System for sealing an annular space in a wellbore

[0001] The present invention relates to a system for sealing an annular space between a tubular element extending into a wellbore and a cylindrical wall surrounding the tubular element, wherein a control line for controlling a downhole device extends in longitudinal direction along the tubular element. In the field of hydrocarbon fluid production from a wellbore it is generally required to seal the annular space formed between a production conduit extending into the wellbore and a surrounding casing or liner, or between the casing or liner and the wellbore wall. In such applications many times one or more control lines for power transmission or signal transmission extend through the annular space. Various packers have been applied to provide such sealing functionality. Some of these have terminal connections at either end for connecting the control lines to the packers. Although such packers may provide adequate sealing capability, it has been experienced that assembly of the packers and control lines to the tubular element at a well site can be difficult.

[0002] U.S. Pat. No. 6,173,788 discloses a packer for sealing an annular space between a tubular element extending into a wellbore and a wellbore casing, wherein a control line for controlling a downhole device extends in longitudinal direction through a recess formed in the outer surface of the packer. It is a drawback of the known system that the control line needs to involve bends at both ends of the packer since the recess is radially displaced from the outer surface of the tubular element. Another drawback of the known system occurs if the tubular element is provided with a plurality of the known packers mutually spaced along the tubular element. Generally such packers are pre-assembled to respective portions of the tubular element, termed “subs”, which are to be connected to adjacent portions of the tubular element by threaded connections. As a result, upon assembly of the tubular element, it may occur that the recesses of the respective packers become non-aligned.

[0003] It is an object of the invention to provide an improved system for sealing an annular space between a tubular element extending into a wellbore and a cylindrical wall surrounding the tubular element, which system overcomes the drawbacks of the prior art.

[0004] In accordance with the invention there is provided a system for sealing an annular space between a tubular element extending into a wellbore and a cylindrical wall surrounding the tubular element, wherein a control line for controlling a downhole device extends in longitudinal direction along the tubular element, the system comprising an annular seal layer extending around the tubular element, the seal layer having an inner surface provided with a recess for radially receiving the control line, the seal layer being provided with a longitudinal slit defining a pair of opposite longitudinal edges which are movable relative to each other between an open position wherein the seal layer can be radially applied to the tubular element, and a closed position wherein the seal layer extends around the tubular element.

[0005] It is thereby achieved that the control line can be extended along the tubular element before the seal layer is radially applied to the tubular element thereby obviating the need to include bends in the control line. In case the tubular element is provided with a plurality of seal layers, it is furthermore achieved that the seal layers can be assembled to the tubular element such that the recesses of the respective seal layers are suitably aligned with the control line.

[0006] It is to be understood that the control line can function to transmit signals to or from the downhole device, for example to actively control the downhole device or to transmit measured signals, or to transmit power to or from the downhole device.

[0007] Preferably the system further comprises fastening means for fastening the seal layer in the closed position thereof to the tubular element.

[0008] The system of the invention can suitably be applied in combination with an inflow control device for controlling inflow of fluid from the earth formation into the tubular element, wherein the control line is arranged to control the inflow control device.

[0009] Suitably each seal layer includes a material susceptible of swelling upon contact with a selected fluid. Thus the seal layer is activated by contact with the selected fluid (for example water or hydrocarbon fluid), which implies that it is no longer required to activate the seal layer by mechanical or hydraulic means. This is an important advantage since such swelling seal layers can be made significantly longer than conventional packers.

[0010] In a preferred embodiment the system of the invention includes a plurality of said seal layers and a plurality of said inflow control devices, the seal layers and the inflow control devices being arranged in alternating order along the tubular element. The annular space is thereby divided into a number of compartments whereby cross-flow of fluid between different compartments is substantially prevented, and inflow of formation fluid from each compartment into the tubular element is controlled by the respective inflow control device in communication with the compartment.

[0011] In order to prevent or reduce formation water bypassing each seal layer through the rock formation opposite the seal layer, it is preferred that the seal layer is significantly longer than a conventional packer. For example, in a preferred embodiment the length of the seal layer substantially corresponds to the length of the respective tubular joint to which the seal layer is applied. In this respect it is to be understood that the seal layer suitably is assembled from a plurality of short seal layer sections positioned adjacent each other along the tubular joint. Seal layer sections having a length of between 0.5-2.0 meter, for example about 1 meter, allow convenient handling on the drilling rig floor.

[0012] The invention will be described in more detail hereinafter by way of example, with reference to the accompanying drawings in which:

[0013] FIG. 1 schematically shows a wellbore in which an embodiment of a conduit and seal layer used in the method of the invention is applied;

[0014] FIG. 2A schematically shows a cross-sectional view of the conduit of FIG. 1;

[0015] FIG. 2B schematically shows the seal layer before application to the conduit;

[0016] FIG. 3 schematically shows a longitudinal section of the seal layer when applied to the conduit;

[0017] FIG. 4 schematically shows a longitudinal section of seal layer when applied to the conduit; and

[0018] FIG. 5 schematically shows detail A of FIG. 4.

[0019] In the drawings like reference numerals relate to like components.

[0020] Referring to FIG. 1 there is shown a wellbore 1 formed in an earth formation 2 for the production of hydrocarbon fluid, the wellbore 1 having a substantially vertical upper section 1a and a substantially horizontal lower section 1b extending into a zone 3 of the earth formation from which hydrocarbon fluid is to be produced. The earth formation zone 3 is fractured whereby there is a risk that water from other formation zones (not shown) enters the lower wellbore section 1b via fractures in formation zone 3. The upper wellbore section 1a is provided with a casing 4 cemented in the wellbore by a layer of cement 5, and a wellhead 6 is arranged on top of the wellbore 1 at surface 7. A production liner 7 extends from the lower end part of the casing 4 into the substantially horizontal wellbore section 1b. A production tubing 9 provides fluid communication between the wellhead 6 and the production liner 7, the production tubing 9 being suitably sealed to the production liner 7 by packer 10.

[0021] The production liner 7 is provided with a plurality of inflow control devices in the form of inflow control valves 12, 13, 14, 15 spaced along the length of the liner 7. Each inflow control valve 12, 13, 14, 15 is electrically connected to a control center 16 at surface via a set of control lines 18 extending along the outer surface of the production liner 7 and the inner surface of the casing 4, so as to allow each inflow control valve 12, 13, 14, 15 to be opened or closed from the control center 16.

[0022] A plurality of seal layers 20, 22, 24, 26 is arranged in the annular space 28 between the production liner 7 and the wall of wellbore section 1b, wherein the seal layers 20, 22, 24, 26 and the inflow control valves 12, 13, 14, 15 are arranged in alternating order along the production liner 7. Each seal layer 20, 22, 24, 26 includes a material susceptible of swelling upon contact with water from a water-bearing layer of the earth formation 2, such material preferably being HNBR elastomer.

[0023] Referring to FIGS. 2A and 2B there is shown a cross-section of the production liner 7 and the seal layer 20 before application of the seal layer to the production liner 7. The set of control lines 18 is enclosed by a cover member 30 which is fastened to the outer surface of the production liner 7 by suitable fastening means (not shown). The seal layer 20 has a longitudinal slit 31 defining a pair of opposite longitudinal edges 32, 34 allowing the seal layer 20 to be movable between an open position (as shown in FIG. 2) in which said edges 32, 34 are displaced from each other so as to allow the seal layer 20 to be radially applied in the direction of arrow 35 to the production liner 7, and a closed position (as shown in FIG. 3) in which said edges 32, 34 are located adjacent each other so as to allow the seal layer 20 to substantially enclose the production liner 7. Furthermore, the seal layer 20 is provided with pairs of bores 36, 38 spaced at regular longitudinal distances along the seal layer 20. The bores 36, 38 of each pair are formed at the respective longitudinal edges 32, 34, and are formed so as to allow a bolt (referred to hereinafter) to be extended through the aligned bores 36, 38 in order to fasten the seal layer 20 to the production liner 7. The seal layer 20 is provided with a longitudinal recess 40 formed at the inner surface thereof for accommodating the set of control lines 18 and the cover member 30.

[0024] In FIG. 3 are shown the production liner 7 and the seal layer 20 after the seal layer 20 has been radially applied to the production liner 7 so as to enclose the production liner 7. The seal layer 20 is clamped to the conduit by a plurality of bolt/nut assemblies 42, each bolt/nut assembly 42 extending through a corresponding pair of the bores 36, 38.

[0025] Referring to FIGS. 4 and 5 there is shown the seal layer 20 and the production liner 7 in longitudinal section. The production liner 7 is assembled from a number of tubular joints 44 having a standard length of about 10 m (30 ft), whereby each seal layer 20, 22, 24, 26 extends substantially the full length of the respective tubular joint 44 to which the seal layer 20 is applied. Each such joint 44 is provided with respective connector portions 48 at opposite ends thereof for interconnecting the various joints 44. The outer surface of the annular seal layer 20 is provided with a plurality of annular recesses 46 regularly spaced along the length of the seal layer 20.

[0026] During normal operation, the production liner 7 is assembled from the respective tubular joints 44 and from respective short sections of tubular element (termed “subs”; not shown) which include the respective control valves 12, 13, 14, 15. Assembly occurs at the well site in progression with lowering of the production liner 7 into the wellbore 1. The set of control lines 18 together with the cover member 30 is fed to the production liner 7, and fixedly connected thereto, simultaneously with lowering of the production liner 7 into the wellbore 1. Each seal layer 20, 22, 24, 26 is then radially applied to the production liner 7 at the desired location thereof in a manner that the recess 40 encloses the cover member 30 (and hence the control lines 18). The seal layer 20 is then moved to its closed position so as to enclose the tubular joint 44, and fixed to the tubular joint 20 by fastening the bolt/nut assemblies 42 extending through the respective pairs of bores 36, 38. The other seal layers 22, 24, 26 are assembled to the respective tubular joints 44 in a similar manner. The production liner 7 is installed in the wellbore 1 such that the seal layers 20, 22; 24, 26 and the inflow control valves 12, 13, 14, 15 are located in the earth formation zone 3 containing hydrocarbon fluid.

[0027] After the wellbore 1 has been suitably completed, hydrocarbon fluid is allowed to flow from earth formation zone 3 into the wellbore section 1a and from there via the inflow control valves 12, 13, 14, 15 into the production liner 7 and the production tubing 9. In the event that formation water enters the annular space between the production liner 7 and the wellbore wall, one or more of the seal layers 20, 22, 24, 26 which become into contact with the formation water will swell until further swelling is prevented by the wellbore wall. The annular recesses 46 enlarge the contact area of the seal layers with formation water, thereby promoting swelling of the seal layers. Once the swollen seal layers 20, 22, 24, 26 become compressed between the production liner 7 and the wellbore wall, further migration of the formation water through the annular space is prevented. In order to determine the location of water inflow, a test is carried by successively opening and/or closing the inflow control valves 12, 13, 14, 15 and simultaneously measuring the inflow of formation water. The location of inflow is determined from an observed reduced (or eliminated) inflow of formation water as a result of closing of one or more specific inflow control valves 12, 13, 14, 15. Once the location of water inflow has been determined, one or more of the inflow control valve(s) 12, 13, 14, 15 at the location of inflow are closed so that inflow of formation water into the production liner 7 is thereby eliminated.

[0028] Swelling of each seal layer 20, 22, 24, 26 also results in adequate sealing of the seal layer against the production liner 7 and the cover member 30 so as to prevent fluid migration between the seal layer and the production liner or the cover member 30.

[0029] Instead of allowing the seal layer to swell by virtue of contact with water from the earth formation, such swelling can be triggered by bringing the seal layer into contact with water-base wellbore fluid pumped into the wellbore.

[0030] Furthermore, the seal layer can be made of a material susceptible of swelling upon contact with hydrocarbon fluid, such as crude oil or diesel. In such application the seal layer can be induced to swell upon contact with hydrocarbon fluid produced from the wellbore. Alternatively the seal layer can be induced to swell by pumping hydrocarbon fluid, such as diesel or crude oil, into the wellbore. The latter procedure has the advantage that premature swelling of the seal layer during lowering of the tubular element into the wellbore, is prevented.

[0031] Also, a hybrid system can be applied including seal layer sections susceptible of swelling upon contact with hydrocarbon fluid, and seal layer sections susceptible of swelling upon contact with water from the earth formation.