The invention relates to an autonomous inflow-control device for a production tubing in a hydrocarbon well, the inflow-control device comprising an inflow pipe which is provided with several packers that are axially spaced apart along a portion of the in- flow pipe, the packers being settable in a fluid-sealing manner against a wellbore wall for the formation of separate inflow sections in an annulus encircling the inflow-control device; and there being, arranged in each inflow section, at least one water-flow shutoff device with a valve-element assembly which is switchable between a first, open position and a second, closed position, the valve-element assembly in the first position forming a fluid flow path by a displaceable valve element being kept at distance from a valve seat by means of at least one water-soluble spacer element.

In many situations in the life of a hydrocarbon well it may be relevant to shut off the inflow of water from a structure into a production tubing. The water that is to be prevented from entering the well pipe may be injection water which has been pumped into a producing layer of the hydrocarbon-containing structure to increase the production, or it may be water following the hydrocarbons when these are flowing out of the producing layer and into the production tubing. In gas wells, the production of water creates great problems connected to the formation of hydrates and reduction of the production rate of the well. To control the inflow of water, mechanical devices such as isolation plugs, straddle packers and downhole devices controlled from the surface are often used today. Such devices often involve costly operation and often give a non-optimal shutoff of partial structures. There are also shutoff devices that are autonomous, that is to say are self- adjusting, in that they are based on hydrocarbons and water having different viscosi- ties, which is often not the case in many reservoirs.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art. The object is achieved through the features that are specified in the description below and in the claims that follow.

The invention builds on the fact that the ability of hydrocarbons and water to dissolve specific materials may be different. A production tubing in a hydrocarbon-producing well is provided with an inflow-control device in the part of the production tubing extending through a hydrocarbon-producing layer (reservoir). The inflow-control device includes several packers that may be set in a fluid-sealing manner against a wellbore wall and divide an annulus between the production tubing and the wellbore wall into separate inflow sections and prevent fluid communication between the various sections of the annulus. Each inflow section is provided with at least one autonomous water-flow shutoff device, which forms a closable fluid inlet connecting the respective annulus section to the pipe bore of the production tubing.

The packers may be swellable packers, for example. The autonomous water-flow shutoff device is configured to keep the fluid inlet open as long as there are hydrocarbons flowing into the production tubing from the associated annulus section, but closes the fluid inlet when water is beginning to enter from the annulus section. A valve-element assembly is kept in an open state by means of a retainer element, for example by a displaceable valve element being kept at a dis- tance from a valve seat by one or more spacer elements. Said spacer element is formed from a solid that dissolves on contact with water. The valve seat is fixed, and the displaceable valve element, which is preferably arranged upstream of the valve seat, is displaceable in the direction of the valve seat. The valve-element assembly is placed in a valve housing which is arranged on the production tubing and which, to- gether with the valve seat, forms an inflow chamber. One or more fluid passages are arranged between the inflow chamber and the pipe bore of the production tubing.

The spacer element may be formed from a water-soluble material, for example a salt or an acid in solid form. Alternatively, the spacer element may be formed as a sacrificial anode, that is to say be formed from a base metal having a galvanic voltage sub- stantially higher than the galvanic voltage of a cathode formed from a nobler metal and arranged near the spacer element, the spacer element being eroded away when there is an electrolytic connection between the spacer element and the cathode in the presence of an electrolyte in the form of water. The cathode may be arranged on or consist of an adjacent element, for example the production tubing, the valve element, the valve seat or the valve housing.

The water-flow shutoff device may include one or more resilient elements, which ensure that the displaceable valve element is displaced towards the valve seat when the spacer element is dissolved by water flow through the water-flow shutoff device. Alternatively, the water-flow shutoff device is arranged in such a way that a pressure difference across the displaceable valve element or gravity provides displacement of the displaceable valve element in the direction of the valve seat.

In one embodiment, the valve seat and the displaceable valve element are formed as annular plate elements encircling the production tubing and being enclosed by the valve housing, the valve seat fitting tightly against the production tubing and the valve housing, and the valve element being axially displaceable on the production tubing and in the valve housing. The valve seat and the valve element are provided with through cut-outs, the cut-outs on the valve seat having a positioning not overlapping the cut-outs of the displaceable valve element. Thereby, when the valve element is displaced into abutment against the valve seat, the cut-outs will be closed, and further inflow from the adjacent annulus section into the pipe bore of the production tubing is prevented .

Said spacer element may be formed from a water-soluble material, for example a salt. The invention is defined by the independent claim. The dependent claims define advantageous embodiments of the invention.

The invention relates more specifically to an autonomous inflow-control device for a production tubing in a hydrocarbon well, the inflow-control device comprising

an inflow pipe which is provided with several packers which are axially spaced apart along a portion of the inflow pipe, wherein

the packers are settable in a fluid-sealing manner against a wellbore wall for the formation of separate inflow sections in an annulus encircling the inflow-control device; and,

in each inflow section, at least one water-flow shutoff device is arranged, hav- ing a valve-element assembly which is switchable between a first, open position and a second, closed position, the valve-element assembly in the first position forming a fluid flow path by a displaceable valve element being kept at a distance from a valve seat by means of at least one water-soluble spacer element, characterized by

said spacer element being formed from a water-soluble salt, or by said spacer element being formed from a base metal with a galvanic voltage substantially higher than the galvanic voltage of a nobler metal forming a cathode arranged near the spacer element.

The valve seat of the valve-element assembly may be annular and surround a portion of an inflow pipe and be arranged in a surrounding valve housing, and the valve element may be axially displaceable along the inflow pipe.

The displaceable valve element may be arranged upstream of the valve seat.

The displaceable valve element may be arranged upstream of the valve seat and form a restriction in the fluid flow path to create a differential pressure across the valve element large enough to displace the valve element towards the valve seat when the spacer element is absent.

The displaceable valve element may be arranged above the valve seat.

At least one resilient element may rest against the displaceable valve element and be arranged to subject the valve element to a force large enough to displace the valve element towards the valve seat when the spacer element is absent.

The valve seat may be provided with at least one first cut-out extending therethrough, and the displaceable valve element may be provided with at least one second cut-out extending therethrough, the at least one first cut-out being non-overlapping with the at least one second cut-out. Screens may encircle the inflow sections.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which :

Figure 1 shows a principle drawing in axial section of a portion of a hydrocarbon well, in which a production tubing with a screen extends through pro- ducing layers in an underground structure in accordance with the prior art;

Figure 2 shows, in a view corresponding to figure 1, a production tubing provided with an inflow-control device according to the invention surrounded by screen; Figure 3 shows a partially cut-away perspective drawing, on a larger scale, of a water-flow shutoff device in the inflow-control device according to the invention, shown here in an open, first position; and

Figure 4 shows, in a view corresponding to figure 3, the water-flow shutoff device in a closed, second position.

Reference is first made to figure 1 which shows a production tubing 2 extending in a manner known per se down a well 12 in producing layers 11, 11', 11" in an underground structure 1 which constitutes a hydrocarbon reservoir. A screen 22 constitutes a section of the production tubing 2 and extends through the producing layers 11, 11', 11". Fluids flow from the producing layers 11, 11', 11" into an annulus 3 encircling the production tubing 2 and the screen 22 and being bounded by a wellbore wall 121 and on into a pipe bore 21 in the screen 22 and the production tubing 2. Here, no device making it possible to stop the inflow from a layer 11, 11', 11", which is beginning to produce water is shown.

Reference is now made to figure 2, in which the production tubing 2 is provided with an inflow-control device 4 according to the invention. An inflow pipe 42 constitutes a portion of the production tubing 2. The inflow pipe 42 is encircled by several packers 41, 41', 41", 41"', which are spaced apart and are arranged to fit tightly against the inflow pipe 42 and the wellbore wall 121. The packers 41, 41', 41", 41"' may be of the swellable-packer type, for example. The packers 41, 41', 41", 41"' define several annulus sections 31, 31', 31" and corresponding inflow sections 43, 43', 43" in the inflow-control device 4. In each inflow section 43, 43', 43", an autonomous water-flow shutoff device 44 is arranged, connecting the respective annulus section 31, 31', 31" in a fluid-communicating manner to the pipe bore 21 of the inflow pipe 42 and the production tubing 2.

Reference is now made to figures 3 and 4. The water-flow shutoff device 44 comprises a valve housing 444 encircling a portion of the inflow pipe 42 and forming an inflow chamber 445, which is in fluid communication with the pipe bore 21 via several inlet openings 446. The inflow chamber 445 is defined by a valve-element assembly 440 in which a valve seat 441 fits tightly against the inflow pipe 42 and against the valve housing 444. A displaceable valve element 442 is arranged to be displaceable between a first position I, in which the valve assembly 440 forms a fluid path 448, as is shown in figure 3, and a second position II, as is shown in figure 4, in which the valve assembly 440 is closed to flow from the respective annulus section 31, 31', 31" to the pipe bore 21. In the embodiment shown, the valve seat 441 and the displaceable valve element 442 are formed as annular plate elements encircling the inflow pipe 42 and being provided with first and second cut-outs 441a, 442a, respectively. The cutouts 441a and 442a of the valve seat 441 and the valve element 442, respectively, are arranged in such a manner that they do not overlap when the valve element 442 is resting against the valve seat 441. Further measures to give a satisfactory sealing between the valve seat 441 and the valve element 442 are obvious to a person skilled in the art and will not be described in more detail here.

In the open position I of the valve-element assembly 440, the displaceable valve element 442 is kept at a distance from the valve seat 441 by means of several spacer elements 443 which are soluble in contact with water, but unaffected by hydroca rbons, for example in that they are formed as blocks of a water-soluble material.

In the embodiment shown, the displaceable valve element 442 is arranged upstream of the valve seat 441. When the inflow-control device 4 is arranged vertically, gravity may work to displace the valve element 442 into abutment against the valve seat 441 when the spacer elements 443 have been dissolved. The cut-outs 442a of the valve element 442 are shown with a smaller cross section than the cut-outs 441a of the valve seat 441 to give a differential pressure across the valve element 442 large enough to displace the valve element 442 towards the valve seat 441 when the spacer elements 443 have been dissolved. Finally, several resilient elements 447 in the form of helical springs, for example, are resting between an end portion of the valve housing 444 and the valve element 442, subjecting the valve element 442 to a force large enough to displace the valve element 442 towards the valve seat 441 when the spacer elements 443 have been dissolved. By combining these, there will be greater certainty that the valve-element assembly 440 will close the fluid flow path 448 when the spac- er element 443 has been dissolved by inflowing water from the respective producing layer 11, 11', 11".

In figure 2, screens 22 encircle the inflow-control device 4 to hold back, in a manner known per se, solid particles carried in the flow of fluids from the producing layers 11, 11', 11" into the respective annulus sections 31, 31', 31". Screens 22 are not essential for the inflow-control device 4 according to the invention to work.

In an embodiment not shown, the spacer elements 443 are formed as a sacrificial a node, that is to say formed from a metal having a high galvanic voltage, for example magnesium or zinc, and arranged near a cathode formed from a nobler metal, for example brass. The cathode may be formed as a separate element, or it may comprise, for example, the inflow pipe 42, the valve element 442, the valve seat 441 or valve housing 444. As long as only hydrocarbons are flowing through the water-flow shutoff device 44, the spacer elements 443 will remain intact, whereas inflowing water will start the galvanic degradation of the spacer element 443, so that the valve-element assembly 440 will gradually close.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative embodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.