WO2014169932A1

WO2014169932A1 - Dispersing solid particles carried in a fluid flow

Info

Publication number: WO2014169932A1
Application number: PCT/EP2013/057775
Authority: WO
Inventors: Rainer Josef HOFFMANN; William George Clark
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2013-04-15
Filing date: 2013-04-15
Publication date: 2014-10-23
Anticipated expiration: 2015-10-15

Abstract

A method an apparatus for dispersing solid particles (4) of wax or hydrate carried in a hydrocarbon fluid flow. A wax control section (2) is located in transport equipment for carrying fluid hydrocarbon, the wax control section (2) arranged to precipitate solid wax from the hydrocarbon fluid and introduce solid particles (4) of any of wax and hydrates into the hydrocarbon fluid flow. A high shear shredder (6) is located downstream of the wax control section (2). The solid particles (4) are allowed to pass through the high shear shredder (6) such that the action of the high shear shredder (6) reduces the particle size of the solid particles(4).

Description

Dispersing Solid Particles Carried in a Fluid Flow

TECHNICAL FIELD The invention relates to the field of dispersing solids carried in a fluid flow, and in particular to dispersing waxy or hydrate solids carried in a hydrocarbon fluid flow.

BACKGROUND Wax deposition at the inside wall of a pipeline for carrying fluid hydrocarbons is a severe problem in a hydrocarbon production infrastructure. When a warm hydrocarbon fluid (or mixture of fluids) oil flows through a pipeline, it comes into contact with the inner walls of the pipeline. The pipeline temperature is typically lower than that of the fluid, and this can cause wax or other hydrate agglomerates to precipitate from the fluid and adhere to the pipeline inner wall. Over time, these solid deposits on the pipeline inner wall increase in thickness and consequently will reduce the internal pipeline cross-sectional area. This leads to a loss of pressure, and ultimately to a complete blockage of the pipeline. The rate of deposition on the inner wall of a pipeline conducting a multiphase fluid stream of hydrocarbons varies according to several parameters, such as the surrounding temperature (subterranean, air, sea water), the fluid stream temperature, the pressure inside the pipeline, the composition of the fluid stream and the distribution of phases in the fluid stream.

Existing technologies that deal with the problem of build-up of waxy deposits include pigging, chemical inhibition, and direct electrical heating.

Pigging involves passing a tool through the pipeline that removes the wax from the pipeline inner wall at regular intervals. Pigging is a complex and expensive operation. If no loop is available, a pig has to be inserted sub-sea using remote-operated vehicles. It is also a risky operation if the thickness of the wax cannot be measured or predicted. If more wax has been deposited than the pig diameter is designed for, this can result in a stuck pig. Chemical inhibition involves the addition of chemicals to the fluid which inhibit wax deposition. Chemical inhibition is expensive due to the fact that an additional pipeline has to be built that supplies the chemicals to the wellhead, and the chemicals themselves are expensive. Chemical inhibition is also inefficient as there are currently no chemicals available that completely eliminate wax deposition. There is always a need of additional pigging operations to remove waxy build-up. Furthermore, the chemicals that are used are typically classified as environmentally very problematic.

Direct electrical heating involves heating the pipeline to maintain it at a temperature above the wax appearance temperature. Electric heating above the wax appearance temperature is very expensive due to both high installation and operational costs. Accordingly, direct electric heating is not feasible for long-distance transport.

Other known methods for removing waxy deposits include US 6,070,417, which discloses a method for making slurry where solids are precipitated and removed mechanically from the surface on which they precipitated, by a runner or pig circulating in a lumen or loop.

US 6,656,366 describes a method for reducing solids build-up in hydrocarbon streams produced from wells. The described method is based on deposition by cooling and mechanical removal of the deposit, by using a runner as above or a helical coil mechanically removing deposits.

EP 334 578 describes the injection of a cold dewaxing solvent in scraping chillers for removing deposits.

WO 2009/051495 describes a technique in which a section of the pipeline is maintained at or cooled to a temperature below the wax formation temperature. This allows wax to build up on the inner wall of that section of the pipeline. The section is subjected to periodic intervals of heating. During the heating, the solid wax that has built up on the inner wall of the pipeline does not re-dissolve, but is loosened from the inner wall in solid particles, and the solid particles are carried away from the section by the fluid flow. This gives rise to a fluid flow containing particles of solid wax. The solid wax particles can be easily removed downstream. This technique is therefore suitable for long distance flow, as it only requires limited sections to be heated (as opposed to heating the entire pipeline), does not rely on expensive or harmful chemicals, and does not require any intervention in the form of a pigging operation. The area of periodic heating is termed herein the "wax control section". A problem arises in the pipeline downstream of wax-control section. Referring to Figure 1 , there is shown a pipeline 1 having a wax control section 2. The direction of fluid flow is shown by arrow 3. Upstream of the wax control section 2, the flow is predominantly fluid. At the control section 2, wax is allowed to precipitate onto the inner wall of the pipeline and is then loosened from the pipeline wall 2. Solid particles 4 of wax are then carried downstream of the wax control section 2 in the fluid flow. These solid particles can themselves form blockages 5 in the pipeline if they start to agglomerate together.

It is a problem to identify where a blockage 5 has occurred and to subsequently clear the blockage 5, which may require a pigging operation.

SUMMARY

It is an object to provide a technique to reduce the risk of build-up of solid particles in a fluid flow carried in a pipeline that may cause a blockage of the pipeline.

According to a first aspect, there is provided a method of dispersing solid particles of wax or hydrate carried in a hydrocarbon fluid flow. Transport equipment for transporting the hydrocarbon fluid flow is provided. A wax control section is located in the transport equipment to precipitate solid wax from the hydrocarbon fluid and introduce solid particles of any of wax and hydrates in the hydrocarbon fluid flow. A high shear shredder is located downstream of the wax control section. The solid particles are allowed to pass through the high shear shredder such that the action of the high shear shredder reduces the particle size of the solid particles. This has the advantage of reducing the size of larger particles, and reduces the risk of the solid particles forming blockages downstream of the high shear shredder.

As an option, the high shear shredder is located in a bypass pipe in fluid connection with a main pipeline. In this case, the method further includes using a valve to close off the pipeline and divert the fluid flow through the bypass pipe. Prior to passing a tool through the pipeline, the valve can be opened and the tool can be passed through the pipeline. This has the advantage of allowing tools such as pigging tools to be passed through the main pipeline without damaging the high shear shredder. As an option, the high shear shredder is a transport booster pump. It therefore performs two functions; boosting flow rate and breaking down solid particles. The solid waxy particles are not sufficiently hard to have a significant impact on the lifetime of the transport booster pump. The high shear shredder is optionally located at a suitable pipeline section. Examples of suitable pipeline sections include a location downstream of and close to the wax control section, and upstream of and close to a pipeline section prone to the formation of agglomerates. Examples of a pipeline section prone to the formation of agglomerates include a pipeline section having a bend, a pipeline section having a change in inner diameter, and a pipeline section having a region that disrupts fluid flow.

According to a second aspect, there is provided a system for dispersing solid particles of any of wax and hydrate carried in a hydrocarbon fluid flow. The system includes transport equipment for transporting the hydrocarbon fluid flow. A wax control section is located in the transport equipment, the wax control section arranged to precipitate wax and introduce solid particles of any of wax and hydrates in the hydrocarbon fluid flow. A high shear shredder is located downstream of the wax control section to break up any large particles of solid wax or hydrates formed in the wax control section and carried in the fluid flow.

As an option, the system is further provided with a bypass pipe in fluid connection with a main pipeline, wherein the high shear shredder is located in the bypass pipe. A valve is also provided that can, in one configuration, divert the fluid flow through the bypass pipe, and in another configuration, allow fluid through the main pipeline.

The high shear shredder is optionally a transport booster pump. It therefore provides the functions of both breaking down solid particles of wax and/or hydrates, and also of maintaining pressure and fluid flow in the transport equipment. As an option, the high shear is located downstream of, and close to the wax control section. As an alternative option, the high shear is located upstream of, and close to, a pipeline section prone to the formation of agglomerates.

The pipeline section prone to the formation of agglomerates is optionally any of a pipeline section having a bend, a pipeline section having a change in inner diameter, and a pipeline section having a region that disrupts fluid flow. As an option, the wax control section comprises apparatus arranged to periodically provide a heat pulse to loosen solid wax deposited on an inner wall of the pipeline by precipitation.

As a further option, the wax control section further comprises an apparatus arranged to cool the inner wall of the pipeline to enhance the deposition of solid wax on the inner wall of the pipeline prior to loosening the solid wax.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 illustrates schematically a cross section side view of a pipeline with a wax control section;

Figure 2 illustrates schematically a cross section side view of an exemplary pipeline with a wax control section and a shredder;

Figure 3 illustrates schematically a further side view of an exemplary pipeline with a wax control section and two shredders; and

Figure 4 is a flow diagram showing an exemplary process. DETAILED DESCRIPTION

As described above, waxy and hydrate solids that form in a pipeline and are carried by fluid flow can agglomerate together and block certain sections of the pipeline, particularly where the fluid flow changes. Fluid flow may change, for example, at a bend in the pipeline.

Blockages typically form when large solid particles agglomerate together. Smaller solid particles fit into the interstices of the agglomerate, and so over time the blockage can prevent fluid flow altogether.

Providing a shredder within the pipeline will not impede the fluid flow, but will break down any solid wax or hydrate carried in the fluid flow to reduce their particle size. The provision of a shredder to reduce the particle size reduces the risk of solid agglomerates of wax and/or hydrates forming which could form a blockage within the pipe.

In long distance transport of hydrocarbons, flow rate and pressure within the pipeline is often maintained by the use of transport booster pumps. In addition to maintaining flow rate and pressure, it has been realised that transport booster pumps typically generate high shear forces. They are therefore suitable for breaking up wax and/or hydrate particles. Figure 2 shows an exemplary implementation.

A pipeline 1 is provided with a wax control section 2 that typically comprises at least a heater for loosening solid waxy deposits that have precipitated on the inner wall of the pipeline 1. As described above, the solid particles that break away from the inner wall of the pipeline 1 are carried away by the fluid flow (the direction of which is shown by arrow 3). It is difficult to control the size of the solid particles that are carried in the fluid flow.

A high shear pump 6 is located in the pipeline downstream of the wax control section 2. As the solid particles pass through the high shear pump 6, the high shear pump 6 acts as a shredder to break up the solid particles into smaller solid particles. This ensures that large solid particles do not continue downstream in the fluid flow and therefore reduces the risk of particles agglomerating to form a blockage within the pipeline 1 . The high shear pump 6 is typically a multiphase pump which has the additional purpose of maintaining fluid flow rate and pressure along the pipeline 1. The waxy and/or hydrate solids are not hard enough to increase erosion of the high shear pump 6, and so the lifetime of the high shear pump 6 is no shorter than it would otherwise be without the presence of waxy/hydrate solids.

While Figure 2 only shows one high shear pump 6, it will be appreciated that over the length of a pipeline, many high shear pumps 6 may be provided at strategic locations. While the primary purpose of the pump may be to maintain fluid flow and pressure in the pipeline 1 , the locations of the pumps 6 can be selected to reduce the risk of blockages, as shown in Figure 3.

Figure 3 shows a high shear pump 6 located close to and downstream of a wax control section 2 to reduce the pipeline distance over which large solid particles are carried. Furthermore, a high shear pump 6 is also located upstream of a physical feature 7 of the pipeline 1 that may be prone to allowing solid agglomerates to form. Examples of such physical features include sharp bends in the pipeline, regions of the pipeline where the inner diameter changes, and regions of the pipeline where other equipment intrudes to disrupt the fluid flow through the pipeline 1.

In most pipelines 1 the inner diameter must remain sufficiently clear to allow a pigging operation. This may be for inspection or cleaning of the pipeline 1. Figure 2 shows an example in which a pipeline section 8 that would otherwise carried the fluid flow is closed off by one of more valves 9, 10. A bypass 1 1 is provided for the fluid flow, and the high shear pump 6 is located in the bypass 1 1.

In normal use, valves 9, 10 are closed and the fluid flow goes into the bypass 1 1 , through the high shear pump 6, and out of the bypass. In the event of a pigging operation or other intervention where a tool is passed through the pipeline 1 , the valves 9, 10 are opened to allow a pig or tool to pass through the pipeline 1 .

The process is described in Figure 4, with the following numbering corresponding to that of Figure 4: 51 . A high shear shredder 6 for reducing the particle size of waxy and/or hydrate solids is located in a bypass 1 1 , with a valve 9 in the main pipeline 1 arranged to either divert fluid flow through the bypass 1 1 or allow fluid flow through the main pipeline 1. As described above, in an exemplary embodiment the high shear shredder is a transport booster pump that serves to maintain fluid pressure and flow rate in addition to reducing the particle size of solids in the fluid flow.

52. In normal use of transporting hydrocarbons, the valve 9 in the main pipeline 1 remains closed and hydrocarbon fluid flow is diverted through the bypass 1 1 before returning to the main pipeline section 1 .

53. The high shear shredder in the bypass reduces the particle size of waxy and/or hydrae solids carried b the fluid flow. S4. If no pigging or other type of intervention operation is required, then the process reverts to step S3. If a pigging or other type of intervention is required, then the process continues at step S5.

55. The valve 9 in the main pipeline 1 is opened.

56. A pig or other type of tool is passed through the main pipeline 1 , but not through the bypass 1 1 , to perform the normal pigging or other operation.

57. After the pig or tool has passed through the main pipeline and beyond the bypass 1 1 , the valve 9 is closed again to ensure that fluid flow is diverted through the bypass 1 1. The process reverts to step S3.

By provided a shredder to reduce the particle size of solids, the risk of solid agglomerates forming downstream of a wax control section is greatly reduced, thereby reducing the need for performing a pigging operation to clear blockages in the pipeline.

It will be appreciated by a person of skill in the art that various modifications may be made to the embodiments described above without departing from the scope of the present disclosure. For example, while an example of a high shear shredder is a high shear transport booster pump, and the high shear transport booster pump can be used to both enhance fluid transport and reduce the particle size of solid waxy particles, it will be appreciate that other types of shredder may be used. Furthermore, a shredder may be dedicated solely to reducing the particles size of solid waxy particles and need not also be used to enhance fluid transport.

Claims

CLAIMS:

1 . A method of dispersing solid particles of any of wax and hydrate carried in a hydrocarbon fluid flow, the method comprising:

providing transport equipment for transporting the hydrocarbon fluid flow;

locating in the transport equipment a wax control section to precipitate solid wax from the hydrocarbon fluid and introduce solid particles of any of wax and hydrates in the hydrocarbon fluid flow;

locating a high shear shredder downstream of the wax control section; and allowing the solid particles to pass through the high shear shredder such that the action of the high shear shredder reduces the particle size.

2. The method according to claim 1 , further comprising locating the high shear shredder in a bypass pipe in fluid connection with a main pipeline, the method further comprising:

using a valve to close off the pipeline and divert the fluid flow through the bypass pipe;

prior to passing a tool through the pipeline, opening the valve; and

passing the tool through the pipeline.

3. The method according to claim 1 or 2, wherein the high shear shredder is a transport booster pump.

4. The method according to any one of claims 1 , 2 or 3, further comprising locating the high shear shredder at a pipeline section comprising any of:

downstream of and close to the wax control section; and

upstream of and close to a pipeline section prone to the formation of agglomerates.

5. The method according to claim 4, wherein the pipeline section prone to the formation of agglomerates comprises any of a pipeline section having a bend, a pipeline section having a change in inner diameter, and a pipeline section having a region that disrupts fluid flow.

6. A system for dispersing solid particles of any of wax and hydrate carried in a hydrocarbon fluid flow, the system comprising:

transport equipment for transporting the hydrocarbon fluid flow;

a wax control section located in the transport equipment, the wax control section arranged to precipitate solid wax from the hydrocarbon fluid and introduce solid particles of any of wax and hydrates in the hydrocarbon fluid flow; and

a high shear shredder located downstream of the wax control section.

7. The system according to claim 6, further comprising a bypass pipe in fluid connection with a main pipeline, wherein the high shear shredder is located in the bypass pipe; and

a valve arranged to, in one configuration, divert the fluid flow through the bypass pipe, and in another configuration, allow fluid through the main pipeline.

8. The system according to claim 6 or 7, wherein the high shear shredder is a transport booster pump.

9. The system according to any one of claims 6, 7 or 8, wherein the high shear is located downstream of, and close to the wax control section.

10. The system according to any one of claims 6, 7 or 8, wherein the high shear is located upstream of, and close to, a pipeline section prone to the formation of agglomerates.

1 1 . The system according to claim 10, wherein the pipeline section prone to the formation of agglomerates comprises any of a pipeline section having a bend, a pipeline section having a change in inner diameter, and a pipeline section having a region that disrupts fluid flow.

12. The system according to any one of claims 6 to 1 1 , wherein the wax control section comprises apparatus arranged to periodically provide a heat pulse to loosen solid wax deposited on an inner wall of the pipeline.

13. The system according to claim 12, wherein the wax control section further comprises a apparatus arranged to cool the inner wall of the pipeline to enhance the deposition of solid wax on the inner wall of the pipeline prior to loosening the solid wax.