METHOD FOR THE REMOVAL OF DEPOSITS ACCUMULATED IN THE PIPELINES OF TRANSPORT OF GAS

Abstract

The present invention relates to a new use of foaming products for the production of a compact foam pig, by means of the forced interaction of gas, water and product, capable of moving huge quantities of water accumulated in the gas production pipelines. The water removal takes place in very quick periods of time and allows an important decrease in the pressure drops with consequent quick increase in the produced gas quantities.

Claims

1. A method for removal of a deposit accumulated in a pipeline for production and/or transportation of natural and/or process gases which flow along the pipeline, the method comprising the following steps: a) blocking the flow of gases along the pipeline; b) providing a compact foam cushion (foam pig) which completely fills-up a section of the pipeline downstream of the blockage and upstream of the deposit; and c) reactivating the flow of gases along the pipeline, thereby pushing the foam pig along the pipeline and carrying the deposit with it.

2. The method according to claim 1 wherein the deposit comprises water and/or condensate materials.

3. The method according to claim 1 wherein the foam pig is produced in situ in the pipeline or is produced externally to the pipeline and subsequently introduced into the pipeline.

4. The method according to claim 1 wherein the foam pig is produced by mixing in a solvent selected from the group consisting of water, aqueous solution, and organic solution; (i) one or more surfactants and (ii) gas or air.

5. The method according to claim 4 wherein the one or more surfactants are selected from the group consisting of: oxyethylated surfactants, oxyethylated phenols, oxyethylated fatty acids, oxyethylated alkyl monoethanolamides, lauryl beta imino-propionates, oxy-ethylene oxy-propylene copolymers, anionic surfactants, acid surfactants, basic surfactants, amphoteric surfactants, and solid soaps.

6. The method according to claim 5 wherein the acid surfactants are selected from the group consisting of: coco-carboxypropionic acid, acrylic acid/dimethyl-diallyl ammonium chloride copolymer, coconut trimethyl ammonium chloride, C9-11 alkyl (linear)-alcohol alkoxy sulphate, C6-10 alkyl (linear)-alcohol alkoxy sulphate, triethyleneglycol-monohexyl-ether sulfate, C14-16 alpha olefin sulfonate, ethylenediamine tetra acetic acid trisodium salt, oleic acid, dodecanoic acid, coconut acid, octadecanoic acid, lauryl acid, myristic acid, hexadecanoic acid, octanoic acid, coco-dimethylamine-oxide, coco-amidopropyl sulfo betaine, coconut-amidopropyl betaine, coconut-amidopropyl amine oxide, tallow bis-hydroxyethyl glycinate, coco-diethanolamide, oleic acid diethanolamide, coco-N,N-bis-hydroxyethyl amide, oxyethylated coco-amine, laurylamine oxide, dihydroxy ethyl C12-15 alkoxypropyl amine oxide, coco-ampho-acetate, coco-ampho-propionate, coco-ampho-hydroxypropyl sulfonate, lauryl-ampho-acetate, lauryl-ampho-dipropionate, capryl-ampho-diacetate, sodium lauryl-imino propionate, disodium tallow iminodipropionate, and stearyl ampho-propyl sulphonate.

7. The method according to claim 3 wherein the foam pig is produced in situ in the pipeline and the method comprises the following steps: closing an initial valve and a final valve that delimit an isolable segment of the pipeline; venting the isolable segment, thereby reducing its pressure about to atmospheric pressure; filling the isolable segment with a mixture of water and one or more surfactants; opening the initial valve, upstream of the isolable segment; opening the final valve, downstream of the isolable segment; and mixing intimately thrust gas with the mixture in solution by strong turbulence downstream of the initial valve; whereby gas pressure pushes the foam pig along the pipeline and the deposit is carried to a collection station.

8. The method according to claim 7 wherein the sequence of all steps is repeated two or more times.

9. The method according to claim 3 wherein the foam is produced externally to the pipeline and the method comprises the following steps: closing a shut-off valve upstream of the deposit; producing the foam pig externally to the pipeline through suitable means; inserting the foam pig inside the pipeline, downstream of the shut-off valve, through a side-load line; and completely reopening the shut-off valve; whereby gas pressure pushes the foam pig along the pipeline and the deposit is carried to a collection station.

10. The method according to claim 9, wherein the suitable means to produce the foam pig is selected from the group consisting of: a mixer, a high flow-rate and high operating pressure pump, an orifice or nozzle, and a pressure reducer.

11. (canceled)

12. (canceled)

13. The method according to claim 1 wherein the foam pig is produced by mixing water and a surfactant in a ratio from 1:3 to 1:1, wherein the surfactant is selected from the group consisting of: coco-carboxypropionic acid, acrylic acid/dimethyl-diallyl ammonium chloride copolymer, coconut trimethyl ammonium chloride, C9-11 alkyl (linear)-alcohol alkoxy sulphate, C6-10 alkyl (linear)-alcohol alkoxy sulphate, triethyleneglycol-monohexyl-ether sulfate, C14-16 alpha olefin sulfonate, ethylenediamine tetra acetic acid trisodium salt, oleic acid, dodecanoic acid, coconut acid, octadecanoic acid, lauryl acid, myristic acid, hexadecanoic acid, octanoic acid, coco-dimethylamine-oxide, coco-amidopropyl sulfo betaine, coconut-amidopropyl betaine, coconut-amidopropyl amine oxide, tallow bis-hydroxyethyl glycinate, coco-diethanolamide, oleic acid diethanolamide, coco-N,N-bis-hydroxyethyl amide, oxyethylated coco-amine, laurylamine oxide, dihydroxy ethyl C12-15 alkoxypropyl amine oxide, coco-ampho-acetate, coco-ampho-propionate, coco-ampho-hydroxypropyl sulfonate, lauryl-ampho-acetate, lauryl-ampho-dipropionate, capryl-ampho-diacetate, sodium lauryl-imino propionate, disodium tallow iminodipropionate, and stearyl ampho-propyl sulphonate,

14. (canceled)

15. (canceled)

16. An industrial plant for production and/or transportation of natural and/or process gases including a pipeline for the transportation of gases, equipped with means for generating a foam pig inside the pipeline itself and suitable for removal of a deposit which impedes flow of the gases through the pipeline.

17. An oil refinery plant having a discharge circuit and a torch, wherein the plant comprises a pipeline in the discharge circuit, preceding the torch, equipped with means for generating a foam pig inside the pipeline itself and suitable for removal of a deposit and of process gas accumulated within said pipeline.

18. The plant according to claim 16 wherein said generating means produces said foam pig within said pipeline at its beginning.

19. The plant according to claim 16 wherein said generating means is represented by at least one segment of the pipeline itself that is (segregable) isolable from the rest of the pipeline by a first upstream valve and a second downstream valve and provided with at least one external valve for opening to the atmosphere for venting internal gas and for loading a foaming agent and at least one valve cut-off for inserting an instrument selected from the group consisting of thermometer, pressure gauge, and others, or for gas sampling, said isolable segment being upstream of the deposit.

20. The plant according to claim 16 wherein said generating means is a foam production means external and in parallel with respect to the pipeline itself comprising a tool for generating the foam and a side-load line for placing the foam in the main line.

21. (canceled)

22. The plant according to claim 17 wherein said generating means produces said foam pig within said pipeline at its beginning.

23. The plant according to claim 17 wherein said generating means is represented by at least one segment of the pipeline itself that is (segregable) isolable from the rest of the pipeline by a first upstream valve and a second downstream valve and provided with at least one external valve for opening to the atmosphere for venting internal gas and for loading a foaming agent and at least one valve cut-off for inserting an instrument selected from the group consisting of thermometer, pressure gauge, and others, or for gas sampling, said isolable segment being upstream of the deposit.

24. The plant according to claim 17 wherein said generating means is a foam production means external and in parallel with respect to the pipeline itself comprising a tool for generating the foam and a side-load line for placing the foam in the main line.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0077] FIG. 1: In the first panel (A) a pipeline with water deposited in the valleys is illustrated. The other panels (B) show the classical operation of the foaming products; the additivation of a large amount of product causes the formation of foam in the first valley full of water. The foam moves relatively easily, dragged by the gas and reaches the second valley; here the foamer concentration at first is not sufficient to cause foam, then the foam formation will be obtained after a considerable series of additivations. When the foamer has reached the critic concentration, it will form foam which will be dragged as far as the subsequent valley and as far as the final triphasic separator.

[0078] FIG. 2: Panel A illustrates schematically the mechanical action for removing liquids exerted by the foam pig (foam pig) according to the invention. Panel B represents one of the embodiments of the invention with foam production in situ. In particular a line segment is represented arranged for loading the foaming product in batch. (1) point for injecting the water/foamer mixture and/or the foam; (2) line section filled up with foam; (A) shut-off valve that delimits the downstream segment; (B) valve cut-off for venting the line and/or for introducing the foam; (C) line venting; (D) shut-off valve of the gas line or initial valve, upstream of the segregated section

[0079] FIG. 3: the figure illustrates schematically a plant with external means for producing foam and for connecting the foam forming means to the line: (1) injection pump foamer/water; (2) static mixer; (3) aperture; (4) pressure reducer; (C) shut-off valve of the gas line.

[0080] FIG. 4: The figure shows a graph of the pressure variation inside the pipeline during the process for removing the liquids.

[0081] FIG. 5: The Figure represents a scheme comprising a refinery discharge network, in the present invention the means for producing the foam pig would form such pig for in situ introduction or formation before or in the initial portion of the Blow-Down network of the refinery shown in figure.

DETAILED DESCRIPTION

[0082] To the purpose of the present invention the following technical terms should be interpreted as explained hereinafter:

[0083] Under line the pipe or pipeline is meant carrying the gas from a first position to a second subsequent position. For example, from the extracting well head to a subsequent processing station.

[0084] Under well head the well surface portion is meant which puts into communication the deposit with the transportation lines.

[0085] Under well head valves the set of valves is meant required to adjust the flows from the well to the transportation lines.

[0086] Under shut-off valve a valve is meant inserted in the pipeline capable of locking the flow inside the line.

[0087] Under shut-off along the pipeline a side pipe having small section is meant for the insertion of an instrument (thermometer, pressure gauge, . . . )

[0088] Under pig a cleaning brush is meant.

[0089] Under foam pig or foaming pig a pad or a piston of sufficiently dense and compact foam is meant which pushed by the pressure of gas outgoing from the well pushes or drags in its stroke along the pipeline the deposits to be removed.

[0090] Under foaming agent or simply foamer an agent is meant including or consisting of a surface-active agent or surfactant or mixtures thereof. The composition of foaming agent usually comprises the surface-active agent or the mixture of surface-active agents, water and other elements thereamong: solvents and co-solvents required to the stability of the formulated product, acids or bases or Salts to modify the pH of the mixture or to improve the surface-active agents' performances. To the purpose of the present invention the words surface active agent and surfactant are to be considered synonyms.

[0091] The expressions upstream and downstream are to be referred to the direction of the gas stream flowing from the well outlet or head towards a peripheral station. The two expressions identify a position preceding or following another position on the line, respectively.

The Foamers

[0092] A very wide series of surface-active substances can be used as foamers (foamers) according to the present invention. Said surfactants are already known in the petrochemical field. A foaming agent according to the invention can include or consist of one surfactant only or a mixture of different surfactants.

[0093] In 1959, Dunning and others tested a series of commercial surfactants such as: oxyethylated surfactants, oxyethylated phenols, oxyethylated fatty acids, oxyethylated alkyl monoethanolamides, lauryl beta imino-propionates, oxy-ethylene oxy-propylene copolymers, anionic surfactants, acid surfactants, basic or amphoteric surfactants.

[0094] Examples of suitable acid surfactants are: coco-carboxypropionic acid, acrylic acid/dimethyl-diallyl ammonium chloride copolymer, coconut trimethyl ammonium chloride, C9-11 alkyl (linear)-alcohol alkoxy sulphate, C6-10 alkyl (linear)-alcohol alkoxy sulphate, triethyleneglycol-monohexyl-ether sulfate, C14-16 alpha olefin sulfonate, ethylenediamine tetra acetic acid trisodium salt, oleic acid, dodecanoic acid, coconut acid, octadecanoic acid, lauryl acid, myristic acid, hexadecanoic acid, octanoic acid.

[0095] Examples of suitable basic surfactants are: coco-dimethylamine-oxide, cocot-amidopropyl sulfo betaine, coconut-amidopropyl betaine, coconut-amidopropyl amine oxide, tall oil bis-hydroxyethyl glycinate, coco-diethanolamide, oleic acid diethanolamide, coco-N,N-bis-hydroxyethyl amide, oxyethylated coco-amine, laurylamine oxide, dihydroxy ethyl C12-15 alkoxypropyl amine oxide.

[0096] The amphoteric surfactants suitable to the invention can be: coco-ampho-acetate, coco-ampho-propionate, coco-ampho-hydroxypropyl sulfonate, lauryl-ampho-acetate, lauryl-ampho-dipropionate, capryl-ampho-diacetate, sodium lauryl-imino propionate, disodium talloil iminodipropionate, stearyl ampho-propyl sulphonate.

[0097] The interfix ampho means amphoteric that is a substance which can behave with acid or basic characteristics depending upon the substance therewith it can interact and it designates the presence of an additional ammonium or nitrogen group in the corresponding molecule or formula of the shown surfactant. For example ammonium, imino, imidazole or equivalents, o equivalenti, conferring the amphotericity feature.

[0098] In particular they can be used even with solid soaps in form of stick. In this association they were used for the Foam Assisted Lift.

[0099] Possible variants and/or additions can be introduced by the persons skilled in the art to the herein described and illustrated embodiment of the invention within the scope of the following claims.

[0100] Thereamong the following surfactants resulted to be particularly effective and then they represent the preferred ones: coco-carboxypropionic acid, acrylic acid/dimethyl-diallyl ammonium chloride copolymer, coconut trimethyl ammonium chloride, C9-11 alkyl (linear)-alcohol alkoxy sulphate, C6-10 alkyl (linear)-alcohol alkoxy sulphate, triethyleneglycol-monohexyl-ether sulfate, C14-16 alpha olefin sulfonate, ethylenediamine tetra acetic acid trisodium salt, oleic acid, dodecanoic acid, coconut acid, octadecanoic acid, lauryl acid, myristic acid, hexadecanoic acid, octanoic acid, coco-dimethylamine-oxide, cocot-amidopropyl sulfo betaine, coconut-amidopropyl betaine, coconut-amidopropyl amine oxide, tall oil bis-hydroxyethyl glycinate, coco-diethanolamide, oleic acid diethanolamide, coco-N,N-bis-hydroxyethyl amide, oxyethylated coco-amine, laurylamine oxide, dihydroxy ethyl C12-15 alkoxypropyl amine oxide, coco-ampho-acetate, coco-ampho-propionate, coco-ampho-hydroxypropyl sulfonate, lauryl-ampho-acetate, lauryl-ampho-dipropionate, capryl-ampho-diacetate, sodium lauryl-imino propionate, disodium talloil iminodipropionate, stearyl ampho-propyl sulphonate.

The Foam Pig

[0101] The production of high-density foam having consistency suitable for preparing a foam pig (foam pig) is performed under the following conditions: water/foamer ratio from 1:3 to 1:1; foam density ranging from 0.1 g/ml and 0.5 g/ml.

[0102] The foam quantity required for each pig or pad launch depends upon the diameter of the pipeline and provides the use of few tens of litres (10, 20, 30) of water/foamer mixture to some hundreds of litres with the purpose of producing some cubic meters of foam (for example 1 to 20).

In-Situ Preparation of the Foam

[0103] The method of the invention provides two possible implementation modes. The first one wherein the foam is produced in situ in a line segment with respect to the whole pipeline (FIG. 2, panel B), the second one wherein the foam is produced externally in a plant parallelly with respect to the line (FIG. 3, panels A and B).

[0104] In the first mode, it results essential that the pipeline line has at least a section of some tens of meters, for example 10, 15, 20, 30 meters, which could be isolated from the remaining portion, positioned in the initial portion, that is little next the well head or however upstream with respect to the areas which have to be cleaned, that is the areas which can accumulate liquids or obstruct with debris. The isolated segment then has to be equipped with one or more valves for closing the well head, which delimit it upstream and which determine the beginning of the segment and it must have a closing valve which delimits it downstream of the initial one, as said at the distance of 10-30 meters (also depending upon the line diameter). Clearly the isolated segment has to be provided with at least one external valve for opening to the atmosphere required for venting the gas remained trapped with consequent drainage of the segment itself. The segment will equally include at least one valve cut-off for the insertion of an instrument (thermometer, pressure gauge, etc) or for gas sampling and for inserting the foaming agent or the foam preformed according to the embodiment of the invention.

[0105] The plant can provide two or more segments which can be isolated in series, as above described, for the sequential production of two or more foam pigs which will reach the line end separator independently.

[0106] This type of plant provides the in-situ production of foams. The procedure for creating the foam can be schematized in few essential steps described by way of example: [0107] Closure of the initial valve in the well head, the production is stopped and the flow of gas downstream will result to be interrupted. In this phase the pressure on the line will remain more or less constant, since the flow of gas is stopped and the line conditions will be static. [0108] Closure of the valve that delimits the downstream segment. [0109] Opening of the vent valve: the gas which fills up the line segment is made to outgo in a controlled and gradual way. Inside the segment the pressure falls to zero, whereas in the remaining portion of the line it is unaltered. [0110] Filling-up of the segregated line section with a mixture of water and foaming agent, in proportions studied specifically to form a foam as much consistent and dense as possible. The preferred ratios are: water/foamer from 1:3 to 1:1; foam density ranging from 0.2 g/ml to 0.3 g/ml.
The preferred water/foamer ratios were detected by means of the following laboratory Test:

[0111] Method: Blender test upon varying the Water-Product ratio (from 90-10 to 10-90).

[0112] Fluids: Products Chimec, (not demi) drinking Water.

[0113] Stirring: 3 minutes at the maximum speed. Test temperature: 20 C.

[0114] The monitored parameters were: Quantity, quality and persistence of the produced foam. All tests were performed the conditions being equal, except for the variability in the Water-Product ratio which reproduces the ratios which can be those used in the field.

[0115] By way of example, the following table shows the tests carried out upon varying the ratio Water/CH Phoenix 6163 (mixture of not ionic surfactants) with the related comments about quantity and quality of the produced foam.

TABLE-US-00001 VOLUME WEIGHT 100 STRUC- PERSIS- CH CC OF TURE TENCE VOLUME PHOENIX FOAM QUANTITY OF THE OF THE WATER (ml) 6163 (ml) (gr) OF FOAM FOAM FOAM 90 10 8 Good Little Low structured 70 30 12 Good Compact Good 50 50 14 Mediocre Mediocre Mediocre 30 70 36 Mediocre Compact Good 10 90 69 Little Little Low structured

[0116] In order to better emphasize the effect of the Water-Foamer ratio about the type of produced foam, the foam fractions collected after stirring where weighed.

[0117] From the performed tests it results that upon increasing the quantity of foamer the foam density increases but it worsens in terms of quantity and quality; it can be concluded that for an effective foaming action it is necessary to avoid using quantities of foamer higher than 70% in mixture with water. Surely the range comprised between 30/70 and 70/30 (Water/Product) could guarantee an effective applicability in the field, but probably the best ratio remains 50/50 to avoid stabilizing excessively the foam.

[0118] The foam pig effectiveness results to be maximum if the isolated pipeline section will be completely filled-up, without leaving empty spaces in the upper portion of the pipeline. [0119] Opening of the initial valve, upstream of the segregated section; the pressure in the segment grows until equalizing to the well head pressure (for a well supplying continuously, often the well head pressure increases considerably once production is closed, until doubling or tripling with respect to the line initial pressure). In this phase the water/foamer mixture is pushed and compressed by the gas downstream, but since the final valve of the section is still closed, the liquid cannot move in any direction. Moreover, the liquid itself is saturated by the gas coming from the well head. [0120] Very gradual opening of the final valve, downstream of the segment; by opening gradually the valve, the gas pressure pushes the liquid towards the downstream line and the opening behaves like an aperture therethrough the liquid passes with growing speed, pushed by the strong pressure of well head, creating a strong turbulence and by mixing intimately the thrust gas with the water and the surfactant in solution.

[0121] The result will be the production of a very consistent foam, formed by the production gas trapped in bubbles in the water thanks to the presence of surfactant which increases the liquid surface tension. The foam will fill-up fully a quite extended line section, much more extended than the segment used for introducing the liquids.

[0122] The so formed foam pig behaves like a chemical pig or foam pig that is like a plunger and, pushed by the gas pressure, it will be able to move water and any debris accumulated along the pipeline line.

[0123] The whole procedure can be concluded in very short periods of time (fractions of one hour or little more) and the production standstill is very limited over time, much shorter than the traditional applications of the mechanical pigs.

External Preparation of the Foam

[0124] In the second mode for forming the foam pig, the foam is produced externally with respect the line of pipes with means such as an autonomous apparatus, device or plant, placed parallelly with respect to the line and introduced in the line through a suitable shut-off, arranged for instruments or samplings.

[0125] In this mode it is not required that there is a segregable line segment, but it is simply required to have a shut-off, or suitable opening, downstream of the closing valve of the line in the well head.

[0126] The required procedures in this case will be: [0127] Closing of the line through the shut-off valve, that is the valve C in FIG. 2b or FIG. 3, for the shortest possible time. [0128] Insertion of the foam loading line through the shut-off described previously. [0129] Starting of the external means for producing the foam and insertion of the same inside the line, downstream of the closed valve. [0130] Once loaded the whole provided foam, total re-opening of the valve. The gas pressure accumulated in the well head will provide a powerful push, by transporting the formed foam pig thanks to the use of the external tool for the whole length of the line and carrying therewith all water and possible little persistent deposits.

[0131] The external means for producing the foam can be any device suitable for the foam production such as: a mixer, a high rate and high operating pressure pump and an aperture or a nozzle or any other method suitable to the foam production.

[0132] Said external means usually is inserted in a line in parallel as schematized by way of example in figures, but it could have even another geometry.

Plant

[0133] The present invention also relates to the industrial plants suitable to implement the method of the invention.

[0134] The industrial plant is a plant for the production and/or transportation of natural or process gases, as above defined, comprising a pipeline for the transportation of gas or pipeline, equipped with means for generating a foam pig (foam pig) inside the pipeline itself and suitable for the removal of deposits which impede the gas flow through the pipeline.

[0135] Alternatively, said plant is an oil-refining plant, equipped with the means for generating a foam pig (foam pig) inside the pipeline of the discharge circuit of said plant and suitable to drainage of said pipeline which is performed between a refining operating cycle and the subsequent one as described above. Under drainage, as said above, the removal of exceeding gaseous residues is meant which have accumulated in the discharge pipeline ahead of the torch combustion area as described above.

[0136] The means for generating the foam pig is represented at least by one segment of the pipeline itself (segregable) isolable from the rest of the pipeline and limited by an initial valve for closing the flow upstream and a final valve for closing downstream and provided with at least one external valve for opening to the atmosphere for venting the internal gases and for loading a foaming agent.

[0137] The isolable pipeline segment has a length ranging from 5 and 40 meters, even depending upon the diameter of the pipeline itself, for example 10, 15, 20, 25, 30, 35 meters. Said segment is provided with one or more additional valve cut-offs for the insertion of an instrument (thermometer, pressure gauge, . . . ) or for gas sampling.

[0138] In a particular embodiment of the invention the plant comprises two or more isolable segments as described above in subsequent series separated from one another by a closing valve.

[0139] In another embodiment, the pipeline does not require an isolable segment, but the means for generating the foam pig (foam pig) is foam production means external and in parallel with respect to the pipeline itself. Such means comprises an apparatus and device suitable for generating the foam and a pipeline for introducing the foam in the main line. The external means for generating the foam can be a mixer, a high-flow rate and high operating pressure pump and an aperture or a nozzle.

[0140] The segregable segment as described above for the in-situ production or the plant in parallel for the external production of the foam are usually placed at the beginning of the pipeline near the well head therefrom the gas outflows. In this case the shut-off valve (well head valve) corresponds to the segment beginning valve or to the flow closing valve in case of external preparation of the foam.

[0141] In each case, the means for producing the foam pig is placed upstream of the pipeline area obstructed by deposits.

[0142] Examples of plants according to the invention are illustrated in FIG. 2, panel B and 3 panels A and B.

EXAMPLES

[0143] The invention is explained hereinafter in all details and operating conditions by means of embodiment examples which are purely by way of example and have no limitative effect.

Example 1

[0144] In order to verify the effectiveness of this technology, a test was performed for the removal of the liquids which have accumulated on a pipeline which transports the gas from a production station to a gas treating central station. The used product is based upon non-ionic surfactants, suitably mixed in water and glycols.

[0145] The purpose of the application is the removal of the water accumulated in the 5 valleys of a line of 15 km: the consequence of the water accumulation in line is the limitation of the gas production due to the accumulated liquid which causes an additional pressure drop.

[0146] The removal of the liquids takes place with the use of the foaming agent CHIMEC Phoenix 6163 by displacement thanks to the implementation of a foam pig.

[0147] The references to this application are the pressure values in line obtained in the last procedure for launching the mechanical pig (pigging), which however has not been performed for several years; on these occasions, the pressure in line was decreased to around 6 bar, value which is to be considered the minimum obtainable once the line is wholly emptied of liquids. The quantity of moved water, then detected as arriving to the central station after pigging, was about 13 m.sup.3.

[0148] The application result depends upon the selection of the suitable product. The used product was properly selected with (above-described) laboratory test, both as chemical composition, and for the volume/volume ratios to be kept between product and water additioned in the line, that is water/foamer ratio ranging from 1:3 to 1:1; foam density ranging from 0.1 g/ml and 0.5 g/ml.

[0149] At last, the application procedure has to be aimed at creating a compact and effective foam front for the purpose of the displacement.

[0150] The use of CHIMEC anti-foaming agent is required for controlling the possible negative effects of the foam and to protect the plant and in particular the separator inletting the central station, having limited volume.

Application Procedure (FIG. 2B)

[0151] CHIMEC foamer was loaded at the beginning of the line in the section comprised between PCV (Pressure Control Valvevalve B in figure) and the shut-off valve positioned few meters upstream of the PCV itself (valve A in figures). The treatment provides two batches of foaming agent and water. The volume of the considered line stump is about 120 litres.

[0152] The loading of each batch consists of foaming agent and water in ratio 2:1. The total loaded liquids are about 120 litres of product Chimec Phoenix 6163 and about 60 litres of water.

[0153] The product introduction in this point guarantees the formation of an effective foam if the valve opening is performed according to the here below illustrated sequence.

[0154] It is important to respect the loading order so that foaming agent and water are introduced in the line segment in small quantities and alternatively (example: 20 litres of product+10 of water for about four times) in order to guarantee an optimum mixing.

[0155] It is important to guarantee the total filling-up of the line by setting to zero the empty volume which would create preferential channels for the passage of gas above the liquid mixture, by preventing the formation of an effective foam due to a low density and persistence of the same.

[0156] During re-opening all valves have to be opened slowly. The procedure consists of operations to be performed preliminarily in the central station, a procedure for applying foamer and antifoam and monitoring activity for the whole treatment.

[0157] Preliminary Procedures in Central Station: [0158] Drainage of the separator so as to have the maximum concentration of initial antifoam and increase in the useful space for the arriving liquids. [0159] Drainage of the pig receiver to allow reliable samplings.

[0160] Application Procedure: [0161] 1. Closing of the valves A and C and depressurizing of the line segment by disassembling one of the manometers of the line stump. Such procedure will be performed according to the plant safety procedures. [0162] 2. Loading of 1 batch in the section A-B (by closing for this purpose valve B, flow rate in manual mode). The loading will have to be performed through the nozzle of one of the manometers as shown in FIG. 2. Another nozzle will have to be kept free for venting the line during loading. [0163] 3. Leaving that the line upstream of the valve A loads due to the well head pressure (in the test about 25 bars are reached). [0164] 4. Pressurizing and launching of 1 batch: B is opened slightly (so that the mixture passes through the restriction). A is opened totally and soon after C partially, the minimum required to allow the passage. The fluid is left to flow in this mode for 5 minutes, after that even the valves B and C are opened totally. [0165] 5. Repeating points 1 to 4 for loading 2 batch. [0166] 6. Injection of the antifoam continuously soon after having launched the first batch of foamer, with dosing pump at 60% (first hour) and 80% (until the arrival of all displaced liquid).

[0167] A digital manometer recorded the course of the pressures in line downstream of PCV. The other monitored parameters were the gas and water productions of the single wells and the overall one.

[0168] The procedure for adding foamer and water lasted few tens of minutes and the group of procedures for creating the foam pig requested to stop the production for about one hour.

[0169] The test had positive result with an important increase in the average gas production. The displaced water was about 13 m.sup.3 and the pressure in line decreased from 15 bar to 6 bar, value analogous to the one obtained with the mechanical pigging procedure. The value of the counterpressure in line which at first was estimated to be around 10 bar decreased to about 0.5 bar as illustrated in FIG. 4.

[0170] After treatment an increase in the overall gas production of 5.9% took place, with some peaks of production for some wells even increased by 138%.

[0171] As already said, in the arrival station (central station) about 13 m.sup.3 of water were collected after less than two hours from the application of the foaming agent.

[0172] The arrival of the water pushed by the foam was well managed by the additivation of the antifoam agent in central station so as not to cause the plant shut down.

Example 2

[0173] On the same line of example 1, the application of the foam pig was repeated, but without using the isolable line segment and the valves already existing for generating foam itself. The foam pig was generated by external means, described in the above-illustrated scheme (FIG. 3, panels A and B). The used amounts of water and product are more or less the same of example 1, but clearly it was not necessary to open and drain the line stump.

[0174] The procedures for introducing the foam into the line took place in few minutes and the production interruption was further shortened.

[0175] The results were fully comparable with those described above, obtained by generating the foam inside the line.

[0176] The application of external means is extremely important since it allows to create the foam pig even in lines which have not segregable stumps and valves at short distance therebetween. With this mode simply shut-off valve is required to stop the production (which is always present in any gas field) and a shut-off (for example an instrument socket) for introducing the foam.

Example 3

[0177] A refinery discharge line, having sizes equal to three inches, was drained by using the foam pig procedure.

[0178] The line had a significant length (greater than 150 m) and had two valleys having big sizes. Then it was necessary to control the behaviour of the foam during the passage of the valleys (water hammer phenomenon, pressure drop, foam drop).

[0179] The application was very positive, it showed that the line route is not an obstacle, no problem for the foam pig to go along the two valleys, the foam was collected in the final container without difficulty. No excessive odour or heat, no hot effluent, complete removal of the pyrophoric risk. The line was cleaned perfectly and the drainage allowed to perform the maintenance work by performing even hot weldings, without additional cleaning. An antifoam was present in the final container to neutralize the foam.

[0180] In the table the main pieces of information are collected, obtained from preceding line drainages with the classical techniques compared to the application of the new technology.

TABLE-US-00002 Classical decontamination Decontamination with vapour with Foam pig Comments Installation 2 hours 2 hours The used materials are duration identical Quantity of required One barrel (200 Less than Very little product to chemical product litres) 50 litres produce the foam Decontamination 24 hours 8 hours Increased duration effectiveness Quantity of from 1 to 5 m3 Less than Effluents consisted of: effluents 200 litres antifoam, foaming product and residual hydrocarbons from the line Effectiveness Zero explosivity Zero explosivity At the beginning the and zero and zero volatile explosivity was about 12% hydrocarbons after hydrocarbons after and there were more than 10 hours 1 hour 10,000 ppm of volatile hydrocarbons HSE Risks of burns No increase in Nitrogen use temperature to be managed