WO2011084042A1

WO2011084042A1 - Process and means for removal of wax deposits in hydrocarbon pipelines

Info

Publication number: WO2011084042A1
Application number: PCT/MY2010/000005
Authority: WO
Inventors: Nagendran C. Nadarajah; Mahendran Suppiah; Ionel Valeriu Grozescu
Original assignee: Kingtime International Limited
Priority date: 2010-01-11
Filing date: 2010-01-11
Publication date: 2011-07-14

Abstract

The Inventor discloses a method of removing paraffinic and/or asphaltic deposits from interior of hydrocarbon carrying pipeline. The method comprises the optional step of introducing microwave absorbing fluid, such as water, into pipeline, such fluid to be in contact with the paraffinic and/or asphaltic deposits, microwave radiation is generated and propagated towards water contained in the deposits and/or microwave absorbing fluid introduced in previous steps to raise the temperature of the water and/or microwave absorbing fluid. The so heated water and/or fluid transmits heat by conduction to the deposits when than liquefies. The slurry so formed is extracted from the pipeline at least one surfactant is introduced into the slurry to prevent clumping of the deposits when cooled.

Description

PROCESS AND MEANS FOR REMOVAL OF WAX DEPOSITS IN HYDROCARBON PIPELINES

Field of Invention

This invention relates to removal of paraffin and/or asphaltic deposits from interior pipeline, hydrocarbon fluid pipelines, storage vessels and similar equipment where waxy crude oils are transported or stored. More particularly the invention relates to a system and method of removing paraffin and/or asphaltic deposits from internal surface walls of long pipelines.

Background of the Invention

Crude oil extracted from wells, often contain N. paraffin which contains linear chain alkanes, Alkanes of Ci to C₄ carbon chain length are in gaseous state, while alkanes of between C₅ to Ci₆ carbon chain length are in liquid state and alkanes of Ci6 and above are generally solid state. Crude oil extracted from wells are often transported to a storage tank or receiving terminals by pipeline means. If the wells are off-shore, then the pipeline means would often be placed undersea. Wax from the extracted crude oil are deposited all along the internal wall surfaces of the pipelines. The deposit of wax within the pipeline creates serious problems. The deposit of wax interrupts the planned flow capacity of the pipeline, which may result in stoppage of the flow of the oil. Several methods have been attempted or adopted to remove the wax deposits from the interior of the pipelines. US Patent No. 4,646,837 discusses some of the prior art methods of removal of wax deposits and their disadvantages or limitations. The said patent itself discloses a process for removing solid wax- containing material from surfaces with a surfactant dispersant and a light hydrocarbon, thereafter flushing the surface with crude oil, and sweeping the surfaces with an emulsion of a sheared solution of the surfactant, the light hydrocarbon and water. The addition of chemical into the crude oil adds downstream problems in removal of the added chemicals. This leads to increased costs of removal of wax deposits.

Another method involves the scraping of the wax deposits by means of mechanical scrapers or pipeline pigs. Scrapers are effective only when the deposits are relatively thin. The method further involves the use of expensive ancillary equipment. Yet in another method, pipelines are electrically heated to remove the wax deposits. The use of electrical heating apparatus in subsea pipelines creates additional risks and hazards, thereby increasing the relative costs of such method. US Patent No. 6,307,191 B1 discloses the use of microwave heating system. The system is provided including a microwave generator, a fluid pipeline having an upstream section and a downstream section, and a waveguide assembly connected to the microwave generator. The microwave heating system substantially prevents or remediates gas hydrate blockages in the upstream section of the fluid pipeline. This system to function requires continuous flowing liquid, it relates to gas hydrate formation but does not address blockages by paraffinic and / or asphaltic deposits. Further it does not address the problem of completely plugged pipelines caused by paraffin and/or asphaltic deposits. Another disadvantage is that microwave will get attenuated at first point of presence of dielectric material, such as water. This would result in localised heating, which if not managed, would be unacceptable as introducing hazards and risks. Thus there is a need for a system that is capable of unplugging and removing solid wax deposits in a hydrocarbon pipeline where there is no or very little flow of crude oil. The system should not create any hazards or risks such as localised overheating. The system should be capable being utilised in subsea fluid pipelines.

Summary of the Invention The invention discloses a method of removing paraffinic and / or asphaltic deposits from interior of hydrocarbon carrying pipeline comprising optionally introducing microwave absorbing fluid into pipeline such fluid to be in contact with paraffinic and / or asphaltic deposits, generating microwave radiation and propagating the radiation towards water contained in the deposits and/or microwave absorbing fluid introduced in previous step to raise temperature of the water and / or the microwave absorbing fluid wherein the water and /or microwave absorbing fluid so heated transmits heat energy by conduction to the paraffinic and / or asphaltic deposits which then liquefies and extracting slurry from the pipeline. At least one type of surfactant is introduced into the slurry before extraction. The surfactant can be mixed with microwave absorbing fluid before or as the microwave absorbing fluid is introduced into the pipeline. A microwave generating unit is mounted onto a pipeline crawler assembly or to a pipeline pig. In another aspect the invention discloses a method of removing paraffinic and / or asphaltic deposits from interior of a hydrocarbon carrying pipeline comprising, generating microwave radiation, transmitting microwave radiation to a microwave guide assembly from which microwave radiation is propagated directly to water containing paraffinic and / or asphaltic deposits or microwave absorbing fluid introduced into a chamber formed between the microwave guide assembly on the paraffinic and / or asphaltic deposits, awaiting the transfer of heat from microwave absorbing fluid onto the paraffinic and / or asphaltic deposits so as to liquefy the paraffinic and / or asphaltic deposits, and extracting the slurry. The microwave generating unit and the microwave guide assembly are mounted onto a crawler or to a pipeline pig. The slurry is extracted through a return conduit mounted through the crawler or the pipeline pig. The microwave absorbing fluid is introduced to chamber formed between crawler unit and paraffinic and / or asphaltic through a fluid bypass channel mounted in the crawler or the pipeline pig.

Microwave radiation is generated in a microwave generator mounted onto the crawler or the pipeline pig or in a microwave generator located outside the crawler or the pipeline pig and is connected to the microwave guide assembly by means of a coaxial cable. The crawler or the pipeline pig is propelled forward by means of liquid or fluid mixture pressure from rear of crawler or pipeline pig, or by use of coiled tubing. Yet in another aspect the invention discloses a crawler adapted for removal of paraffinic and / or asphaltic deposits from the interior of a hydrocarbon carrying pipeline comprising of a crawler with microwave generator, a microwave guide assembly, a fluid bypass channel optionally with pressure differential valve mounted at front end of channel, and a return conduit. Alternatively the microwave generator can be positioned remote from and independent of the crawler. The invention will be further understood from the accompanying drawings and description.

Brief Description of the Drawings

Fig. 1 . drawing illustrating a system of removal of paraffin and/or asphaltic deposits from a pipeline. Fig. 2. shows a schematic cross-sectional view of crawler with a microwave heating system built in.

Fig. 3. shows a schematic cross-sectional view of crawler with a remotely located microwave generating unit.

Description of Preferred Embodiments

Referring to Fig. 1 , the concept of the present invention and a simple model of the present invention is illustrated. A pipeline (10) contains a paraffin and/or asphaltic deposits plug (12) completely preventing the flow of the crude oil. The cause(s) of such plug formation is/are well known in the art and would not be discussed herein. The paraffin and/or asphaltic deposits plug (12) may or may not contain pockets of water. Water is a dielectric material which absorbs microwave energy resulting in increase of its temperature. Hydrocarbon wax is a non- dielectric material and does not absorb any microwave energy and shows no reaction when exposed to microwaves. In this embodiment, water in sufficient amount is introduced into the pipeline, so as to be in physical contact with the paraffin and/or asphaltic deposits (12). Water can be introduced through a conduit (not shown) inserted into the pipeline (10) and the conduit is urged forward until the terminal end is adjacent to the plug (12), a return flow conduit means (14) is also introduced into the pipeline (10) in such a manner that the terminal end of the conduit is adjacent to the solid wax deposit plug (12). To heat the water in the pipeline, microwaves (16) generated from a microwave generating unit (not shown) are propagated from an open end of the pipeline. The propagated microwaves reach the paraffin and/or asphaltic deposits plug (12) and the water introduced earlier. The water subjected to microwaves (16) is heated up. The paraffin and/or asphaltic deposits in contact with the heated water is now heated by conduction and the temperature of the wax paraffin and/or asphaltic deposits begins to rise , and at elevated temperatures above the wax appearance temperature (WAT) of the paraffin and/or asphaltic deposits, it begins to liquefy (or melt). The new liquefied wax flows into the heated water. To prevent clumping into large pieces of the now liquefied wax, suitable surfactants are included in the water introduced earlier. The nature surfactants used in the crude oil industry is well known and will not be described in detail here. If paraffin and/or asphaltic deposits contain significant quantities of water, then there is no necessary of introducing any microwave absorbing fluid. The microwave can be directly propagated towards the paraffin and/or asphaltic deposits. The water in the paraffin and/or asphaltic deposits heats up and then liquefies the paraffin and/or asphaltic deposits in contact with it. The slurry (18) of water, wax deposits and dissolved surfactants are removed from the region adjacent to the paraffin and/or asphaltic deposits plug, by suction through the returns flow conduit means (14). The mixture so extracted is subject to subsequent treatment or disposal. The microwaves (16) are generated by a microwave generating unit placed remotely from the plug (12), preferably on a surface platform or workstation (not shown).

Depending on the shape of the pipeline at the area of plugging (whether it is curved vertically or it is a straight linear portion) mechanical agitators (not shown) may need to be introduced to keep bathing the wax deposits with the heated water, so as to melt the paraffin and/or asphaltic deposits. If the pipeline is only plugged at one curve of the pipeline, the above described method is easy to use and cost effective. The return conduit (4) could also be used to introduce the water and optionally the surfactant through the return flow conduit means (14).

For plugging along the straight linear portion of the pipeline other methods and apparatus need to be used. Fig. 2 shows a schematic drawing of a crawler (20) with built - in microwave radiating system. This embodiment, of the invention, comprises a method of clearing paraffin and/or asphaltic deposits from the interior of the pipe (10). The crawler unit (20) is adapted to house a microwave generator (magnetron) (22), and a microwave guide assembly (24). The crawler (20) has a fluid bypass channel (26) which serves to bring fluid from rear end of the crawler to its forward end. Terminal end of the fluid bypass channel (26) is equipped with a differential pressure valve (34). The forward end of the crawler has a series of nozzles (not shown) to provide turbulence of the liquid infront of the crawler (20). The crawler further includes a return conduit (28). The microwave generator (22) is powered by an external power source, preferably located on topside, and which is electrically connected to the microwave generator (22) by means of a power cable (30). The microwave generator is connected to a microwave guide assembly (24) by means of a coaxial cable (32). The operation of the system and other features of the system not described earlier will now be described. This embodiment of the invention comprises of a system and method of cleaning and removing solid wax deposits from interior of a pipeline (10). A crawler (20) as herein described, and dimensioned to fit in a tight fitting manner within the interior of the pipeline, is introduced into the pipeline by methods known in the art. The crawler is moved forward through the pipeline by the pressure of a liquid or a fluid mixture applied to the rear end of the crawler. Alternatively a coiled tubing method, known in the art, can be adopted to propel the crawler forward. The liquid or the fluid mixture flows through the fluid by pass channel (26), which channel is equipped with a differential pressure valve (34). Valve operational differential pressure range can be set in a desired range. The forward end of the crawler, optionally, has a series of nozzles (not shown) allowing the fluid under pressure in the fluid bypass channel (26), to agitate and suspend discrete solids, such as mist, sand particles, scraped paraffinic and / or asphaltic solids.

On energising the microwave generator unit (or magnetron), microwaves are generated which is transmitted to the microwave guide assembly (24) by means of the coaxial cable (32). The microwave guide assembly (24) is equipped with a wave radiating element (not shown). In this embodiment, the microwave generator unit (22) is incorporated onto the crawler (20). The microwave generator unit is typically a modified magnetron which is used for industrial process heating applications, and is available in a broad size and power range. In the present embodiment, the magnetron generates microwaves at 2.45 Ghz and is powered by through a power cable (30) from a power supply located on topside facilities. The microwaves propagated from the microwave guide assembly heats up the liquid or fluid mixture in front of the crawler. The heated liquid or fluid mixture heats up the paraffinic and / or asphaltic deposits in the interior of the pipeline and infront of the crawler. Water contained or embedded in the deposits also get heated by absorption of the microwaves and the so heated water liquefies the deposit with which at is in physical contact. Upon the deposit being liquefied, it is prevented from clogging together by the presence of surfactant in the liquid or fluid mixture. The slurry comprising of liquid or fluid mixture, liquefied deposit, surfactant and other particulate matters from the deposit is extracted or sucked back through the return conduit (28) to top side facilities for disposal or subsequent treatment.

As the deposit in the interior is liquefied, and the slurry extracted, the crawler unit is propelled forward to continue / repeat the process. It will be appreciated that if the water content originally present in the paraffinic and / or asphaltic deposits is high, then there may not be a necessity to introduce liquid or fluid mixture between the crawler and the deposit. Microwave from the microwave guide assembly can be propagated directly on the deposits. The embedded water therein will absorb the microwave energy and would be heated, which heated water will liquefy or melt the deposit. The slurry so formed will be extracted or sucked through the return conduit from the chamber (36) formed by the chamber and the paraffin and/or asphaltic deposits. Another embodiment of the invention is shown in a schematic manner in

Fig. 3. The system is similar in configuration and method of operation, except the microwave generator (22) is located outside the crawler (20), preferably on the topside facilities. The microwave generator is connected to the microwave guide assembly (24) by a microwave coaxial cable (32). The return conduit (28) can be advantageously be coupled to the coiled tubing (not shown) which tubing is used to move the crawler forward. The use of coiled tubing to move crawler or pipeline pig is known in the art and therefore would not be described herein. The crawlers can be fitted with scrapers to scrap the internal wall of the pipeline. In the present invention the water is used as the microwave absorbing fluid. Other such fluids which are cost effective can also be used. Cationic (cetylpyridinium chloride), nonionic (polyethylene oxides), and anionic (sodium lauryl sulphate) surfactant can be used. In addition to surfactants other ingredients such as stabilizers, descalers, rust inhibitors, and emulsion breakers, and the like can be advantageously added to the liquid or fluid mixture. The term liquid, fluid mixture in this description refers to microwave absorbing fluid, including water. The microwave absorbing fluid can be pre-heated before introduction into the pipeline. This would reduce the time to heat the fluid. The time taken to liquefy the deposits in the pipeline would depend on the amount of water contained in the deposits, the temperature of the liquid or fluid mixture, nature of the deposits.

The present invention, though described in reference to subsea pipelines, is not restricted to such applications only. The embodiments are for illustrative purposes and are not intended to limit the scope of the invention. For example, it will be apparent to a person skilled in the art from the teaching, herein, that the invention can be usefully used to remove wax deposits in other pipelines carrying other types of wax containing liquids.

The foregoing description of the invention and the drawings are merely intended to be explanatory thereof and various changes in the details of the described method and the system may be made within the scope of the appended claims without departing from the spirit of the invention. Although examples have been provided herein to demonstrate the scope and utility of the present invention, the examples are not to be continued as limiting the scope of the invention.

Claims

A method of removing paraffinic and / or asphaltic deposits (12) from interior of hydrocarbon carrying pipeline (10) comprising:

(i) optionally introducing microwave absorbing fluid into pipeline (10) such fluid to be in contact with paraffinic and / or asphaltic deposits (12);

(ii) generating microwave radiation and propagating the radiation towards water contained in the deposits (12) and/or microwave absorbing fluid introduced in step (i) to raise temperature of the water and / or the microwave absorbing fluid wherein the water and /or microwave absorbing fluid so heated transmits heat energy by conduction to the paraffinic and / or asphaltic deposits (12) which then liquefies; iii) extracting slurry (18) formed in step (ii) from the pipeline;

2. A method of removing paraffinic and / or asphaltic deposits from interior of a hydrocarbon carrying pipeline (10) as claimed in claim 1 wherein at least one type of surfactant is introduced into the slurry formed in step (ii) of claim 1 before extraction,

3. A method as claimed in claim 1 wherein a surfactant is mixed with microwave absorbing fluid in step (i) before or as the microwave absorbing fluid is introduced into the pipeline (10),

4. A method as claimed in claim 1 wherein a microwave generating unit (22) is mounted onto a pipeline crawler assembly (20) or to a pipeline pig,

5. A method of removing paraffinic and / or asphaltic deposits from interior of a hydrocarbon carrying pipeline comprising,

(i) generating microwave radiation;

(ii) transmitting microwave radiation to a microwave guide assembly from which microwave radiation is propagated directly to water containing paraffinic and / or asphaltic deposits or microwave absorbing fluid introduced into a chamber (36) formed between the microwave guide assembly on the paraffinic and / or asphaltic deposits; (iii) awaiting the transfer of heat from microwave absorbing fluid onto the paraffinic and / or asphaltic deposits so as to liquefy the paraffinic and / or asphaltic deposits;

(iv) extracting the slurry formed in step (iii);

A method as claimed in claim 5 wherein

(i) a microwave generating unit (22) and the microwave guide assembly (24) are mounted onto a crawler (20) or to a pipeline pig.

(ii) the slurry is extracted through a return conduit (28) mounted through the crawler (20) or the pipeline pig; and

(iii) the microwave absorbing fluid is introduced to chamber (36) formed between crawler unit and paraffin and/or asphaltic deposits through a fluid bypass channel (26) mounted in the crawler (20) or the pipeline pig.

A method as claimed in claim 5 wherein microwave radiation is generated in a microwave generator (22) mounted onto the crawler (20) or the pipeline pig,

A method as claimed in claim 5 wherein microwave radiation is generated in a microwave generator (22) located outside the crawler (20) or the pipeline pig and is connected to the microwave guide assembly by means of a coaxial cable,

A method as claimed in claim 5 wherein the crawler (20) or the pipeline pig is propelled forward by means of liquid or fluid mixture pressure from rear of crawler or pipeline pig, or by use of coiled tubing,

A crawler (20) adapted for removal of paraffinic and / or asphaltic deposits from the interior of a hydrocarbon carrying pipeline comprising of a crawler with microwave generator (22), a microwave guide assembly (24), a fluid bypass channel optionally with pressure differential valve (34) mounted at front end of channel, and a return conduit (28),

A crawler (20) adapted for removal of paraffinic and / or asphaltic deposits from the interior of a hydrocarbon carrying pipeline comprising of a crawler with a microwave guide assembly (24) connected to a remotely positioned microwave generator (22), a fluid bypass channel optionally with pressure differential valve (34), mounted at front end of channel, ad a return conduit (28).