheath deterioration. One approach is to design the cement sheath to mechanically survive physical stresses that may be encountered during its lifetime. Another approach is to employ additives that improve the physical properties of the set cement. Amorphous metal fibers may be added to cements to improve the strength and impact resistance. Addition of flexible materials (rubber or polymers) may confer a degree of flexibility to the cement sheath. Cement compositions may also be formulated to be less sensitive to temperature fluctuations during the setting process.

[0006] A number of proposals have been made concerning "self-healing" concretes in the construction industry. The concept involves the release of chemicals inside the set-concrete matrix. The release is triggered by matrix disruption arising from mechanical or chemical stresses. The chemicals are designed to restore and maintain the concrete -matrix integrity. This concept is described in the following publication: Dry, CM: "Three designs for the internal release of sealants, adhesives and waterproofing chemicals into concrete to reduce permeability." Cement and Concrete Research 30 (2000) 1969-1977. None of these concepts are immediately applicable to well-cementing operations because of the need for the cement slurry to be pumpable during placement, and because of the temperature and pressure conditions associated with subterranean wells.

[0007] More recently, self-healing cement systems have been developed that are tailored to the mixing, pumping and curing conditions associated with cementing subterranean wells. For example, superabsorbent polymers may be added and may be encapsulated. If the permeability of the cement matrix rises, or the bonding between the cement sheath and the tubular body or borehole wall is disrupted, the superabsorbent polymer becomes exposed to formation fluids. Most formation fluids contain some water, and the polymer swells upon water contact. The swelling fills voids in the cement sheath, restoring the low cement-matrix permeability. Likewise, should the cement/tubular body or cement/borehole wall bonds become disrupted, the polymer will swell and restore isolation. Rubber particles that swell when exposed to liquid hydrocarbons may also be incorporated in cements. Like the superabsorbent polymers, the swelling of the rubber particles restores and maintains zonal isolation.

[0008] Detailed information concerning the performance of self-healing cements in the oilfield may be found in the following publications: Le Roy-Delage S et al.: "Self-Healing Cement System— A Step Forward in Reducing Long-Term Environmental Impact," paper SPE 128226 (2010); Bouras H et al.: "Responsive Cementing Material Prevents Annular Leaks in Gas Wells," paper SPE 116757 (2008); Roth J et al.: "Innovative Hydraulic Isolation Material Preserves Well Integrity," paper SPE 112715 (2008); Cavanagh P et al: "Self-Healing Cement— Novel Technology to Achieve Leak-Free Wells," paper SPE 105781 (2007).

SUMMARY

[0009] The present disclosure proposes improvements by providing cement systems with decreased porosity and increased strength.

[0010] In an aspect, embodiments relate to methods for decreasing porosity of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall. A well cementing composition is prepared that comprises water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement. The encapsulated silicate is in the form of particles. The composition is placed in the annular space and allowed to set. The set composition (or set cement) contains calcium hydroxide and has internal voids. The coating is allowed to deteriorate, thereby releasing the silicate. The silicate is allowed to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and decreasing the porosity.

[0011] In a further aspect, embodiments relate to methods for increasing strength of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall. A well cementing composition is prepared that comprises water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement. The encapsulated silicate is in the form of particles. The composition is placed in the annular space and allowed to set. The set composition (or set cement) contains calcium hydroxide and has internal voids. The coating is allowed to deteriorate, thereby releasing the silicate. The silicate is allowed to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and increasing the strength. DETAILED DESCRIPTION

[0012] At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation— specific decisions must be made to achieve the developer's 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. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary and this detailed description, each numerical value should be read once as modified by the term "about" (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, "a range of from 1 to 10" is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that Applicants appreciate and understand that any and all data points within the range are to be considered to have been specified, and that Applicants possessed knowledge of the entire range and all points within the range.

[0013] This disclosure proposes to use a reactive material to modify the mineralogical composition of set cement. This mineralogical modification is the reaction between one or more silicates and soluble calcium hydroxide (portlandite) in the cement. This reaction forms insoluble calcium silicate hydrate (C-S-H) (Eq. 1), filling the pores to create a harder and denser matrix. The benefits of the reaction include (1) lower cement porosity and permeability; (2) higher strength; and (3) better bonding between the cement and the well casing.

Na₂0 · Si0₂ + Ca(OH)₂→ (CaO · Si0₂) · H₂0 + Na₂0 (1)

[0014] The silicate may be encapsulated. The capsules may be added during the preparation of the cement slurry, promoting even dispersion throughout the slurry. An advantage of having the reaction occur after the curing of the cement is that the reactive material will be used only for the purpose of calcium hydroxide consumption.

[0015] For example, C-S-H gel comprises roughly 65 wt% of fully hydrated Portland cement. By contrast the concentration of Ca(OH)₂ usually varies between 15 wt% and 20 wt%. Thus, there may be between 2.0 moles and 2.7 moles of Ca(OH)₂ per kg of set portland cement. From Eq. 8, it follows that the silicate concentration may also be between 2.0 moles and 2.7 moles of set cement to achieve full consumption Ca(OH)₂. Other hydraulic cement blends of the disclosure represent a wider range of Ca(OH)2 concentrations. Thus, the silicate concentration may be between 0.5 and 3.0 moles per kg of hydraulic cement, or between 2.0 and 2.7 moles per kg of hydraulic cement.

[0016] After placement and setting of the cement, several triggers may induce release of the silicate from the capsules, including mechanical stress, exposure to heat, dissolution, swelling or degradation or combinations thereof. Degradation may occur in the form of chemical processes such as hydrolysis. [0017] The disclosed encapsulated silicates may be particularly useful in the context of thermal recovery wells in which the cement sheath is exposed to large well- temperature variations. The purpose of injecting steam downhole is to increase the temperature of the production zone. This temperature increase induces an oil-viscosity decrease. Lower oil viscosity enables better flow of the oil and thus an increase of production. The main issue for the well is that the large temperature increase causes the expansion of the casing (large pipe generally made of steel). This expansion creates high stress on the cement sheath. Such stresses may cause the cement sheath to fail and crack, resulting in a loss of zonal isolation. However, the temperature increase can be used as a trigger to release the silicate. The high temperature may melt or degrade the capsule's shell. Swelling or expansion of the capsule could be the other possibilities for releasing the reactive chemical. The silicate reaction may reinforce the cement sheath while the temperature and the stress increase.

[0018] In an aspect, embodiments relate to methods for decreasing porosity of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall. A well cementing composition is prepared that comprises water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement. The encapsulated silicate is in the form of particles. The composition is placed in the annular space and allowed to set. The set composition (or set cement) contains calcium hydroxide and has internal voids. The coating is allowed to deteriorate, thereby releasing the silicate. The silicate is allowed to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and decreasing the porosity.

[0019] In a further aspect, embodiments relate to methods for increasing strength of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall. A well cementing composition is prepared that comprises water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement. The encapsulated silicate is in the form of particles. The composition is placed in the annular space and allowed to set. The set composition (or set cement) contains calcium hydroxide and has internal voids. The coating is allowed to deteriorate, thereby releasing the silicate. The silicate is allowed to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and increasing the strength.

[0020] For both aspects, coating deterioration may result from mechanical stress, exposure to heat, dissolution, swelling or degradation or combinations thereof. Degradation may occur in the form of chemical processes such as hydrolysis.

[0021] For both aspects, the hydraulic cement may comprise portland cement, lime-silica blends, lime-fly ash blends, lime-blast furnace slag blends or zeolites or combinations thereof. The silicate may comprise one or more alkali silicates, one or more alkaline-earth silicates or methyl silicate or combinations thereof.

[0022] For both aspects, the coating may comprise an epoxy resin, a phenolic resin, a furan resin, a cellulosic polymer, polyvinylidene chloride, poly(methyl methacrylate), polylactic acid, polyglycolic acid, polyvinylalcohol, urea-formaldehyde polymers, silicones, gelatins, lipids, styrene acrylic resins, or waxes or combinations thereof. The encapsulated particles may have diameters between 1 micron and 1000 microns.

[0023] For both aspects, the compositions may further comprise accelerators, retarders, extenders, weighting agents, dispersants, fluid-loss control agents, lost- circulation control agents, antifoam agents, gas-generating agents or fibers or combinations thereof.

[0024] For both aspects, the viscosity of the cement compositions during placement may be lower than 1000 cP at a shear rate of 100 s^-1.

Claims

1. A method for decreasing porosity of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall, comprising:

(i) preparing a well cementing composition comprising water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement, the encapsulated silicate being present as particles;

(ii) placing the composition in the annular space;

(iii) allowing the composition to set, wherein the set composition has internal voids;

(iv) allowing the coating to deteriorate, thereby releasing the silicate; and

(v) allowing the silicate to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and decreasing the porosity.

2. The method of claim 1, wherein the coating deterioration results from mechanical stress, exposure to heat, dissolution, swelling or degradation or combinations thereof.

3. The method of claim 1 or 2, wherein the hydraulic cement comprises portland cement, lime-silica blends, lime-fly ash blends, lime -blast furnace slag blends or zeolites or combinations thereof.

4. The method of any one of claims 1-3, wherein the coating comprises an epoxy resin, a phenolic resin, a furan resin, a cellulosic polymer, polyvinylidene chloride, poly(methyl methacrylate), polylactic acid, polyglycolic acid, polyvinylalcohol, urea-formaldehyde polymers, silicones, gelatins, lipids, styrene acrylic resins, or waxes or combinations thereof.

5. The method of any one of claims 1-4, wherein the silicate comprises one or more alkali silicates, one or more alkaline-earth silicates or methyl silicate or combinations thereof.

6. The method of any one of claims 1-5, wherein the composition further comprises accelerators, retarders, extenders, weighting agents, dispersants, fluid-loss control agents, lost-circulation control agents, antifoam agents, gas-generating agents or fibers or combinations thereof.

7. The method of any one of claims 1-6, wherein the particles have diameters between 1 micron and 1000 microns.

8. The method of any one of claims 1-7, wherein the silicate is present at a concentration between 0.5 and 3.0 moles per kg of hydraulic cement.

9. A method for increasing strength of a cement sheath in a subterranean well having a borehole wall and at least one tubular body, wherein the cement sheath occupies an annular space between the tubular body and the borehole wall, comprising:

(i) preparing a well cementing composition comprising water, a hydraulic cement and a silicate, the silicate being encapsulated by a coating that isolates the silicate from the water and the hydraulic cement, the encapsulated silicate being present as particles with diameters between 1 micron and 1000 microns;

(ii) placing the composition in the annular space;

(iv) allowing the coating to deteriorate, thereby releasing the silicate; and

(v) allowing the silicate to react with calcium hydroxide in the set composition, thereby forming calcium silicate hydrate, filling the voids and increasing the strength.

10. The method of claim 9, wherein the coating deterioration results from mechanical stress, exposure to heat, dissolution, swelling or degradation or combinations thereof.

11. The method of claim 9 or 10, wherein the hydraulic cement comprises portland cement, lime-silica blends, lime-fly ash blends, lime -blast furnace slag blends or zeolites or combinations thereof.

12. The method of any one of claims 9-11, wherein the coating comprises an epoxy resin, a phenolic resin, a furan resin, a cellulosic polymer, polyvinylidene chloride, acrylic polymers, or waxes or combinations thereof.

13. The method of any one of claims 9-12, wherein the silicate comprises one or more alkali silicates, one or more alkaline-earth silicates or methyl silicate or combinations thereof.

14. The method of any one of claims 9-13, wherein the composition further comprises accelerators, retarders, extenders, weighting agents, dispersants, fluid-loss control agents, lost-circulation control agents, antifoam agents, gas-generating agents or fibers or combinations thereof.

15. The method of any one of claims 9-14, wherein the silicate is present at a concentration between 0.5 and 3.0 moles per kg of hydraulic cement.