GB2522882A - Method, downhole system and fluid laden with particles to form a barrier or restriction in a wellbore flow channel - Google Patents

Abstract

A method of forming a barrier or restriction 62 in a flow channel 14, outside a liner 12 in a wellbore, including the steps of expelling a first fluid V1 laden with first particles from a first opening 22 in the liner into the flow channel, expelling a second fluid V2 into the flow channel affecting the flow of the first fluid wherein a barrier or restriction is formed by the settling and aggregation of the particles. The second fluid may be expelled at a second location. The second fluid may be laden with second particles. Where the first particles settle and aggregate is affected by controlling parameters such as, particle density, grain size and shape and the density and flow rate of the fluids. The apparatus for carrying out the method may include packers and the particles may be buoyant and magnetisable.

Description

Method, Downhole System and Fluid laden with Particles to form a Barrier or Restriction in a Weilbore Flow Channel

Description

Field of the Invention

The invention relates to a method, a downhole system and a fluid laden with particles to form a barrier or restriction in a flow channel outside a liner extending in a wellbore in an earth formation.

Background of the Invention

Annular sections of a wellbore drilled in an earth formation can be isolated by providing one or more barriers to fluid flowing in an annulus between a liner and the walls of the wellbore in an earth formation. For example, in existing wellbores, water can be injected in a fracture having a connection with a producing wellbore thus preventing effective sweep of the hydrocarbons towards the production well. Isolation of such sections is therefore made to restore the hydrocarbon production. The annulus of a welibore may also be closed or blocked to isolate abandoned producing zones and prevent water from flowing in the annulus or entering the production conduit. In developments in which water is injected into the wellbore, a blockage or barrier may be used to isolate the zones into which the water is injected.

Summary of the Invention

It is an object of the present invention to provide a method, a downhole system and a material to form a barrier or restriction in a flow channel outside a liner extending in a subsurface weilbore in an earth formation at a desired longitudinal position along the liner and having desired properties.

A more specific aspect of the present invention is that when a fluid laden with particles is expelled through an opening in a liner extending in a horizontal or near-horizontal wellbore from inside of the liner to the flow channel outside of the liner to form a barrier or restriction, the position in the flow channel where the particles settle and aggregate from the fluid and/or other properties of the barrier or restriction shall be controlled and/or undesired blocking of the opening shall be prevented.

The object of the invention is achieved by subject matter of the independent claims. Preferred embodiments of the invention are subject of the dependent claims.

According to a first aspect of the present invention a method for forming a barrier or restriction to fluid flow in a flow channel outside a liner extending in a subsurface wellbore in an earth formation is provided.

A first fluid laden with first particles is expelled through a first opening in the outside wall of the liner from inside the liner into the flow channel outside the liner. In the flow channel the first particles settle out of the first fluid and aggregate, thereby forming the barrier or restriction. Thus, the first fluid laden with the first particles is used to inject the first particles into the flow channel to form the barrier or restriction therein by settling and aggregating of the first particles in the flow channel.

The flow channel may be an annular flow channel between the walls of a subsurface weilbore, eg. an oil drill hole drilled in an earth formation, and the outside ring wall of the liner, e.g. in the form of a conduit longitudinally extending within the wellbore. In other words, the flow channel may be provided along, and/or be partially defined by, the radially outer surface of the liner or conduit.

The flow channel may be at least partially, and optionally wholly, defined between the liner and an inner wall of the wellbore or bore hole in which the liner is located. In particular the liner is an elongate conduit, such as a tubular. However, the flow channel could also be an annular f low channel between a first conduit longitudinally nested within a second conduit extending subsurface in the wellbore. That is, the flow channel may be or comprises a channel suitable for, or configured to allow, flow of a fluid within the flow channel and may not necessarily have a fluid flowing within it at all times. The flow channel may comprise a space, for example, between the liner or conduit and the bore hole wall, earth formation, second outer conduit or other member provided around the liner or conduit.

A second fluid is expelled in the flow channel outside the liner affecting the flow of the first fluid laden with the first particles in the flow channel outside the liner. In the flow channel outside the liner, the second fluid forces the first fluid laden with the first particles away from the first opening, thereby forcing the first particles to form a barrier or restriction in the flow channel outside the liner at a first position in the flow channel outside the liner by settling and aggregating of the first particles at the first position in the flow channel outside the liner. Because the second fluid flows within the flow channel outside the liner at least partially in direction to the first opening and further passes the first opening, the second fluid forces the first fluid laden with the first particles longitudinally away from the first opening and thereby prevents the first particles from blocking the first opening in the liner. In other words, the second fluid affects the first fluid laden with the first particles to form an artificial barrier or restriction to fluid flow in the flow channel outside the liner at the first position by settling and aggregating of the first particles at said desired first position in the flow channel outside the liner. Therewith, the first position where the first particles settle and aggregate can be positioned to be longitudinally away from the first opening assisted by the fluid flow of the second fluid in the flow channel outside the liner.

The second fluid may be expelled through a second opening in the liner from inside the liner to the flow channel outside the liner. In particular, the first and second fluids are expelled into the flow channel at different longitudinal positions along the liner. E.g. the first and second openings are at different longitudinal positions in the liner wall. The first opening may be positioned downstream of the second opening. The first and second fluids, which are different, are expelled substantially

S

simultaneously through the first and second openings, respectively, to force the first particles away from the first opening affected or assisted by the second fluid.

In other words the first and second openings in the liner or conduit are in fluid communication with the flow channel. The second fluid flows through the flow channel, e.g. in a downstream direction from the second opening in the liner, past the first opening in the liner, such that the first and second fluids and the first particles flow further from the first opening in the liner to form the barrier or restriction at the desired first position. It will be appreciated that the fluid flowing in the flow channel comprises a mixture of the first fluid and the second fluid.

The invention is specifically for liners in wellbores which extend horizontal or near-horizontal. In other words, the subsurface portion of the liner in which the first and/or second openings and/or in which the first position, where the barrier or restriction is formed, are located, extends horizontal or near-horizontal, The liner should have to the horizontal an angle of smaller than 30°, preferably smaller than 15°, which shall be understood by "near-horizontal".

Thus, the invention specifically provides a technique for forming barriers or restrictions in horizontal or near-horizontal wellbores in an earth formation.

Advantageously, the first particles of the first fluid can be forced away from the first opening located in a horizontal or near-horizontal section of the liner, thereby preventing the first opening to be blocked. Furthermore, the position where the first particles settle and aggregate to form the barrier or restriction can be controlled by parameters of the first and/or second fluid. Therewith the barrier or restriction can be positioned at a desired subsurface position in the flow channel along the horizontal or near-horizontal section of the liner.

Preferably, more than one barrier or restriction can be formed at different longitudinal positions in the flow channel along the liner. Moreover, by controlling the parameters of the first and/or second fluid, further properties of the barrier or restriction may be affected or controlled, including e.g. at least one dimension, size, radial extent, thickness or extent in the longitudinal direction of the flow channel, permeability to fluid flow, density, porosity or the like.

For example, in situations where a formation or tubular is damaged, e.g. allowing inflow of undesirable material, such as water, one or more barriers or restrictions may be formed in the flow channel at selected separate positions along the liner to isolate the relevant section. In other words, the method may comprise forming multiple artificial barriers or restrictions along the liner. For example, the method may comprise forming a first artificial barrier or restriction and a second artificial barrier or restriction at a position different to that of the first artificial barrier or restriction. The method may comprise varying at least one of the properties or parameters of the fluid, or particles from that used to form the first artificial barrier or restriction in order to form the second artificial barrier or restriction at a different position in the flow channel to the first artificial barrier or restriction.

The one or more artificial barriers or restrictions may be removed again when being no longer needed, e.g. by expelling a further fluid into the flow channel, for example through the first and/or second opening in the liner with high pressure and/or by adding chemicals to the fluid, which chemicals reduce the bonding or friction between the settled and aggregated particles of the previously formed barrier or restriction or dissolve the first and/or second particles.

In particular, a first and/or second hole is created by being punched by a punching tool inside the liner in the circumferential wall of the liner to form the first and/or second opening, respectively, before expelling the first and second fluid through the first and second holes out of the liner.

Advantageously, such holes can be punched at any desired longitudinal position of the liner, which can be reached by the punching tool.

The second fluid is preferably different to the first fluid. The first fluid may have different properties or a different composition to the second fluid. For example, the second fluid may have a lower concentration of particles than the first fluid or may be laden with different particles than the first fluid, or preferably contains substantially no particles. In other words, the second fluid maybe a liquid substantially not being laden with particles or a fluid laden with second particles, which are different from the first particles. If the second fluid is laden with second particles, the second particles may be designed to force the first fluid laden with the first particles forward in the flow channel rather than to quickly settle and aggregate.

Preferably, the first and second fluids are provided at the surface by mixing a first liquid with the first particles and by providing a second liquid, optionally mixed with second particles. The so mixed first and/or the optionally mixed second fluid may then be pumped through a first and/or second fluid supply pipe extending in the liner to the portion of the liner in which the first and second openings are located subsurface.

Advantageously, mixing of the first and/or second fluid laden with particles can be easily provided at the surface and the flow rate, pressure etc. of the first and/or second H fluid can be controlled e.g. by controlling the respective pumps. E.g. the flow rates of the first and/or second fluid can be controlled volumetrically and separately by the first and second pumps, respectively. Furthermore, the type of particles can be changed easily at the surface, if desired.

However, in some examples, the first and/or second fluid may be mixed with the respective particles at a subsurface.

The particles may then stored in a subsurface container.

The method may comprise controlling the formation and/or position of the barrier or restriction by controlling the relative flow and/or fluid velocities of the first and/or second fluids. The method may comprise expelling the first fluid at a first velocity into the flow channel and expelling the second fluid at a second velocity, which may differ from the first velocity, into the flow channel. The method may comprise varying the first and/or second velocities over time.

In particular, the first position in the flow channel outside the liner where the first particles settle and aggregate to form the barrier or restriction can be affected or controlled by controlling at least one parameter of the first and/or second fluid, e.g. by controlling at least one of the following parameters of the fluids or a combination thereof: -density of the first particles, -density of the first fluid, -grain size of the first particles, -grain shape of the first particles, -grain smoothness of the first particles, concentration of the first particles in the first fluid, -flow rate or fluid velocity of the first fluid in the flow channel outside the liner, -viscosity (e.g. kinematic viscosity) of the first fluid, -temperature of the first fluid, -pressure of the first fluid, -density of the second particles, -density of the second fluid, -grain size of the second particles, -grain shape of the second particles, -grain smoothness of the second particles, -concentration of the second particles in the second fluid, -flow rate or fluid velocity of the second fluid in the flow channel outside the liner, S -viscosity (e.g. kinematic viscosity) of the second fluid, -temperature of the second fluid, -pressure of the second fluid.

The size of the particles may be determined by a diameter of the particles, e.g. a mean diameter. For example, the mean diameter of the first particles may be in the range of 0.05 to 5 mm and more preferably in the range of 0.06 to 2mm.

Advantageously, the first position where the first particles settle and aggregate, thereby forming the barrier or restriction can be controlled by controlling the respective fluid parameters. However, the size and/or one or more dimensions of the barrier or restriction, such as a radial and/or longitudinal extent, may also be affected or controlled by controlling or adjusting at least one of the parameters of the first and/or second fluid.

According to a preferred embodiment of the invention, the first fluid is laden subsequently with different types of first particles, preferably first with particles of larger grain size and subsequently with particles of smaller grain size. Particles of different size have different settling and aggregating properties. The first type of first particles, e.g. the larger grain size particles, initially may build-up a barrier or restriction by settling and aggregating out of the first fluid. The second type of first particles, e.g. the smaller grain size particles, with which the first fluid is laden subsequent to the first type of first particles, may then seal the face of the barrier or restriction previously built-up by the first type of first particles.

Advantageously, the impermeability of the finally formed barrier or restriction can so be improved.

In particular, controlling the grain size of the larger grain size first type of first particles and/or the fluid flow velocity in the flow channel outside the liner may be used to affect or control the first position where the first particles form the barrier or restriction in the flow channel outside the liner. In other words, the method may comprise providing different types of first particles over time, for example, by reducing the size of particles in the first fluid to be expelled into the flow channel.

For example, a mean diameter of the larger particles may be in the range of 0.5 to 20 mm and more preferably in the range of 0.5 to 5 mm, and most preferably about 2 mm. The method may comprise forming an initial restriction with the larger particles. The method may comprise subsequently expelling the first fluid laden with particles having a smaller size than the larger particles into the flow channe1 which may seal gaps and/or spaces between the large particles. For example, an average diameter of the smaller particles may be in the range of 0.2 to 1 mm, and preferably about 0.5 mm.

The method may comprise subsequently expelling the first fluid with particles having even smaller size. For example, an average diameter of the even smaller particles may be in the range of 0.06 to 0.2 mm, and preferably about 0.08 mm.

This may help to control the first position where the barrier or restriction is formed at the desired longitudinal position along the liner while still improving the impermeability of the finally formed barrier or restriction.

In some examples, the properties of the fluid may be altered, e.g. by the use of chemicals. The properties may comprise the gelling, friction and/or floating properties of the fluid. For example, the first fluid may include a float enhancer and/or a chemical causing gelling and/or causing a friction reduction.

Therewith, the position where the first particles settle and aggregate may be affected and/or the stability of the barrier or restriction may be improved.

Further preferably, the first particles can be covered with a bonding agent and/or with a bonding enhancing reactant or catalyst and/or with a material which reacts to increase its volume in the flow channel outside the liner. This can be e.g. fluoric acid or a water absorbing polymer.

Advantageously, the stability and impermeability of the finally formed barrier or restriction can be improved therewith.

According to a preferred embodiment of the invention, the first particles may include a first type of particles in the form of magnetizable particles. A switchable magnet, e.g. a solenoid may be placed in the liner. By activating S the switchable magnet, the longitudinal position along the liner where the magnetizable particles settle and aggregate to form the barrier or restriction can be affected by the magnetic field. Generally the settling and aggregation of the magnetizable particles can be enhanced by the magnetic

field.

Advantageously, the longitudinal position of the barrier or restriction along the liner can be controlled and the quality of the barrier or restriction can be improved.

According to a preferred embodiment of the invention the first particles include a second type of particles, which may be non-magnetic particles. Those second type of particles are mixed in the fluid after the magnetizable particles have settled and aggregated and settle and aggregate on the initially formed barrier or restriction of the magnetizable particles.

This allows for improved control of quality and positioning of the barrier or restriction. Furthermore, removal of the barrier or restriction can be improved, if the barrier or restriction is no longer needed.

The invention may include the use of a downhole system which can be moved within the liner from the wellhead at the surface to the subsurface region where the artificial barrier or restriction shall be formed in the flow channel.

The downhole system may be removed after the formation of the barrier or restriction from the subsurface region where the barrier or restriction is formed in the flow channel or may remain subsurface in the liner. In other words the downhole system may be located temporarily in the subsurface region where the barrier or restriction is formed in the flow channel. The downhole system may comprise a downhole tool which is locatable at a horizontal or near-horizontal subsurface portion of the liner or conduit.

The downhole system may include one or more packers. The one or more packers may seal against the inside surface of the annular outside wall of the liner. The one or more packers may be operable to isolate the first fluid from the second fluid whilst within the conduit. The one or more packers may be installed in the liner so as to prevent mixing of the first and second fluid in the liner and the downhole tool. The one or more packers may be provided between the elongate downhole tool and the liner. The one or more packers may comprise a first, second and third packer which plug the liner at desired positions. Between the first, second and third packer a first and second isolated cavity in the liner may be defined by plugging the liner and dividing it into a first and second isolated longitudinal section. Therefore, the packers may bc referred to as isolation packers. The packers may be in the form of expandable, inflatable or swellable packers. It is apparent to the skilled person that having more than three packers shall is not to be excluded.

The first fluid is pumped through a first fluid outlet into the first isolated cavity in the liner, which is in fluid connection with the first opening in the outside ringwall of the liner to expel the first fluid into the flow channel S outside the liner. The second fluid is pumped through a second fluid outlet into the second isolated cavity in the liner, which is in fluid connection with the second opening in the outside ringwall of the liner to expel the second fluid into the flow channel outside the liner.

Thus, the downhole tool defines separate first and second passages from the first and second supply pipes to the first and second openings, respectively, and is configured to separately expel the first and second fluids into the flow channel. The first and second passages may be at least partially defined by the inside of the annular outer wall of the liner in the periphery of the downhole tool. The first and second passages may be defined between, the elongate downhole tool and the annular outer wall of the liner. In other words, the first and second passages may be configured to separately forward and expel the first and second fluids through the first and second openings, respectively, into the flow channel outside the liner.

For example, the liner can be a production or injection conduit located within a wellbore in an earth formation and the downhole system is deployed through the production or injection conduit.

Advantageously, the longitudinal position along the liner where the artificial barrier or restriction is formed can be controlled by the subsurface position to which the downhole system is moved, which is a subsurface position in a horizontal or near-horizontal portion of the liner.

If desired, two or more barriers or restrictions can be formed to isolate or restrict flow in a required portion of the flow channel between the two or more barriers or restrictions. E.g. a barrier or restriction on each side of the openings can be formed by exchanging the first and second fluids. As a result, an upstream and a downstream barrier or restriction can be formed and the openings are located between the upstream and downstream barriers or restrictions once being formed. However, the movable downhole tool can also be placed at different longitudinal positions inside the liner and the first and/or a fluid is expelled through further openings in the liner. By this, a plurality of artificial barriers or restrictions can be formed at different longitudinal positions in the flow channel outside the liner. In other words, the method may comprise moving the downhole tool once a first artificial barrier or restriction is formed to a second different position within the liner and forming a second artificial barrier or restriction.

The downhole system may comprise at least one sensor1 such as a temperature or pressure or flow sensor, e.g. for measuring, monitoring and/or recording properties of the fluid within the flow channel and/or the liner.

The downhole system may be controlled from a location at the surface. The downhole system may be controlled in response to subsurface data, which may be recorded by at least one subsurface sensor. In particular, the downhole system may comprise a subsurface controller for monitoring and/or controlling one or more parameters of the fluids.

Generally, the method may comprise measuring, monitoring and/or recording properties of the wellbore and/or of the first and/or second fluid in the flow channel.

Preferably, the particles are selected from or are a combination of the group of: -mineral based particles, e.g. sand particles, -non-magnetic metal based particles, -magnetic metal based particles, -elastomeric based particles without chemical or physical reactivity, -elastomeric based particles with chemical and/or physical reactivity, -particles with chemical and/or physical reactivity being covered by a time degradable material, e.g. a material with dissolves after a predetermined time in the fluid, and/or by a physical parameter degradable material, e.g. a material with dissolves when a solvent is pumped into the flow channel.

A further aspect of the present invention is the fluid laden with magnetizable particles for being pumped down to a subsurface portion of a liner in a weilbore in an earth formation to be expelled through an opening in the liner to form a barrier or restriction in the flow channel outside the liner, in particular to be used as the first liquid in the method disclosed herein.

The fluid may include a liquid and magnetizable particles mixed with or dispersed in the liquid. Preferably, the mean density of the particles and the liquid do not differ by more than 25%, preferably do not differ by more than 101, so that the particles are buoyant or near-buoyant. As the liquid in the weilbore is typically salt water the density of the liquid is between about 1 and 1.1 g/cm3. The preferred density of the buoyant or near-buoyant magnetizable particles is preferably in the range of 0.8 to 1.1 g/cm3. Advantageously, this may reduce the particle settling velocity so that settling and aggregating at undesired positions along the liner can be reduced, or more generally the effect of the magnetic field on the settling and aggregating of the magnetizable particles can be enhanced.

Such magnetizable particles can comprise a magnetizable metal core having a density significantly larger than the density of the liquid and a covering made of a different material, e.g. plastic, having a density lower than the density of the liquid. By this material combination buoyancy or near-buoyancy of the magnetizable particles can be achieved and designed as desired.

According to a further aspect of the invention a downhole system is provided, which is movable from surface to subsurface within a liner in a wellbore in an earth formation and which is configured to implement the method disclosed herein. The downhole system includes: a first, second and third isolation packer to define a first and second isolated annular cavity in the liner between the first, second and third isolation packer, a first fluid supply pipe extending in the liner when the downhole system is moved to a subsurface position. The first fluid supply pipe is to pump the first fluid from surface via the first fluid outlet in the first isolated cavity between the first and second isolation packer to be expelled through the first opening in the liner to the flow channel.

The second fluid is pumped from the surface via the second fluid outlet in the second isolated cavity between the second and third isolation packer to be expelled through the second opening in the liner to the flow channel. The downhole system may include a second fluid supply pipe extending in the liner when the downhole system is moved to the subsurface position for pumping the second fluid from the surface to the subsurface downhole tool.

Advantageously, the downhole system can be moved from the surface to the desired subsurface position of the liner, so that the longitudinal position along the liner where the artificial barrier or restriction is to be formed ±n the flow channel can be controlled by the subsurface position to which the downhole system is moved.

Preferably, the downhole system comprises a first and second valve in fluid connection with the first and second fluid outlet, respectively, to adjust and/or control flow of the first and second fluid, respectively, in particular the flow rate of the first and/or second fluid in tho first and/or second isolated cavity, respectively. The first and/or second valve may comprise a one-way or back flow preventer valve.

The downhole system may further comprise a punching tool to punch holes in the liner which form the first and second openings in the liner. Alternatively, the openings in the liner may be created by a drilling tool or a perforation gun. According to a preferred embodiment of the invention the downhole tool comprises a control unit to control the first and/or second valve. If desired, the downhole system may be an autonomous downhole system. However, depending on the circumstances the downhole system may also be non-autonomous.

As already indicated, the downhole system may comprise at least one switchable magnet to generate a magnetic field in the flow channel at a defined longitudinal position along the liner in the wellbore. The downhole system may comprise at least two magnets, one magnet on each side of the isolated cavities to form two barriers or restrictions, one on each side of the openings, preferably without moving the downhole system in the liner, It will be appreciated that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilized, either alone or in combination with any other defined feature or in any other aspect or embodiment of the invention. In particular, the present invention is intended to cover a downhole system configurcd to include any feature described herein in relation to the method and/or the fluid laden with particles and vice versa, It will be further appreciated that any feature disclosed herein may be an essential feature of the invention alone, even if disclosed in combination with other features, irrespective of whether disclosed in the

description, the claims and/or the drawings.

The invention is described in more detail and in view of S preferred embodiments hereinafter. Reference is made to the attached drawings wherein like numerals have been applied to like or similar components.

Brief Description of the Figures

It is shown in Fig. 1 a schematic transverse cross-sectional representation of an earth formation with a downhole system in a liner in a wellbore; Fig. 2 an enlarged schematic transverse cross-sectional representation of a horizontal subsurface portion of a liner in a weilbore in an earth formation; Fig. 3 a schematic transverse cross-sectional representation of a downhole tool located in a horizontal portion of a liner according to an embodiment of the present invention; Fig. 4 a schematic transverse cross-sectional representation of a downhole tool located in a horizontal portion of a liner according to an embodiment of the present invention; Fig. S a schematic transverse cross-sectional representation of two artificial barriers in a flow channel between the liner and the wall of a -wellbore formed by a downhole system according to the present invention; and Fig. 6 a schematic transverse cross-sectional representation of a particle for a fluid according to a further aspect of the present invention; Fig. 7 a flowchart of a method for forming a barrier or restriction in a flow channel outside a liner located within a wellbore in accordance with the present invention.

Detailed Description of the Invention

In situations where the liner or conduit is damaged or allows inflow of undesirable material, e.g. water, in a well system, it may be desirable to form one or more barriers or restrictions in the flow channel between the liner and the wellbore in the earth formation at selected locations to isolate the relevant section.

If certain conditions are met, then the particles introduced into the flow channel settle out and aggregate, thereby forming a barrier or restriction. In particular, a model is outlined in the following equation to quantify the particle settling velocity that will allow particles to settle out from a fluid in dependence on various parameters: Ws = (1) C1v+(C2D wherein Ws is the particle settling velocity, Ps is the particle density, p is the fluid density, g is the gravity constant, D is the grain size of the particles, C1 is a grain shape factor of the particles, C2 is the grain smoothness of the particles and v is the kinematic viscosity of the fluid.

(See Ferguson, R.I. and Church, M.A. "Simple Universal Equation for Grain Settling Velocity", Journal of Sedimental Research, 74 (6) 933, 937, 2005, which is incorporated to the present disclosure by reference) By controlling the parameters of the fluid laden with particles, conditions resulting in the particles settling out from the fluid to form a barrier or restriction can be caused at selected locations. According to equation (1) such parameters are particle density, fluid density, particle size, particle shape, particle smoothness and kinematic viscosity of the fluid.

Generally, it is possible to determine or select whether or not the barrier or restriction is formed, the location at which the barrier or restriction is formed and/or various properties of the barrier or restriction, such as a radial extent, thickness, porosity, permeability, etc. In this way, control of such parameters can be used, for example, to selectively form one or more barriers or restrictions at selected locations in the flow channel and having the required properties to control or block the flow in the flow channel and/or to isolate selected sections of the flow channel. However, it will be appreciated that equation (1) represents and idealized situation. Further parameters or properties, including parameters or properties of a further fluid expelled in the flow channel can be used to control the settling and aggregating of the particles and the formation of the one or more barriers or restrictions.

Referring to Fig. 1 a welibore 2 is drilled in an earth formation 4 to exploit natural resources like oil or the like. The wellbore 2 has a vertical section 2a from the surface 6 and is continuously extending via a curved section 2b to a horizontal. section 2c located distal from the wellhead S. The horizontal section 2c may terminate subsurface at a terminating end 2d of the wellbore 2.

A liner 12 in the form of an elongate conduit is located within the welibore 2. The liner or conduit also includes a vertical section 12a beginning at the wellhead S at surface 6 and continuously extends via a curved section l2b to a horizontal section l2c located in the horizontal section 2c of the wellbore 2, The wellbore 2 and the liner or conduit located within the welibore 2 define a flow channel 14 for fluid flow outside the liner 12. The annular flow channel 14 is defined by outside surface 13 of the liner 12 and inside surface 3 of the wellbore 2.

Referring to Fig. 2 a first opening 22 in the form of a hole is provided in the annular outside wall 13 of the liner 12. A first fluid Vl laden with particles is expelled or injected through the first opening 22 from inside the conduit 12 into the flow channel 14 between the liner 12 and the inside wall 3 of the weilbore 2. The first fluid Vi laden with first particles is forced away from the first opening 22 in downstream direction visualised by arrow 26 (right direction in Fig. 1-5) Referring to Pig. 3 a downhole tool 32 of a downhole system 34 is positioned in the horizontal section 12c of the liner 12. The downhole tool 32 defines the subsurface terminating end of the downhole system 34. The elongate downhole tool 32 includes a first, second and third inflatable isolation packer 42, 44, 46 which are sealing against the inside 13 of the well liner 12 to divide the inner volume of the liner 12 in separated isolated sections 43, 45. The first and second isolation packer 42, 44 define the first isolated cavity 43 in-between and the second and third isolation packer 44, 46 define the second isolated cavity in-between.

The first fluid Vl laden with the first particles is provided via a first supply pipe 50 extending longitudinally within the liner 12 to a first fluid outlet 52 in the first cavity 43. From the first cavity 43 the first fluid laden with first particles is expelled through the first opening 22 from inside the liner 12 to the flow channel 14 outside a liner 12.

In this example, a second fluid V2 is provided via a second fluid outlet 54 into the second isolated cavity 45 to be expelled or injected through a second opening 24 in the annular outside wall of the liner 12 from inside the liner 12 into the flow channel 14 outside the liner 12. At least a portion of the second fluid V2 flows from the second opening 24 downstream, represented by arrow 26. The second fluid V2 then forces downstream the first fluid Vl laden with the first particles and being expelled through the first opening 22, which is located downstream the second opening 24. Therewith, the overall fluid flow in the flow channel 14 is effected also by the second fluid V2, and the first particles contained in the first fluid Vl are forced away from the first opening 22, in this example in downstream direction 26, supported by the flow of the second fluid V2. At a first position downstream the first opening 22 the first particles contained in the first fluid Vi settle out of the fluid and aggregate within the flow channel 14, thereby forming an artificial barrier or restriction 62. In this example, the barrier 62 forms a blockage which completely blocks the flow channel 14 around the liner 12 at the first position in the flow channel 14.

The flow of the first and second fluids Vl, V2 is controlled by a first and second valve 56, 58, respectively. A control unit 60 is located within a control box 59 in the downhole tool 32 and controls the first and second valves 56, 58.

The downhole tool 32 further includes a pressure sensor 48 and a temperature sensor 49 which measure the pressure and temperature of the first fluid Vl laden with first particles. In this example, sensors 48, 49 measure the pressure and the temperature in the first isolated cavity 43. Sensors 48, 49 may be attached to the first isolation packer 42 and deliver the measured data to the control unit and/or to a controller at the surface 6 (not shown) Referring back to Fig. 1, the first fluid Vi laden with the first particles is pumped by a first surface pump 72 from a vessel 76 via the welihead 8 in the first supply pipe 50 extending from the surface to the downhoie tool 32. f'lost specifically, the first supply pipe 50 extends through the second and third isolation packers 44, 46 to within the first isolated cavity 43 to provide the first fluid Vl laden with the first particles from the surface to the first fluid outlet 52. The second fluid V2 is pumped by a second surface fluid pump 74 via the wellhead 8 to the downhole tool 32. The flow of the first and second fluids Vl, \72 may be controlled volumetrically by the pumps 72, 74.

In this example, the second fluid V2 is pumped directly through the liner 12 to the second valve 58 and to the second fluid outlet 54. However, it will be appreciated that the downhole system may employ dual completion strings and the second fluid V2 may be pumped through a second supply pipe extending from surface to the downhole tool 32.

Referring to Fig. 4 a further embodiment of the downhole tool 32 is shown. This downhole tool 32 further includes a first and second electric magnet 82, 84. The first electric magnet 82 is located downstream the first and second openings 22, 24 and the second electric magnet 84 is located upstream the first and second openings 22, 24.

In this example, the first fluid Vl is laden with magnetizable first particles. Therewith, the formation of a first barrier 62 and a second barrier 64 is supported by the magnetic fields created by the first and second electric magnets 82, 84 by enhancing the settling out of the particles of the first fluid Vi and the aggregation to form the barriers. For forming the second barrier 64 the first and second fluids Vi, V2 are exchanged.

Referring to Fig. 5 the downhole tool 32 is removed from the portion of the liner 12 where the barriers 62, 64 are formed, so that Fig. 5 shows the desired result achieved by the present invention. As a result, a first and second artificial barriers 62, 64 to flow are created in the flow channel 14 around the liner 12. By the first and second barriers 62, 64 a horizontal section 16 of the flow channel 14 is isolated from the rest of the flow channel 14.

Referring to Fig. 6 an example of a magnetizable particle 92 is shown. The magnetizable particles include a magnetizable metal core 94, e.g. made of iron. It will be appreciated that the density of iron is higher than the density of the liquids typically involved in a wellbore.

The iron core 94 is therefore coated with a plastic cover 96, e.g. a polymeric cover which has a density lower than that of the involved liquids. By selecting appropriate densities and relative diameters of the core 94 and the cover 96, the magnetizable particle 92 can be designed to be buoyant or near-buoyant, e.g. wherein the mean density of the magnetizable particles is in the range of 0.8 g/cm3 to 1.1 g/cm3. Using buoyant or near-buoyant magnetizable particles 92 improves preventing of blockages of the first opening 22. Nevertheless, settling and aggregation of the buoyant magnetizable particles 92 can still be induced or effected by the electric magnets 82, 84.

By controlling the flow of the first and/or second fluids Vl and V2 volumetrically the concentration of first particles in a flow channel 14 can be controlled such, that the first particles settle out and aggregate at a desired position thereby forming the one or more artificial barriers 62, 64 in the flow channel 14 between the inner wall 3 of the wellbore 2 and the well liner 12. Therewith, the flow path defined by the flow channel 14 in the wellbore 2 in the earth formation 4 around the well liner 12 can be closed by implementing the present invention. The one or more artificial barriers £2, 64 formed by the present invention can be positioned as desired by controlling the parameters and/or properties of the first and/or second fluids Vi, V2. Furthermore, the longitudinal and/or radial dimensions of the barriers 62, 64 and/or their impermeability or resistance against flow can be controlled. Inflow and/or outflow between the barriers 62, 64 are still possible. Furthermore, positioning of the one or more artificial barriers 62, 64 is possible under given flow and/or pressure regimes in the earth formation 4.

A method for forming a barrier or restriction 62,64 in a flow channel 14 outside a liner 12 extending in a subsurface welibore 2 in an earth formation 4 is depicted in Fig. 7.

The downhole tool 32 is moved subsurface within the liner (102) . Once the downhole system is positioned, the first fluid Vi laden with the first particles is expelled through the first opening into the flow channel (104) and the second fluid is expelled through the second opening (106) The one or more artificial barriers 62, 64 are formed by settling out and aggregating the first particles in the flow channel (108). Removing the downhole tool 32 from the region of the welihore, where the one or more barriers 62, 64 have been formed (110) It will be appreciated that the above-described embodiments of the invention have been set forth solely by way of example and illustration of the principles thereof and that further modifications and alterations may be made therein without thereby departing from the scope of the invention.