Well packing

[0001] The present application is the U.S. national stage application of International Application PCT/NO01/00275, filed Jun. 29, 2001, which international application was published on Mar. 14, 2002 as International Publication WO 02/20941. The International Application claims priority of Norwegian Patent Application 20004509, filed Sep. 8, 2000.

[0002] The present invention relates to a method of the nature as stated in the introduction of claim 1 for sealing of an annular space between a well wall in a production well for hydrocarbons and a production tubing, to a peripheral annular packer of the nature as stated in the claims 2–10, comprising an expandable element mainly consisting of rubber material, and to the expanding annular packer for application in said method

[0003] Completion of oil wells with sand control screens in open hole is a simple and reliable method by to complete a reservoir section. An oil well normally penetrates formations with varying production features, which, in spite of the fact that the sand control screens are closed on the inside, may cause that undesired well fluid by-passes on the outside of these and flow into the section. Therefore, it may be desired to control or shut off sections, which do not produce desired well fluid. This necessitates sealing the external annulus.

[0004] Today such seal is achieved by application of inflatable, open-hole packers (external casing packers), which are pressurised by injecting a fluid, which is confined by means of a valve system. As soon as the packer is pressurised, it is unable to follow movements in the face of the formation. Further it is sensitive to changes in temperature and pressure, and there are often considerable problems to achieve a complete seal. Another disadvantage is that the installation of the packer is expensive since well operations requiring complicated equipment are requisited.

[0005] From U.S. Pat. No. 4,137,970 a packer is known with an element which by a chemical swelling process result in expansion of the element upon contact with water present in the well at the moment the packer is introduced to the bore hole. The packer element is employed in mining, where water is to be drained from an aquiferous layer above a clay layer. The sealing consists of an expanding packer element. During such a swelling process the packer element will initially expand fast, before it expands slower. This is impractical in an oil well, since the packer will expand before it is placed in the final operating position in the well. This implies that the packer may be put in the wrong position in the well, if it was to be employed in an application like the present invention and cause that the completion string can not be inserted to its planned final position. Application of a medium swelling in water will cause the element to expand upon contact with all regular applied completion fluids or drilling fluids.

[0006] From U.S. Pat. No. 4,633,950 polymer particles are known suspended in a special water based carrier fluid, which by circulation pumping shall be injected into a lost circulation zone. The patent does not relate to a packer element, but to a dispersion which shall trickle into porous/fractured rock. The features of such a dispersion implies that it can not be held in place in order to form a solid plug in the annular space of the well. Further, the particles will upon contact with hydrocarbons expand very rapidly due to the large surface area of the small particles. Only minor impurities of remaining oil in the system will therefore result in an undesired early expansion. Moreover, the particles in such a system will not expand at all if they do not contact hydrocarbons before the well is flowing back. This may lead to the polymer being produced with the produced fluids.

[0007] Most rubbers have a larger absorption capacity and faster swelling in an aromatic and/or naphtenic hydrocarbon than in an aliphatic hydrocarbon. Most rubbers also have considerably less swelling in water based fluid than in an oil based fluid.

[0008] Generally base-oils used in drilling fluids have a higher portion of aliphatic (80–100%) constituents than produced hydrocarbons, normally having 35–80% aliphatic constituents. This implies that most rubbers will have a larger and faster expansion in produced hydrocarbons than in drilling fluids.

[0009] The purpose of the present invention is to enable completion of reservoir sections by complete annular seal, at the same time as the invention allows variations in operational parameters and geological conditions without changing the functionality of the invention. The packer will expand less while the packer is inserted into the well in a drilling fluid or completing fluid than by exposure to hydrocarbons produced from the formation.

[0010] This is achieved by the present method for sealing of an annular space between a well wall in a production well for hydrocarbons and a production tubing with a peripheral annular packer comprising an expandable element mainly consisting of rubber material characterised in that in said element a rubber is used which expands by absorbing hydrocarbons, and that the annular packer is inserted mainly by exposing the expanding element to hydrocarbons included in the product of the well.

[0011] Further the invention provides an expanding annular packer for use in the method for sealing of the annular space, comprising an expanding element consisting mainly of rubber material which is characterised in that the expanding element is directed to expanding mainly by absorbing hydrocarbons produced by the underground formation.

[0012] Further features of the invention are given in the claims 3–10.

[0016] In the following, the invention is further described. The permanent annular packer 2 for use in hydrocarbon production wells, preferably oil production wells, is placed on the outside of a pipe 4, said packer expands by the core 12 swelling upon exposure for and absorption of hydrocarbons. The packer therefore seals the annular space 5 towards the well wall 6. The production well may be an open-hole well or a well with a casing, which is characterised in that the production tubing 4 is drawn in an open hole or that the production tubing 4 is drawn in a casing (not shown), respectively. Thus the annular space 5 consists of the external surface of the production tubing 4 and the bore hole wall, or the external surface of the production tubing 4 and the internal surface in the casing, respectively.

[0017] An oil stream 1 flows past a packer element 2 before the packer element 2 is expanded and sealing towards the well wall 6. A sand control filter 3 is attached to a production tubing 4. A packer element 2′ is expanded and sealing towards the well wall 6 so that a well fluid 7 can not bypass the packer element in the annular space 5.

[0018] An external, protecting mantle 10 equipped with a reinforcement 11 surrounds a core 12 comprising elastic polymer, said coating works as a permeable membrane. The external mantle 10 comprises a rubber with higher resistance and lower rate of diffusion towards hydrocarbons than the core 12. The packer element, which may consist of a mantle 10, reinforcement 11 and core 12, is placed on the outside of a tube 4.

[0019] The packer 2 consists of a core 12 comprising an elastic polymer, e.g. EPDM rubber, styrene butadiene, natural rubber, ethylene propylene monomer rubber, ethylene propylene diene monomer rubber, ethylene vinyl acetate rubber, hydrogenized acrylonitrile-butadiene rubber, acrylonitrile butadiene rubber, isoprene rubber, chloroprene rubber or polynorbornene, said core is swelling in contact with and by absorption of hydrocarbons so that the packer expands. The rubber of the core may also have other materials dissolved or in mechanical mixture, such as fibres of cellulose processed as described in U.S. Pat. No. 4,240,800. Additional options may be rubber in mechanical mixture with polyvinyl chloride, methyl methacrylate, acrylonitrile, ethylacetate or other polymers expanding by contact with oil.

[0020] An external, reinforced mantle 10 protects the core towards direct exposure to drilling fluid and hydrocarbons. At the same time the mantle 10 allows migration of hydrocarbons to the core 12 and swelling (and thus expanding of the packer). The external, reinforced mantle 10 comprises rubber, for example acrylonitrile, hydrogenated nitrile, chloroprene, ethylene vinylacetate rubber, silicone, ethylene propylene diene monomer, butyl, chlorosulphonated polyethylene, polyurethane, ACM, BIMS or other types of rubber having less expansion or slower diffusion than the core and a reinforcement 11, preferably fibre reinforcement, e.g. kevlar, said reinforcement reinforces the external mantle 10. An essential feature of the rubber in the mantle 10 is that it has a swelling in drilling fluids, which is slower than the core 12. With “a higher resistance towards hydrocarbons” is here meant that the rubber only to a small degree swells upon exposure to hydrocarbons.

[0021] Several elastic polymers have a considerable absorption of hydrocarbons without absorption of water, and the polymers in the present invention are predominantly hydrophobic. By immersion in a hydrocarbonaceous medium, hydrocarbons migrate into and through the external mantle 10 and further into the core 12, which is swelling upon absorption of these.

[0022] The present invention provides several benefits compared to state of the art. The packer adjusts continuously to variations in the movements of the formation or washouts of the borehole, which implies that better shutting off/sealing between reservoir sections may be achieved and undesired well fluid can not flow past the packer element in the annular space. There is no need for well operations when installing the packer, which represents cost savings compared to today's methods for installation. The packer has no moving parts and is thus a simple and reliable device. The packer expands faster and more in a produced hydrocarbon, than in a water based or oil based drilling fluid or completion fluid at the same temperature and will thus expand less when the packer is immersed in drilling fluid.

[0023] In another embodiment of the present invention, the core 12 is surrounded by an external mantle of rubber, e.g. a nitrile which is not reinforced.

[0024] In further another embodiment of the present invention, the core 12 is surrounded by an outer web which may be the reinforcement.

[0025] In a further embodiment of the present invention the core 12 is surrounded by an external mantle of rubber, e.g. a nitrile, said mantle in itself does not let hydrocarbons penetrate, but a small part 11 of the core 12 is exposed directly to hydrocarbons through openings in the outer coating.

[0026] In an even further embodiment of the present invention the core 12 is not surrounded by an external mantle, but is exposed directly to hydrocarbons. In this aspect, the core 12 has a composition comprising elastic polymer with sufficient features to fulfil the desired functions of the packers.