Downhole isolation methods and apparatus therefor
The invention provides a method and apparatus for use in a wellbore gravel pack operation. The method comprises providing an apparatus in a downhole annulus. The apparatus comprises a mandrel and a swellable element formed from a material selected to increase in volume when exposed to a downhole stimulus. The method comprises placing a gravel pack below the apparatus via the downhole annulus in which the apparatus is located, and placing a gravel pack above the apparatus. Subsequent to placing the gravel packs, the swellable element is increased in volume to create an annular barrier in the wellbore. The invention allows isolation of multiple intervals of a well in a single gravel pack operation using swellable elastomers, and does not rely on the use of shunt tube alternate path systems.
1. A swellable downhole apparatus comprising:
a mandrel; and
a swellable element on the mandrel, the swellable element comprising a material selected to increase in volume when exposed to a downhole stimulus and arranged on the mandrel to swell in a wellbore annulus to provide an annular barrier between the mandrel and a surrounding wall in a wellbore; and
a radially contracting portion configured to reduce a diameter of a portion of the apparatus, forming a void for accommodating a volume of solid material displaced from the wellbore annulus by the swellable element when it swells to a swollen condition,
wherein the radially contracting portion comprises one or more sacrificial materials,
wherein the sacrificial materials comprise materials that undergo a phase change in the wellbore annulus, decreasing a volume of the sacrificial materials.
2. The apparatus as claimed in claim 1 , comprising a first condition in which the apparatus defines a first volume in the wellbore annulus, and a second condition in which the apparatus comprises the void.
3. The apparatus as claimed in claim 1 , comprising one or more formations on or around the swellable element that are hardened relative to the swellable element.
4. The apparatus as claimed in claim 1 , wherein the radially contracting portion further comprises:
an elastomeric matrix composed of an elastomeric material that swells under wellbore conditions, exposing the sacrificial material to wellbore fluid, wherein the elastomeric matrix binds the sacrificial material.
5. The apparatus as claimed in claim 4 ,
wherein the sacrificial materials disperse into the solid material upon exposure to the wellbore fluid.
6. The apparatus as claimed in claim 1 , comprising a plurality of contracting portions and a plurality of swellable elements arranged alternately on the mandrel.
7. The apparatus as claimed in claim 1 , comprising a device for preventing or restricting solid particles of a gravel pack passing through the annulus.
8. The apparatus as claimed in claim 7 , wherein the device permits passage of solids therethrough with a flow of a carrier fluid, but prevents or restricts solid particles from the gravel pack passing through the annulus in an absence of flow of the carrier fluid.