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A method of creating a zonal isolation above a target zone in an underground wellbore comprises: inserting a slurry injection tubing into the wellbore; arranging within an annular space surrounding said tubing an particle accumulation means, such as an expandable screen or an area where the slurr

A method of creating a zonal isolation above a target zone in an underground wellbore comprises: inserting a slurry injection tubing into the wellbore; arranging within an annular space surrounding said tubing an particle accumulation means, such as an expandable screen or an area where the slurry velocity is reduced; and pumping a slurry comprising a carrier fluid and granular material down via the slurry injection tubing and the target zone and then up into the annular space, such that at least some granular material accumulates and forms an elongate zonal isolation in the annular space between the target zone and the particle accumulation means, which zonal isolation is removable and exerts a limited radial force to the surrounding formation, thereby reducing the risk of formation damage.

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The invention claimed is: 1. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slur

The invention claimed is: 1. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means comprises a means for removing liquid from the slurry, selected from the group consisting of a fluid permeable barrier in the annular space and a fluid return conduit surrounding the slurry injection tubing; wherein during pumping of the slurry at least part of the carrier fluid is removed from the slurry and wherein the granular material is induced to accumulate in a region of the annular space which is located between the target zone and the particle accumulation means, such that the particle accumulation means is arranged between the accumulated granular material and the wellhead. 2. The method of claim 1, wherein the fluid slurry comprises granular material of which the grain size is stepwise or gradually reduced during the injection process thereby inducing an initial batch of coarse granular material to settle and accumulate and subsequent batches of less coarse granular material to settle and accumulate against the annular matrix of coarser granular material. 3. The method of claim 1, wherein before pumping of the slurry into the annular space an auxiliary material is arranged in the annular space, forming a fluid permeable barrier. 4. The method of claim 3, wherein the auxiliary material comprises a solid foam. 5. The method of claim 1, wherein the fluid slurry comprises particles from a swellable material, and a carrier fluid in which the swellable material does not swell, and wherein after accumulation of the swellable particles a swelling fluid is passed through the accumulated particles thereby allowing the particles to swell. 6. The method of claim 1, wherein the granular material is selected from a group consisting of a swellable rubber, resin coated gravel, sand, a natural or artificial proppant, glass, plastic or other beads, hollow beads, beads and/or balls that are coated with glue, resin or fibers, steel or magnetisable metals, fibers, and/or fibers with hooks, and mixture(s) thereof. 7. The method of claim 1, wherein the granular material comprises a material and/or coating which dissolves at an elevated temperature or in a specific fluid. 8. The method of claim 7, wherein the specific fluid is an acidic fluid. 9. The method of claim 7, wherein the specific fluid is a caustic fluid. 10. The method of claim 1, wherein after installation of the zonal isolation in the annulus surrounding the slurry injection tubing a fracturing, stimulation, treatment, formation etching, disposal or other fluid is injected via the slurry injection tubing into the target zone and optionally into the formation surrounding the target zone. 11. The method of claim 10, wherein the outer surface of the slurry injection tubing is provided with a helical ridge and after completion of the fluid injection into the formation via the target zone the slurry injection tubing is rotated such that the helical ridge induces the tubing to move upwardly through the matrix of granular material towards the wellhead. 12. The method of claim 10, wherein the slurry injection tubing comprises a pair of axially spaced expandable screen assemblies and is inserted into the wellbore such that the target zone is located between said assemblies and wherein slurry is injected via an outlet opening in the wall of the tubing into the region of the annular space between the screen assemblies such that at least some granular material accumulates against each screen assembly and a zonal isolation is created at both sides of the target zone. 13. The method of claim 2, wherein the wellbore forms part of a well selected from the group consisting of an oil well, a gas production well, a geothermal well, a water well, a disposal well, and combination(s) thereof. 14. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means comprises an expandable screen assembly which is permeable to the carrier fluid, but impermeable to at least some of the granular material; and the method further comprises: radially expanding the screen assembly within the annular space; and inducing the fluid slurry to flow in longitudinal direction through the annular space such that at least some carrier fluid is induced to flow through the expanded screen assembly and at least some granular material is induced to settle and accumulate against the expanded screen assembly, thereby forming a zonal isolation comprising a matrix of packed granular material in the annular space between the target zone and the expanded screen assembly. 15. The method of claim 14, wherein the expandable screen assembly comprises a radially expandable carrier frame and a permeable barrier layer. 16. The method of claim 15, wherein the radially expandable carrier frame comprises an expandable umbrella-shaped frame, which comprises at least three arms that are each at one end pivotally connected to the outer surface of the slurry injection tubing such that another portion of each arm is induced to swing against the inner surface of the wellbore or well casing in response to expansion of the umbrella-shaped frame. 17. The method of claim 15, wherein the expandable carrier frame comprises a bow-spring centralizer assembly having at least three centralizer blades, which expand against the borehole wall at circumferentially spaced locations. 18. The method of claim 17, wherein at least one centralizer blade is configured to expand against the inner surface of the surrounding wellbore or well casing independently from other centralizer blades, such that the blades each expand against said inner surface even if the surface has an irregular, unround or elliptical inner shape. 19. The method of claim 18, wherein the assembly of bow spring centralizer blades comprises a set of short and a set of long centralizer blades, that are each at one end thereof secured to a first end ring which is secured to the outer wall of the fluid injection tubing and wherein the ends of the short centraliser blades are secured to a second end ring which is slidably arranged around the fluid injection tubing and the ends of the long centralizer blades are secured to a third end ring which is slidably arranged around the outer wall of the fluid injection tubing. 20. The method of claim 18, wherein the assembly of bow spring centralizer blades comprises a set of short and a set of long centralizer blades and the ends of the long centralizer blades are secured to end rings which are slidably arranged around the fluid injection tubing at different sides of a stop collar which is secured to the outer surface of the tubing, and wherein the ends of the short centralizer blades are secured to end rings which are slidably arranged around the fluid injection tubing and which are each located between the stop collar and one of the end rings of the long centralizer blades. 21. The method of claim 17, wherein the ends of the centralizer blades are connected at axially spaced locations to the outer surface of a radially expandable slurry injection tubing, such that the centralizer blades are arranged in a substantially stretched position around the tubing before expansion of the tubing and that the distance between the ends of the stabilizer blades is decreased as a result of the axial shortening of the tubing during the expansion process, whereby the centralizer blades are induced to radially expand within the annulus surrounding the fluid injection tubing. 22. The method of claim 17, wherein a skirt shaped barrier layer is arranged around the slurry injection tubing and secured to an upper section of the centralizer blades such that the skirt shaped barrier layer substantially spans the width of the annular space in response to expansion of the centralizer blades. 23. The method of claim 15, wherein the permeable barrier layer of the screen assembly is established and/or enhanced by pumping into the annular space a fluid slurry comprising fibrous material which is induced to settle against the expanded screen assembly prior to or simultaneously with the granular material. 24. The method of claim 14, wherein the expandable screen assembly comprises a woven pattern of helically coiled fibers, which fibers are secured between a pair of rings that are arranged around the outer surface of the fluid injection tubing and which are moved towards each other such that the helically coiled fibers deform and are at least partly expanded against the inner surface of the wellbore. 25. The method of claim 14, wherein the expandable screen assembly comprises a permeable sack, which is filled with granular material, and which is induced to expand against the inner surface of the wellbore in response to flux of the fluid slurry flowing up through the annular space between the slurry injection tubing and the wellbore. 26. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the slurry injection tubing is radially expanded after inserting a matrix of packed granular material in the annulus between the slurry injection tubing and the wellbore, thereby increasing the packing density and decreasing the permeability of the matrix of packed granular material. 27. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means is provided by a region of the annular space, in which the fluid velocity is reduced and granular material is induced to settle by an increased cross-section of the annular space with respect to an upstream region thereof with regard to slurry flow. 28. The method of claim 27, wherein the region of the annular space in which the fluid velocity is reduced is formed by a washout zone in which the wellbore has a larger width than other parts of the wellbore and/or by a region where the slurry injection tubing or a fluid return conduit surrounding the slurry injection tubing is inwardly tapered or otherwise reduced in outer diameter. 29. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means comprises a means for removing liquid from the slurry, selected from the group consisting of a fluid permeable barrier in the annular space and a fluid return conduit surrounding the slurry injection tubing; wherein during pumping of the slurry at least part of the carrier fluid is removed from the slurry; and wherein the particle accumulation means comprises a fluid return conduit surrounding the slurry injection tubing, which fluid return conduit has a permeable outer wall, and wherein at least some fluid is induced to flow from the annular space into the fluid return conduit. 30. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means comprises a means for removing liquid from the slurry, selected from the group consisting of a fluid permeable barrier in the annular space and a fluid return conduit surrounding the slurry injection tubing; wherein during pumping of the slurry at least part of the carrier fluid is removed from the slurry; and wherein the slurry injection tubing is inwardly tapered or has a stepwise reduced inner and outer diameter in the region between the target zone and the expandable screen assembly, such that the velocity of the slurry in the annular space is reduced when the slurry flows from the target zone towards the screen assembly. 31. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the fluid slurry comprises a cement slurry from which the carrier fluid is removed during accumulation. 32. The method of claim 31, wherein the carrier fluid is selected such that cement does not set in the carrier fluid, and wherein after accumulation of cement particles in the annular space a setting fluid, preferably comprising water, is passed through the accumulated cement particles thereby allowing the cement to set. 33. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means is provided with magnets and the granular material comprises magnetisable components. 34. A method of creating a zonal isolation adjacent to a target zone in an underground wellbore, the method comprising: inserting a slurry injection tubing through a wellhead into the wellbore; arranging a particle accumulation means in an annular space surrounding the slurry injection tubing at a location between the target zone and the wellhead; and pumping a slurry comprising a carrier fluid and granular material via the slurry injection tubing into the annular space, such that at least some granular material accumulates adjacent to the particle accumulation means and the accumulated granular material forms a zonal isolation comprising packed granular material adjacent to the particle accumulation means; wherein the particle accumulation means comprises a means for removing liquid from the slurry, selected from the group consisting of a fluid permeable barrier in the annular space and a fluid return conduit surrounding the slurry injection tubing; wherein during pumping of the slurry at least part of the carrier fluid is removed from the slurry; and wherein the zonal isolation of accumulated granular material is configured such that it has a higher longitudinal permeability than at least a substantial part of the formation surrounding the target section of the wellbore. 35. The method of claim 34, wherein a fracturing and/or stimulation fluid is injected into the formation surrounding the target section of the wellbore and the matrix of granular material has a substantially annular shape and a longitudinal permeability such that during the step of injecting fracturing fluid into the formation fracturing fluid leaks through the matrix of granular material and the change of static pressure in the wellbore fluid over the matrix of granular material is larger than the change of a characteristic formation pressure, such as the fracture-initiation, fracture-propagation or formation-breakdown pressure over the same section in the formation surrounding the matrix.