WO1995018366A1

WO1995018366A1 - Method and apparatus for isokinetic fluid sampling

Info

Publication number: WO1995018366A1
Application number: PCT/NO1994/000209
Authority: WO
Inventors: Bjørn DYBDAHL
Original assignee: Dybdahl Bjoern
Priority date: 1993-12-27
Filing date: 1994-12-21
Publication date: 1995-07-06
Also published as: AU1392995A; GB9612640D0; GB2299167B; NO178807B; AU680715B2; NO934816D0; NO934816L; GB2299167A; NO178807C

Abstract

The invention relates to a method for the treatment and analysis of isokinetic fluid samples, for, on the basis of the analysis, to optimalize the fluid's speed of flow through a separator (1) for a multiphase fluid consisting of e.g. oil/gas/water, where the gas constituent may contain entrained liquid drops/droplets/particles; it being not desired that gas leaving the separator (1) should contain such entrained liquid. Thus, in order to provide a parameter, upon the basis of which the fluid's speed of flow through the separator can be regulated, the separated gas constituent including possibly entrained liquid drops/droplets/particles is subjected to a temperature/pressure treatment, causing said liquid drops/droplets/particles to evaporate/condense, the resultant gas/steam mixture respectively liquid phase is subjected to a density measurement for subsequent analysis. Regulating said separator's speed of flow while fluid samples are density-tested until a low density value has been achieved, one has produced an optimum speed of flow, corresponding to maximum utilization of the separator. The apparatus comprises a container (8) which is heatable/coolable, for thus to cause liquid drops/droplets/particles entrained in the gas constituent to evaporate respectively condense, the container (8) through a discharge line (13) being coupled to a density measuring device (14 respectively 23).

Description

METHOD AND APPARATUS FOR ISOKINETIC FLUID SAMPLING
The present invention relates to methods and apparatus for the treatment and analysis of fluid samples from isokinetic sampling, in order to determine optimal supply of oil/gas/ condensate to a separator.

Optimal supply of oil/gas/condensate, so-called feed, to a separator, is achieved just before some condensate drops (in the order of 2 microns, even if they may be larger as well as smaller than this) accompany the separated gas flow.

According to the present invention one has generally aimed at achieving a parameter decisive for obtaining optimal supply of feed to a separator.

In NO patent application No. 930049 is shown and described a method and an apparatus for further treatment and temporary storing of fluid samples taken isokinetically from a two phase-f luid which under high pressure flows in a pipeline downstreams a tank or a separator.

This known method consists generally in letting the sample fluid flow freely, utilizing its isokinetic speed (first pressure), into a container, wherein is maintained a second pressure which is lower than the first pressure of the fluid, whereafter further fluid is supplied to said container by means of forced fluid flowing, namely until said first fluid pressure is substantially established, operating within said container with a temperature which substantially corresponds to the original temperature of the fluid within e.g. the separator, respectively within a discharge pipeline coupled to the separator, downstream the latter.

The object of this known method and apparatus is substantially to provide isokinetic fluid samples, i.e. fluid samples having original pressure and temperature, for subsequent analysis.

The fluid samples may advantageously be taken by means of a sampling apparatus adapted for isokinetic sampling of the kind as shown and described in NO Patent No. 173,468, and which comprises a probe having two 1800 angularly displaced orifices. When such a probe is inserted into the fluid flow within e.g. a pipe from a separator, it is possible to take two fluid samples simultaneously, namely one in counter current by means of one orifice and one in co-current by means of the second orifice.

The counter current sample may be a relative humid gaseous fluid in the form of a gas stream containing entrained condensate drops (liquid), while the downstream sample usually is a relative dry gaseous fluid.

The method and the apparatus according to the present invention enable i.a. that one through data processing equipment may monitor if relatively much or little condensate in drop or particle form follows the gas out from the separator.

In accordance with the invention, a counter current fluid is entered through a container in a manner known per se. The novel feature of one method consists partly in bringing entrained condensate drops/particles to evaporate, preferably through heating the container and/or a supply pipeline to the same, the container, supply and discharge pipe being insulated in such a degree that the fluid sample arrives at a density measuring device with condensate drops/particles in evaporated form.

Instead of heating the counter current fluid in the container, one may - according to an alternative method of the invention - cool the same, in order to condensate possibly entrained liquid drops/particles, in order to thereafter measure the density of the liquid phase. Then, the liquid is taken out at a shutoff valve which is disposed on a pipeline coupled to the bottom discharge of the container. The density of discharged liquid increases with the amount of liquid condensed out. The liquid can be pumped out from the container by means of a pump. Density measurements - or gas cromatography/infrared photospectroscopy (IR) - may possibly be effected in both of said density measuring devices (density measuring device for gas containing evaporated liquid and density measuring device for condensed liquid).

When heating, a heating temperature of preferably 500C or more above the separator temperature is proposed.

When cooling, a temperature of e.g. 200C below the separator temperature is proposed.

The container is surrounded by a jacket and is heated e.g.

electrically, inductively, through micro waves or by means of water to at least 50 C above the separator temperature.

The resultant gas/steam-mixture flows into an insulated and possibly heated pipe in the top of the container. If'all liquid does not evaporate, remaining liquid may be discharged at the bottom of the container in a manner known per se.

Because of the transition of the entrained condensate drops/particles from a liquid state to steam/gas, the resultant gas/steam-mixture's density, respectively the condensed liquid's density, increases, said density being measurable according to the invention and usable as a parameter for determining the optimal efficiency of the separator at all times. The density measuring device shows whether much or little condensate drops/particles enters into the probe's counter current measuring orifice downstream the gas outlet of the separator. If there is much condensate drops in the counter current gas sample, the density increases as previously mentioned, and this could be read against a curve on a display device.

On the basis of this measured density value, which is compared with a reference value, the speed of the fluid through the separator can be adjusted such that one secures optimal feed supply per time unit and, thus, optimal efficiency at all times.

The density measuring device/devices may suitably be coupled to a computer.

The speed is the same through the fluid sample as in the pipe downstream the gas outlet of the separator, i.e. isokinetic.

Downstream the density measuring device it may advantageously be disposed a flowmeter and, further downstream, a closing valve, in order to adjust isokinetic speed.

Further objects, advantages and features relating to the methods and the apparatus according to the invention will appear-from the following statement, reference being made to the substantially diagrammatical drawing which, in a single figure, shows an example of an embodiment of an apparatus of the invention, as seen in side elevational view/axial section.

Reference is made to the figure of the drawing, wherein reference numeral 1 denotes a separator for a two- or multiphase fluid containing e.g. oil, water and gas, wherein the gas constituent may contain entrained drops/micro drops/ particles of condensate. This fluid mixture enters into the separator 1 through a supply pipe 2. The separator 1 is provided with a bottom outlet pipe 3 for liquid and a top outlet pipe 4 for gas, possibly containing entrained condensate in drop or particle form.

The gas outlet pipe 4 and the liquid outlet pipe 3 are, thus, situated downstream the separator 1.

As mentioned introductorily, it is a desire to be capable of supplying the separator 1 with as much feed as possible, in order to utilize the capacity/degree of filling of the separator maximum at all times.

Optimum supply per time unit, corresponding to 100% efficiency, is defined as achieved just before some condensate drops/particles are entrained in the gas stream.

By means of the shown apparatus, respectively by proceeding in a way enabled by the same, it is possible to monitor whether relatively much or little liquid follows the gas out from the separator. On the basis on corresponding measuring results it is thereafter possible to adjust the speed of the fluid through the separator until optimum supply of feed is achieved.

Reference numeral 5 denotes an apparatus adapted for isokinetic sampling, as shown and described in NO Patent No.

173,468. The apparatus has a probe 5a inserted through a hole in the gas outlet pipe 4. In practice, said hole will be assigned a pipe sleeve with a sealing device.

The probe 5a has a counter current measuring orifice 5a' and a downstream measuring orifice 5a", referred to the direction of flow A in the gas outlet pipe 4.

The counter current fluid sample and the downstream fluid sample taken simultaneously by means of the measuring orifice, respectively 5a' and Sa", are conducted separately through individual pipes within the apparatus 5 to a separate pipeline, respectively 6 and 7.

The pipeline 6 for the counter current sample, usually containing entrained condensate drops/particles in the gas stream, is, according to the invention, preferably heated/ cooled and insulated, so that the temperature in the same upon heating is maintains at a temperature preferably 50"C or more above the temperature of the fluid in the separator 1, respectively in the gas outlet pipe 4, the temperature upon cooling being maintained at 10-200C below the temperature of the fluid in separator/gas outlet pipe.

The counter current sample consisting of gas together with entrained condensate drops/particles is conducted through the pipeline 6 into the middle zone within a container 8, which is surrounded by a jacket 9 and possibly an intermediate insulation 10. The container 8 has a downwardly tapering bottom portion 8a having a discharge pipe 11 for possible liquid that might collect in the bottom area of the container. The discharge pipe 11 may be provided with a shutoff valve 12, from where the liquid possibly may be conducted further for further analysis.

The container 8 is heated or cooled, e.g. electrically, inductively, through micro waves or by means of water, to at least 500C above the fluid temperature in separator 1 or outlet pipe 4, respectively 10-200C below said fluid temperature.

The purpose of the heating of the supply pipeline 6 and the container 8 is to cause condensate drops/particles entrained in the gas flow to evaporate, resultant gas/steam mixture being discharged at the top of the container 8 through a discharge pipe 13 for the gas/steam mixture. Unless the spacing between this discharge pipe 13 and a first density measuring device 14 is very short, it should be heated and/ or insulated. In some cases it may be sufficient to heat only the container 8.

Because of the transition of entrained condensate/liquid drops and particles to steam, the density of the gas within pipeline 6, container 8 and discharge pipe 13 increases.

Thus, when such gas/steam mixture arrives at the density measuring device 14, the latter will indicate a density value which is larger than ideal density value with respect to maximum flowing speed through the separator 1, corresponding to optimum utilization/efficiency of the latter.

Upon cooling of the container 8, entrained liquid drops will be caused to condensate. The resultant liquid is discharged through the closing valve 12, the density of the liquid being measured by means of a density measuring device 23. Reference numeral 24 denotes a pump for pumping the liquid out from the container 8. The density increases in step with the amount of condensed liquid. Density measurements may, possibly, be carried out both in density measuring device 23 and density measuring device 14. Alternatively, measurements may be carried out through gas cromatography/infrared photospectroscopy (IR).

The insulation/heating of the discharge pipe 13 for the gas/steam mixture from the container 8 prevents the steam part from condensing prior to the density measurement being effected. The density measuring device 14 may be coupled to a computer (not shown), wherein the density of the gas/steam mixture at every examination may be read against a reference curve.

After the density measuring device 14, a flowmeter 15 is coupled and, after the latter, a closing valve 16. By means of the flowmeter 15 one may control the fluid's speed of flow through the equipment, so that the fluid sample becomes isokinetic.

By means of the large hole of the probe's 5 co-current measuring orifice 5a", a fluid sample can be taken at low speed, in order to avoid accompanying liquid. This downstream sample is to contain only gas when the density measuring is carried out, i.e. as if the separator 1 was 100% efficient.

Possibly entrained liquid drops/particles are brought to condense/be removed in a spiral 17 and a demister 19 (a droplet separator or an entrainment separator), which is disposed between the spiral 17 and a second density measuring device 18, and which is assigned a shutoff valve 20. As the density measuring device 14, the density measuring device 18 may be assigned a flowmeter 21 having a closing valve 22.

The downstream fluid sample is conducted into the apparatus under the same pressure and temperature as within the gas discharge pipe 4 of the separator. If desired, the density measuring device (14 or 18) may be the very same.

The curve for the density of the downstream fluid will substantially be a straight line parallel to the X-axis of a right-angled coordinate system, while the curve for the counter current fluid densities will raise with increasing density and fall with decreasing density. Increased fluid flowing speed within the separator will, within a not ideal speed area, correspond to increased constituent of entrained liquid particles/drops/droplets and increased density of the resultant gas/steam mixture as measured by means of the density measuring device 14. The proportion between these two curves will give information concerning the efficiency, the points of intersection drawn in a common'coordinate system will define ideal density values for the counter current fluid sample including entrained liquid particles/drops.

Subsequent to the density measuring being carried out during isokinetic conditions, it only remains to regulate the fluid's speed of flow through the separator during fluid sampling until ideal or approximately ideal density value is present.

Claims

1. A method for the treatment and analysis of fluid samples for, on the basis of the analysis, to optimalize the fluid's speed of flow through a separator (1) for a multiphase fluid, wherein the gas constituent may contain entrained liquid drops/droplets/particles, c h a r a c t e r i z e d i n that the separated gas constituent inclusive possibly entrained liquid drops/droplets/particles is subjected to a temperature/pressure treatment, causing said liquid drop/ droplets/particles to evaporate, and that the resultant gas/steam mixture is subjected to a density measurement or gas chromatography/infrared photospectroscopy (IR) for subsequent analysis.

2. A method for the treatment and analysis of fluid samples for, on the basis of the analysis, to optimalize the fluid's speed of flow through a separator (1) for a multiphase fluid, wherein the gas constituent may contain entrained liquid drops/droplets/particles, c h a r a c t e r i z e d i n that the separated gas constituent inclusive possibly entrained liquid drops/droplets/particles is subjected to a temperature/pressure treatment, causing said liquid drops/ droplets/particles to condense and deposit (settle), and that the resultant liquid phase is subjected to a density measurement - or gas cromatography/infrared photospectroscopy (IR) - for subsequent analysis.

3. An apparatus for carrying out a method as defined in claim 1 or 2, comprising a device (5) adapted to take preferably isokinetic fluid samples from a gaseous fluid flowing in an outlet pipe (4) downstream a separator (1), and wherein the device (5) through a first pipeline (6) is connected to the interior of a container (8) into which a fluid sample can enter, c h a r a c t e r i z e d i n that said container (8) is heatable/coolable, in order to cause liquid drops/droplets/particles entrained in the gas constituent to evaporate/condense, and that the container (8) through a discharge conduit (13) is coupled to a density measuring device (14 respectively 23) or a gas cromatograf or a photospectroscope.

4. An apparatus as defined in claim 3, c h a r a c t e r i z e d i n that the container (8) is adapted to be heatable/cooable, e.g. electrically, inductively or by means of microwaves to a temperature at least 500C above the fluid's temperature in the separator (1) respectively in the gas outlet pipe (4) from the same, respectively to a temperature corresponding to e.g. 10-200C below said temperature of the fluid within separator/gas outlet pipe.

5. An apparatus as defined in claim 3 or 4, c h a r a c t e r i z e d in that said first pipeline (6) to the container (8) is heatable/coolable, e.g. to 500C above the fluid's temperature in the separator (1) respectively in the gas outlet pipe (4) from the same, respectively to 10-200C below said temperature of the fluid in separator/gas outlet pipe.

6. An apparatus as defined in one or more of claims 3 - 5, c h a r a c t e r i z e d i n that the container's (8) discharge pipe (13) is insulated and/or heatable/coolable.

7. An apparatus as defined in one or more of claims 3 - 6, c h a r a c t e r i z e d i n that said density measuring device (14) is followed downstream by a flowmeter (15) and, possibly, is coupled to a computer.

8. An apparatus as defined in one or more of claims 2 - 6, wherein two fluid samples are taken within the gas outlet pipe (4) disposed downstream the separator (1), one countercurrently - the counter current fluid sample - and one in the downstream direction - the downstream fluid sample, c h a r a c t e r i z e d i n that - for each fluid sample - at least one density measuring device (14, 23 or 14, 23, 18), which may be followed downstream by a flowmeter (15, 21), and that - for the downstream fluid sample - is disposed a liquid separating means (17, 19), upstream the density measuring device (18).