Multi-phase petroleum stream monitoring system

Abstract: A multi-phase petroleum stream is stratified by causing it to flow down an inclined pipe (7) at a predetermined angle to the horizontal. The stratified stream flows into a gas trap (14) from which the liquid discharges by a liquid exit pipe (21,32) which is connected to a downstream section (38) of the pipeline. A gas accumulator (44) is connected to the stratifying pipe (7) and to the gas trap (14) and collects the gas from them. A gas discharge pipe (70,74) is connected to the accumulator and to the downstream section of the pipeline and allows the gas to flow from the accumulator to the pipeline. A gas flow rate meter (100) is connected to the gas discharge pipe and provides a signal representative of the gas flow rate. A liquid flow rate meter (105) is connected to the liquid discharge pipe and provides a liquid flow rate signal. A percentage water content meter is connected to the liquid discharge pipe and provides a signal representative of the percentage water content of the liquid discharging from the trap.

Description: The present invention relates to monitoring systems for a multi-phase petroleum stream. US-A-1467512 describes a system for monitoring a multi-phase petroleum stream flowing in a pipeline, comprising: a stratifying pipe connected to an upstream section (4) of the pipeline and inclined downwardly to tend to cause statification of the petroleum stream into a predominantly gaseous stream and a predominantly liquid stream by causing the stream to flow down the incline; liquid discharge means connected to a downstream section of the pipeline for allowing liquid from the stratifying pipe to flow into the downstream section of the pipeline; an accumulator connected by connecting pipes to the upper side wall of the stratifying pipe for accumulating gas from the stratifying pipe; and gas discharge means connected to the accumulator for allowing gas to discharge from the accumulator. The present invention is characterized as set out in claim 1. GB-A-2089049 describes the separation of a dual-phase mixed fluid into gaseous and liquid phases, and separately measuring their flow rates, followed by re-mixing of the separated fluids prior to discharge. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which is a partial schematic and partial simplified block diagram of a multi-phase monitoring system according to the invention. With reference to the Figure, a multi-phase petroleum production stream is flowing in a sub-sea pipe 4. Pipe 4 nominally in this example is a 10 cm. diameter pipe. Petroleum stream from pipe 4 is fed into another pipe 7 which is also 10 cm. diameter, but it is inclined downwardly at a predetermined angle to the horizontal in the range of from 10° to 80°. It should be noted that all angles are with reference to the horizontal and can be the same but it is not necessary that the angles actually be the same. In the present example, a preferred angle of 22.5 degrees is used. Pipe 7 is connected to a 25 cm. diameter pipe 14 with a suitable coupling 17. Pipe 14 functions as a gas trap. The end of pipe 14 is connected to a 7.6 cm. diameter pipe 21 through coupling 5 and pipe 21 extends in the horizontal plane. Pipe 21 is connected by another coupling 5 to a two diameter adapter coupling 25, which in turn is connected to a 10 cm. diameter pipe 32. Pipe 32 is connected to pipeline 38 by a coupling 5 and pipeline 38 extends in the horizontal plane, but is not at the same level as the entry pipeline 4. A gas accumulator pipe 44 is connected to pipe 7 by connecting pipes 47 through 50. As can be seen in the Figure, connecting pipes 47, 48 and 49 are relatively close together, while connecting pipe 50 is spaced further apart. A connecting pipe 55 connects pipe 14 to accumulator pipe 44 in a manner so that connecting pipe 55 is located near the upper end of pipe 14. It should be noted that pipe 44 extends above and substantially parallel to the longitudinal axis of pipes 7 and 14. Accumulator pipe 44 has a pipe 59 which is connected to a 90° elbow 64 which in turn is connected to a 10 cm. diameter pipe 70. Again, due to the 90° fitting 64 and the fact that the outlet fitting 59 is perpendicular to the longitudinal axis of pipe 44, the longitudinal axis of pipe 70 is substantially parallel to the axis of pipe 44 and of pipes 14 and 7. Pipe 70 is connected to another 10 cm. diameter pipe 74 by coupling 5 so that the longitudinal axis of pipe 74 is substantially horizontal. Pipe 74 is connected to a 90° elbow 64 which in turn is connected to a pipe 78, which has entry into pipeline 38. As an indication of physical size, the length of the inclined pipeline 7 and 14 carrying liquid is approximately 7.6 metres. The gas accumulator pipe 44 is approximately 5.2 metres in length. The inclined portion of the gas pipe 70 is approximately 1.5 metres in length, while the horizontal portion is approximately 3.2 metres. All angles used in the foregoing example are 22.5°, but as noted before, the angle can lie in the range from 10° to 80°. A conventional gas flow meter 100 provides a signal corresponding to the gas flow rate, while a conventional liquid flow meter 105 provides a signal representative of the liquid flow rate. A percentage water content meter 111, which may be of a conventional capacitive type, provides a signal corresponding to the percentage water content of the liquid flowing in pipe 21. The signals from meters 100, 105 and 111 are provided to a console and recording equipment 120 on an offshore platform (not shown) for review and recordation. In operation, a multi-phase petroleum stream in pipe 4 flows down through pipes 7 and 14 with the assistance of gravity. Due to the downward inclination of the pipe and turbulence in the flowing stream, gas starts breaking free from the liquid and rises to the upper side of pipes 7 and 14 and then enters accumulator 44 by way of the connecting pipes 47 to 50 and connecting pipe 55. The liquid continues down through pipe 7 still yielding gas, to where it reaches pipe 21. Due to the reduced diameter of pipe 21 and the fact that it is horizontal, liquid backs up in the pipe 14, further facilitating gas to accumulate in the upper portion of pipe 14. The trapped gas enters accumulator pipe 44 via the connecting pipe 55 so that the fluid flowing through pipe 21 is substantially all liquid. As the gas builds up in accumulator 44 it forces gas to discharge through pipe 70 which then feeds through pipe 74 and then down to pipe 78 and back into the petroleum stream through discharge pipe 38. The invention as hereinbefore described is a system for monitoring the gas flow rate, the liquid flow rate and the percentage water content of a multi-phase petroleum stream.

Claims: A system for monitoring a multi-phase petroleum stream flowing in a pipeline, comprising: a stratifying pipe (7) connected to an upstream section (4) of the pipeline and inclined downwardly to tend to cause stratification of the petroleum stream into a predominantly gaseous stream and a predominantly liquid stream by causing the stream to flow down the incline; liquid discharge means (21,32) connected to a downstream section (38) of the pipeline for allowing liquid from the stratifying pipe to flow into the downstream section of the pipeline; an accumulator (44) connected by connecting pipes (47-50) to the upper side wall of the stratifying pipe (7) for accumulating gas from the stratifying pipe; and gas discharge means (70,74) connected to the accumulator for allowing gas to discharge from the accumulator; characterized by: an elongate gas trap (14) connected between said stratifying pipe (7) and said liquid discharge means (21,32), said gas trap being of larger diameter than said stratifying pipe and being inclined downwardly from said stratifying pipe to said liquid discharge means; a connecting pipe (55) between the upper end portion of said gas trap (14) and said accumulator (44) to allow gas also to flow from said gas trap into said accumulator; said liquid discharge means (21,32) includes a first pipe and a second pipe, said first pipe (21) being arranged in a horizontal position and connected to the lower end portion of said gas trap (14) and whose diameter is less than the diameter of the stratifying pipe (7) whereby to cause liquid to back up in said gas trap to facilitate gas to accumulate in said upper end portion of said gas trap, and said second pipe (32) connecting the first pipe (21) to the downstream section (38) of the pipeline and having the same diameter as the pipeline; said gas discharge means (70,74) being connected to the accumulator and to the downstream section (38) of the pipeline to allow gas to discharge from the accumulator into the downstream section of the pipeline so as to recombine the petroleum stream; a first flow meter (100) connected to the gas discharge means (70,74) for providing a signal representative of the gas flow rate; a second flow meter (105) connected to the first horizontal pipe (21) of the liquid discharge means for providing a signal representative of the liquid flow rate; and means (111) also connected to the first horizontal pipe (21) of the liquid discharge means for providing a signal representative of the percentage water content of the liquid. A system according to claim 1 characterized in that the incline provided by said stratifying pipe (7) lies in the range of from 10° to 80° to the horizontal. A system according to claim 1 or claim 2 characterized in that the gas trap (14) is a length of pipe of substantially greater diameter than the stratifying pipe (7). A system according to any one of claims 1 to 3 characterized in that the accumulator (44) is connected to the stratifying means (7) and to the gas trap (14) by a series of pipes (47-50) which are slightly smaller in diameter than the stratifying pipe (7). A system according to any one of claims 1 to 4 characterized in that the accumulator (44) comprises a pipe greater in diameter than the stratifying pipe (7) but lesser in diameter than the gas trap (14). A system according to any one of claims 1 to 5 in which the gas discharge means (70,74) includes a first length of pipe (70) connected to the accumulator pipe (44) and having the same diameter as the pipeline, and a second length of pipe (74) arranged in a horizontal position and connected to the first length of pipe (70) and to the downstream section (38) of the pipeline.

Inventors: HATTON GREGORY JOHN, HATTON, GREGORY JOHN
Applicants: TEXACO DEVELOPMENT CORP, TEXACO DEVELOPMENT CORPORATION
Application year: 1988
Main classification: F17D1
IPC codes: G01F15, F17D3, G02B6, F17D1