1. Field of the Invention
This invention relates to a method and apparatus for isolating at least a portion of a tubular. In addition, this invention relates to a method for producing an apparatus for isolating at least a portion of a tubular.
2. Description of the Related Art
In the oil and gas industry, it is generally known that, in addition to hydrocarbons, an underground formation may include a relatively high percentage of water. Typically, where water is present this will underlie the hydrocarbons within the formation.
In reference to FIG. 1 of the drawings, a lower section 10 of a borehole 12 is shown extending from surface (not shown) towards an underground formation 14. The formation 14 comprises both a hydrocarbon reservoir 16 and a region containing water 18, the water 18 shown underlying the hydrocarbon reservoir 16. A well 20 may be completed to a level adjacent the hydrocarbon/water interface within the formation 14 by running a first tubular section, or casing (not shown), into the borehole 12 and supplying cement to the annulus around the tubing section to seal and secure the casing within the borehole 12. The borehole 12 is then extended and a second tubing section, or liner, is run into the borehole 12 and cemented in place, the liner supported by the casing above. The liner 15 adjacent the formation is then perforated to permit hydrocarbons from the reservoir 16 to be extracted to surface.
However, over time and due to the generally higher mobility of the water 18 within the formation 14, for example where relatively viscous hydrocarbons are present, water 18 is drawn towards the base 22 of the well 20 (as shown in FIG. 1 by the dotted lines 24, 26) until water is produced from the well 20. This phenomenon is known as “coning” and may be particularly prevalent in horizontal or deviated wells as water is drawn to the heel of the well, that is, where the well deviates from vertical.
It will be recognised that where water production occurs at the expense of production of hydrocarbons from the well, the recovery efficiency of the well will be adversely affected. The efficiency and utility of a well may be greatly reduced where a high percentage of water is produced from a well and, indeed, in some environments, it is known for a well to produce in excess of 50% water with water production approaching 100% in some areas of the well, while other areas may produce 100% hydrocarbons.
Typically, when water production is identified downhole, it is desired that the water producing zones are isolated in order to prevent this undesirable ingress of water.
For example, isolation may be achieved, for example, by setting mechanical packers across the water producing zone.
In U.S. Pat. No. 7,059,415, which is incorporated herein in its entirety by way of reference, when water production has been observed, a patch is run into the tubular and expanded into contact with the inner wall of the tubular to shut off water production from the respective zone. However, many current approaches may only be adopted after water production has been identified and typically require significant intervention into the well.
Alternatively, International Patent Application WO2004/0022911, which is incorporated herein in its entirety by way of reference, discloses a wellbore device comprising a tubular conduit comprising circular perforations. The device further comprises a swelling elastomer sleeve located about an exterior surface of the conduit. The generally perforations may be closed when the swelling elastomer encounters formation water to prevent inflow of water into the tubular.
As a further alternative, chemical agents may be pumped into the well to shut off unwanted water production. However, where chemical agents are used, it has been found that there are difficulties in targeting the chemicals to the desired location with a high degree of accuracy.