This invention relates to a method of cement lining a wellbore and also to a system for performing such method.
In operation of a wellbore, it is a known practice to provide one or more fixed sensors inside the cement lining for acquiring data related to conditions in and characteristics of ground formations surrounding the wellbore. In order to enable fluid connection between the surrounding formation and a fixed sensor internal of the cement lining, it is known to perforate the cement lining after the cement has set, for example using small explosive charges.
An aim of the present invention is to provide an alternative and improved method of providing fluid pressure communication between the external formation and a fixed sensor inside the lining.
According to one embodiment of the invention, a method of cement lining a wellbore if provided to enable a fixed sensor internal of the lining to sense characteristics of the external formations surrounding the wellbore. At the region of the sensor position, means are utilised before completion of setting of the cement to create, in use, a permanent fluid pressure connection through the cement lining between the external formation and the sensor.
The invention may be practised in various ways.
According to a first embodiment, a cement curing retarder is introduced into the cement slurry in the region of the sensor totally to prevent curing of the cement in that region. In use, the region of uncured cement then provides fluid communication between the formation and the sensor.
Examples of suitable retarders include substances the molecules of which contain a substantial number of —OH groups and high temperature retarders from the family of organophosphate chelating agents. It is important to select a retarder which will not hydrolise during the period over which the sensor is to be used (i.e. over which readings are to be taken from the sensor), which may be several years.
According to a second embodiment, a system is used to increase the permeability of the cement in the region of the sensor, typically by the introduction of gas bubbles into the cement before it has set. The increased porosity of the cement due to the presence of the gas bubbles then provides fluid communication between the formation and the sensor in use.
A suitable system for inducing gas bubbles includes the installation of a small gas container, preferably pressurised, adjacent the sensor and release of the gas by opening a valve, by triggering a small explosive charge, or by chemical reaction if the gas is stored in the container in liquid or solid state. A preferred gas is carbon dioxide, which will slowly react with the cement, leaving interstices in the cement which will become occupied by water, oil or other liquid.
According to a third embodiment, a method is provided to induce cracks in the cement during curing.
Three preferred ways of inducing cracks are firstly the use of a sonic transducer, such as a solenoid or piezo-electric device, to create shear waves in the cement during curing, in the region of the sensor; secondly the addition to the cement during curing, locally to the sensor, of a substance which changes the coefficient of expansion of the cement, additives which are able to increase the rate of expansion of the cement to create cracks being magnesium and aluminium salts, and thirdly the use of bristles, especially metal bristles, attached to the sensor to link the sensor with the external formation.
The curing of the cement is an exothermal reaction, and the bristles induce local cracking by presenting a different rate of expansion as the cement cools down. It is possible to use bristles made of dissimilar metals, which give rise to electrolysis in the cement slurry as it sets, resulting in gas production which promotes the opening of channels in the cement in order to facilitate fluid communication between the formation and the sensor.
According to another embodiment of the invention, there is provided a section of wellbore casing having fixed thereto a sensor and means operative when the wellbore casing is being cement lined for inducing cracks in the cement slurry, as it is setting, in use to enable fluid pressure connection between the sensor and the external ground formation.
The means for inducing cracks in the cement lining may be means for performing any one of the aforedescribed methods.
Although the cement can become solid before it has fully set or cured, as used herein, the completion of the curing or setting process of the cement means the time when the cement reaches its final shear strength. In other words, at a time when the cement has reached its full hardness. In some cases it can take many days or even weeks for the cement to completely cure or set.
In the accompanying drawings, according to embodiments of the invention:
Referring to
After the casing has been installed in the wellbore, and is being cement lined, the substance is expelled from the container 18 into the cement slurry adjacent the sensor 14, as the cement is curing, to treat the cement so that fluid pressure communication is enabled between the sensor and the external ground formation in use.
The container 18 may house a substance more especially but not exclusively a fluid, of any one of several different types.
One option is a substance which will prevent the cement from curing at all locally to the sensor. Examples of such substances, among the many available, are sucrose, mannitol and catechol, but in all cases the particular curing retarder selected should be one which will prevent the cement from curing, locally to the sensor, for the period over which the sensor is to be used (i.e. over which readings from the sensor are to be taken).
Another option for the substance which is to be expelled from the container is a pressurised gas which will locally increase the permeability of the cement by creating bubbles therein. An inert gas such as nitrogen may be used, or a gas such as carbon dioxide which will slowly react with the cement to leave interstices in the cement which will fill with water, oil or other liquid.
Instead of storing the gas in the container under pressure, it could be stored in a liquid or solid state, and it could be released by chemical reaction, as for example by use of a small explosive charge locally to increase the porosity of the cement.
Still another option is to release from the container 18 a substance in the form of a cement additive which locally increases its rate of expansion, whereby to create cracks in the cement as it cures. Examples of such additives are magnesium, magnesium hydroxide, aluminium dioxide and calcium aluminite.
Referring to
Various electrochemical couples are able to achieve forced metal corrosion, including Pb—Al, Ag—Ni, Zn—Mg, Cu—Mg, H2-Ag, H2-Al, H2-Mg, O2-Pb, O2-Ni and O2-Zi.
In
The above-described embodiments are illustrative of the invention only and are not intended to limit the scope of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
0022151 | Sep 2000 | GB | national |
Number | Name | Date | Kind |
---|---|---|---|
2813584 | Teplitz | Nov 1957 | A |
3026936 | Teplitz | Mar 1962 | A |
3120268 | Caldwell | Feb 1964 | A |
3245472 | Myron | Apr 1966 | A |
3468386 | Johnson | Sep 1969 | A |
3887009 | Miller et al. | Jun 1975 | A |
3924677 | Prenner et al. | Dec 1975 | A |
4325291 | Paynton et al. | Apr 1982 | A |
4407365 | Cooke, Jr. | Oct 1983 | A |
4537918 | Parcevaux et al. | Aug 1985 | A |
4775009 | Wittrisch et al. | Oct 1988 | A |
5036916 | Bennett | Aug 1991 | A |
5224556 | Wilson et al. | Jul 1993 | A |
5529123 | Carpenter et al. | Jun 1996 | A |
5829520 | Johnson | Nov 1998 | A |
6131658 | Minear | Oct 2000 | A |
6171386 | Sabins | Jan 2001 | B1 |
20030150263 | Economides et al. | Aug 2003 | A1 |
20030226662 | Linyaev et al. | Dec 2003 | A1 |
20040211564 | Brothers et al. | Oct 2004 | A1 |
20040216872 | Foster et al. | Nov 2004 | A1 |
Number | Date | Country |
---|---|---|
2 185 574 | Jan 1987 | GB |
2 284 626 | Nov 1994 | GB |
WO 9737103 | Mar 1997 | WO |
Number | Date | Country | |
---|---|---|---|
20040180793 A1 | Sep 2004 | US |