Downhole fluid control system

Abstract

A fluid flow control device serving as an inflow port from a fluid reservoir (R) to the interior of a production pipe (S) is in the form of a housing (3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3l). The housing has a primary flow path (18) and a secondary flow path (19). The secondary flow path is in fluid communication with a chamber (B) in which is arranged an actuator (5) for a valve device (4), the valve device arranged to open and close the primary flow path. At least one flow restrictor (1,2) is arranged in the secondary flow path, the flow restrictor arranged to provide a pressure to chamber (B) sufficient to actuate the valve to an open position when the fluid flowing through the secondary flow path is oil, and a pressure sufficient to actuate the valve to a closed position when the fluid has a viscosity and/or density less than oil.

Claims

1. A downhole fluid flow control system comprising: a fluid control module having an upstream side and a downstream side, the fluid control module including a main fluid pathway in parallel with a secondary fluid pathway each extending between the upstream and downstream sides; a valve element disposed within the fluid control module, the valve element operable between an open position wherein fluid flow through the main fluid pathway is allowed and a closed position wherein fluid flow through the main fluid pathway is prevented; a viscosity discriminator disposed within the fluid control module, the viscosity discriminator having a viscosity sensitive channel that forms at least a portion of the secondary fluid pathway; and a differential pressure switch operable to shift the valve element between the open and closed positions, the differential pressure switch including a first pressure signal from the upstream side, a second pressure signal from the downstream side and a third pressure signal from the secondary fluid pathway, the first and second pressure signals biasing the valve element toward the open position, the third pressure signal biasing the valve element toward the closed position; wherein, a magnitude of the third pressure signal is dependent upon the viscosity of a fluid flowing through the secondary fluid pathway; and wherein, the differential pressure switch is operated responsive to changes in the viscosity of the fluid, thereby controlling fluid flow through the main fluid pathway, whereby the valve element is caused to move to the closed position when an undesired fluid with an undesired viscosity passes through the viscosity discriminator.

2. The flow control system as recited in claim 1 wherein the valve element has first, second and third areas and wherein the first pressure signal acts on the first area, the second pressure signal acts on the second area and the third pressure signal acts on the third area such that the differential pressure switch is operated responsive to a difference between the first pressure signal times the first area plus the second pressure signal times the second area and the third pressure signal times the third area.

3. The flow control system as recited in claim 1 wherein the viscosity discriminator further comprises a viscosity discriminator disk.

4. The flow control system as recited in claim 3 wherein the viscosity sensitive channel further comprises a tortuous path of the viscosity discriminator.

5. The flow control system as recited in claim 4 wherein the tortuous path is formed on a surface of the viscosity discriminator.

6. The flow control system as recited in claim 4, wherein the tortuous path further comprises at least one circumferential path.

7. The flow control system as recited in claim 4, wherein the tortuous path further comprises at least one reversal of direction path.

8. The flow control system as recited in claim 1, wherein the third pressure signal is from a location downstream of the viscosity sensitive channel and wherein the third pressure signal is a total pressure signal.

9. The flow control system as recited in claim 1, wherein the magnitude of the third pressure signal increases with decreasing viscosity of the fluid flowing through the secondary fluid pathway.

10. The flow control system as recited in claim 1, wherein the magnitude of the third pressure signal created by the flow of a desired fluid through the secondary fluid path shifts the valve element to the open position and wherein the magnitude of the third pressure signal created by the flow of a undesired fluid through the secondary fluid path shifts the valve element to the closed position.

11. A downhole fluid control method comprising: positioning a fluid flow control system at a target location downhole, the fluid flow control system including a fluid control module having an upstream side and a downstream, a viscosity discriminator and a differential pressure switch, the fluid control module including a main fluid pathway in parallel with a secondary fluid pathway each extending between the upstream and downstream sides, the viscosity discriminator having a viscosity sensitive channel that forms at least a portion of the secondary fluid pathway; producing a desired fluid from the upstream side to the downstream side through the fluid control module; operating the differential pressure switch to shift the valve element to the open position responsive to producing the desired fluid by applying a first pressure signal from the upstream side to a first area of the valve element, a second pressure signal from the downstream side to a second area of the valve element and a third pressure signal from the secondary fluid pathway to a third area of the valve element; producing an undesired fluid from the upstream side to the downstream side through the fluid control module; and operating the differential pressure switch to shift the valve element to the closed position responsive to producing the undesired fluid by applying the first pressure signal to the first area of the valve element, the second pressure signal to the second area of the valve element and the third pressure signal to the third area of the valve element; wherein, a magnitude of the third pressure signal is dependent upon the viscosity of a fluid flowing through the secondary fluid pathway such that the viscosity of the fluid operates the differential pressure switch, thereby controlling fluid flow through the main fluid pathway.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics of the invention will be clear from the following description of embodiments, given as non-restrictive examples, with reference to the attached sectional sketches and drawings wherein:

(2) FIG. 1a illustrates a principle behind the invention and the invented flow control device in a basic form;

(3) FIG. 1b illustrates the correlation between change in pressure inside the chamber (i.e. between the fluid restrictors), and the change in fluid viscosity;

(4) FIG. 2 is a principle sketch of the flow control device of the invention;

(5) FIG. 3 is a principle sketch illustrating a second embodiment of the flow control device according to the invention;

(6) FIG. 4 illustrates a third embodiment of the flow control device according to the invention;

(7) FIG. 5 illustrates a fourth embodiment of the flow control device according to the invention;

(8) FIG. 6 illustrates a fifth embodiment of the flow control device according to the invention;

(9) FIG. 7 illustrates a sixth embodiment of the flow control device according to the invention;

(10) FIG. 8 illustrates a seventh embodiment of the flow control device according to the invention;

(11) FIG. 9 illustrates an eight embodiment of the flow control device according to the invention;

(12) FIG. 10 illustrates a ninth embodiment of the flow control device according to the invention;

(13) FIG. 11 illustrates a tenth embodiment of the flow control device according to the invention;

(14) FIG. 12 illustrates a tenth embodiment of the flow control device according to the invention;

(15) FIGS. 13a and 13b are plots illustrating closing and opening forces for oil and water, respectively, in an embodiment of the invented flow control device configured for autonomously stopping water from entering a flow of oil; and

(16) FIG. 14 is a plot illustrating closing and opening forces as a function of pressure in an embodiment of the invented flow control device configured for autonomously stopping fluid flow at a predetermined pressure difference.

DETAILED DESCRIPTION OF EMBODIMENTS

(17) FIG. 1a illustrates how a fluid F flows into a conduit 3a at a first pressure p.sub.1, through a first flow restrictor 1 and into a chamber B where it attains a second pressure p.sub.2, and then flows through a second fluid flow restrictor 2 before it exits the conduit 3a at a third pressure p.sub.3. When the fluid flow rate and fluid properties (e.g. viscosity, density) are constant, the pressures (p.sub.1, p.sub.2, p.sub.3) are constant, and p.sub.1, >p.sub.2, >p.sub.3.

(18) In FIG. 1a, the first flow restrictor 1 is a porous element and the second flow restrictor 2 is an orifice.

(19) In general, the flow characteristics through a porous medium may be described using Darcy's law (i.e. laminar flow), expressed as:

(20) $\begin{array}{cc}Q=\frac{{\kappa }_{\mathrm{perm}}.Math.A}{\mu }.Math.\frac{\Delta P}{\Delta L}\mathrm{where}\text{:}Q=\mathrm{fluid}\mathrm{flow}\mathrm{rate}\left(\mathrm{units}\mathrm{of}\mathrm{volume}\mathrm{per}\mathrm{unit}\mathrm{time}\right){\kappa }_{\mathrm{perm}}=\mathrm{relative}\mathrm{permeability}\mathrm{of}\mathrm{the}\mathrm{porous}\mathrm{medium}\left(\mathrm{typical}\mathrm{unit}\text{:}\mathrm{Darcy}\right)A=\mathrm{cross}\text{-}\mathrm{sectional}\mathrm{area}\mathrm{of}\mathrm{the}\mathrm{porous}\mathrm{medium}\text{.Math.}\mu =\mathrm{viscosity}\mathrm{of}\mathrm{the}\mathrm{fluid}\left(\mathrm{typical}\mathrm{unit}\text{:}\mathrm{centipoise};\mathrm{SI}\mathrm{unit}\text{:}\mathrm{Pa}*s\right)\Delta P=\mathrm{differential}\mathrm{fluid}\mathrm{pressure}\mathrm{across}\mathrm{the}\mathrm{permeable}\mathrm{medium}\left(\mathrm{typical}\mathrm{unit}\text{:}\mathrm{Pa}\right),\mathrm{and}\Delta L=\mathrm{the}\mathrm{length}\mathrm{of}\mathrm{the}\mathrm{porous}\mathrm{medium}\mathrm{running}\mathrm{parallel}\mathrm{to}\mathrm{the}\mathrm{fluid}\mathrm{flow}.& \left(\mathrm{Equation}1\right)\end{array}$

(21) Thus, when flowing through the porous element 1, the fluid will undergo a pressure drop ΔP (from p.sub.1 to p.sub.2 in FIG. 1a) in accordance with Darcy's law (Equation 1), from which it may be derived that the change in pressure (ΔP) across the porous element is proportional to the fluid viscosity (μ) and the fluid flow rate (Q).

(22) The flow characteristics in a fluid flowing through an orifice or another restrictor (i.e. turbulent flow), may be expressed as:

(23) $\begin{array}{cc}\Delta P=K_{\mathrm{orifice}}\frac{\rho .Math.v^2}{2}\mathrm{where}\text{:}\Delta P=\mathrm{differential}\mathrm{fluid}\mathrm{pressure}\mathrm{across}\mathrm{the}\mathrm{orifice}\left(\mathrm{typical}\mathrm{unit}\text{:}\mathrm{Pa}\right)K_{\mathrm{orifice}}=\mathrm{orifice}\text{-}\mathrm{specific}\mathrm{coefficient}\left(\mathrm{dimensionless}\right)\rho =\mathrm{fluid}\mathrm{density}\left(\mathrm{unit}\mathrm{of}\mathrm{mass}\mathrm{per}\mathrm{unit}\mathrm{of}\mathrm{volume}\right)v=\mathrm{fluid}\mathrm{velocity}\left(\mathrm{units}\mathrm{of}\mathrm{length}\mathrm{per}\mathrm{unit}\mathrm{time}\right)& \left(\mathrm{Equation}2\right)\end{array}$

(24) Thus, when flowing through the orifice 2, the fluid experiences a pressure drop (ΔP) (from p.sub.2 to p.sub.3) which may be described by equation 2. The change in fluid pressure across the orifice is almost independent of viscosity, but proportional to the density and the orifice coefficient, and to the fluid velocity squared.

(25) Therefore, referring to FIG. 1a, the fluid pressure p.sub.2 in the chamber B—between the porous element 1 and the orifice 2—will change if the properties (viscosity or density) of the fluid changes. This is illustrated graphically in FIG. 1b, showing a first (lower) value for p.sub.2 at a higher fluid viscosity (μ.sub.high) and a second (higher) value for p.sub.2 at a lower fluid viscosity (μ.sub.low). This difference between the values for p.sub.2 (ΔP.sub.2) occurring when the viscosity changes (e.g. decreases) may be used to perform work, for example actuate an actuator 5, which in turn may move a piston/body and/or a valve (not shown in FIG. 1a).

(26) Although the invention is explained hereinafter with reference to fluids flowing through a porous element and an orifice, and utilizing the change in viscosity, it should be understood that the invention applies to any combination of fluid flow restrictors where the first provides turbulent flow (completely or substantially) and the other provides laminar flow (completely or substantially), or vice versa.

(27) In general, the present invention utilizes the change in pressure (ΔP.sub.2) that occurs between two different flow restrictors when subjected to fluids of different properties, e.g. oil and water. These properties may be viscosity, as described above, but also density, as is evident from Equation 2. The two flow restrictors are configured to impose different flow characteristics on the fluids. In the example discussed above, the first flow restrictor 1 generates a substantially laminar flow and the second flow restrictor 2 generates a substantially turbulent flow.

(28) FIG. 2 is a schematic illustration of one application of the principle described above, and illustrates an embodiment of the invented flow control device in a basic form (i.e. seals, gaskets and other required ancillary parts known in the art are not shown). A fluid flow (F) enters a housing 3b having a primary flow path (conduit) 18b and a secondary flow path (conduit) 19b. The major portion (F.sub.0) of the fluid (F) flows through the primary conduit 18b and a valve 4b (which initially is open), while a smaller portion (f) of the fluid (F) flows through the secondary conduit 19b via a first fluid restrictor 1 in the form of a porous member (generating laminar flow) and via a second fluid restrictor 2 in the form of an orifice, before it re-enters the primary conduit 18b and exits out of the conduit 18b. When the viscosity (μ) of the fluid (F) flow changes, the pressure p.sub.2 in the chamber B situated in the secondary conduit 19b (defined by the two fluid restrictors) also changes as described above. For example, if a flow of oil F is replaced by water, the viscosity decreases and the pressure p.sub.2 increases (as explained above with reference to FIGS. 1a and 1b).

(29) FIG. 2 furthermore shows (schematically) that an actuator 5b is arranged in the chamber B. The actuator 5b is connected via transmission means 6 (e.g. hydraulic linkage, mechanical linkage or signal cable) to the valve 4b. When the fluid viscosity (μ) changes as described above, the difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b) imparts an actuating force on the actuator 5b, which in turn operates (e.g. closes) the valve 4b. Thus, the conduits and fluid restrictors may be configured and dimensioned such that (when breakthrough is to be prevented) the valve 4b automatically closes when the viscosity (μ) of the fluid (F) drops below a predetermined level. Thus, in an oilfield application, this device prevents unwanted water and/or gas inflow into a production string.

(30) Another embodiment of the invented flow control device is schematically illustrated in FIG. 3. A housing 3c is arranged in a flow path between a fluid reservoir R and the interior of a production pipe S. The housing 3c comprises an inlet 7 in fluid communication with the reservoir R and an outlet 8 in fluid communication with the production pipe S. Inside the housing 3c is a valve member 4c in the form of a movable body or piston (hereinafter also generally referred to as a body). The body 4c is supported in the housing 3c by bellows 9c comprising a structural and resilient member such as a helical spring (not shown). The body 4b further comprises a first fluid restrictor 1 in the form of a porous member. The body 4c and bellows 9c define a chamber B inside the housing 3c, while a second fluid restrictor 2 in the form of an orifice provides a fluid outlet from the chamber B.

(31) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3c through the inlet 7. Inside the housing 3c, the major portion F.sub.0 of the fluid F follows a primary conduit 18c before it exits the housing 3c through the outlet 8 and flows into the production pipe S. The remaining portion f of the fluid F flows through the porous member 1 in the body 4b and into a secondary conduit 19c defined by the chamber B before it exits the chamber B through the orifice 2, and flows into the production pipe S. If water and/or gas enters the flow F, causing the overall viscosity μ to drop, the resulting difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b) is serving to exert a pressure against a body surface 5c. This change in pressure, acting on the body surface 5c, generates a motive force which serves to close the body 4c against the inlet 7, thus preventing fluid from entering the housing 3c.

(32) FIG. 4 illustrates yet another embodiment of the invented flow control device. The housing 3d comprises an upper part 11d and a lower part 12d. The two parts 11d,12d are joined together by a threaded connection 20 with seals (e.g. o-rings) 16b. The housing 3d has an inlet 7 and radially arranged outlets 8. A member 4d is arranged for movement (in the figure: up and down) inside the housing 3d. O-rings 16a seal between the movable member and the housing interior wall. A chamber B is thus defined by the movable member 4d and the lower part 12d of the housing 3d. The movable member 4d (in this embodiment: a piston) comprises a first fluid restrictor 1 in the form of a porous member and a second fluid restrictor 2 in the form of an orifice.

(33) This embodiment of the flow control device further comprises a fluid restrictor element 32, here in the form of a face which serves to progressively choke the flow out of the orifice 2 as the movable piston 4d is moved towards the sealing surface 14.

(34) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3d through the inlet 7. Inside the housing 3d, the major portion F.sub.0 of the fluid F follows a primary conduit 18d before it exits the housing 3d through the outlets 8. A portion f of the fluid F flows through the porous member 1 in the piston 4d and into the chamber B before it exits the chamber though the orifice 2, and is mixed with the flow from the primary conduit. In this embodiment of the control device, the difference in values for p.sub.2 (ΔP.sub.2) as the fluid viscosity μ changes, is serving to exert a pressure against a piston surface 5d. This change in pressure, acting on the piston surface 5d, generates a motive force which serves to close the piston 4d against the inlet 7. The sealing surfaces 14 and 15 are brought together, thus substantially preventing fluid from entering the housing 3d.

(35) FIG. 5 illustrates a further embodiment of the inventive flow control device. The housing 3e comprises an upper part 11e and a lower part 12e, in which the upper and lower parts 11e,12e are joined together by a threaded connection 20 with seals (e.g. o-rings) 16b. The housing 3e has an inlet 7 and radially arranged outlets 8. A member 4e is arranged for movement (in the figure: up and down) inside the housing 3e, guided by a supporting structure 17. Resilient bellows 9e extend between the movable member 4e and the lower housing 12e, thus forming a chamber B together with the movable member 4e and the lower part 12e of the housing 3e. The movable member 4e comprises a first fluid restrictor 1 in the form of a porous member, and the lower housing 12e comprises a second fluid restrictor 2 in the form of an orifice.

(36) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3e through the inlet 7. Inside the housing 3e, the major portion F.sub.0 of the fluid F follows a primary conduit 18e before it exits the housing 3e through the outlets 8. A portion f of the fluid F flows through the porous member 1 in the movable member 4e and into the chamber B before it exits the chamber B though the orifice 2. In this embodiment of the control device, the difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b) as the fluid viscosity μ changes is serving to exert a pressure against a surface 5e on the movable member and thereby to close the movable member 4e against the inlet 7. The sealing surfaces 14, 15 are hence brought together, resulting in a substantially prevention of fluid F from entering the housing 3e.

(37) FIG. 6 illustrates a further embodiment of the invented flow control device. The housing 3f comprises an upper part 11f and a lower part 12f, the upper and lower parts 11f,12f being joined together to form a primary conduit 18f that runs along the interior walls of the housing 3f from the inlet 7 to radially arranged outlets 8. The joining of the two parts 11f,12f may for example be obtained by screw connection or welding (not shown). A piston-shaped member 4f is arranged for translational movement (in the figure: up and down) inside the housing 3f, guided by a suitable supporting structure, thus forming a chamber B situated between a lower surface 5f of the member 4f and the inner walls of the lower part 12f. The movable member 4f comprises a first fluid restrictor 1 in the form of a porous member and a second fluid restrictor 2b in the form of an orifice, thereby forming a second conduit 19f defined by the chamber B. Both the first 1 and the second restrictor 2b extend axially through the member 4f. The size of the orifice 2b opening may advantageously be of variable radial width. Likewise, the lower housing 12f may comprise another second fluid restrictor 2c in the form of an orifice. In yet another embodiment an appropriate filter 22 may be arranged at one or more of the outlets 8 to prevent any impurities such as particles to enter (and thus block or limit) the flow. The movable member 4f and the lower housing 12f are configured to form a fluid restrictor element or area 32a, here in the form of a corner opening, which serves to progressively choke the flow out of the orifice 2b,2c as the pressure builds up in chamber B and in the fluid restrictor area 32a. The purpose of the illustrated protrusions 23 is to avoid complete closure of orifice(s) 2 during flow of fluid phases having lower viscosities than the desired phases such as oil.

(38) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3f through the inlet 7. Inside the housing 3f, the major portion F.sub.0 of the fluid F follows a primary conduit 18f before it exits the housing 3f through the outlets 8. A minor portion f of the fluid F flows through the porous member 1 in the movable member 4f and into the chamber B before it exits the chamber B though the orifice 2b located in the movable member 4f and/or the orifice 2c located in the lower part 12f. Also in the embodiment of the control device shown in FIG. 6, the difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b) as the fluid viscosity μ changes is serving to exert a pressure against the lower surface 5f on the movable member 4f and to close the movable member 4f against the inlet 7. Sealing surfaces 14, 15 on the inside walls of the upper part 11f and the upper surface of the movable member 4f, respectively, are thus brought together to substantially prevent fluid F from entering the housing 3f. Due to its reinforcing stagnation effect the fluid restrictor area 32a contributes to a more efficient closing of the primary conduit 18f during entrance of fluid phases having low viscosities.

(39) FIG. 7 illustrates a further embodiment of the inventive flow control device. The housing 3g constitutes an integral part where its interior are constructed to form a primary conduit 18g running along the interior walls of the housing 3g from the inlet 7 to one or more radially arranged outlets 8. A translationally movable member 4g arranged inside the housing 3g is composed of an upper part 4gu and a lower part 4g1, e.g. joined together by a threaded connection (not shown) and seals (e.g. o-rings) 16g. The upper 4gu and lower 4gl parts of the member 4g may be guided by an appropriate supporting structure (not shown) and configured for opposite directed relative movements (in the figure: up and down) inside the housing 3g. A chamber B is thus defined by the interior walls of the assembled member 4g. The member 4g (in this embodiment: a piston) further comprises a first fluid restrictor 1 in the form of a porous member and two second fluid restrictors 2b,2c, e.g. in the form of an variable and a fixed orifice, respectively, thereby forming a second conduit 19g defined by the chamber B. Alternatively the control device may have just one orifice 2 of either variable type 2b or fixed type 2c, or two fluid restrictors 2 of the same type. As for the embodiment shown in FIG. 6 a filter 22 may be arranged in one or more of the outlets 8 to prevent any impurities such as particles to enter and thus block or limit the flow. The purpose of the illustrated protrusions 23 is to avoid complete closure of orifice 2c during flow of fluid phases with lower viscosities than desired phases such as oil.

(40) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3g through the inlet 7. Inside the housing 3g, the major portion F.sub.0 of the fluid F follows a primary conduit 18g before it exits the housing 3g through the outlet(s) 8. A portion f of the fluid F flows through the porous member 1 arranged in the movable member 4g and into the chamber B before it exits the chamber B through the orifice 2b located on the upper part 4gu of movable member 4g and/or the orifice 2c located on the lower part 4g1 of the movable member 4g. Also in this embodiment of the control device, the difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b), as the fluid viscosity μ changes, is serving to exert a pressure against surfaces 5g on the interior walls of the movable member 4g and therefore to close the upper part 4gu against the inlet 7. The sealing surfaces 14,15 are thus brought together, thus substantially preventing fluid F from entering the housing 3g.

(41) FIG. 8 illustrates a further embodiment of the inventive flow control device. The housing 3h constitutes one part, where its interior is constructed to form a primary conduit 18h running along the interior walls of the housing 3h from a tangential inlet 7 to an outlet 8. A member 4h, in this example formed as a piston, is arranged via appropriate seals 16h to the inside of housing 3h, thereby forming a chamber B between an upper surface 5h of the member 4h and the upper interior walls in the housing 3h. The member 4h may be movable (in this embodiment: a piston going up and down) or may comprise bellows (or any other stretchable means) extending at least partly over the radial cross section set by the interior walls of the housing 3h. Alternatively the member 4h may be a combination of bellows/stretchable means and more rigid material(s). The member 4h may furthermore optionally comprise one or more second fluid restrictors 2 in the form of orifice(s) located e.g. in the center of the member 4h. Further, one or more conduits 24 extending within the housing 3h from the outlet 8 to the chamber B have optionally porous element(s) 1 arranged in the conduit(s) 24. The induced whirls at the outlet 8 creates a high pressure area which results in a higher pressure in chamber B, and thus a more efficient closure. The combination of one or more second fluid restrictors 2 and said conduit(s) 24 constitutes a secondary conduit 19h for flow of a minor portion f of the fluid F.

(42) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3h through the tangential inlet 7. Inside the housing 3h the fluid F follows a primary conduit 18h before it exits through the outlet 8, inducing a high pressure area with whirls. A minor portion f of the fluid F may flow into the conduit(s) 24, optionally through any porous member(s) 1, further into the chamber B and out though the orifice(s) 2 in member 4h. Also in this embodiment of the invention, the difference in values for P.sub.2 (ΔP.sub.2, see FIG. 1b), as the fluid viscosity μ changes, is serving to exert a pressure against the upper surface 5h on the member 4h. The sealing surfaces 14, 15 are brought together and thus substantially prevent fluid F from entering the housing 3h. Alternatively, if there are no second fluid restrictors 2 in the member 4h the stagnation pressure created in a stagnation area 33 and in the chamber B would still effectively force the member 4h down and thus substantially prevent fluid F from entering the housing 3h, either by rigid movement or by expansion of the bellows downward, or a combination thereof.

(43) FIG. 9 illustrates another embodiment of an inflow control device, wherein the housing 3i forms a chamber B having an inlet 7 and an outlet 8 constituting a first fluid restrictor 1 in the form of an orifice and a second fluid restrictor 2 in the form of an opening with an inserted porous material, respectively, thereby creating a second conduit 19i defined by the chamber B. Except for the introduction of a porous material at the outlet 8 creating a mainly laminar flow at its downstream side during use, and the construction of the orifice at the inlet 7 creating a mainly turbulent flow at its downstream side during use, the structural construction of the device is similar or identical to the device disclosed in the publication US 2011/0067878 A1, which hereby is included by reference.

(44) In use, a fluid flow F enters the housing 3i through the inlet/orifice 7,1. If the viscosity of the flowing fluid is sufficiently high, such as oil, a translationally moving member/actuator 4i comprising a piston 24 and spring 25 attached by appropriate seals 16i inside a second chamber 26, is in an open position, i.e. a valve member 27 enabling blocking of the outlet 8 has been lifted by the actuator 4i. This is a consequence of the corresponding high pressure (p.sub.2) formed inside the chamber B due to the high resistance set up by the second fluid restrictor at the outlet 8, which again causes the upward movement of the piston 24.

(45) Likewise, fluids with sufficiently low viscosity such as water or gas would not create sufficient pressure in chamber B to maintain the piston 24 in a raised position, thereby causing a closure of the outlet 8. An upper chamber 28 shown above the piston 24 is set in fluid communication with the outside of housing 3i via an upper conduit 29, thus ensuring a constant downward force of the actuator 4i which corresponds to the prevailing exterior pressure (p.sub.1).

(46) FIG. 10 illustrates an alternative embodiment as disclosed above for FIG. 9 in which the porous material 1 ensuring laminar flow during use is instead arranged within the upper conduit 29, and a channel/nozzle 30 is introduced that extends from the upper chamber 28 and into the output area 31 located downstream of the output 8. In this embodiment the secondary conduit 19j corresponds to the flow through the upper conduit 29 and the channel/nozzle 30.

(47) In use, a minor portion f of the fluid flow F enters the housing 3j through the upper conduit 29 and the porous material 1, and further through the channel/nozzle 30 into the output area 31. At the same time a major portion F.sub.0 of the fluid flow F flows through inlet 7 into the flow path 18j. The porous material 1 and the channel/nozzle 30 are thus acting as the first flow restrictor 1 and the second flow restrictor 2, respectively, while the upper chamber 28 has the same function as chamber B in FIG. 9. If fluids with sufficiently high viscosity such as oil are flowing into conduit 29, the moving member/actuator 4j is in an open position since the high flow resistance from the reactive material 1 creates a correspondingly low pressure in the upper chamber 28 (B), i.e. not sufficient to force the valve member 24 downward and thus causing a closure of the outlet 8. On the other hand, if fluids with sufficiently low viscosity such as water or gas are flowing into the upper conduit 29, the low resistance from the porous material 1 causes a correspondingly high pressure in the upper chamber 28 sufficient to provide a pressure on the surface 5j of the actuator 4j being high enough in order to move the valve member 24 downward, thus closing the output 8.

(48) FIG. 11 illustrates a further embodiment of the inventive flow control device, wherein the housing 3k is constructed having an actuator chamber 28 in its interiors. The device further comprises an inlet 7, a secondary inlet assembly 7′, an outlet 8 and a moving member/actuator 4k situated inside the actuator chamber 28, which actuator 4k comprises a piston 24 and spring 25 connected to the interior walls of the chamber 28 by appropriate seals 16k. The secondary inlet assembly 7′ is arranged upstream of the actuator 4k forming in its interior a pressure chamber B having an opposite situated opening with a porous material 1. Furthermore, one or more channels/nozzles 30 are introduced extending from the chamber B and completely through or around the actuator 4k, thereby forming a second conduit 19k defined by the secondary inlet assembly 7′ and the one ore more channels/nozzle 30. Except for the introduction of a porous material 1 at the secondary inlet assembly 7′, thus forming a mainly laminar flow into the pressure chamber B during use, and the introduction of channel(s)/nozzle(s) 30 through or around the moving member/actuator 4k, thus forming a mainly turbulent flow during use, the structural design of the device is similar or identical to the device disclosed in the publication US 2011/0198097 A1, which hereby is included by reference.

(49) In use, a fluid flow F enters a primary conduit 18k through a primary inlet 7. This fluid flow is then divided into a major portion F.sub.0 of the flow F going around the chamber 28 and a minor portion f of the flow F entering the pressure chamber B through porous material 1.

(50) The minor portion f further into the actuator chamber 28, subsequently through the channel(s)/nozzle(s) 30 and finally through the outlet 8 together with the major portion F.sub.0 of the flow F. The porous material 1 and the channel(s)/nozzle(s) 30 are thus acting as the first flow restrictor 1 and the second flow restrictor 2, respectively, and the pressure chamber B has the same function as chamber B in FIG. 10. If fluids with sufficiently high viscosity such as oil are flowing into the pressure chamber B the moving member/actuator 4k is in an open position since the high flow resistance induced by the porous material 1 causes a correspondingly low pressure (p.sub.2) in the pressure chamber B, i.e. not sufficient to force the piston 24 sideways, thus resulting in a closure of the outlet 8. On the other hand, if fluids with sufficiently low viscosity such as water or gas are flowing into the pressure chamber B the lower resistance set up by the porous material 1 compared with the high viscosity fluid, and the correspondingly high resistance at the channel/nozzle 30, causes a correspondingly high pressure in the pressure chamber B sufficient to move the piston 24 sideways, thus closing the output 8.

(51) FIG. 12 illustrates a further embodiment of the inventive flow control device. The housing 3l comprises an upper part 11l (left slanted lines) and a lower part 12l (right slanted lines), the upper and lower parts 11l,12l being joined together by a threaded connection 20. Various seals 16a-c (e.g. o-rings) are illustrated in the figure to prevent fluid from leaking between the upper and lower parts 11l,12l. The housing 3l has an inlet 7 and radially arranged outlets 8, thereby setting up a primary conduit 18l for the fluid F. A member 4l is arranged for movement (in the figure: up and down) inside the housing 3l, guided by a supporting structure 17. Furthermore, a secondary conduit 19l is arranged from the inlet 7 and extending along the inside walls of the housing 3l, via a chamber B extending beneath the member 4l, that is at the side of the member 4l opposite to the primary conduit 18l, and ends in fluid communication with the outside of the housing 3l at the lower part 12l. A first fluid restrictor 1 in the form of a porous member are situated near the inlet 7 in the upper part 11l and a second fluid restrictor 2 in the form of an orifice are situated in the lower part 12l, the second fluid restrictor 2 being in fluid communication with the outside of the housing 3l. Chamber B thus extends from downstream the first fluid restrictor 1 to upstream the second fluid restrictor 2.

(52) In use, a fluid flow F (e.g. oil from a subterranean reservoir) enters the housing 3l through the inlet 7. Inside the housing 3l, the major portion F.sub.0 of the fluid F follows the primary conduit 18l before it exits the housing 3l through the outlet(s) 8. A portion f of the fluid F flows through the porous member 1 into the secondary conduit 19l, via the chamber B beneath the member 4l and finally exits the chamber B through the orifice 2. In this embodiment of the control device, the difference in values for p.sub.2 (ΔP.sub.2, see FIG. 1b), as the fluid viscosity μ changes, is serving to exert a pressure against a surface 5l on the movable member and to close the movable member 4l against the inlet 7. The sealing surfaces 14, 15 are brought together and thus substantially prevent fluid F from entering the conduit 18l.

(53) Note that for all the above embodiments the invention is not limited to specific material such as porous member for the first or second fluid restrictors or a specific geometry such as an orifice for the other fluid restrictor. In fact, any choice of material and/or geometry is possible as long as one of the restrictors creates a mainly laminar flow and the other restrictor creates a mainly turbulent flow during use. Also, even if directional words such as up, down, below, above, sideways, etc. are used with reference to the drawings, in should be understood that these words are used only for clarity and should not be interpreted as limiting the directional position of the inventive control device.

(54) All of the embodiments of the inventive flow control device described above are autonomous in that they move (to close or open a fluid inlet) based on a changing property (e.g. viscosity μ) of the fluid. The porous member 1, the orifice 2 and the internal dimensions of the housing 3a-k may be designed to suit various applications.

(55) As a first example, reference is made to FIGS. 13a and 13b, showing forces (E) acting on the movable piston 4b-1 in an autonomous flow control device configured for stopping water from entering the desired oil flow phase as a function of pressure drop (p.sub.1−p.sub.3) across the flow control device. E.sub.O denotes the force that opens the control device, while E.sub.C denotes the force that closes the device. It is seen that, while the fluid control device is open when subjected to oil (E.sub.o>E.sub.c) (FIG. 13a), it closes almost instantaneously when subjected to water (E.sub.o<E.sub.c) (FIG. 13b).

(56) For a second example, reference is made to FIG. 14, showing forces (E) acting on the movable piston in an autonomous flow control device configured for stopping any fluid inflow when the pressure differential exceeds a given limit. E.sub.O denotes the force that opens the control device, while E.sub.C denotes the force that closes the device. It is seen that the fluid control device closes at pressure drop (p.sub.1−p.sub.3) of approximately 8 bar.

(57) These examples are intended to illustrate the function of the inventive inflow control device. It should be understood that the fluid flow restrictors 1,2 may be arranged and configured differently, for example essentially reversed in the flow path, if the device is intended to be used in a gas reservoir and it is desirable to prevent water from entering the production.

(58) It should be understood that the inventive flow control device may also be arranged and configured to control and prevent the inflow of other fluids, such as CO.sub.2 (which has been injected into the reservoir) and steam (injected in connection with e.g. so-called Steam-Assisted Gravity Drainage (SAGD) of heavy oil), and water in gas-producing wells.

(59) Although the invention has been described with reference to the control of well fluids (such as oil, gas, water) from a subterranean reservoir, the skilled person will understand that the invented device and method is useful in any application where the objective is to control fluid flow based on the properties (e.g. viscosity, density) of the various fluids in the flow in order to prevent unwanted fluids from entering a fluid flow. Examples of such applications are injection wells, separation processes and steam traps.