Patent Application
20090178800
The field of the invention is a packer for downhole use and more particularly a swelling packer responsive to water containing fluids where the swelling rate is regulated to allow proper placement before a full set.
Packers are used to isolate zones in a wellbore. Many different types of packers have been used over the years. Some of these designs involve mechanical compression that comes from a setting tool that uses relative movement. Other designs use pressure that is converted with a piston to a mechanical force to set the packer. Another packer style is an inflatable where the fluid is pumped through a series of check valves into a sealed annular space between a mandrel and an element. One end of the element is generally fixed to the mandrel with the opposite end riding toward it as the element radially expands from the pumped fluid into the annular space.
More recently, packers have used materials that swell. In one design a structure similar to an inflatable was used and the annular space contained swelling clay such as bentonite. Annular well fluids were admitted into this annular space and distributed with a wick. The swelling clay then enlarged the annular space defined by the sealing element until the assembly closed off the wellbore. Another design used an elastic polymer sensitive to hydrocarbons in the well. There was an inner and an outer layer that was rubber and allowed the hydrocarbons to get through to the inner core. The outer layer had a greater resistance and a lower diffusion rate to hydrocarbons than the core. The outer layer was optionally reinforced. This design is described in U.S. Pat. No. 7,143,832. Also of interest but working in the opposite direction are plugs that can be used downhole and then removed by exposure to well fluids such as is illustrated in U.S. Pat. No. 5,607,017. Packers that use water expandable materials are shown in U.S. Pat. No. 5,048,605 and Japan application 07-334115 filed Nov. 29, 1995 and entitled Borehole Packing Method
What is needed and is the focus of the present invention is a packer that employs swelling and sensitivity to water containing fluids and that has a mechanism to control the swelling of a core until the packer is delivered in its intended location. An outer covering layer is fitted over the core where preferably the outer layer allows water containing fluids to diffuse but that has a substantially lower swelling rate than the core in response to water containing fluids. As a result, the core is protected and its swelling is inhibited long enough to allow it to be properly placed. Alternatively the outer covering can be made to dissolve in water containing fluids as opposed to diffusing water containing fluids and swelling at a lower rate than the core. These and other aspects of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawing, which appear below while understanding that the claims determine the full scope of the invention.
A packer for downhole use responds to water containing fluids by swelling from its core. The core is preferably covered with an outer layer that preferably has a lower rate of diffusion and swelling than the core that it surrounds. Because of this arrangement, the packer can be delivered to the desired location before it is set by swelling of the core. The outer layer can also be responsive to water containing fluids by dissolving slowly to allow time to properly position the packer before the core swells to a sealing relationship with the surrounding tubular or the wellbore wall.
The packer of the present invention is illustrated in
Preferably the core 12 swells more extensively than the outer layer 14. In that manner, the outer layer 14 delays the swelling of the core in the presence of water containing fluids so that the packer P of the present invention can be delivered to the desired location. Stated differently, the balance between the elasticity of the outer polymer network and the osmotic pressure forces is in favor of limiting the swell reaction rate while the balance between the elasticity and the osmotic pressure forces of the inner layer are in favor of swelling (expansion). The net result is the inner layer expands the outer layer, or the outer layer retards the swell (expansion) rate of the inner layer.
The outer layer 14 protects the core from abrasion and other mechanical impacts and regulates the rate that the water containing fluids reach the core 12.
The core 12 can preferably be made from acrylate, acetate or formate salts or one of the following elastomeric polymer materials or combinations thereof: acrylonitrile, nitrile, hydrogenated nitrile, chloroprene, ethylene vinyl acetate, ethylene propylene diene monomer, ethylene propylene, or polynorbornen and acrylic copolymer, super absorbent polymers (SAP), carboxy methyl cellulose or/and a partially modified or fully cross-linked acrylic polymer added.
The outer layer 14 can be made from acrylate, acetate or formate salts or one or more of the following elastomeric polymer materials or combinations thereof: acrylonitrile, nitrile, hydrogenated nitrile, chloroprene, ethylene vinyl acetate, ethylene propylene diene monomer, ethylene propylene, or polynorbornen with an acrylic copolymer added.
The outer layer 14 can be continuous in its coverage of the core 12 or there can be openings or gaps in the outer layer through which water containing fluids can reach the core 12. The outer layer 14 can be in a single or multiple layers. If it is continuous the water containing fluid can diffuse through it to reach the core 12. Alternatively, the outer layer can be made of a material that will dissolve in a water containing fluid such as water containing drilling mud, sea water or saline brines.
The core 12 and the outer layer 14 should preferably have different swelling or diffusion rates with the core 12 swelling substantially more than the outer layer 14 and preferably having a higher diffusion rate for water containing fluids than the outer layer 14. Together the packer P components can take the shape of an irregular wellbore. In the preferred embodiment the packer P responds only to the presence of water containing fluids.
When the outer layer is designed to dissolve in water containing fluids, it simply slowly goes away as the core 12 swells.
The core need not be uniform as far as the material. It can be designed to swell more toward the center of the element initially so that well fluids are displaced to opposed ends that have not yet swelled into contact with the surrounding wellbore.
The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.
