GB2232902A - Fluid/solids analysis device - Google Patents

Abstract

A retorting apparatus (1) is used to determine the solid and liquid content of a drilling mud or slurry, and comprises a retort (4, 5) for containing a sample, microwave (9) or induction heating means for distilling off the liquid phase, and a receiver (11, 14) for receiving and condensing the liquid. Water may be added to maximise carry-over of liquid. <IMAGE>

Description

FLUID/SOLIDS ANALYSIS DEVICE This invention relates to a device for separating and measuring the liquid and solid phases of mixtures such as drilling mud, slurries and discharges from bulk separation equipment used in drilling operations.

In down-hole drilling there are various requirements for monitoring and measuring the condition of the drilling fluid, the efficiency of the separation of mud and drilled solids and for determining the quantity of mud being discharged with the cuttings to the environment. Where oil based muds are concerned, there is a statutory requirement to carry out such measurements.

Typical mud compositions to be analysed have a solids content of 2-40% by volume (which may include drilling mud solids, barite and rock cuttings), the balance being liquid consisting of oil and/or water in any proportions. Cuttings discharges represent rock cuttings from the drill which have been partially separated from the drilling mud. Typically these contain about 50% rock cuttings together with residual mud (including some oil). The oil content requires to be measured as this is controlled by regulations.

The current method is to place a sample of the material to be analysed in a steel retort cup of 10,20 or 50 ml capacity, this being screwed into an upper chamber packed with steel wool, and to distil the liquid components via a tube leading from the top of the upper chamber to an aluminium condenser and thence to a receiver. The cup and chamber are electrically heated by means of an insulated heating jacket and the liquid fraction(s) collected-in a measuring cylinder, the solid residue being weighed when the apparatus has cooled.

The entire operation, including preparation and cleaning, is slow and takes approximately 2 hours.

The current equipment was designed primarily to retort muds as opposed to slurries or bulk discharges.

Since cuttings discharges from bulk separation equipment are predominantly solid and not liquid, and since the component particles vary enormously in size and character, the present retort equipment is less than ideal when used to analyse such materials.

The present invention provides a retorting apparatus for separating and measuring the solid and liquid phases of solid-liquid mixtures, which comprises retort means for containing a sample of the mixture, microwave or induction heating means for heating the sample and distilling off the liquid phase, and a receiver for receiving and condensing the liquid.

The invention also extends to a corresponding method for analysing the solid and liquid content of such a sample.

Thus the present invention provides a means of heating samples by microwave energy or by high frequency/radio induction so allowing for increased sample size and hence greater accuracy, and at the same time shortening the heating cycle and hence the analysis time. The device may be designed around single retort cell operation or offer a multiple cell facility, thus further increasing the sample throughput.

In the case of microwave heating, the retort cup and chamber may consist of ceramics, pyrex glass, Teflon or other suitable material transparent to microwave radiation. Where heating by high frequency/radio frequency induction is concerned, the retort cell is constructed of steel or other suitable metal in which eddy currents can be generated. Induction heating may be by high frequency (e.g. 5-50 kHz) or radio frequency (e.g. 100-800 kHz) induced currents.

In either case the sample cells are usually provided with quick-release mechanisms to allow easy separation of the respective chambers and rapid disconnection from the condenser.

The retort means may be provided with deflector means at an upper end to deflect boiling liquid back downwards so as to promote mixing and even temperature distribution.

The device preferable incorporates an electronic timer along with an optical fibre or infra-red sensor linked to the heating circuitry for controlling the rate of temperature increase and the final temperature of the sample cell. The whole process is preferably controlled by a microprocessor according to keyed instructions entered by the operator. The final temperature is usually in the range 450-550 ~C. A temperature of 5000C + 38iC is prescribed by the American Petroleum Institute Standard.

The technique also provides for the addition of known quantities of additional materials to the samples. Such additions may be made to improve the efficiency of the separation process and may act for example, by increasing the absorption of microwaves or by altering the concentrations of the immiscible liquid fractions to ensure removal of hydrocarbon fractions.

In this respect the addition of known volumes of water to the sample can be used to increase the volume ratio of water to hydrocarbons above 1:1. The effect of this is that despite having a higher boiling point than water, the oil fraction can be separated from the sample. This process is based on the property of immiscible liquid combinations whereby the vapour pressure above the liquids is equal to the combined individual vapour pressures of the component liquids and is independent of the proportions of each component one to another. This results in the liquid combination having a boiling point lower than that of the component parts. The removal of the vapour from above the liquid promotes further evaporation of the liquids until all the liquids are removed.In the case of microwave heating the process is apparently similar to that of steam distillation with the steam being generated by microwave energisation of the water molecules present in the sample and acting as the carrier to the vapour.

The efficiency of this operation may be improved by continued agitation or stirring of the sample during the distillation process.

In order to assist complete vaporisation, the retort may be arranged to rotate, preferable about an inclined axis and/or may include a means for vibrating or otherwise agitating the sample.

The apparatus may also include means for in situ weighing of the initial sample, distillate and residue.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic view of a first embodiment using microwave heating; Figure 2 is a view of a retort for a second embodiment using radio-frequency heating; Figure 3 is a view of a further radio-frequency heated retort for use with muds; and Figure 4 is a block diagram of a radio frequency heating system.

1) MICROWAVE HEATED RETORT SYSTEM In Figure 1 a microwave retorting system 1 in accordance with the present invention comprises a microwave oven 2 beneath which is situated an integral unit 3 for collecting and measuring the distilled liquid fractions.

Within the oven are situated one or more pyrex or ceramic retorts each comprising a lower cup 4 of suitable capacity connected to an upper section 5 by means of a flanged joint, Teflon (Trademark) seal and clip 6. The sample to be analysed is placed in the cup, or in a disposable container placed within the cup, and the sample heated to the required temperature in the oven. Temperature control is achieved by means of infra-red or fibre-optic sensors 7 situated immediately beneath the respective retort cells, signals from the sensors being fed to the microprocessor 8 which in turn controls the output from microwave generator 9. The rate of temperature increase is optimised to maximise liquid carry-over and minimise charring.

Distillates from the various sample chambers are taken by delivery tubes via ports 10 in the base of the oven to water-cooled or air-cooled (shown) condensers 11 and liquid phases collected in graduated cylinders 14.

In the case of air-cooling, the condensers are of a multi-vaned aluminium construction (11) and provided with forced air-cooling by means of a fan unit (12) and inducting (13) arranged in the lower part of the device as shown.

The microwave or induction heaters enable the sample to be heated up to the required distillation temperature (which can be as high as 250-300 ZC for some drilling oils) and up to a final temperature of approximately 500'C in a relatively short time so that the analysis can be carried out quickly.

2. INDUCTIVELY HEATED RETORT SYSTEM A block diagram of the radio frequency (R.F.

hereinafter) heating system is given in Figure 4. It comprises an A.C. input to a power supply which in turn, provides the D.C. supply for the Mosfet inverter, and also the D.C. control volts.

On initiation of the system, the control circuit will start the Mosfet inverter which in turn will energise the workhead with R.F. power. The resulting eddy currents in the walls of the retort produce rapid heating and consequent vaporisation of the water and oil in the mud or cuttings sample.

The drive circuit is the interface between the control circuit and the Mosfet inverter. The protection circuit monitors the system and protects it against faulty conditions. The A.C. input is single phase 240 volts, 50/60 Hz or 120 volts Hz; though in some circumstances it may need to be a three phase 480 volt supply.

Details of the retort, which is fabricated from 310 grade non-magnetic stainless steel, are given in Figure 2. The retort 20 comprises an upper section 21 fitted onto a lower section 22, with a flat lid 23 having a central aperture 24 interposed therebetween.

The lower section 22 is filled with sample and then the lid is fitted; any excess sample being displaced through the aperture so as to provide a measured sample volume (50ml or 100ml). A steel wool plug may be fitted into the upper section which helps retain solids on boiling. The upper section 21 has a conical upper end 25 leading to an outlet 26 through which vapour passes to a condenser (not shown).

For mud samples it may be necessary to replace the flat lid shown in Figure 2 with a thicker lid, 33 on the underside of which a groove 34 is machined as shown in Figure 3. Figure 3 also shows induction coils 30 for heating the sample 32. A plug of steel wool 35 is fitted into the upper section to help prevent bumping over of solids on heating. The lower section of the retort is partially filled with a measured volume of the sample, so as to leave a space above. As boiling mud and steam rise at the sides of the retort, they are deflected downwards into the centre of the sample chamber to provide stirring and more even heating of the sample.

The inductive R.F. heated retort system has the following features: 1. Designed to be modular with work heads, electronics, condensers etc. which are removable and interchangeable.

2. There may be from one to six stations to allow for simultaneous and independent analysis of up to six samples.

3. The equipment is housed in a cabinet constructed primarily of aluminium in a robust rectangular form, with removable/hinged covers to enclose all controls etc., and to facilitate safe transportation.

The cabinet houses: a) Work heads and coils which are built into insulated chambers designed to house the retort assemblies.

b) Water cooled condensers vertically positioned above a location to hold the distillate collection and measurement vessel.

The connection between the retort side arm and the condenser is a push-fit "0" ring seal which is easily replaceable.

c) Power supplies built into the lower compartment of the cabinet, typically having an A.C. input of 240 V, 50Hz.

d) Inverter modules, which are plug in interchangeable units.

e) Insulated retort chambers with a ceramic lining and lid, and 1 inch (25mm) total thickness of insulation all round.

4. Power to each work head is sufficient to vaporise all the water and base oil contained within a 100 ml sample of drilling fluid ("mud") or solids discharge ("cuttings"), leaving a completely dry residue. Depending on sample type, this will take in the order of 15 to 25 minutes.

5. The height of the coils is at least 0.75 of the total height of the retort to minimise condensation of distillate in the upper part of the assembly.

6. The heating of each individual retort is thermostatically controlled. The temperature sensor for this control is flush with the lagged base of the retort chamber, centrally located, and therefore in contact with the central area of the base of the sample chamber. The temperature range is 500C+/- 38 C.

7. A digital temperature readout may be provided for each individual retort.

8. Variable time and power controls may be provided to enable the establishment of the optimum sequence for mud and cuttings. Alternatively, an automatic heating sequence may be provided.

9. For each work station the controls/indicators on the system will be: a) A.C. input on/off switch and indicator.

b) Sequence running indicator.

c) Unit heating indicator.

d) Start sequence push button.

e) Step sequence push button.

Additional optional controls may include: a) Digital temperature display.

b) Variable power control.

c) Variable time control.

10. The outline specification of each heater unit is as follows: Input voltage 120 volts 50/60 Hz or 240 volts 50/60 Hz switchable.

Frequency range 100 to 150 kHz Maximum power input 900 watts.

Power output (heat into retort) 500 to 1000 watts.

Times range: auto sequence.

Temperature of retort 5000C +/-38 C thermostatically controlled.

Claims (15)

1. A retorting apparatus for separating and measuring the solid and liquid phases of solid-liquid mixtures, which comprises - retort means for containing a sample of the mixture; - microwave or induction heating means for heating the sample and distilling off the liquid phase; and - a receiver for receiving and condensing the liquid.

2. An apparatus according to claim 1 which employs microwave heating means.

3. An apparatus according to claim 1 which employs induction heating means.

4. An apparatus according to claim 3 wherein the induction heating means uses a radio frequency of 100 150 kHz.

5. An apparatus according to any preceding claim provided with temperature control means for controlling the rate of temperature increase, and the final temperature.

6. A method of separating and measuring the solid and liquid phases of a solid-liquid mixture, which comprises - placing the sample in a retort means; - heating the sample using microwave or induction heating means and distilling off the liquid phase; and - condensing and collecting the distilled liquid.

7. A method according to claim 6 which employs microwave heating.

8. A method according to claim 7, which comprises the addition to the sample of microwave absorbing material to promote the absorption of microwave energy.

9. A method according to claim 6 which employs inducting heating.

10. A method according to claim 9 wherein the induction heating uses a radio frequency of 100 - 150 kHz.

11. A method according to any of claims 6 to 10 wherein the rate of temperature increase and final temperature are automatically controlled according to a predetermined regime.

12. A method according to any of claims 6 to 11 which further comprises the addition of a known volume of water to the sample to promote distillation of the liquid phase.

13. A method according to claim 12 wherein the sample contains hydrocarbons-and the ratio by volume of water to hydrocarbons is greater than 1:1.

14. A retorting apparatus substantially according to any embodiment described in conjunction with the drawings.

15. A method of separating and measuring the solid and liquid phases of a solid-liquid mixture substantially as described in conjunction with the drawings.