Method and system for removing deposits within a pipe or pipeline

Abstract

A fluid flow processing plant for pig-free removal of wax and hydrate deposits in hydrocarbon production flowlines may include at least one cooling flowline. Further, the fluid flow processing plant my include cooling means arranged to cool the fluid in the at least one cooling flowline over a cooling section until the fluid reaches a temperature at or near the cooling flowline's surrounding temperature (T.sub.sea) and at least one vehicle arranged on or near the outer circumference of the cooling flowline. Furthermore, each vehicle may include at least one sleeve configured to at least partly surround an outer circumference of the cooling flowline, deposit removing means being configured to remove deposits situated on an inner wall of the cooling flowline, and a propulsion unit configured to drive the vehicle bi-directionally on the cooling flowline.

Claims

1. A fluid flow processing plant for pig-free removal of wax and hydrate deposits in hydrocarbon production flowlines, the fluid flow processing plant comprising: a plurality of cooling flowlines, wherein the plurality of cooling flowlines are arranged in a parallel configuration; cooling means arranged to cool a fluid in each cooling flowline over a cooling section until the fluid reaches a temperature at or near an ambient temperature of the fluid flow processing plant; and at least one dedicated vehicle arranged on or near an outer circumference of at least one of the plurality of cooling flowlines, wherein the at least one dedicated vehicle is dedicated to the fluid flow processing plant such that an extent of movement of the at least one dedicated vehicle is restricted by one or more of the plurality of cooling flowlines in normal operation of the fluid flow processing plant, wherein each vehicle comprises: at least one sleeve configured to at least partly surround the outer circumference of the at least one of the plurality of cooling flowlines; deposit removing means being configured to remove deposits situated on an inner wall of the at least one of the plurality of cooling flowlines such that, in the normal operation of the fluid flow processing plant, blockages of the at least one of the plurality of cooling flowlines formed by deposits are prevented from occurring; and a propulsion unit configured to drive the vehicle bi-directionally on the at least one of the plurality of cooling flowlines in the normal operation of the fluid flow processing plant, wherein the deposit removing means includes heating means configured to heat the inner walls of the at least one of the plurality of cooling flowlines, thereby allowing heat induced removal of the deposits.

2. The fluid flow processing plant according to claim 1, wherein the deposit removing means comprises vibration means, the vibration means being configured to cause vibrations of the inner wall of the at least one of the plurality of cooling flowlines, thereby allowing vibration induced removal of the deposits.

3. The fluid flow processing plant according to claim 1, further comprising: a feed flowline fluidly connectable to a fluid reservoir; and an export flowline, wherein the at least one cooling flowline establishes fluid communication between the feed flowline and the export flowline.

4. The fluid flow processing plant according to claim 1, wherein the plurality of cooling flowlines are configured in a combination of stacked and parallel thereof.

5. The fluid flow processing plant according to claim 1, wherein the plurality of cooling flowlines are connected to the feed flowline and the export flowline via an inlet manifold and an outlet manifold, respectively.

6. The fluid flow processing plant according to claim 1, wherein the fluid flow processing plant is supported on a seabed below a body of water and connected in fluid communication with one or more subterranean fluid reservoirs producing a hydrocarbon containing flow having a temperature that is higher than an ambient seawater temperature.

7. The fluid flow processing plant according to claim 3, further comprising: a return line fluidly connected between the export flowline and the feed flowline.

8. The fluid flow processing plant according to claim 1, wherein the heating means is configured to heat the inner wall by heat pulses of finite time durations.

9. The fluid flow processing plant according to claim 8, the time durations of the heat pulses are set to be long enough to remove a major part of the deposits from the inner wall within the cooling section.

10. The fluid flow processing plant according to claim 8, wherein the time durations of the heat pulses are short enough to avoid any substantial melting of a major part of the deposits within the cooling section.

11. The fluid flow processing plant according to claim 1, wherein each vehicle is retrievably connected to the outer circumference of the at least one of the plurality of cooling flowlines by at least one hinged sleeve.

12. The fluid flow processing plant according to claim 1, wherein the fluid flow processing plant is configured to provide cold flow subsea transport of hydrocarbons.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a schematic illustration showing the principle of wax deposition and deposit removal using return line in accordance with prior art;

(3) FIG. 2 is a perspective view of a fluid processing subsea plant in accordance with the invention with a cooling section and return line;

(4) FIG. 3 is a top view of a part of the fluid processing subsea plant illustrated in FIG. 2, showing deposits within one of the cooling flowline;

(5) FIGS. 4a and 4b are a radial view and an axial view of a part of a cooling flowline and a vehicle used in the fluid processing subsea plant in accordance with the invention;

(6) FIG. 5 is an axial view of a part of the cooling flowline and a second vehicle used in the fluid processing subsea plant in accordance with the invention;

(7) FIGS. 6a and 6b are a radial view and an axial view of a part of the cooling flowline and the vehicle of FIGS. 4a and 4b, including illustrations of deposits within the cooling flowline; and

(8) FIG. 7 is a radial view of a part of the cooling flowline, a third vehicle and two internal pump pistons arranged in series.

DETAILED DESCRIPTION OF A PREFERENTIAL EMBODIMENT

(9) FIG. 1 shows the principle of wax deposition and deposit removal using a return line 3 with a dedicated pump 5. A feed flowline 16 situated in an ambience 18 such as seawater at a temperature T.sub.sea guides warm hydrocarbon well fluid 19 at temperature T.sub.well from a wellhead. A flowline 3 such as the return line 3 add a cooler additive fluid 20 at a temperature T.sub.add to the well flow 19. The additive fluid 20 may be the same fluid as the well fluid 19 or contain additives or seed particles 21. The mixture between the additive fluid 20 and the well fluid 19 forms a precipitating flow 22 having a mixture temperature T.sub.mix. The additives 21 in the additive fluid 20 may promote the precipitation or crystallization of particles 23 in the well flow, which in the absence of the additive fluid 20 would have had a tendency of depositing on the inner wall 2b of the flowline 2. Further downstream of the flowline 2 the mixed fluid 22 obtains a temperature of or near the ambient temperature T.sub.sea and the precipitation comes to a halt, resulting in a cooled export flow 24. However, during the cooling of the precipitating flow some deposits 12 of the precipitating material 23 within the flow 22 will be deposited onto the inner walls 2b of the flowline 2. Hence, it is a need for means 11 to remove such deposits 12 located within a cooling section 8 of the relevant flowline 2, i.e. the section within the flowline 2 where deposits 12 are depositing on the inner walls due to the mainly intentional cooling.

(10) FIG. 2 and FIG. 3 gives a perspective view and a top view, respectively, of at least a part of fluid processing plant 1 in accordance with one embodiment of the invention. The plant 1 comprises a line supporting frame 26 resting on a seabed, a feed flowline 16, an export flowline 17, a plurality of cooling flowlines 2 situated between the feed flowline 16 and the export flowline 17, a return line 3 guiding a fraction of the fluid in the export flowline 17 back to the feed flowline 16 and a so-called Pipeline End Manifold (PLEM) 25 (FIG. 2 only) receiving well fluids 19 from e.g. wellheads, satellites, etc. (not shown).

(11) The return line 3 is equipped with a valve 4 and a pump 5 in order to control the fraction of the fluid flow. The transition from the feed flowline 16 to the multiple cooling flowlines 2, and the transition from the multiple cooling flowlines 2 to the export flowline 17, is controlled by an inflow manifold 6 and an outflow manifold 7, respectively. Comparably warm well fluids 19 are fed from subterranean reservoirs into the cooling flowlines 2. Here, heat exchange with the ambient seawater 18 takes place by thermal convention through the walls of the flowlines. When the fluids reach the outflow manifold 7, the temperature of the well fluids is ideally on the same level as the temperature of the seawater (T.sub.sea), and the cooler well fluids 24 are fed into the export flowline 17. The efficiency of the heat exchange will increase with the number of the cooling flowlines 2 and its individual dimensions. The cooling flowlines 2 are in FIGS. 2 and 3 shown in a parallel configuration. However, other configurations are possible such as stacked, mutually and/or individually helical, mutually and/or individually elevated, or a combination of these configurations. During the operation of the processing plant 1, a dedicated vehicle 9 is moved back and forth on the outer circumference 2a of the cooling flowline 2 in order to remove the inside deposits 12 (FIG. 3 only) of the cooling pipes 2 using vehicle integrated or coupled deposit removing means 11 (see FIGS. 4a and 4b), for example heating elements 11 and/or ultrasonic transducers 11. As explained above in connection with FIG. 1,the illustrated return line 3 with its pump 5 and valve 4 will further contribute to the cooling of the warm well fluid 19 by means of reinserting the cooled fluid 24 exiting the cooling flowline 2 back into the well fluid 19, optionally with appropriate additives or seed particles 21 added.

(12) An example of a vehicle 9 that may be used with the inventive plant 1 is illustrated in FIGS. 4a and 4b in a radial view and axial view, respectively, relative to the direction of the cooling flowline 2. The vehicle 9 is arranged in order to at least partly enclose the outside pipe wall 2a of the cooling flowline 2 within a complementary semi-cylindrical recess. The support onto the pipe 2 is achieved by two rollers or wheels 13 arranged on diagonally opposing sides of the pipe 2, enabling movements in either direction along the pipe 2 (indicated by double arrow M in FIG. 4a). External cleaning elements (wipers, brushes, or bristles) may conveniently be arranged at both ends of the vehicle 9 in order to sweep away debris, fouling and/or ice on the outside of the pipe 2 which otherwise might impede the vehicle's 9 movements along the pipe 2. Such cleaning of the pipe exterior 2a also improves the heat-exchange between the fluids 22 in the pipe 2 and the surroundings 18 (i.e. air if on land, seawater if subsea). The external cleaning elements may be extended in a circumferential and/or longitudinal direction in order to sweep a greater surface area of the outer pipe wall 2a. Deposits 12 to be removed are shown (FIG. 4b) in form of a layer covering the inside wall 2b of the pipe 2. Furthermore, heating elements and/or ultrasonic tranducers 11 for removing the deposits 12 are shown as four bars arranged within the vehicle, along the axial direction of the pipe 2.

(13) The wheels 13 are in the illustrated embodiment driven by an electric motor which may be powered by on-board batteries or from an external source via an umbilical 15. The wheels 13 may be rubber wheels, rolling directly on the pipe outer wall. The wheels 13 may also be gear wheels, rolling in a pitch rack 14 in a rack-and-pinion configuration. Other propulsion units may for example be based on various winch and/or thruster configurations.

(14) FIG. 5 shows a second embodiment involving a second vehicle 9 enclosing a larger part of the outside pipe wall 2a. The second vehicle comprises here two parts separated by a pivotable hinge connection 6. Furthermore, four wheels 13 are arranged symmetrically or near symmetrically around the circumference of the pipe 2 in order to obtain a higher operational stability of the vehicle movements. However, the invention includes any distribution of the wheels that may assist the desired longitudinal vehicle movement.

(15) Schematic presentations of the above mentioned first or second vehicle 9 during operation are shown in FIGS. 6a (top, cross sectional view) and 6b (radial view), providing an illustration of the removal process of deposits from the inner wall of the pipe/cooling flowline 2, thus creating precipitated particles that are being washed away by the flow of the mixed fluid 22.

(16) FIG. 7 shows a top view of another embodiment of the invention, where at least one of the vehicle 9, referred to as a third vehicle, constitutes a clamp system comprising one or more magnetic spools/clamps 9 arranged in a retrievable manner along the pipe and mutually connected by dedicated links 32. The required power and communication signals may be distributed throughout the entire clamp system 9,9 through dedicated cables 15 forming part of, or arranged together with said links 32. Moreover, two pump pistons 30 are in this embodiment arranged inside the pipe 2 that may be driven longitudinally by locking magnetically to the outside clamp system 9,9, i.e. the retrievable clamps 9 work as a modular linear actuator or pump acting through the pipe wall 2. The magnetic force can be provided by means of inductive spools or permanent magnets. A one-way pivotable valve 31 is arranged at one longitudinal end of the two pump pistons 30 and configured such that it stays in a closed position when the pistons 30 are moving faster than the flow 22 relative to the flow direction and in an open position when the pistons 30 are moving slower than, or opposite to, the flow 22 relative to the flow direction. Consequently the pistons 30 may improve the production by pumping/pushing the fluid 22, preferably with a speed significantly higher than the flow velocity. If required the pistons 30 may also allow the flow 22 to pass through by the implementation of the valve 31. As explained above an improved effect is achieved when the two (or more) pump pistons are configured to perform a reciprocally alternating pumping act. In this particular embodiment the pipe walls are non-magnetic or near non-magnetic. The pump pistons 30 may be relocated to a parking position outside the cooling section 8, enabling maintenance and/or receiving/launching of other pump pistons. The magnetic clamp(s) may also act as an inductive pipe heater. The total clamp system 9,9 may be stationary arranged on the pipe and/or scaleable.

(17) Other embodiments of the vehicle 9 may be found in the publication WO 2012/093079 which is hereby included by reference.

(18) In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.