GB1569533A

GB1569533A - Method of transporting a viscous oil through a pipeline

Info

Publication number: GB1569533A
Application number: GB1798378A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1977-08-16
Filing date: 1978-05-05
Publication date: 1980-06-18
Also published as: FR2400668A1; JPS5432816A; FR2400668B1; NL185864B; DE2835664C2; DE2835664A1; NL7709005A; CA1094131A; NL185864C

Description

(54) A METHOD OF TRANSPORTEG A VISCOUS OIL THROUGH A PIPELINE (71) We, SHELL INTERNA TIONALE RESEARCH MAATSCHAP PIJ B.V., a company organised under the laws of The Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of transporting a viscous mineral oil through a pipeline.

A known method comprises transporting a viscous oil through a pipeline in the form of a continuous phase wherein the oil is surrounded by an annular layer of a liquid with a lower viscosity, and wherein these two liquids are substantially mutually insoluble. The oil moves as a protracted core centrally through the pipeline and the lowviscosity liquid, which is preferably water, forms a lubricating layer between the oil and the wall of the pipeline.

The low viscosity of the water greatly facilitates pumping. This method allows the transport of high-viscosity oils through a pipeline, which would otherwise be too expensive or ultimately become technically impossible, because of the high pressure drops. Special inlet devices are known to introduce the water in the appropriate way around the oil into the pipeline.

This known method and embodiments of special inlet devices are described in applicant's British patent specifications No.

1,168,608 published on 29th October 1969, No. 1,389,231, published on 3rd April 1975 and No. 1,389,232, published on 3rd April 1975.

It is very important to prevent that the viscous oil touches the wall of the pipeline and sticks to it, since this would considerably increase the pump resistance. Particularly when the transport of oil is interrupted, special steps must be taken to ensure that the oil transport can be started again.

A possible way to deal with this problem is to fill the pipeline entirely with water before the oil transport is interrupted.

However, in long pipelines this solution is time consuming and expensive. In addition, it is unsuitable if the transport has to be stopped rapidly, for instance in cases of failure of equipment. In this respect, the present invention provides considerable improvements.

The invention comprises a method of transporting through a pipeline a viscous mineral oil surrounded by an annular layer of a liquid with a lower viscosity, the low-viscosity liquid and the oil being substantially mutually insoluble, wherein the low-viscosity liquid is a solution of an alkali metal silicate in water.

The term alkali metal silicate refers to compounds such as sodium and potassium silicates which may have the meta- or the orthostructure. The molar ratio of SiO2 to metal oxide may be in the range between 1 and 4.

The use of a solution of an alkali metal silicate in water as the low-viscosity liquid has considerable advantages. The solutions concerned, of which some are known as water-glass, have a gel structure. This means that the solution has elastic properties. A yield stress has to be exceeded to break through the liquid layer. Consequently the oil cannot break easily through the surrounding annular layer as is the case when pure water is used as the low-viscosity liquid. In addition, the silicate has the attractive property of making the wall of the pipeline oil-repellent, which has the advantage that should the oil break through the annular layer and touch the wall of the pipeline, the oil does not immediately stick to that wall.Furthermore it is important that the alkali metal silicate solution is found to have a cleaning effect when the wall of the pipeline has still become fouled with oil.

A suitable solution consists of 0.2-1.0%w sodium silicate in water. The quantity of the solution can be at least 1%v based on the oil volume. With this small quantity of solution stable operation of the pipeline is found to The possible.

An advantageous effect is achieved when, as a preparation for an interruption of the transport, the supply of the solution is raised to a quantity of at least 4%v based on the oil volume until the contents of the entire pipeline has this composition. Then the transport is interrupted and after the interruption the transport is resumed under the original conditions. For a satisfactory transport of a thick oil in a commercial pipeline, with for instance an internal diameter of 20 cm, a quantity of solution of 1%v based on the oil volume, has been found to be sufficient. However when the transport is interrupted for a long time, fouling of the wall of the pipeline is found to occur.By forming before the interruption an annular layer of the solution which occupies at least 4%v based on the oil volume, resumption of the transport with a reduction of the quantity of the solution to IO/ov based on the oil volume is found to be possible, even after a stagnancy of twenty or thirty hours.

When unforeseen circumstances have still caused fouling of the wall of the pipeline, it is to be recommended to raise the supply of the solution temporarily to a quantity of at least 10%v based on the oil volume. Instead, it is possible to replace the supply of the oil by a supply of the solution until at least 5%v of the entire pipeline has been filled with solution, after which the transport is resumed under the original conditions. It is not necessary here to bring the contents of the pipeline to a standstill. Each of these two temporary measures results in a clean wall of the pipeline.

The invention will now be elucidated with the aid of a few examples.

Experiments were carried out in a horizontal pipeline system having an internal diameter of 5 cm and consisting of a steel tube of 3 m long connected to a glass tube of 4.5 m long. The steel tube had an oxide layer on the inside and had welded seams with uneven spots at the surface of up to 2 mm. The sharpest bend was 90" with a radius of curvature of 1.5 times the pipeline diameter. A residual oil, which had a viscosity of 1000-1300 cP at the test temperature and a density of 970 kglm3, was passed through the pipeline at a rate of 1 m/s.

Before-hand the system had been filled with an 0.3%w solution of Na,SiO3 in water.

I The oil was passed through the pipeline while surrounded by an annular layer of a solution of 0.1vow Na2SiO3 in water which occupied 5%v based on the oil volume.

Within two hours the pressure drop in the steel tube increased from 1.7 to 3.3 times of that of 100%v clean water, as a result of oil sticking to the wall, of the pipeline, as was visible in the glass tube. After two hours of passing oil through the pipeline in the above manner, the solution was replaced by a solution of 0.2%w Na2SiO3 in water. The oil was passed through the pipeline under otherwise the same conditions. The pressure drop in the steel tube gradually decreased and fell in six hours to about twice that of 100%v clean water. In the glass tube the wall was seen to become gradually cleaner.

Further experiments were carded out in horizontal pipeline system having an internal diameter of 20 cm and consisting of a steel tube as used for pipelines in actual practice. The pipeline was 1 km long and had 22 bends each of 90" and each with a radius of curvature of 1.5 times the pipeline diameter. There were uneven spots (to a size of 3 mm) on the inner surface of the wall of the pipeline as a result of welds. A residual oil, which had a viscosity of 7602200 cP, depending on the temperature, and a density of 958 kg/m3, was passed through the pipeline at a rate of 1 m/s.

II The oil was passed through the pipeline while surrounded bv an annular layer of a solution of 0.2%w Na2SiO3 in water which occupied 1%v based on the oil volume. The viscosity of the oil was 2200 cP. These conditions allowed stable operation of the pipeline for an indefinite time. The pressure drop was about 3 times that of 100%v clean water.

III After the experiment mentioned sub II, the quantity of solution was raised to 8%v based on the oil volume. After the entire pipeline had been filled with this composition, the transport was interrupted for 15 days. After this period restarting of the oil transport proceeded smoothly.

IV After the wall of the pipeline had been strongly fouled with oil, the oil transport was continued with a solution of 0.2%w Na2SiO3 in water surrounding the oil as an annular layer, which solution occupied 10%v based on the oil volume. After a few hours the wall of the pipeline was clean again.

WHAT WE CLAIM IS: 1. A method of transporting through a pipeline a viscous mineral oil surrounded by an annular layer of a liquid with a lower viscosity, the low-viscosity liquid and the oil being substantially mutually insoluble, wherein the low-viscosity liquid is a solution of an alkali metal silicate in water.

2. A method as claimed in claim 1, wherein the solution consists of 0.2-1%w sodium silicate in water.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. found to have a cleaning effect when the wall of the pipeline has still become fouled with oil. A suitable solution consists of 0.2-1.0%w sodium silicate in water. The quantity of the solution can be at least 1%v based on the oil volume. With this small quantity of solution stable operation of the pipeline is found to The possible. An advantageous effect is achieved when, as a preparation for an interruption of the transport, the supply of the solution is raised to a quantity of at least 4%v based on the oil volume until the contents of the entire pipeline has this composition. Then the transport is interrupted and after the interruption the transport is resumed under the original conditions. For a satisfactory transport of a thick oil in a commercial pipeline, with for instance an internal diameter of 20 cm, a quantity of solution of 1%v based on the oil volume, has been found to be sufficient. However when the transport is interrupted for a long time, fouling of the wall of the pipeline is found to occur.By forming before the interruption an annular layer of the solution which occupies at least 4%v based on the oil volume, resumption of the transport with a reduction of the quantity of the solution to IO/ov based on the oil volume is found to be possible, even after a stagnancy of twenty or thirty hours. When unforeseen circumstances have still caused fouling of the wall of the pipeline, it is to be recommended to raise the supply of the solution temporarily to a quantity of at least 10%v based on the oil volume. Instead, it is possible to replace the supply of the oil by a supply of the solution until at least 5%v of the entire pipeline has been filled with solution, after which the transport is resumed under the original conditions. It is not necessary here to bring the contents of the pipeline to a standstill. Each of these two temporary measures results in a clean wall of the pipeline. The invention will now be elucidated with the aid of a few examples. Experiments were carried out in a horizontal pipeline system having an internal diameter of 5 cm and consisting of a steel tube of 3 m long connected to a glass tube of 4.5 m long. The steel tube had an oxide layer on the inside and had welded seams with uneven spots at the surface of up to 2 mm. The sharpest bend was 90" with a radius of curvature of 1.5 times the pipeline diameter. A residual oil, which had a viscosity of 1000-1300 cP at the test temperature and a density of 970 kglm3, was passed through the pipeline at a rate of 1 m/s. Before-hand the system had been filled with an 0.3%w solution of Na,SiO3 in water. I The oil was passed through the pipeline while surrounded by an annular layer of a solution of 0.1vow Na2SiO3 in water which occupied 5%v based on the oil volume. Within two hours the pressure drop in the steel tube increased from 1.7 to 3.3 times of that of 100%v clean water, as a result of oil sticking to the wall, of the pipeline, as was visible in the glass tube. After two hours of passing oil through the pipeline in the above manner, the solution was replaced by a solution of 0.2%w Na2SiO3 in water. The oil was passed through the pipeline under otherwise the same conditions. The pressure drop in the steel tube gradually decreased and fell in six hours to about twice that of 100%v clean water. In the glass tube the wall was seen to become gradually cleaner. Further experiments were carded out in horizontal pipeline system having an internal diameter of 20 cm and consisting of a steel tube as used for pipelines in actual practice. The pipeline was 1 km long and had 22 bends each of 90" and each with a radius of curvature of 1.5 times the pipeline diameter. There were uneven spots (to a size of 3 mm) on the inner surface of the wall of the pipeline as a result of welds. A residual oil, which had a viscosity of 7602200 cP, depending on the temperature, and a density of 958 kg/m3, was passed through the pipeline at a rate of 1 m/s. II The oil was passed through the pipeline while surrounded bv an annular layer of a solution of 0.2%w Na2SiO3 in water which occupied 1%v based on the oil volume. The viscosity of the oil was 2200 cP. These conditions allowed stable operation of the pipeline for an indefinite time. The pressure drop was about 3 times that of 100%v clean water. III After the experiment mentioned sub II, the quantity of solution was raised to 8%v based on the oil volume. After the entire pipeline had been filled with this composition, the transport was interrupted for 15 days. After this period restarting of the oil transport proceeded smoothly. IV After the wall of the pipeline had been strongly fouled with oil, the oil transport was continued with a solution of 0.2%w Na2SiO3 in water surrounding the oil as an annular layer, which solution occupied 10%v based on the oil volume. After a few hours the wall of the pipeline was clean again. WHAT WE CLAIM IS:

1. A method of transporting through a pipeline a viscous mineral oil surrounded by an annular layer of a liquid with a lower viscosity, the low-viscosity liquid and the oil being substantially mutually insoluble, wherein the low-viscosity liquid is a solution of an alkali metal silicate in water.

3. A method as claimed in any one of

the claims 1-2, wherein the quantity of the solution is at least 1%v based on the oil volume.

4. A method as claimed in any one of claims 1-3, comprising, as a preparation for an interruption of the oil transport, raising the supply of the solution to a quantity of at least 4%v based on the oil volume until the contents of the entire pipeline has this composition, interrupting the transport and after the interruption resuming the transport under the original conditions.

5. A method as claimed in any one of claims 1-4, comprising, after fouling of the wall of the pipeline, temporarily raising the supply of the solution to a quantity of at least 10%v based on the oil volume.

6. A method as claimed in any one of claims 1-4, comprising, after fouling of the wall of the pipeline, replacing the supply of the oil by a supply of the solution until at least 5%v of the entire pipeline has been filled with solution, after which the transport is resumed under the original conditions.

7. A method of transporting through a pipeline a viscous mineral oil surrounded by an annular layer of a liquid with a lower viscosity as claimed in claim 1, substantially as described hereinbefore and with reference to the examples.