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Title:
METHOD FOR CEMENTING A WELL
Document Type and Number:
WIPO Patent Application WO/2014/058338
Kind Code:
A1
Abstract:
The invention relates to a method for cementing a well (10), in which a liquid cement mixture is pumped into an annulus (12) between a casing (14) of the well (10) and the formation rock (16) surrounding the well (10) and is subsequently left to set. According to the invention, after pumping the cement (18) into the annulus (12), it is subjected to an acoustic treatment.

Inventors:
NIKOLIN, Ivan Vladimirovich (Skobolevskaya 23-4-163, Moscow, 2, 117042, RU)
Application Number:
RU2012/000828
Publication Date:
April 17, 2014
Filing Date:
October 12, 2012
Export Citation:
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Assignee:
SIEMENS AKTIENGESELLSCHAFT (Wittelsbacherplatz 2, Muenchen, 80333, DE)
International Classes:
E21B28/00; E21B33/14
Domestic Patent References:
WO2012110762A1
Foreign References:
US20110011576A1
US20110048711A1
US6009948A
US4658897A
Other References:
PERTERS, S.; STOCKIGT, M.; R6SSLER, C.: 'Influence of Power-Ultrasound on the Fluidity and Setting of Portland Cement Pastes; 17' INTERNATIONAL CONFERENCE ON BUILDING MA- TERIALS 23 September 2009,
Attorney, Agent or Firm:
LAW FIRM "GORODISSKY & PARTNERS" LTD (MITS Alexander Vladimirovich, POPOVA Elizaveta VitalievnaB. Spasskaya Str., 25, bldg., Moscow 0, 129090, RU)
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Claims:
CLAIMS

1. Method for cementing a well (10), in which a liquid cement mixture is pumped into an annulus (12) between a casing (14) of the well (10) and the formation rock (16) surrounding the well (10) and is subsequently left to set, characterized in that after pumping the cement (18) into the annulus (12), it is subjected to an acoustic treatment.

2. Method according to claim 1, characterized in that the acoustic treatment is applied by at least one acoustic wave source (22) within the casing (14).

3. Method according to claim 2, characterized in that the at least acoustic wave source (22) is moved along a substantial part of the length of the well (10) during the treatment.

4. Method according to claim 1 or 2, characterized in that the acoustic treatment is applied by at least two acoustic wave sources (22) emitting acoustic waves (26) of different wavelengths.

5. Method according to claim 1 or 2, characterized in that the at least one acoustic wave source (22) emits acoustic waves (26) of at least two different wavelengths. 6. Method according to any one of claims 2 to 5, characterized in that the at least one acoustic wave source (22) is lowered into the casing (14) by means of a cable (24) providing electrical energy to the at least one acoustic wave source (22).

Description:
METHOD FOR CEMENTING A WELL DESCRIPTION

The invention relates to a method for cementing a well according to the preamble of claim 1.

Productive oil and gas wells are stabilized by inserting a metal casing into the borehole and filling the space between the casing and the surrounding formation rock, the so called annulus, with cement, to provide zonal isolation between the geologic strata and the casing.

The cement has to be stable and free of cracks over the lifetime of the well, which can exceed 30 years, while exposed to the high pressure and temperature and geomechani- cal stress within the formation.

The mechanical properties of the cement develop during hydration, which reduces the hydrostatic pressure and leads to formation of a bond between the cement and the casing and formation. During this phase, shrinkage or expansion of the cement can happen as a result of contact with mobile formation water. Further influences on cement quality relate to stresses imposed on the wellbore by drilling and completion practices and to later changes in the lithostatic pressure and temperature by production and injection of gas and liquids, as well as to subsidence of the formation in reaction to resource extraction.

As a consequence of such stresses or as a consequence of improper setting, the cement can develop cracks or connected pores impeding its barrier function. This can lead to the formation of micro-annuli between cement and casing or formation, which allow for the flow of liquids outside the casing itself. A large fraction of connected pores can furthermore lead to a significant bulk permeability of the cement. Cracks can also lead to a connection between the inside of the casing to the formation rock, allowing liquids and gas to flow from the wellbore into the formation. Such defects can lower the performance of the well and, in the worst case, lead to an uncontrolled outflow of oil or gas into the environment.

Cement quality is therefor of utmost importance for the stability and safety of a well. Cements used are mixtures of cementitious materials such as fly ash and slag cement, aggregate like gravel, limestone, granite or sand, water and chemical admixtures. The latter include accelerators or retarders, plasticizers, pigments, silica fume or high reactivity metakaolin. Another typical admixture is micro silica, which has a relatively high cost and poses an inhalation risk to the operator's health. The quality of the cement is not only influenced by its composition, but also by the quality of the mixing of its components. Typically, the cement is mixed before pumping it into the annulus by mechanical means such as rotary mixers or rotor-stator- mixers. These techniques often are insufficient to break up agglomerates of cement particles. While the outer particles of such agglomerates come in contact with water, the inner particles remain dry, leading to a slow and incomplete hydration of the cement.

It is furthermore known to employ ultrasonic waves for the mixing of cement (Perters, S., Stockigt, M., Rossler, C. (2009): Influence of Power-Ultrasound on the Fluidity and Setting of Portland Cement Pastes; 17 th International Conference on Building Ma- terials, September 23 rd -26 th 2009, Weimar). Ultrasound treatment lowers the initial and final set time and hydration time. Cavitational shear forces introduced by ultrasonic treatment further improve deagglomeration and dispersion of micron- and nano- sized materials in the cement. It has been shown that CSH-phases (calcium silicate hydrate) growing to needle-like structures during hydration of the cement grow to about five times the size in ultrasound-treated cement compared to non-treated cement.

However, ultrasonic mixing is rarely employed during the cementing of wells, and, if so, only prior to pumping the cement into the annulus, since it is generally assumed that the mixture quality stays constant during pumping. Given the complex geophysi- cal conditions along the wellbore, this assumption has to be questioned.

Cementing methods, as currently applied, often lead to the formation of large, connected pores and other non-uniformities in the set cement, impairing the cement- casing and cement-formation bond and resulting in poor zonal isolation. Often, such problems have to be repaired, leading to high costs and delays. It is therefore the objective of the present invention to provide a method according to the preamble of claim 1 which increases the quality of the cement in the annulus of a well.

This objective is achieved by a method according to claim 1.

For cementing a well, a liquid cement mixture is pumped into an annulus between a casing of the well and the formation rock surrounding the well and is subsequently left to set.

According to the invention, after pumping the cement into the annulus, it is subjected to an acoustic treatment. Acoustic waves powerful enough to shake the cement mixture in the annulus improve the mixing quality and help to overcome delamination and disintegration of the mixture during pumping. Nano- and micro-scale agglomerates are broken up, ensuring a proper hydration of the cement.

Furthermore, the acoustic treatment shakes remaining dust and bubbles from the casing surface facing the annulus, bringing the casing in full contact with the cement mixture and thereby improving the cement-casing bond. On the formation side, the acoustic treatment also leads to a cleaning of the formation surface and improves the penetration of cement into formation pores. In general, pores and cracks throughout the cement are reduced in size and number, leading to an overall improvement of cement quality.

In a preferred embodiment of the invention, the acoustic treatment is applied by at least one acoustic wave source within the casing. This allows to specifically direct the acoustic waves to particular portions of the well to be treated.

In a further preferred embodiment of the invention, the at least acoustic wave source is moved along a substantial part of the length of the well during the treatment, allowing to cover the whole of the wellbore with equal quality. If is furthermore advantageous, if the acoustic treatment is applied by at least two acoustic wave source emitting acoustic waves of different wavelengths. This increases the efficiency of the acoustic treatment and leads to a particularly good cement quality.

As an alternative, the at least one acoustic wave source emits acoustic waves of at least two different wavelengths, lessening the weight to be lowered into the casing.

Preferably, the at least one acoustic wave source is lowered into the casing by means of a cable providing electrical energy to the at least one acoustic wave source. Multiple acoustic wave sources can be attached to the same cable at predetermined dis- tances.

In the following part, the invention and its embodiments is explained in detail with reference to the drawings, which show:

FIG 1 A schematic drawing of a longitudinal section through a wellbore during the performance of an embodiment of a method according to the invention; and FIG 2 a schematic drawing of a longitudinal section through a wellbore during the performance of an alternative embodiment of a method according to the invention, using multiple acoustic wave sources.

In order to stabilize a well 10 for oil or gas production, an annulus 12 between a casing 14 and the surrounding formation rock 16 is filled with cement 18. The cement 18 is prepared from cementitious materials such as fly ash and slag cement, aggregate like gravel, limestone, granite or sand, water and chemical admixtures. The latter include accelerators or retarders, plasticizers, pigments, silica fume or high reactivity metakaolin. The particular composition depends on the geophysical conditions within the well 10. The cement 18 is subsequently mixed, usually by mechanical means such as rotary mixers, and pumped down the well 10 within the casing 14, where it replaces the drilling mud and finally rises into the annulus 12. However good the quality of the mixing was, pumping and exposition to the extreme temperature and pressure conditions within the well 10 can impede the quality of the cement 18, leading to the formation of bubbles 20 in the bulk of the cement 18 as well as on the boundaries between cement 18 and casing 14 or formation rock 16.

To improve the quality of the cement 18, an acoustic shaker 22 is lowered into the casing by a cable 24, which doubles as electrical connection for the acoustic shaker 22. The shaker 22 emits acoustic waves 26, which penetrate the casing 14 and propa- gate through the cement 18 and formation rock 16. During their propagation, the acoustic waves 26 shake dust and bubbles from casing 14, break up bubbles 20 within the bulk cement 18 and penetrate into the pores of the formation rock 16. This reduces the porosity of the cement 18 after setting and improves the bond between cement 18 and casing 14 and formation rock 16, respec- tively.

Furthermore, the acoustic treatment also acts positively on the hydration process of the cement 18. During hydration, nano-scale hydration products, such as calcium hydrates, form in the setting cement 18. Nanoparticles of silica or nanotubes turn into nanoparticles of cement during this process. Smaller particles within the cement 18 are of advantage, since they lead to a shorter particle distance and an denser and less porous material, increasing the compressive strength and reduces the permeability of the cement 18. However, nanoparticles added to the cement 18 tend to form agglomerates during wetting, mixing and pumping. Unless these particles are well dispersed, agglomeration reduces the accessible particle surface leading to inferior cement prop- erties.

Acoustic treatment by acoustic waves 26 is an efficient means for the mixing, wetting and dispersing of such nanoparticles in the cement 18, allowing for the use of micro- or nanosilica as well as nanotubes. The acoustic treatment ensures that the entire surface of each particle is exposed to water, which leads to better concrete hardening, higher compressive strength and density. This is especially important for high performance concretes with low water content and a high dosage of admixtures.

As FIG 2 shows, it is possible to use multiple acoustic shakers 22 connected to the same cable 24 and operating at different wavelengths. Alternatively, a single shaker can emit at multiple wavelengths. This allows for an optimization of the acoustic spec- trum employed to treat the concrete. For example, ultrasonic treatment is particularly effective for dispersing micro- and nano-scale agglomerates, while larger bubbles 20 are removed more efficiently at greater wavelengths.

In conclusion, the method described above leads to a better quality of the concrete 18 due to better and more uniform mixing and wetting of cement components and it re- duces porosity and crack content of the cement 18. Furthermore, the acoustic treatment improves the contact between cement 18 and casing 14 and formation rock 16, respectively. Delamination and demixing of the cement 18 during pumping can be overcome and nano-sized admixtures are properly dispersed. Reduced hardening and setting times lead to faster well completion procedures. Overall, the wellbore integrity and lifetime are increased.

List of reference signs

10 well

12 annulus

14 casing

16 formation rock

18 cement

20 bubbles

22 acoustic shaker

24 cable

26 acoustic wave