GB2226963A

GB2226963A - Processing crude oil

Info

Publication number: GB2226963A
Application number: GB8928475A
Authority: GB
Inventors: Jon Hermstad
Original assignee: Norwegian Contractors AS
Current assignee: Norwegian Contractors AS
Priority date: 1988-12-22
Filing date: 1989-12-18
Publication date: 1990-07-18
Anticipated expiration: 2009-12-18
Also published as: NO885706L; GB2226963B; GB8928475D0; NO885706D0

Abstract

Crude oil from an offshore oil well is subjected to gravity separation in a submerged vessel or vessels incorporated in the platform (not shown), from which 1 separated gas, oil, water and slurry are removed by separate pipelines. The vessel(s) may have remote level sensors to control the removal of different phases. <IMAGE>

Description

EQUIPMENT AND METHOD FOR PROCESSING CRUDE OIL The present invention relates to equipment and a method for processing crude oil which is produced from offshore, subsea wells.

The invention shall in the following be described in connection with production of crude oil from offshore gravity platforms, but it shall be understood that the invention can also be utilized in connection with other types of oil production, for instance from submerged plants located on the sea bottom.

More particularly, the invention relates to a plant and a method for initial cleansing/separation of produced crude oil in order to separate oil, gas, water and mineral particles (slurry) prior to that the oil/gas is transported either through pipelines to shore, is pumped aboard tank vessels at the oil field, or is being stored in accessible cells on the submerged part of the platform.

It is today common to carry out such initial treatment of the crude oil on the platform deck by means of mechanical processing units which separate oil, gas, water and sl rry, respectively, from each other.

Such processing units are expensive and heavy and consume a great part of the limited accessible space aboard the platform deck. Such units further represent a substantial risk for fire and explosions.

In accordance with the present invention the initial cleansing/separation of the crude oil from the well is carried out without use of expensive, heavy processing units, and without occupying space on the platform deck.

This object is in accordance with the present invention fulfilled in that the crude oil is separated in large hollow spaces or cells.

By carrying out the separation in cells in the platform structure the separation can be accomplished without use of the before-mentioned mechanical processing units, at the same time as space on the platform deck is vacated and the total weight of the platform is being reduced. Further, the risk of fire and explosions on the deck is reduced substantially in that the crude oil is being processed at a lower level in closed processing cells below the deck.

The method in accordance with the present invention may either entirely replace processing equipment for crude oil located on the platform deck in a manner which is usual today, or it can be combined with deck based processing equipment having a simpler design than what is usually required.

In accordance with the invention the crude oil which contains, in addition to oil and gas, also water and slurry, is pumped into a chamber (cell) in the platform. Water and slurry, which are heavier than oil, will sink to the bottom in the chamber. The gas will be separated from the oil as it is lighter than the oil, and because the oil pressure will be substantially lower than the original reservoir pressure. The gas will accumulate uppermost in the chamber or cell.

The sediments from the water and slurry can be removed through outlets at the bottom of the cell. Gas from the top of the cell can be transported out of the same in pipes to the platform deck where it either can be burned, be utilized aboard, or be exported from the platform.

Subsequent to that sufficient quantities of gas, water and slurry have been separated from the oil by means of gravity, oil can be conveyed out of the cell and transmitted over to storage cells for storage, or be directely transmitted to a pipe system.

The invention shall be illustrated in the following by means of an example in connection with sketches showing the principles, wherein: Figure 1 is showing one single processing cell, Figure 2 is showing several processing cells in series, and Figure 3 is showing an embodiment of a processing cell, a storage cell and a buffer cell.

Figure 1 is illustrating the invention in its simplest form wherein the separation takes place in one single cell.

The cell forms part of a platform structure (not shown) and is located below the water line. Figure 1 is showing the situation wherein the constituents of the crude oil are separated into a slurry layer 4 lowermost in the cell and a layer of water 5 above the layer of slurry. The cleansed crude oil 6 rests on the water layer, and the gas 7 has accumulated uppermost in the cell.

The crude oil is supplied to the cell from the subsea well through a pipeline 8. The cell is shown resting on the sea bottom 3, but may obviously have any selected position in the submerged part of the platform.

Stabilized oil with acceptably low content of gas, water and slurry is transported out of the cell through a pipeline 9 for export.

Separated gas is removed from the cell in a pipeline 10 to the platform deck, where it is further processed.

Bottom deposited water is removed through pipeline 11, and slurry through pipeline 12. The pumping of the slurry may be enhanced in that water is flushed into the cell through a pipe 11 whereafter slurry and water are being pumped out through the pipe 12, and slurry and water may also be pumped through a pipe 12, possibly by means of air which is supplied through a pipe 13.

In order to supervise the situation in the cell a system for measuring the pressure in gas and liquids, respectively, is being arranged, and also a system for measuring the level for the oil and water surfaces. Liquid pressures can be measured directly hydraulically, by means of piezo-electrical meters, or by means of pendling rod meters or other types of meters.

A supervising system is indicated in Figure 1 including a measuring unit 14 having sensors positioned in the cell.

Level measurements of the surface of oil and water can either be based on pressure measurement or for instance directly by means of a series of electrical resistance meters positioned along a vertical axis. It is also possible to measure the position of the liquid surfaces by accustical methods. Furthermore, it will be possible to take samples of oil and water for control and supervision of the cell.

In Figure 1 is shown one single processing cell. It shall, however, be pointed out that it will be practical to utilize a series of processing cells. Such cells can either be operated individually, or they can be coupled together such that they operate in common or in several groups of processing cells, such as shown in Figure 2, wherein three processing cells la, lb and lc are coupled together in a group. The inter-coupling can be provided by means of openings 15 between the cells, and need not necessarily be controlled by active operation of valves.

The number of openings between the processing cells and the size of the openings and the level for such, can be selected and adapted to the particular mode of processing used in connection with cleansing of the crude oil.

When practised in connection with a Condeep platform one or several of the cells in the caisson can be utilized as processing cells. Other cells in the Condeep caisson which are not utilized as processing cells can for instance be used as storage cells for storing of already processed oil.

Figure 3 is showing how a processing cell can be used together with an oil storage system as described in applicant's earlier filed Norwegian patent application No. 87 0904. The internal liquid pressure in the process cell may be monitored by measuring the pressure in the storage cell 16 which communicates with hydrostatic water pressure via the water cell 17.

Water in the water cell can either communicate separately to the ambient sea, or the water can be cleansed via a separate pipe system 18 and a cleansing modul 19 as shown in Figure 3 with stitched lines.

Claims

1. Means for processing crude oil produced from offshore subsea oil wells, c h a r a c t e r i z e d in that the means comprises at least one submerged process cell for gravity separation of crude oil in oil, gas and mineral particles, respectively.

2. Means in accordance with claim 1, c h a r a c t e r i z e d in that said at least one process cell is located in the caisson of an offshore platform.

3. Means in accordance with claim 1 or 2, c h a r a c t e r i z e d that the means comprises inside a gravity platform two or more submerged cells (la, lb or lc) coupled together in one group or groups of communicating, cooperating process cells.

4. Means in accordance with claim 3, c h a r a c t e r i z e d in that said means comprises a simplified means for after-cleansing and separation on the platform deck.

5. Method for processing crude oil produced from offshore, subsea oil wells, c h a r a c t e r i z e d in that the crude oil components of oil, gas and mineral particles are separated by gravity in at least one cell in a submerged gravity platform.

6. Method in accordance with claim 5, c h a r a c t e r i z e d in that the oil is cleansed and separated in at least a number of submerged cells, for instance in a submerged gravity platform.

7. Method in accordance with claims 5 and 6, c h a r a c t e r i z e d in that two or more of the submerged platform cells are coupled together in a group of communicating, cooperating process cells.

8. Method in accordance with claims 5 to 7, c h a r a c t e r i z e d in that the crude oil is subjected to an after-cleansing and separation in a simplified cleansingand separation means on the deck of the platform.

9. Method in accordance with claims 5 to 8, c h a r a c t e r i z e d in that the cleansed oil is exported in a pipe system to the shore or to a tank vessel, or is being stored in accessible cells in the submerged part of the platform.